Download Complications of Laser in situ Keratomileusis

Review Article
Complications of Laser in situ Keratomileusis:
Etiology, Prevention, and Treatment
Renato Ambrósio Jr, MD; Steven E. Wilson, MD
ABSTRACT
PURPOSE: To review the etiology, prevention,
and management of laser in situ keratomileusis
(LASIK) complications.
METHODS: Review of literature and the experience of the authors.
RESULTS: Careful preoperative screening is
critical to prevention of many potential complications of LASIK. Flap complications that occur during surgery are typically managed by replacement
of the flap and repeating the surgery or applying
special methods such as transepithelial photorefractive keratectomy weeks to months following
the initial procedure. A common source of serious
complications is the use of a microkeratome that
functions after improper assembly. Timely treatment of postoperative complications such as diffuse
lamellar keratitis, flap striae, and infection is
critical to an optimal outcome.
CONCLUSION: Most complications of LASIK can
be treated effectively and have minimal effect on
the final outcome after surgery, if appropriate
methods are used for management. [J Refract Surg
2001;17:350-379]
PREOPERATIVE MEASURES TO REDUCE COMPLICATIONS
M
any laser in situ keratomileusis (LASIK)
complications can be avoided through careful patient screening and preparation for
surgery. The first step in preparing a patient should
be assessment of expectations. The staff and surgeon must educate the patients while striving to
understand the motivation for seeking refractive
correction. The simple question. “Why are you considering refractive surgery?” will often reveal a
From the Department of Ophthalmology, University of Sao Paulo, Sao
Paulo, Brazil (Ambrósio) and the Department of Ophthalmology,
University of Washington, Seattle, WA (Wilson).
Supported in part by EY10056 from the National Eye Institute and an
Unrestricted Grant from Research to Prevent Blindness, New York, NY.
Dr. Wilson is a consultant to Allergan, Inc., Irvine, CA.
Correspondence: Steven E. Wilson, MD, Department of Ophthalmology, Box 356485, University of Washington, Seattle, WA 98195
Received: November 13, 2000
Accepted: February 16, 2001
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misconception about what LASIK can achieve. For
example, patients with presbyopia will often
respond that they want to be able to see distance
and near without ever needing glasses. Patients
with amblyopia will commonly respond that they
are hoping the procedure will restore their vision.
Many patients will assert that they want to “see
20/20 without ever wearing glasses again.” These
types of misconceptions need to be identified and the
expectations brought in line with what is achievable. The staff and the surgeon need to accept that
there will always be patients who simply will not
understand the limitations of surgery. An example
is the patient who, despite counseling about the
reality of LASIK, repeatedly asks, “So I’m going to
be 20/20 after LASIK, right?” Do not hesitate to tell
such as patient that they are not a candidate for the
procedure. Careful screening will help the surgeon
and staff avoid hours of wasted time dealing with a
disappointed patient and reduce exposure to
litigation.
Each surgeon should understand the limits of
LASIK and avoid extending the procedure beyond
these limits, where the efficacy and safety of the
procedure is compromised. Ultimately the surgeon
must decide for himself or herself what limits will be
based on: important patient factors such as refractive error, corneal curvature, and corneal thickness,
as well as the limitations of the specific laser and
technique. For example, we never attempt correction beyond +5.00 diopters (D) of hyperopia or
-12.00 D of myopia corrected to the corneal plane
because of increased risk of reduced vision
quality.1-4 However, in some eyes even these limits
are excessive depending on the preoperative corneal
curvature or corneal thickness. The concept of
establishing limits and sticking to them is critical to
the safe and effective application of LASIK.
Candidates for LASIK should have a stable
refraction, normal corneal topography, and corneas
that are free of diseases that predispose to complications. Refractions may be unstable due to
Journal of Refractive Surgery Volume 17 May/June 2001
LASIK Complications/Ambrósio and Wilson
Figure 1. Corneal topographic axial maps (Humphrey Atlas) of preoperative abnormalities. A) Contact lens warpage. This
pattern resolved to normal with-the-rule astigmatism 6 weeks after removal of a gas-permeable contact lens. B) Keratoconus with a central
cone pattern. C) Early keratoconus with a peripheral cone pattern in an eye with advanced keratoconus in the opposite eye. D) An asymmetric bow-tie in an otherwise normal patient.
progressive myopia, cataract, corneal ectasia, or
other factors. LASIK can still be an appropriate
treatment for a patient with progressive myopia, as
long as the patient understands and accepts that
although a high proportion of the myopia can be corrected, there is a high likelihood of return of myopia
over time. Many of these patients happily accept the
prospect of having mild to moderate myopia, if their
high myopia can be markedly reduced.
There are several important points regarding
contact lens management.5-6 1) Corneas must have
normal and stable corneal topographic patterns
prior to surgery or there will be avoidable errors
introduced into the correction and the potential for
permanent introduction of irregular astigmatism as
a result of the superimposed laser ablation. There is
no hard evidence that this can happen, but it seems
reasonable to consider this likely. 2) If a patient has
contact lens warpage, there is no way to determine
how long the contact lenses must be removed to
allow the warpage to resolve. 3) Warpage with gaspermeable or hard contact lenses that is superior
Journal of Refractive Surgery Volume 17 May/June 2001
riding often simulates keratoconus (Fig 1A).5 Our
typical protocol is to remove soft contact lenses for
3 days and rigid contact lenses for 3 weeks prior to
the preoperative examination. These time frames
will allow warpage to resolve in the majority of
patients, based on our prior studies.5-6 If warpage is
still present at the preoperative examination, the
patient is followed at 2- to 4-week intervals until
corneal topography becomes normal and stable.5 In
rare cases, such warpage may take 6 to 12 months
to resolve. Occasionally a patient with permanent
warpage will be detected. If significant irregular
astigmatism is present, LASIK is probably contraindicated.5
Keratoconus is another disorder that needs to be
detected prior to refractive surgery (Fig. 1B).6 Some
surgeons have used photorefractive keratectomy
(PRK) or LASIK to treat myopia associated with
mild to moderate keratoconus.7,8 Although results
have been acceptable with relatively short followup, much longer observation is necessary to support
a stromal thinning procedure for treatment of a
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LASIK Complications/Ambrósio and Wilson
Figure 2. Map-dot-fingerprint changes consistent with epithelial basement membrane degeneration. The box shows a magnified view of the
indicated area with arrows noting maplike irregularities at the level of the basement membrane. This eye should be considered for PRK
rather than LASIK.
disease that is characterized by progressive stromal
thinning over a period measured in decades. Serious
complications have been reported.9,10 Keratoconus
has been associated with chronic keratocyte apoptosis11 and LASIK or PRK can trigger high levels of
keratocyte apoptosis associated with the surgery.12
Although direct evidence is lacking, it seems plausible that the triggering of accelerated keratocyte
apoptosis could be associated with an accelerated
disease process. At the least, the patient should be
advised of the potential complications associated
with application of LASIK to a cornea that has true
keratoconus.
Although most surgeons exclude patients with
frank keratoconus from consideration from LASIK,
the most common difficulty arises in distinguishing
early keratoconus from a normal relatively asymmetric astigmatism pattern (Fig 1C). Corneal thickness measurements can be helpful. Corneas with
measurements thinner than 500 µm more likely
represent true keratoconus. However, even this is
not diagnostic because many patients are seen with
completely normal corneal topography and corneal
thickness less than 500 µm. Thus, some of these
patients may be normal with asymmetric astigmatism. If there is concern that a particular patient
has early keratoconus, based on the topographic
pattern and corneal thickness, then the best course
is to delay consideration for 1 or 2 years, with monitoring. Automated indices are available to help
with detection of keratoconus.13,14
True keratoconus is characterized by progression.
Unfortunately, relatively quiescent periods and
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progressive periods also characterize true keratoconus. Thus, it is possible that the period of observation coincides with a period of quiescence in an
individual patient. Despite the best of intentions,
surgeons will be likely to operate on some patients
who have true keratoconus unless all patients with
keratoconus-like topographic patterns are excluded.
Ultimately, each surgeon must decide how to
manage these patients.
Epithelial basement membrane degeneration is
another disorder that should, when possible, be
detected prior to LASIK (Fig 2). The presence of this
disorder predisposes to flap complications and irregular healing associated with epithelial sloughing at
the time of flap formation. The typical map-dotfingerprint opacities in the epithelium should lead
the surgeon to be wary of performing LASIK.
Patients with mild to moderate myopia or hyperopia
may be best treated with PRK. It is clear that there
are patients with poor epithelial adhesion typical of
epithelial basement membrane degeneration with
no map-dot-fingerprint opacities in the epithelium.
These patients are currently undetectable and the
first sign of the problem is typically a large epithelial slough at the time of LASIK surgery in the first
eye. Many of these patients do well despite slower
visual recovery after surgery if a bandage contact
lens is worn for several days to a week following the
procedure. This is not always the case, however, and
some of these patients develop regression, diffuse
interface keratitis, and other complications. If a significant slough is noted in the first eye, there is high
risk of a similar occurrence in the second eye and
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LASIK Complications/Ambrósio and Wilson
consideration should be given to changing to PRK in
the second eye.
Dry eye is a challenging and potentially serious
problem in LASIK patients. Many patients who present seeking LASIK have mild to moderate dry eye
and resulting contact lens intolerance. Many of
these patients undergo LASIK and have uneventful
courses with excellent results. Complications such
as abnormal wound healing seem more likely to
occur in patients with severe dry eyes.
There is another associated problem that we refer
to as LASIK-induced neurotrophic epitheliopathy.15,16 LASIK-induced neurotrophic epitheliopathy
is attributable to interruption of sensory nerve
input to the epithelium of the LASIK flap. This
results in a transient abnormality of the flap epithelium associated with punctate epithelial erosions
and rose bengal staining. This condition occurs in
1% to 2% of eyes with no evidence of pre-existing dry
eye. However, our impression is that it is more common and more severe in patients who have preexisting dry eye disease. The patients who develop
severe LASIK-induced neurotrophic epitheliopathy
may have marked visual disability due to epithelial
abnormalities overlying the pupil that may last for
6 months or longer. Because of concerns about healing and development of severe LASIK-induced neurotrophic epitheliopathy, we consider any patient
with more than mild corneal rose bengal staining or
a Schirmer test without anesthesia less than 2 mm
in 5 minutes not to be a candidate for LASIK. Even
patients with less severe signs of dry eye may be
better candidates for PRK, since a condition like
this is rare following this surface procedure that
ablates only the corneal sensory nerve endings.
Patients with autoimmune disorders occasionally
seek LASIK. Surgeons are rightfully concerned that
the patient could develop chronic keratitis or
corneal melting syndrome. Our general rule is to not
offer refractive surgery to any patient with ocular
manifestations of autoimmune disease or one who is
on systemic medications for autoimmune disease.
We have operated on patients with vague histories
of autoimmune disorders that have little in the way
of symptoms and signs of disease without encountering problems after LASIK. If we have concerns,
we ask the patient to have a rheumatologic evaluation to determine whether there is active disease. If
we are concerned that the patient may have active
autoimmune disease, we do not proceed with surgery.
The effect of keloids frequently arises in a busy
refractive surgery practice. Previous studies demonstrated that keloids were not associated with
Journal of Refractive Surgery Volume 17 May/June 2001
increased complications in PRK.17 Following this
lead, we have performed LASIK on more than
20 patients with a history of keloids without any
scarring or other related complications. For the
most part, keloids do not appear to be a significant
concern for patients considering LASIK.
The question of whether to perform LASIK in a
patient with glaucoma is frequently raised due to
concern about a reduction in the measured intraocular pressure following surgery and the potential for
iatrogenic nerve damage. To our knowledge, there
has been only a single report of a nerve defect that
may have been attributable directly to LASIK.18
Since this was only a single case, it is impossible to
ascertain whether this was truly associated with
LASIK or a mere coincidence in a patient with a
family history of glaucoma. We believe it is better to
advise against LASIK in patients with severe glaucoma. We consider performing LASIK in patients
who are glaucoma suspects, patients who have mild
glaucoma, and patients who have moderate wellcontrolled glaucoma. We advise the patient that a
new baseline for intraocular pressure will need to be
established by their glaucoma specialist. We also let
them know that there is no way at present to be
sure there is no risk. We also discuss PRK as an
option in patients with low to moderate myopia.
Ultimately, we allow the informed patient to make
the decision in consultation with the ophthalmologist who treats the glaucoma.
There are other less common situations that arise
in which the surgeon must make a decision about
whether LASIK should be considered. In general,
the surgeon needs to use common sense in determining whether a particular patient should have
LASIK. When there is significant doubt, the best
course of action is typically not to proceed.
INTRAOPERATIVE COMPLICATIONS
An optimal laser room environment is critical for
good laser performance. The laser needs to be set up
and tested per the manufacturer’s recommendations. The temperature should be maintained
between 18° and 24° C and the humidity should be
kept at a stable level within the range recommended by the manufacturer. The key is consistency. An
environmental control system that maintains constant temperature and humidity and a LASIK
nomogram established at those settings may be an
important factor in the accuracy and precision of
correction in LASIK. Air filtration units are recommended to maintain a clean atmosphere and
promote standard laser ablation rates.
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LASIK Complications/Ambrósio and Wilson
Proper assembly of the microkeratome is critical.
There is disagreement about whether the surgeon or
a technician should assemble the instrument. It has
been our practice, for a number of years, to have a
well-trained and experienced technician assemble
the microkeratome. No complications attributable
to this have been noted. If an expert technician is
not available, the surgeon should perform the
assembly. It is important that the surgeon test run
the microkeratome just before it is placed on an eye
to make sure it is functioning normally.
The excimer laser should be checked for optimal
beam profile, alignment, and other parameters
according to the manufacturer’s recommendation.
Improper fluence can result in an undercorrection or
overcorrection. Poor beam homogeneity can cause
an irregular ablation such as a central island or
peninsula. Consistency is key. Establish protocols
with your staff in consultation with instrument
manufacturers and do not depart from them. Do not
hesitate to cancel a full day of surgery if a critical
instrument is not functioning perfectly.
There are a number of different intraoperative
complications (Table) that deserve special discussion. These complications will be covered in following sections.
Anesthesia and Marking for Cyclotorsion
Topical anesthesia is preferred because it is simple, efficacious, and avoids complications related to
retrobulbar and peribulbar infiltration. In addition,
these latter methods are associated with poor fixation by the patient on the laser LED target. Mild
sedation with oral diazepam (5 or 10 mg) can be considered, but in our opinion, it is rarely necessary.
Topical anesthesia should be used sparingly and
should be carefully dosed. Usually two applications
just as the procedure begins are sufficient. A toxic
effect on the corneal epithelium can result from
excessive topical anesthetic. This will exacerbate
epithelial adhesion problems that may be noted in
patients with occult epithelial adhesion disorders
and patients with diabetes mellitus.
A mistake that is frequently made is application
of anesthetic to both eyes prior to beginning a bilateral case. Topical anesthetics break down corneal
epithelial barrier function. Thus, if the second eye
also receives topical anesthetic prior to beginning
surgery on the first eye, a minimum of 7 to 10 minutes of exposure will occur prior to surgery in the
second eye. During this time interval, corneal
hydration will be altered, with unpredictable effects
on the nomogram and the accuracy and precision in
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Table
Surgical and Postoperative
Complications of LASIK
1. Inadequate alignment with astigmatism axis
2. Irregular flap cuts
A. Partial Flaps
B. Thin Flaps
C. Donut-shaped flaps
D. Decentered flaps
E. Free caps
3. Complications due to improper microkeratome assembly or
defective blades
4. Intraoperative bleeding
5. Intersecting microkeratome cuts
6. Excimer laser ablation-related complications
A. Input errors
B. Decentered ablations
C. Central Islands and peninsulas
7. Microkeratome-induced epithelial defects
8. Postoperative pain
9. Postoperative flap complications
A. Striae
B. Flap displacement
10. Epithelial growth within the interface
11. Interface debris
12. Regular astigmatism
13. Irregular astigmatism; glare, halos, poor visual quality
14. Overcorrection
15. Undercorrection and regression
16. Corneal ectasia
17. LASIK-induced neurotrophic epitheliopathy
18. Diffuse lamellar keratitis (DLK)
19. Infection
20. Retinal complications
the second eye. Thus, the carefully established
LASIK nomogram will be altered. We recommend
applying anesthetic in the second eye just prior to
beginning surgery in that eye.
Infiltrative anesthesia may be considered rarely
for producing good exposure of sunken eyes or in
eyes with narrow interpalpebral fissures. Lateral
canthotomy is a better alternative for dealing with
deep-set eyes or narrow palpebral fissures because
fixation is maintained. Our experience with the
Automated Corneal Shapper (Chiron, ACS,
Emeryville, CA) and the Hansatome (Bausch and
Lomb, Rochester, NY) microkeratomes indicates
that this is rarely necessary, even in Asian eyes.
It is our opinion that general anesthesia should
not be used for LASIK. Proper centration is currently not possible without the cooperation of the
patient fixing on the LED target. This is the case
even with lasers that use a tracking system.
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LASIK Complications/Ambrósio and Wilson
A reference mark should be placed with a gentian
violet pen or other suitable marker while the patient
is in the seated, head erect position so that cyclotorsion that occurs when the patient lies down can be
detected. Unless a mark is placed for reference,
astigmatic correction could be improperly placed,
resulting in undercorrection of astigmatism or even
introduction of astigmatism at a different axis.
Some surgeons prefer to place these reference
marks at the 3 and 9 o’clock positions. Others prefer
the 6 o’clock position. It doesn’t matter where the
mark is made as long as the reticle of the laser can
be aligned with it.
Some surgeons do not mark for astigmatism. In
the majority of patients, this likely results in minimal, if any, error. However, we have noted cyclotorsion in excess of 20° in some eyes. Induced astigmatism is likely to be generated when this degree of
cyclotorsion is present.
Periocular Cleaning and Draping
The eye should be prepared for LASIK as though
it were going to be an intraocular procedure.
Patients should be instructed not to wear make-up
on the day of surgery or for at least 4 days afterward
because of the risk of introducing infectious material beneath the flap or into the eye prior to complete
healing of the epithelium.
We prefer to prep the eyelids with Betadine
swabs such that the lashes and surrounding area
are fully treated. Any Betadine that gets into the
eye should be removed since the toxicity of this solution could be one cause of diffuse interface keratitis.
Removal of the Betadine is facilitated by use of an
aspirating lid speculum. Our practice is to apply the
first dose of anesthetic prior to the Betadine scrub
and the second dose after the scrub, so that any
Betadine that gets into the eye is diluted and
removed by the aspirating lid speculum. We do not
recommend topical antibiotics prior to surgery since
no data suggest this decreases the incidence of postoperative infection, and infections are rare.
Some type of sterile drape that effectively captures the lashes should be used. A convenient product that we prefer is a simple oval Tagaderm drape
1624W from 3M (Minneapolis, MN), cut in half. One
-half of the drape is applied to the lower lid and onehalf to the upper lid. An advantage of this drape is
that it will re-stick after removal if it is initially
placed improperly. There are many other drapes
that are effective and individual surgeons should
find one they feel comfortable with and use it consistently. Also, the controls on the excimer laser
Journal of Refractive Surgery Volume 17 May/June 2001
Figure 3. An aspirating lid speculum is useful for removing
meibomian secretions, sponge fragments, and other debris from the
surface of the eye. It also allows irrigation to be performed beneath
the flap without soaking the patient.
should be draped; these controls are a source of
iatrogenic infection.
The use of sterile gloves by the surgeon is recommended. There are many excellent LASIK surgeons
who do not use sterile gloves. However, it is clear
that even repeated washing with Betadine or another surgical antiseptic does not eliminate the flora
that reside on the hands and beneath the nails. It
would be hard to justify not having used gloves in
the event of infection.
Exposure of the Eye
Attention to adequate exposure is a critical step
in avoiding LASIK complications. Deep orbits, previous orbital fractures, prominent foreheads, small
eyes, and narrow palpebral fissures should alert the
surgeon to possible intraoperative problems. The
surgeon should discuss steps that might be necessary in advance with the patient, including lateral
canthotomy, converting to PRK, or abandoning
surgery.
We prefer a modified wire speculum with aspiration (Fig 3). There are, however, many specific models of lid specula that are adequate. The key is good,
secure retraction of the lids with excellent exposure.
Once the lid speculum is in position, the patient’s
head can be positioned with the neck flexed or
extended, depending on the individual patient, to
center the cornea in the palpebral fissure.
Many micorkeratomes, such as the Hansatome,
the Automated Corneal Shaper, and the Innovatome
(Inovative Optics, Albuquerque, NM) can be used
without a lid speculum because the suction ring
itself acts as the lid speculum. This is useful for eyes
with a small palpebral fissure to avoid a lateral
canthotomy. We recommend that only experienced
LASIK surgeons attempt this maneuver.
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LASIK Complications/Ambrósio and Wilson
Inadequate Suction and Intraocular Pressure
The suction ring serves two major purposes: it
provides a stable platform to control passage of the
microkeratome head. It also hardens the globe to
provide depth control during the microkeratome
pass. If the globe is too soft, the blade cannot engage
the tissue properly. This may result in a thin flap,
donut-shaped flap, or free cap. When a buttonhole
flap is created, the blade has broken through the
epithelium to the surface in the center of the cornea
and then returned back into the stroma. A thin or
buttonhole flap may also be created if the cornea is
steeper than 48.00 D prior to surgery. A cap may
also be created when suction is low and is more likely with corneas that are relatively flat prior to surgery.
In rare cases, the thin microkeratome cut does
not extend all the way through the epithelium, but
actually passes through the layers of the epithelium
tangent to the surface. The flap will not have a hole
in the center, but there will be a shiny area produced by the epithelial layers adherent to the stroma in the center of the bed beneath the flap. If this
is noted, the flap should be replaced without ablation. If this epithelium is scraped away, the bed will
be irregular in shape and the refractive outome will
be unpredictable. Similarly, if the ablation is performed over this island of epithelial tissue, a central
island will be produced.
All irregular flaps should be returned to their
original position without laser treatment. This will
be facilitated if the surface of the cornea was
marked for orientation prior to beginning the procedure. In most cases, surgery can be repeated after
approximately 3 months, with excellent results. In
some situations, alternative treatment is needed
(discussion follows).
If suction is broken during passage of the microkeratome, the blade will tend to surface. If this
occurs, an irregular flap or cap with a cut through
the central cornea may result.19 This potentially
serious complication may be reduced by more modern instruments such as the Bausch and Lomb
Hansatome that automatically stops if suction is
broken during passage of the microkeratome head.
However, this type of complication may still occur
despite these safety features. The cap or flap should
be replaced in its original position. In some cases,
the cornea will heal with surprising clarity and consideration can be given to repeating the procedure
later. In other eyes, scarring may occur and necessitate other approaches, such as transepithelial phototherapeutic keratectomy, with or without PRK.
The best treatment for inadequate suction is
356
prevention. We prefer to use a pneumotonometer
(Mentor Ophthalmics, Santa Barbara, CA, or Solan,
Jacksonville, FL) to insure that the intraocular
pressure is greater than 75 mmHg when the microkeratome head is placed in position. Other surgeons
think the Barraquer tonomoter (Bausch & Lomb,
Rochester, NY) is adequate.
When suction is inadequate the suction ring
should be examined to insure that debris is not clogging the suction ports. The speculum, drapes, and
lashes should be inspected to insure they are not
impeding contact between the suction ring and the
globe. Additional anesthetic can be applied to
improve suction between the ring and globe. If these
items appear normal, the suction line should be
changed to insure it is free of defects. Chemotic or
redundant conjunctiva may also obstruct the suction port on the ring, especially if the globe is small.
In this situation, a smooth-surfaced instrument can
be used to push away the subconjunctival fluid just
prior to application of the ring. If everything else
has been excluded, it is useful to have a back-up
power/suction component so that proper function of
this unit can be confirmed.
There have been no reports of retinal vascular
complications caused by the relatively high intraocular pressure required in this procedure. This possibility is still a concern in patients with systemic diseases known to compromise the circulation.
MICROKERATOME-RELATED COMPLICATIONS
DURING FLAP CREATION
Lamellar refractive surgery has several advantages over photorefractive keratectomy: less postoperative pain, quicker visual recovery, and no
corneal haze overlying the entrance pupil in uncomplicated cases. However, flap complications are
inherent to the surgery and have the potential to
produce serious visual loss.
The frequency of flap complications is higher
early in the “learning curve” and can be reduced
with experience and attention to detail. However,
flap complications still occur, even in the hands of
the most experienced surgeons (Marinho A, Pinto
MC, Pinto R, et al. LASIK for high myopia.
Ophthalmic Surg Lasers 1996;27(suppl):S517-S520;
Bas AM, Onnis R. Excimer laser in situ keratomileusis for myopia. J Refract Surg 1995;
11(suppl):S229-S233).19-25
Flap complications may range from insignificant
to catastrophic (Fig 4A). The incidence of all LASIK
complications reported in the literature ranges from
0.7% to 11.8 % (Bas AM et al, 1995, cited above;
Journal of Refractive Surgery Volume 17 May/June 2001
LASIK Complications/Ambrósio and Wilson
Figure 4. A) Corneal topography (TMS, Computed Anatomy) from
a LASIK case in which the surgeon proceeded with ablation despite
a partial flap that terminated with insufficient room to apply laser
ablation. This typically results in irregular astigmatism and flattening
adjacent to the flap edge due to double ablation of the bed and flap
or the tethering effect of the uncut stroma directly adjacent to the
cornea overlying the entrance pupil. There is also a central island.
B) A buttonhole or donut-shaped flap. The flap was put down without ablation. Scarring occurred in the central cornea 2 months later
at the point the microkeratome blade passed from the stroma
through the epithelium and back again. C) A flap complication with
a central cut through the visual axis. A line of scarring (arrow) is visible overlying the pupil and haze can be noted throughout the area
where the microkeratome cut to the surface.
A
B
Kremer FB, Dufek M. Excimer laser in situ
keratomileusis. J Refract Surg 1995;11(suppl):S244S247; Fiander DC, Tayfour F. Excimer laser in situ
keratomileusis in 124 myopic eyes. J Refract Surg
1995;11(suppl):234-238).26-31 Recent studies with
large sample sizes of 1062, 1019, and 3998 eyes
reported an intraoperative complication rate of
2.1%, 2.2%, and 0.68 %, respectively.22,24,31 Newer
microkeratomes such as the Hansatome, with closed
heads that pivot on a pin, have been shown to be
safer than microkeratomes with paired tracks.32
Flap complications may be reduced to as low as 1 in
500 to 1 in 1000 cases with appropriate patient
selection in the hands of an experienced and talented surgeon using a well-designed instrument.
It is important to prepare the patient for a potential flap complication prior to surgery. Our custom is
to remind the patient that a flap complication can
occur and that in the event of an irregular flap, no
laser ablation will be performed. This preparation
will prevent the patient from panicking in the event
of a flap abnormality and reduce the chance that the
surgeon will feel pressured to go ahead with the
ablation when it is not appropriate to do so.
Journal of Refractive Surgery Volume 17 May/June 2001
C
Irregular flap cuts rarely lead to significant visual
loss and generally do not result in a change in
refractive error unless the surgeon proceeds with
the ablation. Most of the time the procedure can be
repeated a few months later. The sections that follow detail some of the specific microkeratome-related complications that occur and discuss approaches
to management.
Eyelid Complications
With some microkeratomes it is possible to nick
the eyelid during flap formation. For example, this
may occur with the Hansatome. Typically, this is a
small superficial scrape or cut that heals without
sequelae. The best way to avoid this trauma to the
eyelid is to obtain excellent exposure with the eyelid
speculum. With the Hansatome, the incidence can
be reduced to nearly zero by rotating the handle of
the suction ring gently toward the surgeon while
placing the head on the pin and moving the
microkeratome head into position. This maneuver
lifts the gear track away from the lid. As the microkeratome begins its passage, the handle is returned
to the upright position. After completing the flap,
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LASIK Complications/Ambrósio and Wilson
the handle is again rotated toward the surgeon as
the microkeratome head returns to the starting
position. It is also useful to retract the lower eyelid
inferiorly with the blunt end of a forceps.
Incomplete Flaps
Occasionally, the micokeratome head will stop
prior to clearing the 6- to 6.5-mm diameter zone
needed for unhindered ablation. Application of the
laser treatment with such a flap will result in nasal
flattening and irregular astigmatism, even if the
hinge of the flap is protected from the laser beam
(Fig 4B). Our practice is to return the flap to the bed
without ablation unless there is at least 1 mm of bed
between the intended ablation periphery and the
flap edge in eyes with myopia. It is necessary to protect the hinge from the ablation in LASIK for hyperopia. This does not appear to have a significant
effect on the quality of correction.
Some surgeons attempt manual extension of the
flap using a lamellar dissecting blade. We believe
this should not be done.
Thin Flaps and Donut-shaped Flaps (Buttonholes)
Flap buttonholes are more likely to cause loss of
best spectacle-corrected visual acuity than free or
incomplete flaps. Preoperative mean corneal curvature greater than 48.00 D and previous ocular
surgery, such as corneal transplantation, are the
most important risk factors. Any reduction in
intraocular pressure during passage of the microkeratome increases the chance that there will be a
thin or donut-shaped flap.
Surfacing of the blade during creation of the flap,
resulting in a donut-shaped flap or a cut through
the central cornea, is often associated with scarring
or epithelial ingrowth into the interface that may
compromise the surgeon’s ability to successfully
repeat the LASIK procedure at a later time
(Fig 4C). If the lamellar cut was superficial, then the
excimer laser can be used to eliminate the epithelial
or scar opacity within the central cornea and rehabilitate the eye by performing a no-touch transepithelial PRK.33 This technique is most successful if
used within the first few weeks following the complicated procedure before scarring or epithelial
ingrowth become advanced. Delaying until a dense
scar has formed will predispose to irregular astigmatism because the scar will ablate differently with
the excimer laser compared with the adjacent clear
stroma. The best approach is to protect the irregular
flap with a bandage contact lens and proceed when
the best spectacle-corrected visual acuity is nearly
358
at the preoperative level or has stabilized for 2 to
3 weeks. With this approach, the thin corneal cap or
flap and associated epithelial growth or scarring can
be eliminated over a 6-mm-diameter area of central
cornea. Residual lamellar tissue in the periphery
remains in place and usually has no effect on vision.
In the case of low myopia or hyperopia, it may be
necessary for the surgeon to utilize a combination of
PTK and hyperopic ablation to eliminate an offending flap defect. In some cases, more than one procedure separated by months may be required to eliminate the central cut or donut-shaped flap and provide sufficient refractive correction to prevent anisometropia. During the interval between procedures,
we use a soft contact lens to improve the patient’s function.
A central corneal scar associated with a transverse cut that emanated from what was a normal
140- to 180-µm-deep lamellar cut cannot, in most
cases, be addressed with transepithelial PRK. This
is because corneal tissue removal would be excessive and predispose to ectasia. A gas-permeable contact lens may be of benefit. In some cases, however,
a rotational autograft or penetrating keratoplasty
may be needed to restore vision.
Decentered Flaps
Decentered flaps can be as problematic as decentered ablations. Performing an ablation with a
decentered flap, even if the ablation is centered on
the entrance pupil, may yield unpredictable spherical and astigmatic corrections. Typically, flap decentrations are attributable to an inexperienced surgeon improperly aligning the suction ring with the
limbus or migration of the ring on the corneal surface when suction is applied. When placing the suction ring, the surgeon should confirm the position of
the inferior limbus and strive to maintain the base
in that position while suction ramps up through posterior pressure on the suction ring. Suction should
be turned off at the first sign of migration of the
microkeratome ring so that a deep impression gutter is not formed. Such a gutter will tend to repeatedly return the suction ring to the decentered position. Sometimes the surgeon must wait for 5 to
10 minutes for such a gutter to disappear prior to
proceeding. Occasionally, it is necessary to intentionally decenter the microkeratome suction ring in
the opposite direction a small amount so that when
suction is applied, migration stops in the appropriate location. Rarely is it necessary to cancel the case
and come back on another day.
Corneal contour appears to have some role in
decentation of the flap. If the microkeratome ring
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LASIK Complications/Ambrósio and Wilson
has a tendency to decenter in one eye, a tendency to
decenter in the same manner (nasal or temporal) is
commonly present in the second eye. Slight decentration in the direction opposite to the anticipated
migration is often helpful in obtaining centration
after the suction is applied.
In the event that a decentered flap is formed, we
follow the guideline of not proceeding unless the
ablation can be placed so that 1 mm of bed is left
between the ablaton peripheral edge and the flap
margin. There may be major changes in the contour
of the cut in the 1 mm of stromal bed next to the flap
margin, and incorporating this area into the ablation may induce unpredictable refractive results. It
is not clear why this should occur if the flap is of
plano power, but we have noted this in several
cases. Perhaps the augmented wound healing
response at the edge of the flap is a factor.
One of the developments that has reduced this
problem has been the introduction of microkeratomes with larger diameter flaps. This is one of the
reasons we prefer newer microkeratomes such as
the Hansatome, the Moria Carriazo-Barraquer
(Paris, France) or the Innovatome. If significant
decentration of the flap is noted, the best course of
action is to return the flap to its original position
and repeat the procedure 3 to 6 months later.
Free Caps
Occasionally, a surgeon will find that an inadvertent free cap has been produced. This is most likely
to occur with corneas flatter than 38.00 D prior to
surgery. In some cases, the cap is not visible on the
surface of the cornea. If this occurs, the microkeratome head should be disassembled carefully since
the cap is probably inside the instrument. If the cap
has normal thickness and diameter, the excimer
laser ablation can still be performed with excellent
results. Replacement of the cap in its original position with the epithelium up is facilitated if the surface was marked for orientation prior to surgery.
Severe irregular and regular astigmatism are common if the surface was not marked and the cap ends
up rotated relative to its original position. The few
moments that are required for marking the flap is
insignificant compared to the amount of time and
anxiety the surgeon will expend on one of these complicated cases. In rare cases, sutures are needed to
anchor a free cap that will not adhere or becomes
displaced. Sutures should be removed as soon as the
epithelium heals to minimize scarring.
In the event one is faced with an apparently eroneously positioned cap, it may be possible to approx-
Journal of Refractive Surgery Volume 17 May/June 2001
imate the appropriate position (Robert Maloney,
MD, unpublished data, 2000) by remembering the
optical rule that when a corrective cylinder is placed
off axis, a new cylinder is introduced at an angle of
45° to the bisector between the true cylinder axis
and the axis at which the corrective cylinder is erroneously placed. In some cases, more than one
attempt at repositioning may be required to align
the flap near its correct position.
Erroneous Microkeratome Assembly
A potentially catastrophic complication of LASIK
is human error in failing to place the plate that controlls depth of cut into instruments, such as the
Automatic Corneal Shaper. This omission has unfortunately occurred in several cases reported at meetings. It results in perforation of the cornea and
entrance into the anterior chamber in an eye pressurized to more than 65 mmHg, causing serious
damage to the iris, lens, ciliary body, and other
structures in the eye. It is critical that the surgeon
never engage the microkeratome head without
checking for the presence of a correctly positioned
depth plate.
Other microkeratomes that are currently on the
market can also be assembled incorrectly and still
function to produce a flap. For example, when this
occurs with the Innovatome microkeratome, a thick
flap is produced. This is unlikely to be detected by
the surgeon until drops of aqueous humor appear
during the ablation. Although the cornea may recover from the localized endothelial damage in the center of the ablation, these corneas are likely to be at
risk for developing ectasia, since the remaining posterior bed is limited.
Corneoscleral perforations have also been reported to occur during formation of a corneal flap.34 This
may result in vitreorelinal complication.
Newer designs, such as the Hansatome and the
Carriazo-Barraquer (from Moria) have eliminated
the potential for these severe complications since
they have a fixed depth plate and components of the
microkeratome cannot be inserted incorrectly to
produce a functional microkeratome. Before purchasing any microkeratome, we recommend determining whether the instrument will function if any
of the components are inserted incorrectly. If use following improper assembly is possible, then the
instrument should be avoided.
Intraoperative Bleeding
Intraoperative bleeding at the edge of the flap
tends to be more of a nuisance than a complication.
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LASIK Complications/Ambrósio and Wilson
Bleeding of the perilimbal corneal vessels has been
reported as the most frequent complication of
LASIK performed by an experienced surgeon
(Velasco-Martinelli EJ, Tarcha FA. Superior hinge
laser in situ keratomileusis. J Refract Surg
1999;15(suppl):S209-S211).35 This occurs most commonly with wide diameter flaps. MacRae and colleagues36 presented two cases in which blood
entered the interface after a small hemorrhage from
peripheral corneal vascularization after formation
of the flap. Although bleeding was controlled and all
visible blood cells were removed at the time of
surgery, both patients developed a focal interface
keratitis on the first postoperative day.
The most common cause of intraoperative hemorrhage is corneal neovascularization from pannus
related to long-term contact lens wear. The
micropannus is usually superior. Other causes are
decentration of the microkeratome and a small
corneal diameter relative to the diameter of the
microkeratome. Preoperative examination should
include detection of pannus and the extent to which
the vessels encroach into the peripheral cornea so
that precautions may be taken. The preoperative
use of topical vasoconstrictors like neosynephrine
and naphcon can be considered. We typically apply
vasoconstrictor only in those cases where we suspect
there will be bleeding, and wait 3 to 5 minutes prior
to proceeding. Once the flap is formed, it is also
helpful to wait approximately 1 minute before lifting the flap if bleeding is detected. This will tend to
tamponade the vessels. In the event that the blood
approaches the ablation zone, it may be necessary to
interrupt the ablation to clear the blood with a
sponge before proceeding.
Bleeding can rarely be extensive and difficult to
control. In such a case, returning the flap to its original position while irrigating the interface with balanced saline solution (BSS) will typically clear the
blood from the interface and tamponade the vessels.
In our experience, the ablation can almost always be
completed prior to this maneuver. Significant bleeding is so rare that we typically avoid decentering the
flap to avoid localized micropannus because of the
risks outlined in the previous section. A BSSmoistened Chayet sponge drain (Ultracell, North
Stonington, CT) is also an option for managing these
rare cases during ablation. The sponge is placed
around the flap so that any bleeding is wicked away
from the flap edge.
360
Intersecting Microkeratome Cuts and Other
Irregular Flap Cuts
When a LASIK flap is recut, there is a risk of
intersection between the new interface and the original interface. When this type of intersection occurs,
a sliver or disc of stromal tissue may be produced.
Displacement of these amputated tissue pieces may
result in irregular astigmatism that cannot be corrected unless the proper position can be found.
Recutting with a Hansatome following an original
Automated Corneal Shaper flap has been reported
to be associated with a high risk of these complications. It may be helpful to use a deeper cutting
microkeratome for the second flap, however, this
does not eliminate the possibility of an intersection
because of the variability in true flap thickness relative to the specified thickness with all microkeratomes.
Most flaps can be lifted 5 to 7 years after surgery.
The authors believe this should always be attempted prior to considering recutting of the flap. At times
the healing is so extensive that lifting is not possible
and recutting must be considered. It may be better
to avoid enhancement in these cases.
Atypical flap cuts may also be noted after corneal
transplantation, radial keratotomy (RK), arcuate
keratotomy (AK), or automated lamellar keratoplasty (ALK). In the authors’ experience, flap complications attributable to prior corneal transplantation,
RK, or AK, occur at increased frequency relative to
corneas that have not had previous surgery, but still
are relatively rare if incisions are well healed. We
wait at least 1 year after the incisional procedure
before considering LASIK.
If slivers, free discs, or other anomalies of the
stroma are noted after microkeratome passage, the
surgeon should make every effort to return the stromal components to their original position in an
attempt to limit irregular astigmatism that commonly occurs in these situations. Never discard free
tissue pieces. Future reposition procedures designed
to reduce induced irregularity can only be undertaken if the fragments are retained. Take the time
to try to reapproximate the pieces and protect the
surface with a bandage contact lens for the first day
to increase the chance of an acceptable outcome.
Other Microkeratome-related Problems
Blade chatter is occasionally noted when the flap
is lifted and the bed is examined. In some cases this
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LASIK Complications/Ambrósio and Wilson
Figure 5. A defective blade that was detected prior to LASIK
surgery. Note multiple notches (arrows) in the blade.
may be attributable to a blade defect or jerky transition of the micokeratome head. In our experience,
such chatter is rarely of visual significance since it
is typically mild and even after ablation the posterior surface of the flap and the bed tend to reapproximate. However, if the chatter is extensive, the flap
should be replaced without performing the ablation.
The procedure can be repeated after approximately
3 months. These types of flap irregularities can be
reduced by careful inspection of blades for defects
(Fig 5) and avoiding reuse of blades for different
patients.
EXCIMER LASER ABLATION-RELATED COMPLICATIONS
Temperature, Humidity, and Input Errors
The laser suite environment is critical for optimal
performance of the excimer laser. The manufacturer’s recommendations for temperature and humidity should be strictly followed if a precise nomogram
is to be produced and maintained. It may be necessary to install a humidity and temperature control
system in the operating suite to achieve this
uniformity.
The excimer laser must be monitored for appropriate alignment and ablation profile at regular
intervals. All laser manufacturers provide guidelines specific to their instrument. Test plates are
available to independently evaluate ablation profiles. Lack of homogeneity can be attributable to
expected wear on the excimer laser optics and may
result in undercorrection, overcorrection, or other
anomalies such as central islands.
A nomogram should be established for individual
lasers and surgeons for optimal accuracy and precision in laser correction. Even surgeons using the
same laser in a single operating suite will
Journal of Refractive Surgery Volume 17 May/June 2001
frequently have differing outcomes based on variations in technique. Once established, a nomogram
should be continually monitored for variations that
may occur with differing humidity, optics changes,
and other factors.
Erroneous computer input is a common source of
error in the application of laser energy in performing LASIK or PRK. Undercorrection attributable to
operator error can be corrected by enhancement.
Overcorrection to hyperopia and axis misalignment
may be difficult to correct. The surgeon should
always verify input into the excimer laser before
beginning ablation. At our center, the surgical plan
is positioned in front of the surgeon adjacent to the
laser terminal. Correct input of the parameters is
verified by direct surgeon observation. This simple
approach will eliminate many input errors.
Hydration of Tissue
Hydration of the stromal bed should be rigidly
controlled. For example, if the surgeon typically
sponges the intended ablation zone with a dry or
moist sponge, this practice should be rigidly followed in generating and following the excimer laser
nomogram.
It has been mentioned that excessive topical
anesthetic will also alter hydration of the corneal
stroma due to effects on epithelial barrier function.
In addition, fluctuation in the time between first
application of the anesthetic and laser ablation is a
source of inconsistency in stromal hydration. Our
practice is to apply a single drop of anesthetic just
prior to prepping of the eye. Once the prep for the
individual eye is completed, another drop of anesthetic is applied and LASIK is performed immediately.
Decentration of Ablation
Decentration of ablation is a common complication in LASIK patients (Fig 6A). This is most common in cases performed by inexperienced surgeons
where insufficient attention is paid to centering the
laser mires on the entrance pupil. All refractive surgical procedures should be centered on the entrance
pupil. The ablation should be stopped immediately
and the mires repositioned prior to proceeding if
deviation from the pupil is detected. An eye tracker
that follows eye movements may be useful, but even
this is not foolproof. Patient cooperation and fixation are still critical to alignment of the entrance
pupil to the line of sight.37 There have been a number of reports of decentered ablation using lasers
with trackers that are typically attributable to
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LASIK Complications/Ambrósio and Wilson
A
B
instrument malfunction or loss of patient concentration.
Centration is especially critical in the treatment
of hyperopia. The steepening induced by treatment
of hyperopia may result in induced astigmatism and
poor visual quality unless centration is optimal. The
higher the level of correction, the more critical centration becomes. For this reason, and because
regression may also induce irregularity, we limit
hyperopic LASIK correction to less than +4.00 D.
Some measures can be taken to improve patient
fixation. First, careful instruction should be given to
the patient to insure that he or she has correctly
identified the fixation target. Microscope and room
lighting should be reduced to a minimum. We have
observed that elimination of sedation with Valium
and other medications significantly improves
patient attention. In our experience, such sedatives
are rarely needed.
Topographic Central Islands and Peninsulas
Excimer lasers damage their own optics by
362
Figure 6. A) Decentered ablation in a patient
who had LASIK. The surgeon should strive to
center the ablation on the entrance pupil.
Decentration can be caused by patient fixation error or can result from undetected fixation loss by the patient. Note that decentration
such as this can also occur when a tracker is
used. The patient still must maintain focus on
the fixation target. B) A central island at
1 month after LASIK (TMS). Central islands
can be due to optics degradation, transfer of
a drop of moisture onto the stromal bed during flap lifting, a vortex of plume, hydration
inhomogeneity that develops during high
ablations, or other causes. C) A peninsula
that was detected at 1 month after LASIK
(TMS). The underlying factors are similar to
those for central islands.
C
slowly ablating the glass. Such degradation results
in inhomogeneity of the ablation. One of the most
common complications is a central island (Fig 6B)
attributable to a cold spot in the center of the optics,
although virtually any anomaly is possible.
Peninsulas (Fig 6C), off-center islands, divots, and
other abnormalities can occur. Optics should be
monitored according to the manufacturer’s protocol.
Our preference is to perform callibration after every
two or three eyes. The surgeon should be prepared
to terminate treatment at the first sign of problems.
It is important that patients be informed of the possibility of cancellation in the event of equipment
malfunction prior to the day of surgery so that they
are prepared for unexpected rescheduling.
A common cause of ablation irregularity is a drop
of moisture falling on the ablation zone during lifting of the flap. It is important to dry the flap margin
with a sponge just prior to lifting. Any drop that
falls on the ablation zone immediately changes the
hydration at that point, resulting in irregular
hydration across the ablation. Even immediate
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LASIK Complications/Ambrósio and Wilson
drying with a sponge will not completely eliminate
this spotty hydration, although this still should be
done. This irregular hydration may result in irregularity of the ablation. The splashing of fluid from the
cornea onto the laser lenses can also damage the
optics.
Ablation zone irregularity will typically produce
symptoms of poor vision quality, monocular diplopia, halos, and starbursts. These can be difficult to
treat. In some cases, the abnormalities will decrease
or disappear over time. If they persist and the irregularity is not likely to be attributable to flap striae
or other surface problems, then an attempt at
smoothing can be made. Our preferred technique is
to lift the flap, as in preparation for an enhancement. Then, a small drop of Healon (Pharmacia,
Peapack, NJ) diluted to 0.2% sodium hyaluronate
(1:5) with BSS, is applied to the ablated zone and
immediately smoothed over the zone with a spatula
so that there is a thin film. The solution will tend to
fill the valleys and expose the peaks of the irregularity. The broadbeam laser in phototherapeutic
(PTK) mode with a 6.0-mm ablation zone is then
centered on the entrance pupil and a few bursts are
applied. The smoothing agent is distributed again
with the spatula and a few more bursts of PTK are
applied. This maneuver is repeated 5 to 10 times. A
decrease in the irregularity of the surface is obvious
at the time of surgery when this technique is perfomed properly. The bed is then irrigated with BSS
and the flap returned into position using the same
technique as with enhancement. This treatment can
be repeated and in some cases eliminates or
markedly improves the patient’s symptoms.
Epithelial Complications
Flap epithelial defects occur only in a small percentage of eyes when appropriate technique is used
in performing LASIK. Epithelial defects can cause
pain and photophobia. They also prolong visual
recovery. The risk of infection is also increased.
Some surgeons believe the incidence of epithelial
ingrowth is significantly higher in eyes with an
epithelial defect on the flap. Flap displacement may
also be more common because of alterations in flap
adhesion. Diffuse interface keratitis may be triggered by an epithelial defect. Wetting the surface of
the cornea with proparacaine just prior to passage
of the microkeratome seems to decrease the incidence of epithelial abrasion. Use of a salt containing
solution prior to the ablation should be avoided
because of potential damage to the microkeratome
motor and gears. Patients with epithelial adhesion
Journal of Refractive Surgery Volume 17 May/June 2001
abnormalities are especially prone to epithelial
defects.
In the authors’ experience, an epithelial defect
does not necessarily predispose to a poor outcome.
Regression—likely related to an augmented wound
healing response—is frequently noted in these eyes.
Use of a bandage contact lens increases patient comfort and may decrease the frequency of related flap
displacements or epithelial ingrowth. If an epithelial abrasion occurs in the first eye of a patient, then
there is a high likelihood of occurrence in the second
eye. Thus, if there is a large abrasion, it is prudent
to postpone treatment of the second eye.
POSTOPERATIVE COMPLICATIONS
Pain
Most patients experience only mild discomfort
following LASIK. Typically, this manifests as mild
burning or stinging lasting for a few hours after
surgery. A foreign body, gritty, or dry sensation is
commonplace. As with any surgical procedure, variability in tolerance plays a significant role in determining the level of these subjective symptoms.
Complaints of severe pain may herald more severe
complications such as a displaced corneal flap, diffuse lamellar keratitis, or infection. Thus, severe
pain on the night of surgery or even mild pain more
than 1 day after surgery warrants an examination.
Nonsteroidal anti-inflammatory agents and bandage contact lenses reduce perioperative discomfort.
Rarely do patients need narcotic analgesics for a few
days after surgery. Lubrication is another important
adjuvant since many of these eyes have mild neurotrophic epitheliopathy or underlying dry eye.
Patients frequently report dysesthesias for
months or even years after LASIK. Such patients
report discomfort on pushing on the globe through
the eyelid. This is likely attributable to deinnervation hypersensitivity associated with the cutting
and incomplete regeneration of the corneal sensory
nerves. This sensation seems to diminish over time,
but in some cases may never completely resolve. No
other sequalae have been associated with this
sensation.
Postoperative Flap Striae and Wrinkles
Flap striae or wrinkling is relatively common
after LASIK (Fig 7).38 Fortunately, most striae do
not appear to significantly affect the quality of vision.
Striae are most commonly related to disparity
between the curvature of the posterior surface of the
flap and the bed following ablation. Thus, the
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LASIK Complications/Ambrósio and Wilson
A
B
Figure 7. A) Flap striae resulted in symptoms of decreased quality of vision and 20/400 uncorrected visual acuity at 1 day after LASIK.
Application of fluorescein and use of cobalt blue lighting facilitates detection of striae. B) At 1 week after lifting of the flap and irrigating with
50% balanced salt solution, striae were undetectable and uncorrected visual acuity was 20/20.
incidence of striae appears to increase as the level of
correction increases. Alternatively, striae may be
introduced during the procedure by touching the
flap with a sponge, improper insertion of a contact
lens, removal of an eyelid speculum, or some other
manipulation. Many of these striae are not
detectable with the operating microscope, prompting some surgeons to inspect the flap at the slit
lamp immediately after surgery. In other cases,
striae may not be detected until 1 or more days following surgery. These late occuring striae are presumably due to patient eye rubbing, pressure on the
eye while sleeping without a protective shield, the
patient touching a drop applicator to the cornea,
eyelid blinking that partially dislodges the flap, or
some other mechanism.
Every effort should be made to eliminate flap
striae as soon as they are identified and deemed to
be visually significant so that permanent irregular
astigmatism can be prevented. Frequently the
patient will report visual abnormalities that correlate with striae as early as the day after LASIK
surgery. This should prompt immediate intervention, since the longer striae are present, the more
difficult they are to eliminate. Any reduction in best
spectacle-corrected visual acuity present 1 week
after surgery should dictate careful inspection for
striae that may be difficult to detect at the slit lamp.
In many cases, these are detectable by inspection of
the red reflex with a funduscope. Immediate intervention is advised if visually significant striae are
detected.
Technique for elimination or reduction of striae
should include lifting of the flap. We believe that it
is less traumatic to rest the flap against the superi-
364
or conjunctiva rather than a sponge or metal spatula. The flap should be irrigated profusely (3 to 5 cc)
with sterile solution and smoothed with repeated
stroking of the posterior surface with a rounded
spatula. Gentle stretching of the flap with a pair of
forceps may be helpful. It is our preference to utilize
a relatively hypotonic saline solution such as 50%
balanced salt solution diluted with sterile water to
promote hydration of the flap due to the difference
in osmotic pressure between the tissue and the solution.39 Some have advocated merely using sterile
water for this irrigation, but such a wide disparity
in osmotic pressure, and the dramatic reduction in
tissue osmotic pressure, are likely to be more toxic
to both the epithelial cells and keratocytes. Other
surgeons believe that use of phosphate buffered
saline is sufficient.
Once the flap is returned to the stromal bed, further smoothing can be performed by stroking the
surface of the flap with a moist sponge while taking
advantage of the tethering effect of the hinge.
Finally, a bandage contact lens should be placed into
position to help prevent displacement of the
hydrated flap.
In our experience, only marginal improvement in
the appearance of the striae is noted immediately
following these maneuvers, but striae are often completely eliminated the next day. This is especially
likely if intervention is performed within approximately 1 week of the original procedure.
Presumably this indicates that further swelling of
the flap occurs in the hours following the procedure.
Some surgeons have advocated gently scraping
away the epithelium overlying the striae at the time
of this intervention to “release traction.” This could
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be useful in some cases, especially when intervention has been delayed, but there is increased risk of
diffuse lamellar keratitis (DLK) associated with the
epithelial defect. We have not been impressed with
“flap irons” and other devices used to press out striae without lifting the flap. Some surgeons, however,
have reported these instruments to be useful.
We believe it can be helpful to attempt removal of
striae regardless of how long they have been in
place. In some cases, subjective symptoms are
improved despite little apparent improvement in
the appearance of striae.
At times it is impossible to eliminate flap striae
or even reduce them substantially. It may be necessary to fit a gas-permeable contact lens to improve
visual function if symptoms persist despite attempted removal.
Postoperative Flap Displacement
Flap complications such as displacements may
also occur following surgery. In fact, Stulting and
colleagues22 noted that postoperative flap complications were almost two times as common as intraoperative flap complications. Thus, a flap my be displaced or lost in the first few days after LASIK.
However, flap displacement occurs most commonly
in the first 24 hours following LASIK, before the
epithelium has had time to heal over the lamellar
entry site. This is why the first postoperative day
examination so important. We believe this examination is so critical that it should be performed by the
surgeon. This, however, is controversial.
There are many potential causes of flap displacement. Not allowing sufficient time for the flap to
adhere to the bed is one potential cause. The optimal time is not known, but is likely to be related to
the overall technique. For example, despite irrigation of the flap and bed, we have found that
1 minute is sufficient if the flap is protected with a
contact lens. Recommendations of other surgeons
vary from 30 seconds to 5 minutes. The central
cornea should be maintained moist and the periphery dry to facilitate adhesion of the flap to the bed.20
There is controversy regarding the mechanism of
flap adhesion. Some speculate it is attributable to
endothelial pumping with return of the flap to its
original position and restoration of epithelial barrier function. We believe that a much longer period of
time is needed to restore hydration equilibrium in
the stroma following irrigation of the flap and bed.
We believe that the flap is most likely held in position the first day following surgery by simple tissue
adhesion.
Journal of Refractive Surgery Volume 17 May/June 2001
Although rare, the corneal flap can be displaced
from the bed many years following LASIK. Lemley,
and colleagues41 reported a patient who developed
partial dislocation of the flap from air bag deployment 17 months after LASIK. Patients should also
be told to avoid holding an infant, participating in
sports, or other activities that could lead to flap displacement by a finger or other object for several
days after surgery. It is a good policy to advise
patients to wear safety glasses in any environment
in which they could be struck in the eye for several
weeks after LASIK.
Flap displacement can be caused by excessive
pressure patching of the eye, patient rubbing of the
eye, or the posterior margin of the eyelid catching
the edge of the flap and flipping the flap out of position. Use of a soft contact lens, without patching, on
all eyes for the first 24 hours after LASIK or
enhancement may reduce the incidence of flap displacement. Using this technique, we have had only
two displacements out of a total of more than
3000 cases, both during the first 24 hours following
surgery. We recommend the Bausch and Lomb
Soflens 66 F/M base curve contact lens. Even after
LASIK for -12.00 D or more, or +6.00 D, this contact
lens usually fits well. The rather wide diameter of
the contact lens allows it to act as a glide to prevent
the eyelid from catching on the edge of the flap until
the epithelium has closed. Use of superior flap
hinges that can be created with the Hansatome,
Moria, and other microkeratomes may further
decrease the incidence of this complication since the
upper lid is less likely to catch on the edge of the flap.
Loss of the flap is relatively rare. It may still
occur, however, in the case of an inadvertent cap or
even with a flap if displacement occurs and the
hinge is severed by blinking. If the cap cannot be
located, severe irregular astigmatism and unpredictable refractive change may occur. Some surgeons have reported treating this complication by
crafting a new cap from a donor eye. The pressure in
the donor eye must be increased by fluid injection.
The microkeratome can then be used to form a new cap.
Epithelial Growth Within the Lamellar Interface
Ectopic epithelium growing within the LASIK
lamellar interface can produce significant morbidity.20,22,41-43 The term epithelial ingrowth may not be
appropriate in many cases since epithelial debris
may be implanted by the microkeratome blade
during flap creation.
The frequency of this complication appears to
vary from surgeon to surgeon and the associated
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LASIK Complications/Ambrósio and Wilson
factors are poorly understood. In a recent study of
1013 eyes by Stulting and coworkers22, 14.7% were
reported to have epithelial growth within the interface, with 1.7% of all of the eyes in the study requiring surgical intervention for epithelial ingrowth.
Conversely, in a recent study of 783 consecutive eyes
that had primary LASIK and 108 eyes that had
LASIK reoperation, only three eyes developed
epithelial growth within the interface.43 Only one of
these cases required intervention by the surgeon.
The reason for this major difference in incidence
between the two series is not clear. Stulting and
coworkers22 asserted that patients with anterior
basement membrane dystrophy were at increased
risk, but the other study did not note this association.
Precautions taken at the time of surgery can
lower the rate of epithelial growth within the interface. A discussion of factors that may be associated
with this complication and precautions that can be
taken to prevent it will provide some insight.
Epithelium within the interface is a potential
complication of all lamellar refractive surgical procedures, including LASIK, automated lamellar keratoplasty (ALK), and epikeratoplasty. When the
microkeratome blade cuts through the peripheral
epithelium, there will always be some epithelial tissue that adheres to the blade. This epithelial tissue
may be deposited within the interface during passage of the blade. Reusing a blade for multiple flaps
may increase the likelihood that this will occur since
the blade will become dull. If the epithelial tissue
contains viable cells, then these cells may proliferate and produce a nest of tissue within the interface.
Most of the time these cells will have limited proliferative potential and, if so, a nest of cells may
appear, stop expanding, and remain stable for years
within the interface. Occasionally, the nest of cells
will continue to expand and may produce more significant complications that dictate intervention.
The most common mechanism of epithelial
growth within the interface is ingrowth from the
periphery. This may be related to the morphology of
the flap edge with the incidence being lower in eyes
that have a flap with a scalloped edge, such as that
produced with the Hansatome microkeratome. In
other cases, a minor flap edge lift, for example by
the eyelid, may allow a peripheral tongue of epithelium access to the interface. Alternatively, the surgeon may not detect a tongue of epithelium that is
lying on the peripheral bed and replace the flap so
that this tissue is captured beneath the flap. This is
a common mechanism with LASIK enhancements.
366
Finally, epithelium may grow into the interface
from a central defect in the flap or cap. For example,
when a thin donut-shaped flap is produced or the
flap has a split in the center, there is increased risk
that epithelium can grow down from the surface and
into the interface.
Epithelial growth within the interface can be held
to a minimum by taking a few precautions at the
time of surgery. There are many excellent techniques for LASIK. One technique will be described
here to illustrate steps that may be helpful in preventing epithelial growth within the interface. An
aspirating lid speculum, which attaches to suction
with ports adjacent to the conjunctival surface, is
helpful to remove tears, epithelial debris, and
mucous from the fornix. An aspirating lid speculum
also allows liberal irrigation to eliminate any
implanted epithelium. Aspirating specula are commercially available from several sources. After the
laser correction is applied to the stromal bed, the
flap and bed are irrigated with BSS delivered with a
smooth-tipped cannula with an attached 0.2-µm filter. The cannula tip is used to dislodge any debris
that is not visible on both the flap and in the bed
during irrigation. This may be followed by a brief
sweeping of the bed and flap with lint-free sponges
(for example, a Merocel sponge, Solan Ophthalmic
Products, Jacksonville, FL). This sponge maneuver
is designed to remove epithelial debris that is not
visible through the operating microscope. Finally,
the bed and flap are irrigated one final time with filtered BSS, prior to smoothing the flap back into
position.
Other surgeons have different approaches.
Another common technique is to wait to irrigate the
lamellar interface after the flap has been rotated
back into position. A cannula is inserted beneath the
flap and profuse interface irrigation is performed
with filtered BSS. A recent study with a relatively
low rate of epithelial growth within the interface
after LASIK used this method.43
Some method of irrigation after flap preparation
is useful not only for reducing the incidence of
epithelial debris and other foreign materials within
the interface, but also to dilute agents that might
cause diffuse lamellar keratitis.
LASIK enhancement may be associated with a
higher risk of epithelial growth in the interface,
especially if a spatula is inserted through the
epithelium and used to break open the interface by
sweeping along the flap edge. Epithelial tissue will
adhere to the spatula and be transferred onto the
interface using this approach. If some of these cells
Journal of Refractive Surgery Volume 17 May/June 2001
LASIK Complications/Ambrósio and Wilson
A
B
Figure 8. A) A small island of epithelial growth within the interface that remained stable without growth and did not require intervention. The
inset shows a magnified view of the epithelial nests (arrows). B) Epithelial growth overlying the pupil (arrow) after LASIK should be removed.
The inset shows a magnified view of some of the epithelial nests (arrows).
are viable, they may grow. Even though they are not
stem cells, they may be transient amplifying cells
with considerable proliferative potential. It is
preferable to break open the interface at a single
clock hour 180° from the hinge, grasp the edge of the
flap gently with 0.12 forceps or smooth curved forceps, and gently peel back the flap. This will typically give a smooth edge of epithelium and limit
introduction of epithelium into the interface. Any
prominent adhesions between the flap and the bed
can be broken with a dry, lint-free sponge.
Otherwise, interface precautions are identical to
those for the primary LASIK procedure.
If epithelial growth within the interface is noted
following LASIK, then treatment is dependent on
the extent and location of the ectopic epithelial tissue. A small nest of epithelium that is present in the
periphery can be left alone (Fig 8A) if it does not
progress or affect visual acuity (ie, by lifting the flap
to induce irregular astigmatism). Clinically significant epithelial growth within the interface can
affect vision by two primary mechanisms. First, it
may grow to infringe on or cover the pupil (Fig 8B).
If the epithelium within the interface continues to
grow and threatens the pupil, then the flap should
be lifted and the epithelium removed. A more common complication of epithelial growth within the
interface is induction of irregular astigmatism
because of localized lifting of the flap. This can produce a pseudodecentration on corneal topography. A
decrease in best spectacle-corrected visual acuity or
uncorrected visual acuity attributable to effects of
the interface epithelium on the flap should prompt
intervention. Some patients also experience a
foreign body sensation when there is epithelial
Journal of Refractive Surgery Volume 17 May/June 2001
ingrowth at the flap margin. This is an indication
for removal of the epithelium, even if it is confined
to the periphery.
Rarely, epithelium within the interface can
induce tissue necrosis in the overlying flap or melting of the edge of the flap. This is caused by the
anterior stroma of the flap being deprived of nutritional factors derived from the aqueous humor. The
first sign of impending necrosis is often inflammation in the stroma overlying the area of ectopic
epithelium. A spontaneous epithelial defect occurring on the surface above a nest of epithelium is
another danger sign.44 Detection of inflammation or
a spontaneuos epithelial defect should prompt
immediate removal of the epithelium from the interface.
Typically, the epithelium can be scraped gently
from the bed and flap with a scalpel or spatula.
Some have advocated only lifting the sector where
the epithelial ingrowth is located. We believe lifting
the entire flap provides better access and decreases
the chance that irregular astigmatism will be
induced by asymmetric lifting of the flap. Once the
nest of epithelium is removed, the interface should
be irrigated with filtered BSS and cleaned with a
lint-free sponge, as was described for primary
LASIK.
Epithelial ingrowth may recur—although
rarely—after repeated removal. In these rare cases,
manual removal of the epithelium can be augmented with a dusting of both the bed and posterior flap
surfaces with the excimer laser in PTK mode to
ablate nests of cells that cannot be seen.20 Care
must be taken when using the laser with this
technique so that severe irregular astigmatism is
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LASIK Complications/Ambrósio and Wilson
not induced by overlapping, multiple laser bursts.
Central corneal ablation should be performed, centered on the entrance pupil. Only three or four pulses of the laser are required to irradicate a monolayer of epithelial cells. Since the visible epithelium
will have already been removed with a spatula or
scalpel, only a few pulses should be used. It is rare
that there is a need for this laser augmentation.
Lamellar Interface Debris
Foreign materials may be introduced beneath the
flap during the LASIK procedure. These include
mucous or oil from the tear film, metal shavings or
other materials from the microkeratome blade, particles from a sponge, red blood cells, and lashes. No
lubricating oils or other liquids should be used on
the microkeratome because they can contaminate
the interface.
Small particles that are in the periphery and not
associated with keratitis or corneal vascularization
can be left undisturbed. If foreign bodies overly the
entrance pupil should probably be removed.
Regular Astigmatism
Changes in regular astigmatism are common
after LASIK. In some cases, uncorrected visual acuity will be limited by regular astigmatism, even
though the spherical equivalent refraction of the eye
has been corrected to plano. In these cases, toric
enhancement can be performed to decrease regular
astigmatism. If the surgeon works in a location
where hyperopic astigmatism ablation is not available, then astigmatic keratotomy (AK) remains an
option.
Some surgeons have used AK beneath the flap at
the time of the primary LASIK procedure. However,
there have been reports of serious perforations and
resulting difficulty obtaining flap adherence with
this technique. Our preference is to use AK as a
later procedure when the spherical refractive error
has been reduced or eliminated with LASIK.
Typically, AK is performed using a rectangular
blade and the Lindstrom-Casebeer nomogram with
an optical zone diameter of 7 mm. Since the initial
blade setting with this nomogram is the central
corneal thickness (that has been reduced by LASIK
ablation) + 40 µm, the initial AK tends to be conservative. If necessary, re-cutting within the original
incision is easily performed a few weeks later.
Limbal AK is also an option for low levels of astigmatism.
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Irregular Astigmatism, Glare, Halos, and Other
Disturbances of Visual Quality
Irregular astigmatism and an associated loss of
best spectacle-corrected visual acuity is a common
complication of LASIK. There are many factors that
contribute to irregular astigmatism following
LASIK, including irregular flap cuts, flap misalignment, flap striae, ablation decentration, and epithelial growth within the interface.
A common irregularity that may be noted following LASIK is a central island or peninsula. There
appears to be more of a tendency to generate central
islands or peninsulas with LASIK than with PRK.
To some extent, this may be related to the higher
corrections that are attempted with LASIK. Another
possibility is a “wetter” stroma at the level of LASIK
relative to PRK. There also seems to be more of a
tendency for fluid to accumulate in the center of the
ablation during LASIK, resulting in excimer laser
energy absorption by water rather than stroma.
Anti-island software should be utilized with all
broadbeam lasers. Scanning excimer lasers do not
appear to have a proclivity to form central islands,
although they have been noted in rare instances.
In the authors’ experience, there is little tendency for a central island to spontaneously resolve over
time following the LASIK procedure. Thus, central
islands associated with LASIK may be treated within a few months of the primary procedure.
To a large extent, treatment of islands and peninsulas remains an art. Attempts can be made to measure the diameter and height of the island and to
enter a corresponding custom ablation into the
excimer laser. However, caution should be taken in
applying such a technique since computerized
corneal topography instruments are notoriously
inaccurate in making measurements in the center of
the cornea. Thus, when using the topographic map
to guide central island treatment, one should be conservative in applying treatment. In some cases, the
flap must be lifted more than once to apply laser
energy to eliminate a central island. Peninsulas are
typically even more difficult to treat and usually
attempts to eliminate them are unsuccessful.
Decentration can result in severe irregular astigmatism overlying the entrance pupil.20 This can
cause glare, monocular diplopia or multiplopia, and
halo phenomenon.23 Patient fixation tends to be
more difficult after the flap is lifted. To some extent,
this can be remedied by performing the ablation
under the lowest possible illumination so that the
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LASIK Complications/Ambrósio and Wilson
patient can see the fixation target. Thus, the
illumination should be very dim, while still allowing
the surgeon to monitor the entrance pupil upon
which the ablation should be centered. For example,
with the VISX S2 laser, the ring light should be
turned off and the side illumination placed at its
lowest setting just prior to beginning the ablation.
Once decentration has occurred, correction can be
difficult and at present is more art than science.
One difficulty is that there is no epithelium to use as
a masking agent, as there is to treat decentration
following PRK. Viscous agents such as methylcellulose or diluted Healon can be used to mask the area
that has already been ablated, while attempting to
reablate overlying the entrance pupil. Some surgeons have proposed using an identical ablation
that is similarly decentered 180° in the opposite
direction. Only anecdotal reports have demonstrated the efficacy of these approaches in eyes that have
had LASIK. Hopefully, scanning lasers will eventually be able to perform custom ablations driven by
real time corneal topography and wavefront analysis. Until then, the best treatment is prophylactic
and the surgeon should strive to insure that the primary ablation is centered overlying the entrance pupil.
How significant is irregular astigmatism following LASIK? In a study of 995 eyes that underwent
LASIK with the Summit Apex Laser using a custom
nomogram, Stulting and coworkers22 reported that
3.3% of eyes lost two or more lines of best spectaclecorrected visual acuity with 1 year of follow-up.
Irregular astigmatism was attributed primarily to
microkeratome complications, flap wrinkles, and
ablation abnormalities. Our experience with the
ACS microkeratome was similar, with 2.9% of eyes
having lost two lines of best spectacle-corrected
visual acuity with follow-up of 6 months (Wilson,
unpublished data). Our more recent studies with
the Hansatome microkeratome and the VISX S2
laser have demonstrated that loss of two or more
lines at 1 year after LASIK can be lowered to 1% for
eyes with -8.00 D or less of myopia prior to surgery
(Wilson, unpublished data). This percentage
remains significant, especially when one considers
that the magnification effect should result in all
eyes gaining one or more lines of best spectaclecorrected visual acuity, at least for corrections above
5.00 to 6.00 D. Irregular astigmatism with loss of
best spectacle-corrected visual acuity may be the
most significant complication that limits the efficacy and safety of LASIK. The primary treatment is to
strive to avoid all of the factors that are associated
with irregular astigmatism. Time is an ally.
Journal of Refractive Surgery Volume 17 May/June 2001
Irregular astigmatism, as measured with quantitative descriptors such as the surface regularity index
(SRI), tends to decrease over time following the procedure. However, even with new microkeratomes
and smoother laser ablations, irregular astigmatism
is likely to remain a complication of LASIK because
many of the factors that contribute to it are independent of these instruments.
In some cases, a rigid gas-permeable contact lens
must be fit to restore vision following LASIK. If the
irregular astigmatism is associated with scarring,
for example with a small central irregular cap, or a
rigid contact lens cannot be fit or tolerated, then a
penetrating keratoplasty may be required to restore
vision.
Glare and halos are more common in patients
treated for high myopia or high hyperopia. In some
patients these are only noted at night. They are typically attributable to optical imperfections resulting
from laser correction (Boxer-Wachler BS, Frankel
RA, Krueger RR, Durrie DS, Assil KK. Contrast sensitivity and patient satisfaction following photorefractive keratectomy and radial keratotomy. Invest
Ophthalmol Vis Sci 1996;37(suppl):S19). Many surgeons believe that large pupil size is a risk factor for
glare and halos.45 As the pupil dilates, it seems more
likely that glare, halos, and other visual imperfections would be attributable to the junction between
ablated and un-ablated cornea. However, we have
noted many patients who have no glare or halos
despite having a high correction with large pupils.
On the other hand, we have had patients complain
of glare and halos despite small pupils with a low
correction. Clearly, other factors such as patient perception, centration, irregularity of the ablation, and
irregular healing are also important. In general,
however, we have a full discussion with the patient
about the potential complications and are reluctant
to offer LASIK to patients with high myopia
(greater than -5.00 or -6.00 D) and pupils larger
than 7 mm.
Pupillometers can be useful, but the room lighting must be standardized for the measurements to
be meaningful. We have found that videokeratoscope images provided along with topographic maps
on instruments such as the Humphrey 992 topographer are useful for estimating the size of the pupils
and providing a permanent record. These videokeratoscope images are obtained with constant lighting
and can easily be correlated with pupil size measured with a pupillometer.
Larger ablation diameters may be helpful in
reducing these complications, although consideration
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LASIK Complications/Ambrósio and Wilson
must also be given to the thickness of the stroma
ablated. There is hope that custom cornea ablations
that eliminate higher order aberrations will be of
benefit, but conclusive evidence is not yet available.
Gas-permeable contact lenses can be useful for
these patients if the optical imperfections are significant. We have noted that providing spectacles that
correct approximately the -0.50-D myopic shift
induced by spherical aberration (attributable to
pupil dilation at night) can be helpful.
Overcorrection
Overcorrection is disappointingly common following LASIK. As with many LASIK complications, the
best treatment is prophylactic. It is important to utilize a LASIK ablation nomogram developed for the
specific laser being used because there are typically
large reductions of 20% or more for LASIK compared to PRK when performing high corrections.
Typically, this is obtained from another surgeon utilizing the same laser and then adjusted based on
early results with increasing levels of correction.
In most cases, overcorrection is attributed to a
wound healing response that is less than the average person. There are, however, other causes. For
example, a common source of overcorrection for
inexperienced surgeons is delay in proceeding to
ablation once the flap is lifted. This results in dessication of the stromal bed and an increase in the
amount of tissue removed per pulse. This interval
should be standardized for the individual surgeon.
Over time, this consistent interval will be incorporated into the nomogram developed by the individual surgeon.
Fortunately, most lasers can now perform hyperopic treatment. Our experience is that enhancement
for hyperopia is highly effective since the amount of
overcorrection is typically 1.00 D or less. Use of
enhancement for hyperopia is facilitated by having
a large flap. Thus, the approximately 9.5-mmdiameter flaps generated with the Hansatome or
Innovatome microkeratomes are optimal. If a smaller flap has been used, the results may not be as good
since the ablation diameter for the hyperopic
enhancement must be reduced, and this is associated with a greater tendency for regression.
Undercorrection and Regression
Early dogma claimed that there was no regression following LASIK. This followed from the erroneous belief that there was no wound healing associated with LASIK. Recent studies, however, have
demonstrated conclusively that wound healing
370
occurs following LASIK (Wilson SE. Role of apoptosis in wound healing in the cornea. Cornea
2000;19(suppl 1):S7-S12).46-51 It seems likely that
regression in LASIK is attributable to stromal
remodeling and/or epithelial hyperplasia.52 Sources
of regression are thought to be a greater than average wound healing response or complications that
promote healing. For example, a thin flap may be
associated with regression since the stromal wound
healing response and epithelium-modulating
growth factor production are more likely to be in
proximity to the epithelium. This probably promotes
epithelial hyperplasia. Other factors such as epithelial defects produced by the microkeratome and diffuse interface keratitis are also likely to be associated with a stronger wound healing response and
regression. The higher the level of correction, the
more likely regression due to wound healing will
occur. In our experience, regression is most common
in hyperopic corrections, especially those over
+5.00 D.
Fortunately, most regression that occurs following LASIK is treated easily by lifting the flap and
reablating with the excimer laser. In the authors’
experience, most flaps can be lifted for years after
the primary procedure. Some surgeons prefer to
recut a new flap. This is easily done, but there is a
higher risk of serious flap complications.
A surface ablation excimer laser technique can
also be applied with caution in eyes in which there
is concern about lifting an existing flap or cutting a
new one. Transepithelial PRK can be applied to correct a small amount of myopia in these cases. It is
probably wise to limit these PRK corrections to eyes
with only a small amount of myopia (less than
-1.50 D) that are at least 1 year removed from the
primary procedure, since higher corrections have
been associated with significant haze and regression. Care should be taken in applying this PRK
enhancement method until more cases have been
studied. Many surgeons believe it is contraindicated.
Early regression of refractive effect after LASIK
for myopia appears to be a consequence of an
increase in corneal thickness that is probably due to
thickening of the epithelium. Lohmann and colleagues52 reported regression related to postoperative epithelial hyperplasia. An increase of 10 µm in
epithelial thickness resulted in approximately
1.00 D of regression.
The study of the corneal microstructure using
new methods like ultrasound biomicroscopy, optical
coherence tomography53, and confocal microscopy
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LASIK Complications/Ambrósio and Wilson
may give us important information such as the
thickness of the cornea posterior to the flap. Such
measurements can help the surgeon distinguish
between epithelial hyperplasia and stromal remodeling as the cause of the refractive regression.53
Progressive Corneal Steepening After LASIK
Corneal steepening can occur after LASIK and
may progress to ectasia, producing a keratoconuslike clinical appearance. Some reports suggest this
is even possible after treatment of relatively low
myopia.54 It is especially important to detect early
keratoconus or forme fruste keratoconus preoperatively since kerectasia may occur with rapid progression.55,56 Geggel and colleagues57 presented a
case of unilateral iatrogenic keratectasia that developed 10 months after bilateral LASIK. This case
involved enhancement surgery using a broad-beam
excimer laser to treat -6.60 D of myopia. The ectasia
progressed rapidly over a 12-month period.
Preoperative corneal thickness and depth of
excimer laser ablation must be evaluated before
LASIK to ensure that adequate posterior corneal
stroma is preserved. Previous experience with
lamellar surgery suggests that at least 250 µm of
central posterior stromal tissue and more than half
the original corneal thickness should be preserved
to maintain long-term corneal integrity and avoid
postoperative corneal steepening. If a 160-µm flap is
created for LASIK, the average 550-µm cornea will
have 140 µm of corneal stroma available for
ablation.
Depending on the excimer laser, ablation zone
size, and ablation nomogram used, the maximal
LASIK correction for the average cornea ranges
from 10.00 to 15.00 D.58 Of course, the 250-µm posterior bed thickness that is recommended by many
experts is merely an estimate. In rare cases, this
may be insufficient.
There is a significant standard deviation in flap
thickness obtained with all currently available
microkeratomes. A more conservative approach is to
assume the flap is 40 µm thicker than the average
flap thickness obtained with the specific microkeratome that is being used. This may limit corrections
in many patients to less than -8.00 D of myopia.
Anterior bulging of the posterior corneal surface
has been correlated with residual corneal bed thickness using measurements performed with the
Orbscan slit scanning corneal topography/pachymetry system.59-63 This remains controversial, however,
since the accuracy of these measurements has not
been verified64-65 and posterior ectasia is commonly
Journal of Refractive Surgery Volume 17 May/June 2001
noted with this instrument, even in thick corneas
that underwent low corrections.64,65 Many of these
may be artifact.64,65
Videokeratography is fundamental to the screening of candidates for refractive surgery. Appropriate
preoperative detection and management of corneal
topographic abnormalities are essential steps in
every corneal refractive surgical procedure. A higher incidence of keratoconus has been reported in
prospective refractive surgery patients than the
general population, most likely due to selfselection.6 Patients with irregular astigmatism
caused by corneal ectasia do not achieve good vision
with spectacles and tend to opt for rigid contact
lenses or seek refractive surgery. It is important to
identify these patients since they are more likely to
have an unacceptable outcome.
Dry Eye and LASIK-induced Neurotrophic Epitheliopathy
Dry eye and other ocular surface disorders are
frequent following LASIK. Lindstrom and colleagues66 reported 3.4% incidence of dry eye after
hyperopic LASIK.
Patients with mild to moderate dry eye frequently pursue refractive surgery because of increasing
intolerance to contact lenses. Many of these patients
are asymptomatic unless they are wearing contact
lenses and most do well after LASIK. The health of
the ocular surface should be optimized prior to
surgery with non-preserved artificial tears and ointments. Consideration should be given to punctal
occlusion for patients with persistent corneal rose
bengal staining despite frequent artificial tears and
bedtime ointments. Topical 0.05% cyclosporine
treatment may be beneficial, but this medication is
only available on a custom basis in the USA and the
available formulations are not well tolerated. If
Restasis (Allergan, Irvine, CA) is eventually
approved, then this formulation may be much better
tolerated and, therefore, more likely to improve the
ocular surface prior to refractive surgery. Severe dry
eye patients are not good candidates for LASIK. We
have consulted on several of these patients with
serious wound healing problems and persistent
epithelial defects.
Many patients have dry eye symptoms for several months following LASIK. This is common even if
the patient had no symptoms or signs of dry eye
prior to surgery. Most of these patients have no
signs of dry eye after LASIK either. Other patients
develop mild to severe punctate epithelial erosions,
punctate epithelial keratopathy, and rose bengal
staining confined to the flap (Fig 9). We have found
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LASIK Complications/Ambrósio and Wilson
A
B
Figure 9. A) Rose bengal staining, punctate epithelial erosions, and punctate epithelial keratopathy (arrow) of the cornea in an eye that had
LASIK. The patient had no history of dry eye prior to LASIK and was diagnosed with LASIK-induced neurotrophic epitheliopathy. Note the ample
tear lake at the inferior lid margin. Similar changes occurred in the left eye. The condition resolved by 6 months after surgery. B) Higher
magnification view of the cornea of another patient with LASIK-induced neurotrophic epitheliopathy. Arrow indicates slit beam on anterior surface where punctate epithelial erosions are best seen.
that corneal rose bengal staining develops in
approximately 2% of eyes that did not have this sign
prior to LASIK (Wilson, unpublished data). Some
investigators have suggested that tear production
may be decreased following LASIK, but we have
noted little difference in the Schirmer test without
anesthesia between patients with corneal rose bengal staining and those without it at the same time
points after surgery, if there was no dry eye prior to
surgery. It makes physiological sense that LASIK
would have little effect on tear production because
only the central corneal nerves are severed. The
peripheral corneal and conjunctival nerves that contribute to the ocular surface–central nervous system–lacrimal gland loop remain intact.
Our observations suggest that corneal surface
abnormalities that develop after LASIK are attributable to LASIK-induced neurotrophic epitheliopathy due to temporary interruption of the corneal
nerves during formation of the flap.15,16 The corneal
epithelium is known to derive neurotrophic factors
from the corneal nerves.67-69 Consider the corneal
pathology that frequently develops in response to
trigeminal neuropathy secondary to trauma or
tumors or experimental denervation in the rabbit
cornea.70 Evidence that the condition noted in
LASIK patients is related to trigeminal denervation
is, 1) development of the condition in many eyes
with no signs or symptoms of dry eye prior to
surgery, 2) changes are for the most part confined to
the flap with the peripheral cornea being spared,
3) the area of the cornea around the hinge where
nerve trunks are spared remains normal, 4) tear
372
production monitored with the Schirmer test without anesthesia is relatively normal, and 5) the condition typically resolves approximately 6 to
8 months after LASIK. This corresponds well with
the length of time required for regeneration of the
nerves into the flap after LASIK.68,69
Patients with signs of preexisting dry eye also
develop LASIK-induced neurotrophic epitheliopathy. In fact, our experience is that they develop it
more frequently and more severely than patients
without dry eye prior to LASIK. Development of
LASIK-induced neurotrophic epitheliopathy is suggested by marked worsening of corneal surface
abnormalities in these dry eye patients.
Many patients with LASIK-induced neurotrophic
epitheliopathy are asymptomatic since the central
cornea is hypoesthetic for several months after the
procedure. If, however, the ocular surface pathology
affects the corneal epithelium overlying the
entrance pupil, these patients may have frustrating
fluctuating vision and decreased best corrected visual acuity that persist until the condition resolves.
Treatment of these patients is limited to frequent
non-preserved artificial tears and ointments at bedtime. Some patients seem to benefit from punctal
occlusion, even though they have normal tear levels.
The main treatment for these patients is reassurance that the condition typically resolves by 6 to
8 months after surgery. If the eye has normal tear
levels, then soft contact lenses may improve the
visual problems by masking the surface abnormalities until the nerves regenerate. Contact lenses
should not be used in eyes with low tear levels due
Journal of Refractive Surgery Volume 17 May/June 2001
LASIK Complications/Ambrósio and Wilson
Figure 10. Diffuse lamellar keratitis (Grade 1)
at 1 day following LASIK enhancement with
lifting of the flap. Note diffuse inflammation at
the level of the interface (arrows). The inset
shows a magnified view of the area indicated
by the box. This patient had mild symptoms of
discomfort. The symptoms and signs resolved
after 3 days of topical corticosteroid
treatment.
to the increased risk of microbial infection. We use a
Schirmer test without anesthesia of 8 mm or more
as an adequate level.
LASIK-induced neurotrophic epitheliopathy
typically recurs with enhancement. We suggest
enhancing one eye at a time when LASIK-induced
neurotrophic epitheliopathy develops after primary
LASIK.
Interestingly, patients who have PRK do not
appear to develop a LASIK-induced neurotrophic
epitheliopathy-like syndrome. This may be attributable to only the nerve endings being ablated.
Therefore, nerves regenerate more quickly68 and the
regenerating nerve endings are already in close
proximity to the overlying corneal epithelium. For
this reason, we consider PRK as an alternative to
LASIK for patients with low myopia and mild or
moderate dry eye prior to surgery.
Diffuse Lamellar Keratitis
Smith and Maloney thoroughly described diffuse
lamellar keratitis (DLK) (American Academy of
Ophthalmology, San Francisco, CA, November,
1997).71 Other reports have appeared since that
time (Linebarger EJ. Diffuse lamellar keratitis:
trouble in paradise? ASCRS Film Festival, Grand
Prize Winner, 1999).20,41,72-78 It has also been called
sands of the Sahara syndrome (Bobby Maddox, MD,
El Paso, TX, coined the phrase), because of the characteristic wavy appearance at slit-lamp examination.
DLK is characterized by pain, photophobia, and
reduced vision associated with diffuse non-infec-
Journal of Refractive Surgery Volume 17 May/June 2001
tious inflammation at the level of the interface during the first few days after LASIK (Fig 10). It may
be multifocal in some cases. There is little or no
anterior chamber reaction and the conjunctiva is
relatively uninflammed. In severe cases, it is associated with stromal necrosis and irregular astigmatism.
Infection should always be considered in DLK.
We suggest culture and initial treatment with fortified antibiotics (amikacin 20 mg/ml and vancomycin
50 mg/ml every hour) until infection has been ruled
out, even if topical corticosteroids are also started at
the time of diagnosis. Some surgeons feel that the
specific diagnosis can be made based on the appearance at the slit lamp and, therefore, the toxicity of
fortified antibiotics can be avoided. However, we
have seen two cases of infectious keratitis in which
treatment was inappropriately delayed because of
erroneous diagnosis of DLK. Both cases had severe
vision loss.
The incidence of DLK is highly variable. One
report noted an incidence of approximately 1 in
500.74 Some high volume LASIK surgeons have
reported never seeing a case in their own practice.
We have seen only two mild cases in 3000 LASIK
procedures. Others have experienced focal outbreaks of DLK that have included dozens of
patients.
Grading systems have been proposed to distinguish the level of inflammation associated with
DLK (Hatsis, American Society of Cataract and
Refractive Surgery, San Diego, CA, April 1998). In
373
LASIK Complications/Ambrósio and Wilson
this system, DLK is graded from 1 (mild) to
4 (severe). Another grading system has been
proposed by Linebarger (Linebarger, 1999, cited
above).75
Stage 1 DLK is typically seen on day 1
postoperatively as white, granular cells in the
periphery with sparing of the visual axis.
Stage 2 Typically seen on postoperative day 2 or
3, shows white cells in the visual axis.
Stage 3 DLK involves an aggregation of cells
clumped in the visual axis and associated with haze
and reduced vision.
Stage 4 Involves central stromal necrosis, melt,
and secondary hyperopia with irregular astigmatism.
Grading systems of this type are subject to
observer bias, but may be useful for communication
among surgeons. Patients with mild cases (grade 1)
typically have normal vision and little or no symptoms. At the other extreme, severe (grade 4) cases
typically have decreased vision and severe pain
associated with marked interface inflammation and
necrosis that results in topographic flattening of the
corneal contour, secondary irregular astigmatism,
and poor vision.
Many potential etiologies for DLK have been proposed (Linebarger, 1999, cited above).75-77 Most of
these are based on speculation without supporting
data. These have included betadine from surgical
preps, impure balanced salt solution, retained meibomian secretions and other tear film components,
metallic debris, use of improper detergents, talc
from gloves, thermal effects from the excimer laser,
lubricants on the microkeratome or blades, topical
medications such as anesthetics, bacterial cell wall
hypersensitivity, and biofilms from inadequate sterilization protocols. The cause is likely multifactorial.
The microkeratome or blade can be excluded in
cases that occur following enhancement with lifting
of the flap. Virtually all of these factors can be
excluded in cases where DLK occurs following a
simple epithelial defect in eyes that had prior
LASIK.78
The bacterial cell wall hypersensitivity mechanism could have been the underlying factor in a
recent epidemic of DLK.77 The authors suggested
that the microkeratome or irrigating cannula
became contaminated by bacteria. These bacteria
may reside in water left standing in the sterilizer. If
the contaminated instruments are cleaned and left
to dry, bacteria could proliferate on residual trace
protein and the bacterial cell count could increase
significantly. If the instruments are then autoclaved
374
prior to surgery, the bacteria will be killed, but heat
stable lipopolysaccharides may be produced. The
lipopolysaccharides are not detoxified by autoclaving. This hypothesis holds that lipopolysaccharides
cause an inflammatory reaction that digest stromal
collagen. Lipopolysaccharide is a highly variable
polysaccharide chain covalently attached to lipid A.
Lipid A is the toxic moiety of lipopolysaccharide.
Water should not be left standing in the basin in
sterilizers. This promotes the growth of bacteria and
could trigger DLK.77 Whether or not this is the true
mechanism of DLK, it appears prudent after each
surgery day to clean the autoclave and water basin,
rinse thoroughly with distilled water, completely
dry the interior of the microkeratome and basin,
and let the instrument stand dry. We recommend
discussing appropriate care of the microkeratome
with the manufacturer.
There is new experimental evidence for another
endogenous mechanism for DLK. DLK has been
noted after epithelial abrasions following LASIK.78
It has also been noted in eyes following LASIK that
subsequently developed epithelial ingrowth at the
same site.20,35 This potential involvement of the
corneal epithelium led to searches for a mechanism.
A recent study (Hong, Lee, Liu, and Wilson, unpublished data, 2000) has demonstrated that interleukin-1 (IL-1) stimulates corneal fibroblasts to produce monocyte chemotactic and activating factor
(MCAF) and other chemotactic factors. MCAF and
these other cytokines attract monocytes. In the case
of LASIK it seems that the interface would offer a
path of least resistence for penetration of cells into
the corneal stroma. Interleukin-1 is released from
corneal epithelial cells in large amounts following
cell injury or death. These data suggest that injury
to the surface epithelium or epithelial debris left
within the LASIK interface triggers production of
factors that are chemotactic for inflammatory cells
via interleukin-1 release. This mechanism could
account for many DLK cases.
Surgical technique may limit DLK, whatever the
underlying mechanism. Many high volume practices
that have noted little DLK include interface irrigation after the ablation as a step in LASIK. This
includes our own center where the interface is typically irrigated with 1 to 2 cc of 0.2-µm filtered BSS
just prior to replacing the flap to its original position. This seems likely to decrease the concentration
of any exogenous or endogenous factors that might
be involved in the induction of DLK. In our experience, this irrigation does not increase the rate of
flap displacement, perhaps because we routinely
Journal of Refractive Surgery Volume 17 May/June 2001
LASIK Complications/Ambrósio and Wilson
use a Bausch and Lomb Soflens 66 F/M base curve
lens for the first night after surgery.
The majority of eyes that develop DLK will
respond rapidly to intensive topical corticosteroid
treatment. Our preference is to use Pred Forte 1%
every hour. Other corticosteroids appear also to be
effective, but fluoromethalone likely has insufficient
penetration and anti-inflammatory activity to be
optimal for this purpose. With treatment, the interface inflammation typically subsides over a period of
a few days to a week and the corticosteroids are
tapered as this decrease in inflammation is noted. A
small number of patients will progress with intensive corticosteroid treatment and other patients will
present with severe inflammation. Progression
despite intensive corticosteroid treatment or presentation with severe DLK should prompt lifting of
the flap, cleaning with lint-free sponges, and profuse irrigation with 0.2-µm filtered balanced salt
solution. Intensive topical corticosteroid treatment
should be continued or instituted. Some surgeons
add oral prednisone 60 mg per day with tapering as
the inflammation subsides. We recommend that cultures for bacteria and fungus be taken in these cases
despite surgeon certainty of the diagnosis.
Eyes with severe DLK are at high risk for stromal
necrosis that may be focal and result in haze, irregular astigmatism, and hyperopic shift. Some of
these cases benefit from Healon/PTK smoothing
once the DLK has completely resolved. However,
several months should pass before such treatment is
attempted since a significant amount of improvement can occur spontaneously.72
Gas-permeable contact lenses are useful in severe
cases that do not improve spontaneously. Rarely is
penetrating keratoplasty needed to restore vision.
Infection
Microbial keratitis is an uncommon complication
following LASIK. Standard practices include the
use of sterile instruments and gloves, along with the
application of antibiotics. Preparing and draping
the eyelids and the laser hand controls will decrease
exposure to bacterial and fungal pathogens. We prefer to use a Betadine swab to clean the eyelids and
eye lashes, taking care not to transfer Betadine into
the eye. An adhesive-backed plastic drape is applied
so that the eyelashes are covered. A fluoroquinolone
antibiotic is applied four times per day for 5 to
7 days after surgery.
A number of prominent surgeons do not use
gloves during LASIK and do not report infection as
a complication. Other surgeons prefer to wear
Journal of Refractive Surgery Volume 17 May/June 2001
surgical gloves. In the event of infection it would be
difficult to defend not using gloves.
The augmented risk of bilateral simultaneous
LASIK compared with sequential LASIK appears to
be low. Nevertheless, it is important to inform the
patient of the serious potential risk in the event that
bilateral, simultaneous infection occurs.79 Bilateral
surgery should probably not be performed on
patients with a known history of impaired immunity. A bilateral microbial infection was reported80 in a
human immunodeficiency virus-infected patient
with no history of opportunistic infections and a
T-helper lymphocyte count of 300 cells/mm3.
Watanabe and colleagues81 also reported a case of
bilateral staphylococcal bacterial keratitis after
LASIK.
Infectious agents that have been reported after
LASIK include virus, bacteria (including atypical
mycobacteria and norcardia), fungus, and parasite
(Al-Reefy M. Bacterial keratitis following laser in
situ keratomileusis for hyperopia. J Refract Surg
1999;15(suppl):S216-S217).82-93 Culture-negative
ulcerative keratitis has also been reported to occur
after LASIK. These cases have been responsive to
topical corticosteroids and may represent severe
DLK. Infection must be ruled out in these rare
cases.94,95
0ne case of abscess with endophthalmitis has
been reported.96 Corneal abscess, hypopyon, and an
intense vitreous cellular reaction associated with
endophthalmitis developed 3 days after uneventful
astigmatic myopic LASIK. The patient was immediately given intravenous ciprofloxacin and topical
vancomycin and ceftazidime. The hypopyon resolved
1 day after therapy was instituted. The infecting
organism was Streptococcus pneumoniae. Bestcorrected visual acuity 7 months later was 20/25
with a refractive error of -4.00 D. A stromal scar was
believed to be responsible for the reduction in
visual acuity.
If an infiltrate is noted, it should be treated as
infectious until proven otherwise. Consultation with
a cornea and external disease specialist is advised.
Treatment must be aggressive because of the potential for rapid progression due to the interface
extending across the cornea.
The deeper location of the typical microbial infection in LASIK makes it more difficult to obtain adequate access for culture and potentially decreases
effective penetration of antimicrobial therapy. When
infiltrates are noted within the stroma, it is recommended that the flap be lifted to obtain sufficient
material for culture. This also allows antibiotics to
375
LASIK Complications/Ambrósio and Wilson
be applied directly to the interface. Cultures are
critical and should include tests for bacteria,
fungus, and acanthameoba. Acid-fast infection
should be evaluated using the Ziehl-Nielson stain.
Fortified antibiotics (amikacin 20 mg/ml and vancomycin 50 mg/ml) should be applied every hour
around the clock until the infection is controlled.
These medications can be adjusted based on the
results of culture and sensitivity testing. Some cases
of lamellar interface infection following LASIK do
not respond to surface application. It may be necessary to retract the flap with sutures to gain sufficient penetration of the antibiotics. Rarely, the flap
may have to be removed if the infection cannot be
controlled.
Fungal keratitis is a potentially devastating condition. It occurs most commonly following an injury
involving vegetable matter. More than 60 species of
fungi have been reported to cause keratomycosis,
with the causative organism varying by geographic
locale.97 We consulted on a case of fungal keratitis
where there was delayed diagnosis resulting in the
need for penetrating keratoplasty. Always obtain
fungal cultures when microbial infection is
suspected.
Candida and Aspergillus species are the most
common fungal infections in the northern United
States and Fusarium species are most common in
the southern United States. Aspergillus appears to
predominate internationally. In one series, topical
amphotericin B was used when a diagnosis of
Candida species infection was made; natamycin
was used in non-candidal infections.98 Fungal keratitis can occur in the early postopoerative period or
several months after the LASIK procedure. Risk factors for the development of fungal keratitis include
trauma and excessive topical corticosteroid use.90,91
Although nocardia keratitis is a rare condition, a
high index of clinical suspicion should be maintained in agricultural workers or in patients with
trauma who have patchy stromal infiltrates.
Sulfonamides are the initial drug of choice, but gentamycin is an effective alternative. Nocardia keratitis responds well to medical treatment if it is diagnosed early.99
Pérez-Santonja and colleagues93 and Nascimento
and colleagues100 described interface opacities in
patients who had uncomplicated myopic keratomileusis. Nocardia asteroides keratitis was confirmed by microbiologic work-up and guided the
correct treatment.
Several cases of non-tuberculous mycobacterial
keratitis have been reported.87-89,101 Almost all of
376
these opportunistic infections have occurred following accidental or surgical ocular trauma, usually
associated with the use of local corticosteroids.
Cultures and sensitivity testing are critical to determine appropriate treatment. Mycobacterium chelonae represents a rare and insidious cause of infection
after LASIK. Diagnosis can be difficult and is often
delayed. Mycobacterium keratitis complicating
LASIK may be difficult to eradicate until the
sequestered stromal infiltrate is drained. Rapid
recognition of the causative organism and aggressive medical and surgical management of the infection, may improve the outcome. Reviglio and colleagues89 reported a case of Mycobacterium chelonae
infection centrally on and under the flap 1 month
after LASIK. This patient’s condition did not
improve with antibiotics, but responded to penetrating keratoplasty. Gelender and colleagues88 reported
two cases of mycobacterium keratitis following
LASIK. Topical fortified amikacin, clarithromycin,
tobramycin, and ciprofloxacin eventually controlled
the infections. Topical prednisolone acetate and bandage contact lenses were used to control inflammation and pain. The infiltrates were slow to resolve.
Eventually local necrosis eroded through the flaps.
This was followed by rapid clearing of the infiltrates. Scarring of the cornea developed at the site
of necrosis. Chung and colleagues87 reported a case
of Mycobacterium chelonae keratitis after LASIK
that was successfully treated with medical therapy
and flap removal, along with intensive topical clarithromycin 1% and Ocuflox (Allergan, Inc, Irvine,
CA) over 5 weeks.
Ultraviolet exposure associated with excimer
laser keratectomy appears to be an efficient trigger
for the reactivation of latent HSV-1.102-107 Cases of
herpetic keratitis have been reported after excimer
laser surgery. We have effectively treated several
patients with a remote history of herpes simplex
keratitis. These patients were treated with acyclovir
200 mg five times a day beginning 3 days before
surgery and continuing for 1 month after surgery.
None of these patients developed breakthrough
infections. Herpes simplex reactivation should
always be considered in the differential diagnosis of
patients with persistent corneal epithelial defects
after refractive or therapeutic excimer procedures.108
Retinal Complications After LASIK
There is no evidence that LASIK triggers retinal
complications. It has been hypothesized that the
increase in intraocular pressure to levels greater
Journal of Refractive Surgery Volume 17 May/June 2001
LASIK Complications/Ambrósio and Wilson
than 60 mmHg with the microkeratome ring 3 to
4 mm posterior to the limbus may exert traction at
the vitreous base and trigger retinal breaks (Kim
HM, Jung HR. Laser assisted in situ keratomileusis
for high myopia. Ophthalmic Surg Lasers
1996;27:S508-S511).34,109-110 Eyes with high myopia
are at risk for retinal detachment. With the large
number of patients undergoing LASIK, there will be
a timing correspondence between surgery and retinal detachment in some patients. For example, one
study found that retinal detachment occurred in
four (0.25%) of 1,554 eyes of four (0.45%) of
878 patients.121 In another study, Arevalo and colleagues34 reported on the vitreoretinal complications in 29,916 eyes that underwent LASIK. In that
study, 14 eyes experienced rhegmatogenous retinal
detachments, two eyes experienced corneoscleral
perforations with the surgical microkeratome when
a corneal flap was being performed (one experienced
a vitreous hemorrhage and the other later experienced a rhegmatogenous retinal detachment), four
eyes experienced retinal tears without rhegmatogenous retinal detachment, and one eye had a
juxtafoveal choroidal neovascular membrane. The
incidences reported in studies of LASIK
patients22,111-112 are consistent with incidences
reported in patients with myopia who have not had
LASIK.113 Loss of best spectacle-corrected visual
acuity may occur due to macular hemorrhage.22,109,110 Both of these complications are more
common in high myopia in the absence of LASIK.
Preoperative and postoperative fundus examinations are, however, important in the detection of
complications and treatment at an early stage.
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