Download Original Article The Efficacy, Predictability, and Safety of Epi

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Original Article
The Efficacy, Predictability, and Safety of Epi-Lasik for The Correction
of Myopia
Faisal M. Tobaigy, MD; Leonard Ang, MD, Phd; Dimitri T. Azar, MD
Abstract
Purpose. To report the refractive and visual results of epithelial laser in situ keratomileusis (Epi-LASIK) for the
treatment of myopia.
Design. Retrospective non-comparative consecutive case series.
Methods. Sixty nine eyes of 40 patients had Epi-LASIK for the treatment of low myopia or myopic astigmatism.
All epithelial separations were performed with the Visijet/Gebauer microkeratome. Primary outcome variables
included uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest refraction,
epithelization time, pain, haze and complications.
Results. Preoperatively, the mean spherical equivalent (SE) was -3.9 diopters (D) ± 1.6 D (range -.75 to -7.00 D)
and the mean LogMAR BSCVA was 0.0131±0.041 (range -0.10 to 0.12). On the final visit, the mean SE was 0.27+0.53D (range -2.50 to 0.50D), the mean logMAR UCVA was -0.079±0.13 (range -0.48 to 0.12) and the
mean LogMAR BSCVA was 0.0039 ± 0.053 (range -0.18 to 0.1). 95.1% of eyes achieved a vision of 20/40 or
better, and 70.5% achieved a vision of 20/25 or better. 73.8% and 95.1% of eyes were within +0.5D and +1.0D,
respectively. Complete epithelialization occured in 6.2 ±1.4 days (range 3 to 8 days); 93.4% of eyes had clear
corneas or only trace haze at the final postoperative visit; 94.7% of eyes had no or minimal pain.
Conclusions. Epi-LASIK is a safe, effective and predictable method for the treatment of low to moderate myopia
and myopic astigmatism.
Key Words: Epi-lasik, epithelial laser in situ keratomileusis
W
ith the rapid evolution of refractive surgery and
availability of wide range of treatment modalities, the surgeon can select the right procedure for the
patient according to his or her needs and limits. In the
early nineties, PRK was the most commonly performed
refractive surgery and continued to be popular until
the introduction of LASIK. Each procedure has its own
From the Department of Ophthalmology, Massachusetts Eye and Ear Infirmary and the Schepens Research Institute, Harvard Medical School, Boston, Massachusetts, United States of America.
Correspondence to Faisal M. Al-Tobaigy, MD, Assistant Professor of Ophthalmology, College of Medicine, Jazan University. PO Box 114, Jazan,
Kingdom of Saudi Arabia. Telephone: 00966-07-3217800; Fax: 00966-073217800; E-mail: [email protected]
risks and benefits. While PRK is safe and effective, the
risk of getting corneal haze, especially in high myopia,
is high. Postoperative pain, slow rehabilitation, and a
long stabilization period are other limiting factors in
PRK. LASIK has no postoperative pain, a faster recovery period, less regression, and no haze even in high
myopia. On the other hand, it is considered to be a
higher risk procedure because of flap-related complications (free cap, incomplete flap, irregular flap, button holes, and lost flaps), interface related complications (epithelial ingrowth, deep lamellar keratitis, and
interface debris), flap-related corneal biomechanical
instability, and iatrogenic keratectasia.1-9
LASEK and Epi-LASIK may combine the advan-
Saudi Journal of Ophthalmology, Volume 22, No. 4, October – December 2008
216
tages of PRK and LASIK while avoiding the disadvantages of both.6,10-13 They avoid all of the flap-related
complications and the risk of keratectasia associated
with LASIK and have relatively faster recovery periods
with slightly less pain and haze than PRK.
LASEK, which involves the creation of an epithelial flap with dilute alcohol solution, is effective in treating low to moderate refractive errors. Despite the encouraging clinical results of LASEK, the toxic effect of
alcohol on the epithelium and the underlying stroma
remain a concern.14
Epi-LASIK represents a recent development in
refractive surgery technology and makes use of a proprietary motorized blunt oscillating blade to mechanically separate the corneal epithelium en toto
from the stroma, without the use of alcohol or
chemicals.15,16 There is a recent trend towards surface ablation for correcting refractive errors. LASEK
or Epi-LASIK are good choices for patients with low
to moderate myopia and myopic astigmatism, corneal thinning with no signs of keratoconus, extreme
keratometric values, i.e. steep or flat corneas, deep
set eyes and small palpebral fissure, recurrent erosion syndrome, dry eye, glaucoma suspect, a wide
scotopic pupil, scleral buckle, and for patients who
are more predisposed to trauma like military personnel and athletes. All of these aspects should be
carefully analyzed when choosing the procedure
which fits the patient’s needs and expectations, with
special emphasis on patient personality, occupation,
corneal thickness and curvature, pupil size, corneal
and ocular pathology, and degree of ametropia.
Pain tolerance is a very important factor that may
influence the choice of surface ablation vs. LASIK.
While the corneal flap might frighten some patients,
postoperative pain and discomfort may stop others from
undergoing surface ablation. Another important issue
is corneal thickness and biomechanical stability of the
cornea after the procedure. The presence of low corneal thickness may lead to keratectasia after LASIK. It
is known that once the flap is formed, it no longer
significantly contributes to the biomechanical stability
of the cornea. The remaining bed, hence, is the determining part of the corneal strength and should not be
less than 250ºm or not less than half the original corneal thickness.
Extreme keratometric values are risk factors for
intraoperative flap-related complications. Steep corneas (> 48D) have a risk of buttonhole and thin flaps,
while flat corneas (<40D) have risk of a free caps.
This, in-turn may lead to asymmetric astigmatism
and irregular ablation pattern. LASEK and EpiLASIK may be considered for these kinds of corneas
to avoid such complications. Postoperative glare and
halos are related in part to pupil size and optical
zone treatment. The ablation zone should be larger
than the pupil size in order to avoid such complications. The ablation zone is usually reduced to preserve corneal tissues in LASIK for small pupils but
not for larger pupils. Patients with large pupils will
benefit from LASEK or Epi-LASIK as this may allow increasing the ablation zone without endangering the remaining bed.
Presence of ocular pathologies will influence the
procedure choice. For example, dry eye patients are
more prone to neurotrophic keratitis after LASIK than
after LASEK and Epi-LASIK since the LASIK flap
transects the corneal nerve. Patients with glaucoma
and nerve fiber layer loss may be at risk of exacerbation of the condition due to the acute rise in intraocular pressure caused by the suction ring.
Epi-LASIK is not recommended for patients who
have had any previous corneal surgery or pathology
that could have damaged Bowman’s layer including RK,
LASIK, PRK, LASEK, Epi-LASIK, corneal ulcer, and
corneal scars.
In a retrospective non-comparative consecutive
case series, we evaluated this technique for the correction of low to moderate myopia and myopic astigmatism.
PATIENTS AND METHODS
Patients
This study comprised 69 eyes of 40 consecutive
patients treated at the Massachusetts Eye and Ear Infirmary. The charts of these patients were retrospectively reviewed. Sixty one eyes were aimed for full correction of ametropia while 8 eyes were intentionally
under-corrected. These later 8 eyes were excluded from
further analysis. We also excluded all the patients with
previous history of corneal or refractive surgery or corneal diseases that could affect epithelial or stromal healing. All study patients had stable refraction prior to
surgery. All operations were performed by the same
surgeon. This study was approved by the Institutional
Review Board of the Massachusetts Eye and Ear Infirmary.
The preoperative evaluation included uncorrected
visual acuity (UCVA), best spectacle-corrected visual
acuity (BSCVA), manifest and cycloplegic refractions,
ocular dominance, slit lamp examination, keratometry,
Saudi Journal of Ophthalmology, Volume 22, No. 4, October – December 2008
217
tonometry,
pachymetry,
computerized
videokeratography (Orbscan), mesopic pupil size measurement using a pupillometer, and dilated fundus examination.
Surgical Procedure
The periocular skin around the operative eye was
cleaned with 5% betadine solution and dried with a
sterile gauze. A sterile drape was placed around the
eye, and a drop of topical anesthetic (0.5%
proparacaine) was instilled. A lid speculum was inserted to ensure adequate exposure. After irrigation
with balanced salt solution, the corneal epithelium
was dried with sponge and the cornea was marked
with a standard LASIK marker, followed by irrigation to remove any ink remnants.
The subepithelial separator used was the Visijet/
Gebauer EpiLift microkeratome. The preassembled
handpiece was applied to the eye, with the central
circular opening centration around the limbus. The
suction was activated by a foot pedal. By depressing
the foot pedal, the oscillating blade moved across the
corneal plane, separating the epithelium, leaving a 2to 3-mm nasal hinge. The suction was released, and
the device was removed from the eye. The epithelial
sheet was reflected nasally using a moistened Merocel
sponge or a spatula, revealing the underlying corneal
stroma. The exposed area had a diameter of approximately 9 mm.
Excimer laser ablation was initiated immediately
thereafter. All treatments were performed with the
VISX S4; (VISX Inc, Santa Clara, CA) excimer laser, and corrections attempted to achieve emmetropia. The treatment zone in each case equaled patient’s
mesopic pupil measurement and ranged from 6 to 8
mm. The epithelial sheet was carefully repositioned
using the straight part of an anterior chamber irrigating cannula, with intermittent irrigation with
balanced salt solution to help facilitate proper repositioning of the epithelial sheet. The separated epithelial sheet often extends beyond the original position when repositioned. Care was taken to realign
the epithelial flap using the previous marks and to
avoid epithelial defects.
A combination of 0.1% diclofenac sodium,
moxifloxacin and 1% prednisolone acetate eye drops
were applied to the eye. A bandage contact lens (Soflens
66, Bausch and Lomb) was placed thereafter, and kept
in place until complete re-epithelization of the corneal
surface. The postoperative regimen included topical
moxifloxacin and 1% prednisolone acetate eyedrops 4
times per day for 1 week. The topical steroid was continued for another week and tapered over two months.
Lubrication was prescribed as and when required.
Patients were reviewed every day or every other
day until corneal epithelial healing was complete. After complete re-epithelization, patients were followed
up at 1 and 3 months.
At postoperative day 1 the patients were asked by
the examining physician to grade the severity of pain
as follows: no pain, mild, moderate or severe pain.
Subepithelial haze was graded as follows: 0 = clear cornea, +0.5 = trace haze that was barely visible on slitbeam illumination, +1 = mild haze that was easly visible on slit-beam illumination, +2=dense patches of
haze affecting the vision, +3 = moderate haze somewhat obscuring iris details and 4 = marked haze obscuring iris details.
RESULTS
Sixty one eyes of 40 patients who underwent EpiLASIK were studied, 17 patients were male and 23 were
female. The mean age was 36.8± 8.8 years (range 2254 years, median 34). The mean preoperative spherical equivalent refraction was -3.9 diopters (D) ± 1.6 D
(range -.75 to -7.00 D). The mean preoperative
LogMAR BSCVA was 0.0131±.041 (range -.10 to .12).
The mean follow up period was 14.2 ± 8.6 weeks (range
4 to 35 weeks).
Epithelial Separation and Postoperative Re-epithelization
Epithelial separation was successfully performed
with the epikeratome in all eyes without complications. Tow eyes had a small island of epithelium on
the surface which was removed with a blade. The
epithelium was easily repositioned over the corneal
surface and the edges were aligned to the initial margin but often the epithelial flap extended beyond
the margin. Postoperatively the epithelium remained
attached without significant breakdown or
dislodgement. A front of new epithelium migrated
from the corneal periphery toward the center of the
corneal surface. As healing progressed, the migrating new epithelium gradually replaced the epithelial sheet over 3-7 days. The mean time for complete epithelization was 6.2 ± 1.4 days (Fig. 1).
Efficacy
The mean LogMAR UCVA at day 1, 7, and at the
final visit were -0.38±0.22 (range -1.3 to 0), -.25±.18
(range -.7 to 0), -.079±.13 (range -.48 to .12) respec-
Saudi Journal of Ophthalmology, Volume 22, No. 4, October – December 2008
218
Figure 1. Epithelization time.
Figure 2. LogMAR uncorrected visual acuity.
tively (Fig.2). 75% of eyes had UCVA of 20/40 or
better by postoperative day 7. At the final visit, 95%
and 70.5% of eyes had UCVA of 20/40 and 20/25 or
better respectively (Fig. 3). The efficacy index which is
the ratio of mean postoperative UCVA to mean postoperative BSCVA was 0.81.
of BSCVA. One eye underwent PTK with Mitomycin
C which led to improvement of his UCVA to 20/30.
The third eye had grade 1 haze which resulted in a
reduction of BSCVA from 20/16 preoperatively to 20/
25 postoperatively. Overall, the safety index which is
the ratio of mean postoperative BSCVA to mean preoperative BSCVA at the final visit was 0.98
Predictability
The mean postoperative spherical equivalent
was -.27±0.53D (range -2.50 to 0.50D). Forty five eyes
(73.8%) were within ± 0.50 D and 58 eyes (95.1%) were
within ± 1.00 D of the attempted correction (Fig. 4).
Safety
The mean postoperative BSCVA LogMAR was
0.0039 ± 0.053 (range -0.18 to 0.1). At the final follow-up visit, 3 eyes (4.9%) lost two lines (Fig.5). One
patient had grade 2 haze in both eyes and lost 2 lines
Figure 3. Uncorrected visual acuity at day1, 7, and at the
final visit.
Corneal Haze and Postoperative Complications
At the final visit, 93.4% of eyes had clear corneas
or only trace haze. Only 3 eyes developed grade 1or 2
haze. No eye developed grade 3 or 4 haze. No other
complications were observed (Fig. 6).
Postoperative Pain
29.5% of patients experienced no pain, 59% had
mild pain, and 3 patients (4.9%) had moderate pain.
no patient reported severe pain (Fig. 7).
Figure 4. Percentage of eyes within ± 0.50 D and ± 1.0D.
Saudi Journal of Ophthalmology, Volume 22, No. 4, October – December 2008
219
DISCUSSION
Figure 5. Difference of BSCVA (gain/loss) lines from the
preoperative baseline.
Figure 6. Corneal haze score.
Figure 7. Pain score.
A major advantage of surface ablation over
LASIK is the avoidance of flap-related complications
(buttonhole, free cap, incomplete microkeratome
pass, epithelial ingrowth, deep lamellar keratitis, flap
melt, interface debris, and traumatic flap dislocation). While iatrogenic keratectasia can occur after
LASIK, it is unheard of after surface ablation.
PRK, LASEK and Epi-LASIK share the biomechanical advantage of surface ablation; however, EpiLASIK was introduced with a hope to overcome the
main drawbacks of both PRK and LASEK, namely
pain, haze and epithelial toxicity caused by alcohol.
The epikeratome separates, rather than cuts, epithelium from Bowman’s membrane with no toxicity
from alcohol.17
Mechanical corneal epithelial debridement results in keratocyte cell loss through programmed cell
death (apoptosis) within hours of debridement.18-20
The lost keratocytes are replaced through proliferation and migration of the peripheral keratocytes
which change their phenotype to that of
myofibroblast-like cells. This is accompanied with
overproduction of collagen and glycosaminoglycans
that may result in corneal haze. 21
It has been shown that keratocyte apoptosis may
be reduced with application of amniotic membrane
22
or collagen shields. 23 Mohan et al found that
keratocyte apoptosis occurs in the debrided area but
not beneath some epithelial islands. 24 The corneal
epithelial sheet is essential in maintaining balanced
epithelial stromal interaction and, if damaged, may
lead to production of inflammatory cytokines 25,26
and myofibroblast transformation.21
Preserving the epithelial flap may prevent inflammatory cytokine production from the damaged
epithelial cells that occurs during epithelial debridement in PRK and render the basement membrane
in place to support the epithelial sheet. The epithelial flap may also serve as a mechanical barrier between the tear film and the bare stroma. This may
inhibit the corneolacrimal reflex and reduce influx
of tear fluid which contains many factors such as
Fas antigen and Fas ligand, 27 transforming growth
factor beta, 28 and tumor necrosis factor alpha.24,29
Furthermore the viable epithelial flap may speed
healing and visual recovery, reduce discomfort, and
reduce the incidence of haze.
In our series the mean epithelization time post
operatively was 6.2 ± 1.4 days (range 3-8 days).
Saudi Journal of Ophthalmology, Volume 22, No. 4, October – December 2008
220
98.2% of eyes (98.2%) had complete epithelization
by the postoperative day 7, and only one eye had
complete epithelization on postoperative day 8. This
is comparable to the previous reports on Epi-LASIK16
and LASEK5,30-33 which described epithelization time
ranging from 3-9 days.
As in all surface ablation procedures, pain remains a limiting factor for Epi-LASIK. In our study,
94.7% of eyes had no or minimal pain. Although
Epi-LASIK is associated with more pain than LASIK,
results of our study as well as previous reports suggests16 that Epi-LASIK may be associated with less
discomfort than LASEK. This may be attributed to
better viability of epithelial cells after Epi-LASIK
compared to alcohol assisted epithelial removal in
LASEK.
Forty six percent of eyes had UCVA of 20/40
or better at postoperative day 1. This was improved
to 75% by postoperative day 7. At the final visit,
95% of eyes had UCVA 20/40 or better and 70.5%
of 20/25 or better. The relatively slower visual recovery after Epi-LASIK is similar to the pattern of
visual recovery after LASEK and PRK5,12,31-36 rather
than after LASIK. This is apparently due to epithelial wound healing process.
The main drawback of surface ablation, including Epi-LASIK is the risk of haze formation especially for higher degrees of myopia. Although the
safety index in our study was near 1 at the final postoperative visit and most patients had no or trace haze
(93.4%), 3 eyes lost 2 lines of BSCVA due to haze
formation. One eye necessitated the use of Mitomycin C for treatment of haze.
This study has certain limitations:
1. The retrospective nature of the study.
2. Relatively short duration of follow-up.
3. The lack of standardized pain scoring scale.
In conclusion, although the parameters measured in this study such as haze, UCVA, BCVA,
Spherical equivalent can change after 3 months, our
results suggest that Epi-LASIK has a good safety,
efficacy, and predictability profile. Despite it is a very
promising procedure for low to moderate myopia,
haze formation is still a major concern, especially in
higher degrees of ametropia. Further prospective
controlled studies with longer follow-up are needed
to evaluate the long-term safety and stability of EpiLASIK.
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