Download American Academy of Optometry: Case Report 1

The Scleral Lens Education Society: Case Report 1
Management of Pellucid Marginal Corneal Degeneration with
the Use of a Gas Permeable Scleral Contact Lens
Brett Larson, O.D.
2560 Associated Rd #12
Fullerton, CA 92835
(714) 393-9890
[email protected]
Abstract
Pellucid Marginal Corneal Degeneration (PMCD) is a progressive, non-inflammatory,
idiopathic disease affecting the cornea. Currently, very little is known about the cause of
this condition and there is no cure, however, much can be done to manage patients with
this condition and improve their quality of life. Treatment of PMCD depends greatly on
the severity of the condition or the patient’s stage of progression. Of all treatment
modalities, gas permeable (GP) contact lenses provide the clearest vision for the patient.
Although fitting patients with PMCD with gas permeable lenses is a challenge due to
high amounts of corneal irregularity and the high probability of corneal complications,
scleral lenses can provide the patient with clear vision, improved comfort, and reduced
risk of future corneal complications.
Key words: Pellucid marginal corneal degeneration (PMCD), irregular astigmatism,
ectasia, scleral lens.
Introduction
Pellucid marginal corneal degeneration (PMCD) is a relatively rare, bilateral,
progressive, ectatic corneal disorder characterized by a noninflammatory thinning of the
inferior peripheral cornea1. One of the more specific characteristics of PMCD is an area
of corneal protrusion that occurs above the area of thinning rather than within this area as
is seen in keratoconus. Typically, a 1 to 2 millimeter area of non-ectatic normal cornea
separates the area of the corneal thinning from the limbus itself1,6,13. Topography can aid
in the diagnosis of PMCD. A topographical map of the cornea will show inferior corneal
steepening with a claw like pattern and against-the-rule astigmatism. Although PMCD
commonly has an inferior presentation, superior PMCD has also been reported in the
literature6. Patients typically present in their third to fifth decade of life with decreased
visual acuity secondary to high amounts of irregular corneal astigmatism1,13. Reported
complications of PMCD are hydrops and spontaneous perforation7,14.
Successful management of PMCD relies heavily on the severity of the condition. In its
early stages, PMCD can be managed with the use of spectacles. Patients with high
amounts of regular or irregular astigmatism cannot be managed with glasses and need to
utilize gas permeable contact lenses in order to achieve acceptable visual outcomes3,8.
Surgical options for the correction of PMCD include intrastromal corneal rings, and
several different types of deep lamellar and penetrating keratoplasty2,13,14. All of these
surgical procedures, however, have a high probability of still requiring the patient to wear
gas permeable contact lenses even after surgery is completed.
A scleral contact lens is defined as a lens 18 millimeters or larger in diameter that
completely vaults over the corneal surface and rests on the sclera. These lenses are a
viable option in the management of PMCD because of their high probability to center
over the cornea as opposed to small diameter corneal lenses11,16. Mechanical irritation of
the ectatic portion of the cornea is also less likely because of the corneal vault that occurs
with these lenses. Studies have shown that scleral lenses provide similar and often
improved visual outcomes when compared with corneal contact lens designs11,15.
Case Report
Patient #1, a 51-year-old Hispanic male, presented to the clinic on 17 July 2008. He had
been referred by an outside optometrist for the fitting of a gas permeable contact lens OD.
The fitting of this lens was for the treatment of what he reported as “unilateral
keratoconus OD only”. The patient reported reduced vision OD with “blurry, distorted,
and double vision” occurring constantly. He had been diagnosed with keratoconus three
years prior but suspected that he had suffered from the condition since his early 20’s.
The patient reported that he was “not eager” to be fit with gas permeable lenses having
attempted to wear them in the past without success due to discomfort. The patient
showed no other significant ocular history and his medical history was negative. He
denied taking medications in any form or having any allergies. He had a family history
of diabetes, high blood pressure, and glaucoma. His blood pressure was 118/76. The
patient was pleasant and oriented to time, place and person.
The patient’s last eye examination had been completed in June 2008. The referring
doctor reported that the patient was “intolerant to gas permeable contact lenses” and
“should consider surgery to successfully wear disposable soft lenses”. His record showed
other wise healthy eyes with an unremarkable fundus evaluation. Subjective refraction
was reported as +1.25-6.75 x 060 OD and -1.00-0.50 x 100 OS with visual acuities of
20/50- and 20/20 respectively.
The patient presented wearing soft toric disposable contact lenses with powers of -2.252.75 x 070OD and -0.75-0.75 x 100 with resulting acuities of 20/400 and 20/20
respectively. The habitual lenses centered well, had good rotational stability and moved
well on blink. He reported wearing +1.75 OTC readers over his contact lenses when
reading with adequate vision. The patient’s uncorrected distance visual acuity was
counting fingers at distance and near OD and 20/40 at distance, 20/25 at near OS. Best
corrected visual acuity showed 20/50 OD and 20/20 OS with a manifest refraction of
+1.25-6.75 x 060 OD and -1.00-0.50 x 100 OS. Pinhole acuity was not documented.
Pupils were equally round and reactive to light with no afferent pupillary defect OU.
Confrontation visual fields were full to finger count OD/OS. Extraocular muscles were
unrestricted in all gazes. Binocularity measures were not performed at this visit
secondary to decreased visual acuity OD. Intraocular pressures were 16mmHg OD and
OS at 10:20 a.m. with Goldman applantation tonometry. Slit lamp examination revealed
the bulbar and palpebral conjuntiva to be white and quiet OU, clean eyelid margins and
lashes OU, brown irises OU, clear lenses OU, and open anterior chambers that were deep
and quiet OU. Evaluation of corneal health with the slit lamp showed inferior corneal
thinning and associated Fuch’s Striae OD, and clear corneal tissue OS. An undilated
examination of the poster pole with a 90 diopter fundus lens revealed cup-to-disc ratios of
0.3 round OU. Retinal arteries and veins had a normal appearance with a ratio of 2/3
respectively. Macular areas were flat and avascular with a positive foveal reflex OU.
The fundus background was homogenous with no significant retinal findings.
Corneal topography was taken OD/OS. OD topography showed an irregular corneal
surface with a corneal toricity of approximately 14 diopters. Simulated keratometry
showed values of 37.17 x 51.53 diopters with corneal steepness increasing in the inferior
1/3rd of the cornea. The topographical pattern OD was indicative of pellucid corneal
degeneration. OS simulated keratometry values were recorded as 41.00 x 41.26 diopters.
The topographical pattern showed a nearly spherical corneal surface with no signs of an
irregular surface. The patient was therefore diagnosed with unilateral pellucid marginal
corneal degeneration (PMCD) OD.
The differential diagnoses in this case include:
1. Pellucid Marginal Corneal Degeneration (PMCD)
 On topography, PMCD has a “claw-like” appearance with the inferior portion
of the cornea steepening drastically as compared to the superior cornea.
 This type of patient will typically show a large amount of against-rule-corneal
toricity and against-the-rule astigmatism on refraction.
2. Keratoconus

On topography, keratoconus has the appearance of localized steepening which
is commonly inferior and temporal (although the localized area can be located
anywhere on the cornea).
 Ocular signs will include Fleischer’s ring, Fuch’s striae, and Munson’s sign in
advanced cases.
3. High Amount of Regular Corneal Astigmatism
 On topography, regular astigmatism will show a somewhat symmetrical bowtie-pattern rather than a localized area of steepening (as in keratoconus) or a
claw like appearance (as in PMCD).
 Patients with high amounts of regular corneal astigmatism will not show signs
of corneal thinning such as Fuch’s striae for example.
 Regular astigmatism theoretically should be correctable to 20/20 visual acuity
with glasses if there are no other confounding factors present (such as
amblyopia).
Several small diameter trial lenses designed for fitting corneas with keratoconus were
placed on the right eye in order to determine the most appropriate contact lens. The goal
of the fitting process was to determine the particular base curve, diameter, and peripheral
curve system that would provide adequate lens centration and movement while still
maintaining acceptable ocular health by lightly touching, or completely vaulting the area
of corneal ectasia. After several trial contact lenses were placed on the eye, the following
order was placed OD:
Material: Fluroperm 60
Base Curve: 52.75(6.39)
Power: -13.75 DS
Diameter: 8.8
Optic zone: 6.3
Secondary curve: 8.8
Tertiary curve: 12.50
Although this particular lens tended to decenter inferiorly, it was determined that this lens
was a good “starting point” to begin the fitting process. The patient was counseled on the
risks of PMD and was scheduled to return in 1 week for a dispensing of the ordered gas
permeable lens.
Follow up #1
The patient returned on 23 July 2009 to have his gas permeable contact lens dispensed.
He reported no changes to his vision or ocular symptoms. His visual acuities through his
habitual soft toric disposable lenses were consistent with the previous examination
(20/400 OD and 20/20 OS). The previously ordered lens with the following parameters
was placed on the right eye and fit and vision were assessed.
Material: Fluroperm 60
Base Curve: 52.75(6.39)
Power: -13.75 DS
Diameter: 8.8
Optic zone: 6.3
Secondary curve: 8.8
Tertiary curve: 12.50
With the gas permeable lens in place, the patient’s vision improved to 20/20- OD. Fit
assessment showed that the lens was decentered inferiorly, had minimal movement on
blink, showed moderate apical touch inferiorly over the ectatic portion of the cornea, had
small bubbles superiorly within the optic zone, and displayed minimal peripheral
clearance. The patient reported poor comfort with the lens in place. It was determined
that the lens would not be dispensed at this visit, and instead would be re-ordered with a
steeper base curve to reduce the amount of corneal touch, a smaller optic zone to
eliminate the bubbles within optic zone, and a steeper tertiary curve to reduce the amount
of edge lift. The re-ordered lens would have the following parameters.
Material: Fluroperm 60
Base Curve: 53.50(6.31)
Power: -14.00DS
Diameter: 8.8
Optic zone: 6.0
Secondary curve: 8.7
Tertiary curve: 12.0
The patient was rescheduled to return in 1 week to dispense the new gas permeable lens.
Follow up #2
The patient returned on 4 August 2008 for the dispense of his new gas permeable lens
OD. He, again, reported no changes to his vision or ocular symptoms. His visual acuities
through his habitual soft toric disposable lenses were consistent with previous visits
(20/400 OD and 20/20 OS). The previously ordered lens with the following parameters
was placed on the right eye and the fit and vision were assessed.
Material: Fluroperm 60
Base Curve: 53.50(6.31)
Power: -14.00DS
Diameter: 8.8
Optic zone: 6.0
Secondary curve: 8.7
Tertiary curve: 12.0
With the gas permeable lens in place, the patient’s vision improved to 20/20- OD. Fit
assessment showed that he lens was decentered inferiorly, had minimal movement on
blink, showed a feather three point apical touch inferiorly over the ectatic portion of the
cornea, had no bubbles within the optic zone, and had average peripheral clearance. The
patient reported poor comfort with the lens in place. The lens was dispensed to the
patient and he was scheduled for a contact lens progress evaluation two weeks later. The
patient was educated on the importance of full and complete blinking throughout the day
in order to adequately wet the lens and achieve sufficient lens movement. He was
informed that lens wear should be slowly increased over the next two weeks in order to
adequately become accustomed to the lens.
Follow up #3
The patient returned on 18 August 2008 for a two week follow up on the previously
dispensed lens OD. He had been wearing the lens for two hours that day and had
achieved an average wear time of 8 hours per day. The patient reported inadequate
comfort throughout the day. “Systane” artificial tears had been utilized as needed in an
attempt to improve comfort with no relief. The patient also reported “flare and glare” in
the evening, and “ghosting” of images that occurred constantly with lens use.
The patient’s visual acuities through the GP lens OD and habitual soft toric disposable
lens OS were consistent with the previous visit (20/20 OD, 20/20 OS). Fit assessment of
the GP lens OD showed that the lens was riding inferiorly on the cornea. A feather three
point touch, no movement on blink, and minimum peripheral clearance with lens seal off
were also noted. When the lens was removed, the cornea displayed a mild compression
ring where the lens had been sitting with a ring of grade 2 SPK at the lens border. Mild
staining was also reported in the area of the cone apex.
The patient was advised to continue to wear the current GP for as many hours per day as
possible to continue building up his wear time. The lens would be re-ordered with a
larger overall diameter for better centration, a larger optic zone in order to reduce the
symptoms of flare and glare, and a flatter peripheral system in order to reduce the risk of
lens seal off and impression rings on the corneal surface. The re-ordered OD lens would
have the following parameters.
Design: Dyna Z Intra-limbal
Material: Boston XO
Base Curve: 47.50(7.11)
Power: -8.75DS
Diameter: 10.8
Optic zone: 8.5
Peripheral Curve: 1.5 steeps flatter than base curve.
The patient was scheduled to return in 1 week to dispense the new GP contact lens OD.
Follow up #4-19
Over the following 10 months the patient’s contact lens parameters were repeatedly
changed in an attempt to improve lens centration, eliminate symptoms of flare and
ghosting, and improve movement on blink. Each of these lenses was a large diameter
“Dyna Z Intra-limbal” lens design. The trial lenses were routinely dispensed to the
patient at each visit for a week long trial. At the end of each trial period, it was
determined that the lens provided inadequate corneal health and comfort. Each lens
consistently provided the patient with 20/20 vision OD.
On 1 July 2009, the optometrist providing care to the patient was replaced by a new
provider (Dr. Brett Larson). Under this new provider, it was determined that a scleral
lens would need to be fit OD in order to achieve the desired outcome. The patient was
scheduled for a fitting on 3 August 2009.
Follow up #20
The patient returned on 3 August 2009 to be fit with a gas permeable scleral lens OD.
The patient had been wearing a previously dispensed gas permeable lens with the
following parameters for 2 weeks.
Design: Dyna Z Intra-limbal
Material: Boston XO
Base Curve: 50.50(6.68)
Power: -10.00DS
Diameter: 11.2
Optic zone: 8.8
Peripheral Curve: 10 steeps flatter than base curve.
The patient reported reduced flare, glare and ghosting of images. Improved comfort and
clarity of vision were also observed. He had been using Systane artificial tears as needed
for improved comfort OD with the lens in place. The lens had been worn an average of
11 hours per day with no complications reported. The patient did not admit to sleeping in
his lens.
Fit assessment of the lens showed inferior centration, inadequate movement on blink,
minimal peripheral clearance and lens seal off. When the lens was removed, the patient
had an impression ring inferiorly where the lens had been sitting and grade 2 SPK at the
lens border and at the apex of the ectatic area. The patient was advised to wear this lens
as little as possible and for a maximum of five hours per day. He was also advised to use
artificial tears four times per day until a scleral lens fit could be finalized.
A Jupiter scleral gas permeable contact lens was placed on the patient’s eye OD and a fit
assessment was completed. Because the clinic only had a fitting set with a diameter of
18.2, this diameter was used in the fitting process. A contact lens with a base curve one
diopter steeper than steepest keratometry reading OD was selected as the initial trial lens.
Design: Jupiter Scleral Lens
Base Curve: 52.00(6.49)
Diameter: 18.2
Power: -12.75
Peripheral Curve: Series B
Fit assessment of the lens showed good centration, full corneal clearance with a tear lens
approximately 400 microns in width, inadequate limbal clearance on the nasal and
temporal edges of the cornea, and minimal blanching of the conjunctival vessels. The
over refraction for this trial lens was plano DS with a resulting acuity of 20/20 OD. A
scleral lens was designed and ordered with the following parameters:
Design: Jupiter Scleral Lens
Base Curve: 52.00(6.49)
Power: -12.75 DS
Diameter: 18.8mm
Optic Zone: 8.2
Peripheral Curve 1/Width: 6.89mm/2.6mm
Peripheral Curve 2/Width: 8.35mm/0.7mm
Peripheral Curve 3/Width: 12.75mm/1.5mm
Peripheral Curve 4/Width: 14.75mm/0.5mm
The above lens was ordered with a diameter of 18.8mm rather than 18.2mm in order to
achieve adequate limbal clearance while maintaining lens centration and corneal
clearance. Peripheral curves three and four were also flattened slightly from the standard
trial lens parameters in order to more evenly distribute the weight of the lens over the
conjunctiva and eliminate blanching of conjunctival vessels.
The patient was informed that he would be notified when the lens was received, and
could then be scheduled for a follow-up examination where the lens would be dispensed.
He was instructed to wear the smaller diameter habitual lens for a maximum of five hours
per day until the dispensing appointment for the scleral lens.
Follow up #21
The patient returned to the clinic on 16 September 2009 for dispense of his new scleral
lens OD. The patient had no changes to his visual or ocular health complaints. He
reported mild irritation when wearing his habitual GP lens for longer than five hours. He
reported adequate vision OD/OS when wearing his habitual contact lenses. He achieved
20/20 vision OD/OS with his habitual contact lenses. When a slit lamp evaluation was
performed with no lenses in place, grade 2 SPK was seen at the highest point of the
cornea, an impression ring where the lens edge typically sat was also present with
associated grade 2 SPK at the edge of the corneal impression OD. The following trial
lens was place on the eye OD and fit and vision were assessed.
Design: Jupiter Scleral Lens, OD only.
Base Curve: 52.00(6.49)
Power: -12.75 DS
Diameter: 18.8mm
Optic Zone: 8.2
Peripheral Curve 1/Width: 6.89mm/2.6mm
Peripheral Curve 2/Width: 8.35mm/0.7mm
Peripheral Curve 3/Width: 12.75mm/1.5mm
Peripheral Curve 4/Width: 14.75mm/0.5mm
Fit assessment showed adequate centration, full corneal clearance with a tear lens
approximately 400 microns in width, adequate limbal clearance on the nasal and temporal
edges of the cornea, and average blanching of the conjunctival vessels. There was not
movement on blink. The over refraction for this trial lens was plano DS with a resulting
acuity of 20/20 OD.
Because of the blanching of the conjunctival vessels, it was decided that this lens would
not be dispensed. Instead, the lens was reordered with the following parameters.
Design: Jupiter Scleral Lens, OD only.
Base Curve: 54.00(6.25)
Power: -14.75 DS
Diameter: 18.8mm
Optic Zone: 8.2
Peripheral Curve 1/Width: 6.89mm/2.6mm
Peripheral Curve 2/Width: 8.35mm/0.7mm
Peripheral Curve 3/Width: 13.25mm/1.5mm
Peripheral Curve 4/Width: 15.25mm/0.5mm
In the above lens order, peripheral curves three and four were flattened slightly in order
to allow increased blood flow of the conjunctiva and decrease signs of blanching. The
base curve was steepened by two diopters in order to compensate for the loss in overall
sagittal height that occurs by flattening the peripheral curves.
The patient was, again, informed that he would be notified when the lens was received,
and could then be scheduled for a follow-up examination where the lens would be
dispensed. He was instructed to wear the smaller diameter habitual lens for a maximum
of five hours per day until the dispensing appointment for the scleral lens. He was
offered soft disposable lenses to be used as piggyback lenses, but declined the offer
reporting that he’d “prefer to wait for the next dispensing visit”.
Follow up #22
The patient returned on 23 September 2009 for dispense of his new scleral lens OD. As
reported previously, the patient had no changes to his visual or ocular health complaints.
He reported mild irritation when wearing his habitual GP lens OD for any period of time.
He reported adequate vision OD/OS when wearing his habitual contact lenses. He had
20/20 vision OD/OS with his habitual contact lenses. When a slit lamp evaluation was
performed with no lenses in place, grade 2 SPK was seen at the highest point of the
cornea, an impression ring where the lens edge typically sat was also present with
associated grade 2 SPK at the edge of the corneal impression OD. The following trial
lens was place on the eye OD and fit and vision were assessed.
Design: Jupiter Scleral Lens (OD only)
Base Curve: 54.00(6.25)
Power: -14.75 DS
Diameter: 18.8mm
Optic Zone: 8.2
Peripheral Curve 1/Width: 6.89mm/2.6mm
Peripheral Curve 2/Width: 8.35mm/0.7mm
Peripheral Curve 3/Width: 13.25mm/1.5mm
Peripheral Curve 4/Width: 15.25mm/0.5mm
Fit assessment of the lens showed good centration, full corneal clearance with a tear lens
approximately 300 microns in width, adequate limbal clearance in all locations, and no
blanching of the conjunctival vessels. There was no movement on blink. The over
refraction for this trial lens was plano DS with a resulting acuity of 20/20 OD. The
patient reported good comfort and vision.
The lens was left on the patient’s eye for 40 minutes in order to assess the fit after the
lens was allowed to settle. After 40 minutes of wear, the fit remained the same in every
regard accepting the fact that the tear lens was decreased from approximately 300
microns to approximately 250 microns in width.
The patient received instruction on application and removal of the lens and the lens was
dispensed. He was told to slowly build up wear time over the next week and return for a
final follow up appointment. The final appointment was scheduled for the evening in
order to be able to assess the fit after a full day of wear.
Follow up #23
The patient returned to the clinic on 30 September 2009 for a final follow up on the
scleral lens dispensed one week previously OD. He had been wearing the lens for 10
hours previous to the appointment and reported wearing the lens for an average of 15
hours per day with good vision and comfort. The patient reported that the irritation felt
with the previous lens was no longer present.
Presenting visual acuities were 20/20 OD/OS. Fit assessment of the lens showed good
centration, adequate corneal clearance with a tear lens width of approximately 250
microns, adequate limbal clearance, no movement on blink, and no blanching of the
conjunctival vasculature.
Slit lamp examination after lens removal was performed to assess ocular health after lens
wear. The cornea showed no staining and no lens impression marks from the previous
smaller diameter lens. The conjunctival and limbal areas also displayed no staining.
The lens was finalized and the patient was instructed to wear the lens full time. He was
scheduled for a 6 month progress evaluation to assess corneal health and lens wear.
Six Month Progress Evaluation
The patient reported to the clinic on 23 March 2010 for a progress evaluation to assess
ocular health and lens wear with the scleral lens OD. The patient had been wearing the
lens for 11 hours that day and reported average wear time of 15 hours per day with good
vision and comfort.
Presenting visual acuities were 20/20 OD/OS. Fit assessment showed good centration,
adequate corneal clearance with a tear lens width of approximately 250 microns,
adequate limbal clearance, no movement on blink, and no blanching of the conjunctival
vasculature. As was found in the previous visit, assessment of the ocular surface showed
no corneal staining or compression rings. The conjunctival and limbal areas also were
healthy with no signs of staining.
The patient was instructed to continue full time wear of the scleral lens OD and soft
disposable lens OS. He was scheduled for a comprehensive examination in six months
for a yearly evaluation.
Discussion
PMCD is defined as a progressive noninflammatory ectatic corneal disorder involving the
inferior cornea in a crescent like shape1. The corneal ectasia typically extends from the
4-o’clock position to the 9-o’clock position, 1-2mm from the limbus. One of the
differentiating factors of PMCD from other ectactic corneal disorders, such as
keratoconus, is that the ectatic portion of the cornea is found above the area of thinning,
rather than being located at the area of thinning1,6,13. Although rare, superior PMCD has
also been reported.
Differentiating PMCD from other ectactic corneal disorders based on topography has
been the source of much debate. Commonly, PMCD appears as an area of rapid
steepening inferiorly. The steep portion of the cornea has the appearance of “crab claws”
or “kissing birds” coming together typically near the visual axis4. It has also been noted
that the central portion of the eye appears to be flattening in the vertical meridian
producing an against-rule-astigmatic appearance. Although corneal ectasia associated
with keratoconus is frequently located in the inferior portion of the cornea, it has a more
localized presentation and will not have the “crab claw” appearance4. Some reports have
mentioned the presence of PMCD and keratoconus within the same patient4,6. This is
another source of controversy among researchers.
Patients with PMCD typically present in their fourth to fifth decades of life with reduced
visual acuity due to high amounts of irregular astigmatism. The disorder is more
prevalent in the male population than in females1. There seems to be no connection
between ethnicity and disease prevalence13. PMCD is usually a bilateral condition,
although there have been a few isolated case reports of unilateral presentation as was the
case with this patient. Data regarding the genetic component of PMCD is lacking in
current literature. Some articles assume that PMCD has a similar inheritance pattern to
keratoconus, but, this has yet to be proven or substantiated4. As with keratoconus, studies
have shown that the progression of PMCD decreases dramatically with age and tends to
stabilize in the fifth and sixth decade. Two commonly reported complications that occur
with PMCD are corneal hydrops and corneal perforation1,7. Both of these conditions are
reported to occur at or near the area of corneal thinning.
The mode of management for PMCD depends completely on disease severity. Early in
the disease process, patients can be managed with spectacles or toric soft contact lenses
with moderately successful results8. In more moderate to severe cases, the patient will
need to be fit with GP lenses in order to obtain acceptable visual acuity5. Several surgical
procedures have been attempted in the literature with variable results. Even in the
presence of surgery, however, the majority of reported cases have still necessitated the
use of GP lenses in order to obtain adequate vision5.
Gas permeable contact lenses have been documented as a successful and consistent way
to provide clear vision for patients with irregular corneal surfaces9,11. Although GP
lenses are commonly used for management of PMCD, they can be one of the most
challenging treatment methods to achieve successfully. The difficulty with PMCD is the
challenge of successfully designing a contact lens that will provide clear vision, adequate
comfort, and maintain the health of the corneal surface11. The collaborative longitudinal
evaluation of keratoconus (CLEK) studies reported that contact lenses fit excessively too
flat will cause the lens to come in contact with the area of corneal ectasia10. Excessive
contact with these areas results in corneal scarring. Therefore, when fitting patients with
corneal irregularities, it is important the lens be fit steep enough to avoid unnecessary
contact with the ectatic area. Small diameter lenses tend to center themselves over the
steepest portion of the eye causing the lens to drop down in cases with inferior steepness
such as PMCD. Inferiorly decentered lenses result in less than adequate vision for the
patient and may result in harmful contact with the ectactic area. Larger diameter lenses
(Greater than 10mm and less than 12.9mm) have the ability to vault over the area of
ectasia successfully and center over the visual axis8. In extreme cases, however, these
lenses will attract bubbles under the optic zone resulting in blurry and distorted vision.
A scleral lens is defined as a lens with a diameter of 18mm or greater11. These lenses
vault over the corneal and limbal area completely and rest on the sclera. Though there
are few published cases regarding the use of these lenses in the treatment of irregular
corneas, they have many features that may be of great benefit to the patient.
Scleral lenses aid in lens centration secondary to the fact that they do not rely on corneal
curvature to determine lens position. This makes it possible for any patient, regardless of
corneal irregularity to successfully wear contact lenses (provided they do not have other
confounding factors). Because these lenses have no contact with the cornea, studies have
shown that the risk of corneal scarring is much lower than with a smaller diameter lens11.
Other studies have also shown that scleral lenses provide improved comfort for the
patient due their large diameter and decreased interaction with the lid margins15. In many
cases, this provides a valuable option for those patients who were otherwise considered to
be “contact lens intolerant”. These lenses are also designed to hold a reservoir of liquid
throughout the day that slowly exchanges with the patient’s tears on blink12. These
lenses have been researched predominantly for their use in dry eye therapy and other
severe ocular surface diseases9. This ability to maintain a “liquid bandage” over the
cornea for extended periods of time provides relief and healing for many of these
conditions.
Conclusion
This case demonstrates the many characteristics of PMCD and the role of scleral lenses in
the management of this and other severe corneal irregularities. In all cases, PMCD can
be most accurately diagnosed through the use of corneal topography and careful
evaluation with a slit lamp. Although it may be difficult to differentiate PMCD from
keratoconus, it is important to know their differences in order to provide patients with the
most appropriate care possible. Management of PMCD is determined by the severity of
the condition. The most common, and successful, non-surgical option in the management
of PMCD is the use of GP lenses. GP scleral lenses provide numerous benefits to PMCD
patients by way of improved vision, comfort, fit, and corneal health.
Bibliography
1. Ambrosio R, Klyce S, Smolek M, Wilson S. Pellucid marginal corneal
degeneration. Journal of Refractive Surgery 2002; 18:86-87.
2. Busin M, Kerdraon Y, Scorcia V. Combined wedge resection and beveled
penetrating relaxing incisions for the treatment of pellucid marginal corneal
degeneration. Cornea 2008; 27(5): 595-600.
3. Dominguez C, Shah A, Weissman B. Bitoric gas-permeable contact lens
application in pellucid marginal corneal degeneration. Eye and Contact Lens
2005; 31(5): 241-243.
4. Ertan A. Differentiating keratoconus and pellucid marginal degeneration.
Journal of refractive surgery 2007; 23:221-222.
5. Gruenauer-Kloevekorn C, Fischer U, Duncker G. Pellucid marginal corneal
degeneration: evaluation of corneal surface and contact lens fitting. British
Journal of Opthalmology 2006; 90:318-323.
6. Lee B, Jurkunas U, Harissi-Dagher M, Poothullil A. Ectatic disorders associated
with a claw-shaped pattern on corneal topography. American Journal of
Ophthalmology 2007; 144(1): 154-157.
7. Lee W, O’Halloran H, Grossniklaus H. Pellucid marginal degeneration and
bilateral corneal perforation: case report and review of literature. Eye and
Contact Lens 2008; 34(4): 229-233.
8. Ozbek Z, Cohen E. Use of intralimbal rigid gas-permeable lenses for pellucid
marginal degeneration, keratoconus, and after penetrating keratoplasty. Eye and
Contact Lens 2006; 32(1): 33-36.
9. Pullum K, Buckley R. Therapeutic and ocular surface indications or scleral
contact lenses. The Ocular Surface 2007; 5(1):40-48.
10. Szczotka L, Barr J, Zadnik K. A summary of the findings from the collaborative
longitudinal evaluation of keratoconus study. Optometry 2001; 72(9): 574-584
11. Segal O, Barkana Y, Hourovitz D. Scleral contact lenses may help where other
modalities fail. Cornea 2003; 22(4): 308-310
12. Smith G, Mireskandari K, Pullum K. Corneal swelling with overinight wear of
scleral contact lenses. Cornea 2004; 23(1); 29-33
13. Sridhar M, Mahesh S, Bansal A, Nutheti R. Pellucid marginal corneal
degeneration. Opthalmology 2004; 111(6): 1102-1107
14. Tzelikis P, Cohen E, Rapuano C. Management of pellucid marginal corneal
degeneration. Cornea 2005; 24(5): 555-560.
15. Visser E, Visser R, Lier H. Advantages of toric scleral lenes. Optometry and
Vision Science 2006; 83(4); 233-236.
16. Ye P, Sun A, Weissman B. Role of mini-scleral gas permeable lenses in the
treatment of corneal disorders. Eye and Contact Lens 2007; 33(2): 111-113.