AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Multimedia
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Multimedia
• References

Background

Schalaeppi first coined the term pellucid marginal degeneration in 1957. This bilateral, noninflammatory, peripheral corneal thinning disorder is characterized by a peripheral band of thinning of the inferior cornea. The cornea in and adjacent to the thinned area is ectatic.

Pathophysiology

The etiology of this disorder has not been clearly established, but collagen abnormalities, as seen in keratoconus, have been reported. The thinned and presumably weakened cornea may protrude as a result of the positive intraocular pressure.

Frequency

United States

This condition is rare, and the exact incidence and prevalence are unknown. However, the incidence may be considerably underestimated, as this condition is often misdiagnosed as keratoconus.

Mortality/Morbidity

• Deterioration of visual function results from the irregular astigmatism induced by asymmetric distortion of the cornea. The deterioration in visual function is commonly severe.
• Refractive surgery, such as photorefractive keratectomy (PRK), can cause severe corneal haze, and results with laser-assisted in situ keratomileusis (LASIK) may be unpredictable.

Race

No racial preponderance has been identified.

Sex

An equal distribution exists between the sexes.

Age

Patients usually are aged 20-40 years at the time of clinical presentation.

CLINICAL

Section 3 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Multimedia
• References

History

The disease is usually asymptomatic, except for the progressive deterioration in uncorrected and spectacle corrected visual acuity caused by the irregular astigmatism induced by the corneal ectasia.

Episodes of corneal hydrops with resultant pain, as seen in keratoconus, have been reported, but they occur only rarely.

Physical

Uncorrected visual acuity is often severely reduced. Visual acuity, as measured by using a pinhole, is close to normal. Refraction and keratometry show against-the-rule astigmatism. Visual acuity typically cannot be restored by using a spherocylindrical combination of lenses. Overrefraction with a rigid trial contact lens restores normal visual acuity. However, patients who wear rigid contact lenses to treat pellucid marginal degeneration often experience glare and decreased contrast sensitivity despite achieving good Snellen acuity. It is unclear if this condition is due to the corneal disease or the contact lens wear.

Results of slit lamp examination are characterized by a peripheral band of thinning of the inferior cornea from the 4-o'clock position to the 8-o'clock position (see Media file 1). This thinning is accompanied by 1-2 mm of normal cornea between the limbus and the area of thinning. Corneal ectasia is most marked just central to the band of thinning. The central cornea is usually of normal thickness, and the epithelium overlying the area of thinning is intact.

Both eyes are usually affected, but the degree of involvement may be asymmetric. The area of thinning typically is epithelialized, clear, avascular, and without lipid deposits.

On careful slit lamp evaluation, prominent lymphatics often are detected at the inferior limbus parallel to the area of thinning. Vertical striations at the level of the Descemet membrane (similar to the Vogt striae) may be seen in rare instances.

Causes

The cause is unknown.

DIFFERENTIALS

Section 4 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Multimedia
• References

Other Problems to be Considered

Keratoglobus
Terrien marginal degeneration
Furrow degeneration
Peripheral corneal melting disorders (eg, Mooren ulcer)

WORKUP

Section 5 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Multimedia
• References

Other Tests

• Computerized videokeratography is extremely useful in detecting and diagnosing early disease, which may not be readily detectable on slit lamp evaluation.
• • Videokeratography shows low corneal power along the central vertical axis, increased power as the inferior cornea is approached, and high corneal power along the inferior oblique meridians.
  • The videokeratographic pattern has a classic butterfly appearance (see Media file 2). 
• Pachymetry may reveal a thinning of the inferior cornea.
• • This is a reversal of the typical pattern in which the cornea thickens from the center to the periphery.
  • If any part of the peripheral cornea is thinner than the center, this is a cause for concern.

Histologic Findings

Histologic examination shows an area of thinning that is epithelialized, clear, and avascular. The stroma is thinned, and the Bowman layer may have breaks or may be completely absent in the affected area. Typically, lipid deposits are absent, and a normal-appearing endothelium and the Descemet membrane are present. In acute hydrops, breaks in the Descemet membrane with swelling of the stroma and inflammatory cell infiltrate may be seen.

TREATMENT

Section 6 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Multimedia
• References

Medical Care

Spectacle correction usually fails early in the course of this disease as the degree of irregular astigmatism increases. In early-to-moderate cases, contact lenses are beneficial in providing visual rehabilitation.

• Spectacles and toric hydrophilic contact lenses are useful in mild pellucid marginal degeneration.
• Spherical hydrophilic contact lenses cannot correct the astigmatism associated with this condition.
• Hybrid contact lenses, which are easier than other lenses to fit to the ectatic cornea, may provide good vision for some patients; however, their poor oxygen permeability often leads to corneal neovascularization, which may adversely affect the prognosis for future corneal transplantation.
• Rigid gas permeable contact lenses provide excellent oxygen transmission to the cornea but are harder than the other lenses to fit.
• • Problems in fitting result from the flattening of the superior cornea and the high degree of against-the-rule astigmatism that often causes the lens to dislocate inferiorly.
  • The upper eyelid may support large-diameter rigid lenses with a high edge lift, but they often cause marked irritation and move excessively with movements of the eyelids, causing the patient's vision to periodically blur.
  • Rigid gas permeable contact lenses may improve the vision of patients with pellucid marginal degeneration, as in those with keratoconus. However, evidence that these lenses have any effect on the progression of the disease is lacking.

Surgical Care

In patients who cannot tolerate contact lenses or in those who do not achieve adequate visual acuity with rigid contact lenses because of the degree of ectasia, surgery may be considered.

A number of surgical procedures have been performed to provide visual rehabilitation. Standard-sized penetrating keratoplasty may produce poor results because the inferior edge of the transplant has to be sutured to an abnormally thin cornea, causing a high degree of postkeratoplasty astigmatism in the short- and long-term period. Continued thinning of the host cornea in the inferior aspect produces a situation similar to the situation that indicated surgery.

• Large-diameter grafts have been tried to remove as much of the affected cornea as possible, with good success. However, because of the proximity to the limbus and its blood vessels, these grafts may be prone to rejection.
• • Regular-sized grafts that are deliberately decentered in the inferior aspect also work poorly. The degree of astigmatism is large because of the decentering, and the incidence of rejection is high because of the proximity to the limbus.
  • Thermokeratoplasty and epikeratophakia are of only historical interest because the results obtained with these techniques are extremely poor.
• Excision of a crescentic wedge of corneal tissue from the inferior cornea, followed by tight suturing, has been reported to reduce the corneal ectasia.
• • The procedure is usually well tolerated; however, the effect is typically short lived, and thinning and ectasia recur.
  • In addition, this procedure may be hazardous in inexperienced hands. Several instances of wound dehiscence and resultant flat anterior chambers with its attendant problems have been reported with attempts of this procedure.
  • Crescentic lamellar keratoplasty, in which a crescentic transplant is performed to reinforce the area of thinning, has been described, but it may result in a high degree of astigmatism that necessitates subsequent central penetrating keratoplasty.
• Currently, the combination of peripheral lamellar crescentic keratoplasty, followed by a central penetrating keratoplasty after a few months is a favored surgical treatment.
• • The lamellar transplant restores normal thickness to the inferior cornea and enables good edge-to-edge apposition at the time of penetrating keratoplasty, reducing the possibility of high postkeratoplasty astigmatism.
  • Furthermore, the central graft that is now sutured to normal-thickness host tissue can be treated with videokeratography-guided selective removal of sutures and astigmatic keratotomy in the usual way to reduce any residual astigmatism.
• Ophthalmologists have begun performing the 2 operations in the same sitting, with encouraging results, though this approach is technically difficult.
• • Performing 2 keratoplasty procedures at different times necessitates the use of 2 separate corneas. By performing the 2 procedures in the same sitting, tissue from the same donor may be used, potentially reducing the antigenic load.
  • In addition, when the operations are completed as staged procedures, central penetrating keratoplasty is almost always needed.
  • Furthermore, the lamellar graft soon becomes vascularized, and prolonged topical steroid application is often needed. In young patients, this long-term use of steroids may result in posterior subcapsular cataracts.
  • Because a central graft almost always is needed, performing both procedures at the same time significantly decreases the time needed to attain best-corrected acuity. This consideration is important, as patients are often young and in the active and working phase of their lives (see Media file 3).
• Long-term follow-up care is important in reducing the incidence of rejection of the central penetrating graft.

Consultations

Treatment of pellucid marginal degeneration with either contact lenses or surgery requires considerable experience. A cornea specialist should be consulted to ensure the best visual outcome.

FOLLOW-UP

Section 7 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Multimedia
• References

Further Outpatient Care

• Patients should receive follow-up care as needed.

Complications

• Corneal hydrops similar to that seen in keratoconus, with disruption of the endothelial basement membrane and hydration of the adjacent corneal stroma, rarely occurs in pellucid marginal degeneration.
• Keratoglobus causes generalized thinning of the cornea.
• • The thinning is most marked at the limbus, extending circumferentially for 360°.
  • The whole cornea protrudes, in contrast to the regional thinning seen in keratoconus and the inferior paralimbal thinning in pellucid marginal degeneration.
• Terrien marginal degeneration affects an age group similar to that affected by pellucid marginal degeneration.
• • Terrien marginal degeneration can be bilateral.
  • Although this condition can be associated with large amounts of astigmatism, it can be differentiated from pellucid marginal degeneration because the superior cornea is predominantly affected and because the area of thinning is often associated with vascularization and lipid deposition.
• Furrow degeneration has some features of pellucid marginal degeneration.
• • An intact epithelium is present, and the area of corneal thinning is not vascularized, at least in the acute phase.
  • The differentiating feature is that the area of thinning is closer to the limbus with virtually no intervening zone of normal cornea, unlike the findings in pellucid marginal degeneration.
  • Furrow degeneration occasionally involves the superior cornea, and an associated adjacent area of scleritis may be present.
  • Edges of the furrow are steeper than the gradual attenuation seen in pellucid marginal degeneration.
  • Furrow degeneration occurs adjacent to the lipid deposition in arcus senilis, which is typically observed in elderly patients.
• Peripheral corneal melting disorders, such as Mooren ulcer, or peripheral melting secondary to rheumatologic disorders are characterized by pain.
• • This pain may be severe in cases of Mooren ulcer.
  • Associated findings include an epithelial defect over the area of thinning and corneal vascularization adjacent to the area of thinning in the acute phase.
• Contact lens-induced warping of the cornea can mimic the appearance of pellucid marginal degeneration on corneal topography.

Prognosis

• No large-scale longitudinal studies of pellucid marginal degeneration have been reported.
• • Quantifying the proportion of patients who eventually require surgery is difficult.
  • Contact lens fitting and surgical correction are more difficult with pellucid marginal degeneration than with keratoconus.
• In a follow-up of their ongoing longitudinal study of keratoconus, Rabinowitz and Rasheed have observed 31 patients with pellucid marginal degeneration up to 8 years.⁶
• • Five patients have required corneal transplantation in 1 eye, and one patient has required transplantation in both eyes.
  • The data must be interpreted with caution because these observations may have been affected by selection bias.

MISCELLANEOUS

Section 8 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Multimedia
• References

Medical/Legal Pitfalls

• With the increased application of refractive surgery, identifying patients with early pellucid marginal degeneration is extremely important because photorefractive keratoplasty can lead to poor results, with central corneal scarring and irregular astigmatism.
• Incisional techniques (eg, astigmatic keratotomy) are contraindicated because they are highly unlikely to correct the irregular astigmatism and because they may result in corneal perforation in unsuspected cases of pellucid marginal degeneration.
• LASIK is contraindicated because of the high likelihood of worsening irregular astigmatism.

MULTIMEDIA

Section 9 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Multimedia
• References

Media file 1:  Slit lamp image of the inferior cornea in a patient with advanced pellucid marginal degeneration. Image illustrates inferior corneal thinning, a hallmark of this disease.
	View Full Size Image
Media type:  Photo

Media file 2:  Corneal topography of early (right eye) and moderate (left eye) pellucid marginal degeneration.
	View Full Size Image
Media type:  Image

Media file 3:  Image shows simultaneous central penetrating keratoplasty and inferior peripheral lamellar keratoplasty performed to treat pellucid marginal degeneration.
	View Full Size Image
Media type:  Photo

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Multimedia
• References

1. Javadi MA, Karimian F, Hosseinzadeh A, Noroozizadeh HM, Sa'eedifar MR, Rabie HM, et al. Lamellar crescentic resection for pellucid marginal corneal degeneration. J Refract Surg. Mar-Apr 2004;20(2):162-5. [Medline].
2. Krachmer JH. Pellucid marginal corneal degeneration. Arch Ophthalmol. Jul 1978;96(7):1217-21. [Medline].
3. Kymionis GD, Aslanides IM, Siganos CS, Pallikaris IG. Intacs for early pellucid marginal degeneration. J Cataract Refract Surg. Jan 2004;30(1):230-3. [Medline].
4. Maguire LJ, Klyce SD, McDonald MB, Kaufman HE. Corneal topography of pellucid marginal degeneration. Ophthalmology. May 1987;94(5):519-24. [Medline].
5. Rabinowitz YS. Keratoconus. Surv Ophthalmol. Jan-Feb 1998;42(4):297-319. [Medline].
6. Rasheed K, Rabinowitz YS. Results of combined lamellar and penetrating keratoplasty for pellucid marginal degeneration [abstr]. Ophthalmol Suppl. 1997;Oct:191.
7. Schanzlin DJ, Sarno EM, Robin JB. Crescentic lamellar keratoplasty for pellucid marginal degeneration. Am J Ophthalmol. Aug 1983;96(2):253-4. [Medline].

Article Last Updated: Sep 11, 2007