eMedicine Specialties > Ophthalmology > Cornea

Pellucid Marginal Degeneration

Author: Karim Rasheed, MD, MSc, MRCO, Attending Ophthalmologist, Sani Eye Center
Coauthor(s): Yaron Rabinowitz, MD, Chairman, Division of Ophthalmology, Cedars-Sinai Medical Center; Clinical Associate Professor, Departments of Ophthalmology and Pediatrics, University of California at Los Angeles
Contributor Information and Disclosures

Updated: Sep 11, 2007

Introduction

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

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.

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