Excerpt from Pellucid Marginal Degeneration

Synonyms, Key Words, and Related Terms: PMD, corneal thinning, keratoconus, corneal ectasia

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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.

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