Pellucid Marginal Degeneration (PMD) Workup

Updated: Oct 30, 2017
  • Author: Jean Deschênes, MD, FRCSC; Chief Editor: Hampton Roy, Sr, MD  more...
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Workup

Imaging Studies

Optical coherence tomography (OCT) and Scheimpflug-based corneal imaging systems can illustrate inferior corneal thinning (see image below).

Optical coherence tomography (OCT) of cornea with Optical coherence tomography (OCT) of cornea with moderate pellucid marginal degeneration.
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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 (or crab-claw) appearance, as shown in the image below.

Corneal topography of early (right eye) and modera Corneal topography of early (right eye) and moderate (left eye) pellucid marginal degeneration.

The most common topographic patterns are the "crab-claw" pattern, present in 61.7%-75% of patients, followed by inferior steepening, seen in 18%-22.2% of patients. [6, 11]

Representative photographs of corneal topography. Representative photographs of corneal topography. Courtesy of the Japanese Journal of Ophthalmology, published by the Japanese Ophthalmological Society.

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.

Orbscan may reveal a typical "kissing birds" appearance. [12]

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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.

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