Signs of pellucid marginal degeneration should rule out refractive surgery

Pellucid marginal degeneration is a subtle condition that could lead to corneal ectasia following laser eye surgery. Although it is atypical and rare, clinicians should learn how to identify pellucid and screen patients for it preoperatively, said Yaron S. Rabinowitz, MD, director of ophthalmology research, Cedars Sinai Medical Center, Los Angeles.

In pellucid marginal degeneration, corneal thinning typically occurs from the 4 to the 8 o'clock position approximately 1 mm from the inferior limbus. Another difference between pellucid marginal degeneration and keratoconus is that the onset of pellucid tends to be in the 30s, rather than around the time of puberty.

The key to recognizing early cases of pellucid is topography, Dr. Rabinowitz said. Patients may appear clinically normal and have normal pachymetry, if it is performed centrally or paracentrally. However, since the cornea typically gets thicker from the center to the periphery, clinicians should be suspicious if there is little difference between the central and inferior pachymetry.

The presence of "crab claw" topography will indicate pellucid, but in early cases what will more likely be seen is inferior flattening characterized by an isolated inferior blue spot. Patients with either sign should be considered pellucid suspects and poor candidates for refractive surgery, Dr. Rabinowitz said.