National survey of pellucid marginal corneal degeneration in Japan.

PURPOSE: A national survey was conducted in Japan to analyze the clinical characteristics of pellucid marginal corneal degeneration (PMD).

METHODS: A questionnaire was sent to all members of the Japan Cornea Society requesting demographic and clinical findings on PMD patients who had been examined between 2008 and 2010. The presence of band-shaped peripheral corneal thinning, detected by slit-lamp biomicroscopy or by a pachymetric map, was set as the diagnostic criterion of PMD.

RESULTS: Most of the participating facilities relied on either slit-lamp biomicroscopy or corneal topography as diagnostic tools for the detection of PMD. Data on 347 patients (579 eyes) were returned from the participating facilities for analysis, among which 162 eyes in 84 men and 24 women, with a median onset age of 37 years, met the PMD criteria. Of the 108 patients (162 eyes) with classical PMD, unilateral involvement was found in 25 % of patients (27 eyes). In 17 of the 27 eyes for which topographic findings for the contralateral eye were available, seven eyes were either keratoconus or had a suspected diagnosis of keratoconus. An association with allergic disease was found in 24 eyes (22.2 % of patients). Approximately half of the patients had 1.0 or better spectacle-corrected distance visual acuity, and only 5 % showed 0.1 or worse. The mean keratometric value was 45.7 diopters. On corneal topography, 100 eyes (61.7 %) showed the topographic "crab-claw pattern," and the remaining eyes showed other patterns, including inferior steepening (22.2 %) and an irregular pattern (10.5 %).

CONCLUSIONS: We conducted the largest clinical survey of PMD to date and found a male predominance, a relatively high prevalence of unilateral involvement, and associated allergic diseases.