Characteristics of corneal topographic and pachymetric patterns in patients with pellucid marginal corneal degeneration.

Purpose: To determine the characteristics of the shape of the cornea in patients with pellucid marginal corneal degeneration (PMD) and to compare these characteristics to those of eyes with keratoconus and eyes of normal subjects.

Methods: This was a retrospective, cross-sectional case-series in which 49 eyes of 33 patients with PMD, 51 eyes of 51 patients with keratoconus and 53 eyes of 53 subjects with normal corneas (controls) were examined and compared. For all eyes, we obtained the topographic patterns of the axial power maps, anterior and posterior elevation maps and pachymetric maps using a rotating Scheimpflug camera. The eyes were classified into the respective patterns by visual inspection of these maps.

Results: In eyes with PMD, the most common axial power map pattern was the crab claw pattern (78 %) followed by the inferior steepening pattern (18 %). In eyes with keratoconus, the most common pattern was the inferior steepening pattern (67 %). The most common pattern in the elevation maps for both surfaces was the asymmetric island in eyes with PMD and keratoconus. Although the decentered pattern, including the decentered oval (27 %) and decentered round (20 %) pattern, on pachymetric map was specific to eyes with PMD, the incidence of these patterns was relatively low.

Conclusions: The similarity in the topographic and pachymetric patterns in eyes with PMD and keratoconus suggests that they may be a continuity of the same disorder with different phenotypes.