Clinicians who are trying to distinguish between pellucid marginal degeneration (PMD) and keratoconus should take a closer look at their widefield spectral-domain OCT parameters, a recent study suggests. The researchers found corneal sublayer pachymetry showed good reliability in detecting the two conditions.

This prospective, cross-sectional study included 69 eyes (59 with keratoconus, 10 with PMD) of 69 patients. The investigators generated pachymetry maps of the total cornea, epithelium and stroma. They found that overall repeatability of sublayer pachymetry was comparably good in both keratoconus and PMD. They noted that measurement reliability in keratoconic eyes was a negative function of Kmax.

Compared with keratoconus, the investigators discovered that PMD exhibited higher total cornea (526±31µm vs. 503±30µm) and epithelium (56±7µm vs. 51±5µm) values in the inferotemporal 2mm to 5mm sector as well as a lower epithelium value in the inferior 7mm to 9mm sector (52±5µm vs. 57±5µm). They added that the calculated ratio between total cornea in the inferotemporal 2mm to 5mm sector and in the inferior 7mm to 9mm sector yielded the highest diagnostic accuracy for distinguishing between PMD and keratoconus.

Mohr N, Shajari M, Krause D, et al. Pellucid marginal degeneration versus keratoconus: distinction with wide-field SD-OCT corneal sublayer pachymetry. Br J Ophthalmol. October 14, 2020. [Epub ahead of print].