Evaluation of epithelial, stromal, and corneal thickness maps in the distinction between pellucid marginal degeneration and inferior keratoconus (pellucid-like)

To distinguish between these two ectasias, which can be confused with each other, using epithelial, stromal, and total corneal thickness maps in patients with pellucid marginal degeneration (PMD) and inferior keratoconus (I-KC) that have similar topographic features. This prospective cross-sectional study included 114 eyes of 73 patients (56 eyes with PMD, 58 eyes with I-KC). All measurements were obtained using MS-39 AS-OCT. The values in the epithelial, stromal, and corneal thickness maps were recorded. There was no significant difference in mean age between the two groups (p = 0.061). In PMD patients, minimum epithelial, stromal, and total corneal thickness values in the inferotemporal (IT), inferior (I), inferonasal (IN), and nasal (N) zones within 6–8 mm and 8–10 mm areas were significantly thinner than in the I-KC group (p < 0.05). In the I-KC group, minimum and average epithelial thickness values in the central 2 mm area, in the IT and temporal (T) zones within 2–4 mm areas, and in the IT zone within 4–6 mm areas were significantly thinner than in the PMD group (p < 0.05). To distinguish PMD from I-KC, the IT 2–4 min./IN 8–10 min. difference in stromal thickness had an AUC of 0.878, with 79.5% sensitivity and 76% specificity; in epithelial thickness, the IT 2–4 min./IN 6–8 min. ratio reached the highest diagnostic accuracy, with an AUC of 0.855, 78.6% sensitivity, and 79.7% specificity (p < 0.001). Patients exhibiting crab-claw patterns on the sagittal curvature map can differentiate between PMD and I-KC using pachymetric values and combinations of epithelial, stromal, and corneal thickness maps obtained with wide-field AS-OCT.