Distribution Of Corneal Epithelium Thickness In Ectasia-Specific Marker Points In Healthy And Keratoconus Eyes

To examine the epithelial thickness (ET) distribution in healthy and keratoconus eyes using a swept-source OCT (SS-OCT) based anterior segment tomography.

Prospective, monocentric, and observational study performed at the Department of Ophthalmology, University Hospital Carl
Gustav Carus, TU Dresden, Germany

This study enrolled patients with healthy eyes (CT, n=50) and clinical keratoconus (KC, n=50). All patients underwent SS-OCT measurement (ANTERION, Heidelberg Engineering GmbH, Germany) of the cornea to determine tomographic parameters. Following standard parameters were assessed: mean epithelial thickness (mean-ET), standard deviation of ET (sd-ET), thinnest epithelial thickness (thin-ET), and the average ET in 2 to 6 mm zone. Additionally, ET were manually measured in ectasia specific locations such as the anterior tangential steepest curvature (Kmax-tan), sagittal steepest curvature (Kmax-sag), thinnest corneal thickness (TCT), and maximum posterior elevation (Elev-post). For statistical analysis, an ANOVA and unpaired t-test were used.

The meanET was 50.2 µm in the KC group and did not differ from the CT group with 50.3µm (P=0.87). However, there was a significant difference in the sd-ET, the average ET in the 2 mm zone, and in the 4 mm zone between the two groups (P<0.001). With regard to the thin-ET, the groups were statistically significantly different at 36µm (KC) and 42µm (CT, P<0.001). In the KC group, ET were 43±5, 46±6, 40±8, and 41±6 over Kmax-tan, Kmax-sag, TCT, and Elev-post, respectively, which was statistically different between the points (P<0.001), except for TCT and Elev-post. The location of thin-ET was closest to the location of TCT and Elev-post (P>0.05), and farthest to Kmax-tan and Kmax-sag (P<0.05).

The ET distribution is significantly different in specific regions of keratoconus eyes. In the central corneal zone, the epithelial thickness differed significantly between healthy and KC eyes. It has been found that the epithelium is the thinnest in locations who are associated with the weakest part of the KC cornea, namely TCT and Elev-post, and not to the steepest part. This might be play a role in screening of early KC and for planning of customized cross-linking treatments.