Detecting Subclinical Keratoconus By Biomechanical Analysis In Tomographically Regular Keratoconus Fellow Eyes

The purpose of this study was to analyze the biomechanical characteristics in tomographically regular keratoconus fellow eyes.

The David J Apple Center for Vision Research and International Vision Correction Research Center (IVCRC), Department of Ophthalmology, Heidelberg University Hospital, Heidelberg, Germany

In this retrospective, consecutive case series, 916 eyes of 458 patients were queried to identify tomographically regular fellow eyes. Outcome measures included best-corrected visual acuity (BCVA), tomographic Scheimpflug analysis using Pentacam AXL (Oculus, Wetzlar, Germany), and biomechanical assesssment using Corvis ST (Oculus, Wetzlar, Germany). Tomographic changes were assessed via analysis of the anterior and posterior curvature, K-max, thinnest corneal thickness (TCT), the Belin/Ambrosio Deviation Display (BAD-D), and the ABCD-Grading. Biomechanical changes were analyzed using Corvis Biomechanical Index (CBI) and Tomographic Biomechanical Index (TBI).

Thirty-four tomographically regular fellow eyes were identified and included. Overall, the mean BCVA was -0.02 ± 0.13 logMAR. Tomographic analysis showed mean K-max of 43.87 ± 1.21 D, mean TCT of 532 ± 23 µm, and mean BAD-D of 1.02 ± 0.43. Biomechanical analysis demonstrated mean CBI of 0.28 ± 0.26 and mean TBI of 0.34 ± 0.30. While normal CBI-values were observed in 16 (47%) of 34 eyes, only 13 eyes (38%) showed a regular TBI and 7 eyes (21%) showed no signs of tomographic (BAD-D, ABCD) or biomechanical (CBI, TBI) changes.

Very asymmetric corneal ectasia with a regular tomography in the keratoconus fellow eye is rare. In such cases, a biomechanical analysis can help to detect early signs of corneal ectasia. In our analysis, the TBI showed the highest sensitivity for detecting a biomechanical abnormality in such cases.