Staging of Keratoconus Indices Based on Localized Corneal Biomechanics Stress-Strain Index Map

To assess Stress-Strain Index (SSI) map parameters and to establish a new corneal-biomechanics-based staging (CBBS) system and the diurnal variation of SSI.

Hospital-based cross-sectional study.

Seventy-eight keratoconus subjects.

A total of 78 keratoconus (KC) subjects were included in this study. All subjects had corneal tomography (Pentacam HR, Oculus) and biomechanical measurements (Corvis ST, Oculus) 5 times a day, which were at 8:30, 11:30, 14:30, 17:30, and 20:30. Stress-Strain Index value was obtained from Corvis ST, and SSI map parameters were derived from a customized SSI map generator (Matlab runtime 9.8). An analysis of variance was used to compare the SSI map parameters among varying stages of KC groups. The best performing parameters according to the Youden index were subsequently used to create the CBBS system. Cohen κ statistics and contingency tables were used to compare CBBS and topographic KC classification (TKC) systems.

Stress-Strain Index map parameters were used for analysis: mean inside cone SSI, mean outside cone SSI, minimum SSI, and maximum SSI.

Significant diurnal variations were observed in mean inside cone SSI (F = 5.536, P < 0.001) and Min SSI (F = 6.031, P < 0.001) without any clinical significance. Mean inside cone SSI had the highest area under the curve value and sensitivity among the 3 KC stages and was used to establish the CBBS system. Cohen κ statistics (0.652, P < 0.001) and contingency tables (76.9% KC eyes were of the same stage) showed good agreement between CBBS and TKC systems.

A new corneal-biomechanics-based KC staging system was established on the basis of localized corneal biomechanics (mean inside cone SSI). There was no clinically significant diurnal variation in localized corneal biomechanics based on SSI map parameters.

The authors have no proprietary or commercial interest in any materials discussed in this article.