Determining Stress Distribution in a Longitudinal Keratoconus Cohort.

PURPOSE: To investigate whether stress distribution patterns can predict biomechanical progression in keratoconus eyes using longitudinal data.

METHODS

The corneal contribution to stress, (CCS) = r/2t, was calculated based on the Hoop stress formula without intraocular pressure. Here, r is radius of curvature and t is corneal thickness. CCS was calculated from Pentacam tangential curvature and thickness maps (Oculus, Wetzlar, Germany) and investigated the difference in magnitude of stress between the 2-mm zones of minimum and maximum CCS (CCSmin, CCSmax), and the difference between them (CCSdiff). We included patients with diagnosed keratoconus and healthy controls. Exclusion criteria were use of contact lenses, previous corneal surgery, corneal scar, other corneal diseases, and bad quality of Pentacam images. A linear mixed model was used to determine predictive ability of CCSdiff. A P -value <0.05 was considered significant.

RESULTS

A total of 114 eyes of 70 patients with keratoconus and 31 eyes of 31 healthy controls were included with a mean age of 24 ± 6 and 24 ± 4 years, respectively. Patients with keratoconus had a mean follow-up time of 2 years (range 0.2-13.6 years). At baseline, in keratoconus, CCSmax was 8.3 ± 1.1 and CCSmin was 6.6 ± 0.6. For healthy eyes, mean values were 7.4 ± 0.5 and 6.5 ± 0.5, respectively. CCSdiff correlated significantly with maximum zonal tangential curvature (Cspot) (r = 0.83, P < 0.001). CCSdiff at baseline predicted progression over time of Cspot ( P < 0.001).

CONCLUSIONS

The difference between minimum and maximum stress contribution, CCSdiff, changes in time, and its baseline values predict progression in patients with keratoconus.