Cone location and corneal stiffness in keratoconus

Abstract

Purpose : To investigate the relationship between central corneal stiffness in keratoconic patients as a function of severity of disease and distance of the keratoconic cone from the center.

Methods : Pentacam tomography and Corvis ST biomechanical response metrics were prospectively acquired in 67 eyes of 41 subjects diagnosed with keratoconus. The severity of disease, represented by the magnitude of the 2mm diameter zone around the steepest point of Kmax (Km spot), and the distance of Kmax from the center of the map (Kmax dist) were independently compared via univariate regression analyses to four biomechanical metrics: stiffness parameter at first applanation (SP-A1) and highest concavity (SP-HC), both of which increase with increasing stiffness, as well as deformation amplitude ratio at 2mm (DA Ratio Max) and integrated inverse radius (Int Inv Radius), both of which decrease with increasing stiffness. Statistical analyses were performed in SAS with significant threshold set at p < 0.05.

Results : Km spot was found to have a statistically significant negative relationship to both SP-A1 and SP-HC (p<0.0001; R² = 0.483) and (p<0.0001; R² = 0.215), respectively, and a significantly positive relationship to DA Ratio Max and Int Inv Radius (p< 0.0001; R² = 0.588) and (p<0.0001; R² = 0.693), respectively. In terms of Kmax dist, both SP-A1 and SP-HC yielded a weaker, though significantly positive relationship (p = 0.013; R² = 0.091) and (p = 0.023; R² = 0.077), respectively, while DA Ratio Max and Int Inv Radius yielded a significantly negative relationship (p = 0.002; R² = 0.137) and (p = 0.0002; R² = 0.190), respectively.

Conclusions : In keratoconic patients, the corneal stiffness decreases by all biomechanical metrics as severity of disease increases in a continuous manner. In addition, all biomechanical metrics of central corneal stiffness increase as the distance of the keratoconic cone from the center also increases. This is consistent with the focal nature of the biomechanical weakening in keratoconus.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.