Dynamic corneal biomechanics in different cell layers: in keratoconus and normal eyes

PURPOSE This study aimed to determine the relationship between corneal cellular structures and biomechanical deformation parameters in keratoconic (KC) and healthy eyes. METHODS In this prospective comparative study, 29 eyes of 29 KC patients were age- and gender-matched with 28 eyes of 28 healthy individuals using frequency matching. Corneal parameters examined included the density of basal epithelial cells, anterior keratocytes, posterior keratocytes and endothelial cells as assessed by in vivo corneal confocal microscopy (HRT III-RCM, Heidelberg Engineering, www.heidelbergengineering.com). Additionally, the coefficient of variation of endothelial cell size (CV) and the percentage of hexagonal endothelial cells (HEX%) were measured by specular microscopy (Konan NSP-9900, Konan Medical, www.konanmedical.com). Further, biomechanical deformation parameters were derived from Corvis Scheimpflug Technology (Corvis ST, Oculus, www.oculus.de). All cellular and biomechanical deformation parameters in KC and normal groups were compared, and the relationship between cellular and biomechanical parameters calculated. RESULTS In the KC group, the highest concavity (HC) delta arc length and maximum delta arc length were associated with endothelial cell density (Beta = -0.39, p = 0.03 and Beta = -0.60, p ˂ 0.001, respectively). Furthermore, there was a significant association between HC deflection length and HEX% (Beta = -0.67, p = 0.001). In the normal group, HC delta arc length and HC deflection length were significantly associated with endothelial cell density (Beta = 0.46, p = 0.02; and Beta = -0.51, p = 0.01, respectively). HC time, HC deformation amplitude and applanation 1 delta arc length were associated with CV (Beta = 0.50, p = 0.01; Beta = 0.27, p = 0.009; and Beta = -0.57, p = 0.002, respectively). Applanation 1 and applanation 2 deformation amplitudes were associated with HEX% (Beta = -0.49, p = 0.005; and Beta = -0.46, p = 0.02). CONCLUSIONS Biomechanical deformation parameters were significantly correlated with endothelial cell properties in both KC and normal groups, thereby indicating the importance of the integrity of endothelial cells to the biomechanical properties of both KC and normal corneas.