Videokeratoscopic indices in relation to epidemiological exposure to keratoconus

Background To establish the relationship between videokeratoscopic indices and the degree of epidemiological exposure to keratoconus in three groups of clinically normal subjects. Methods Cross-sectional study in which 75 subjects lacking clinical signs of keratoconus were divided into three groups according to epidemiological exposure to the condition: 25 fellow eyes of subjects with clinical signs on the contralateral eye only (the “fellow eye” group), to be compared to 25 first-degree relatives of patients with keratoconus (the “relatives” group) and 25 controls without a family history of the disease (the “control” group). Qualitative patterns and quantitative parameters describing curvature (central curvature), irregularity (root mean square of the higher-order corneal wavefront aberration), and asymmetry (inferior-superior dioptric asymmetry, Zernike vertical coma) obtained from videokeratoscopy were used for comparison between groups. Results Members of the fellow eye group featured a greater number of asymmetric curvature patterns and increased values in indices describing asymmetry and irregularity than subjects included in both control and relatives groups. Control and relatives groups were not significantly different. Despite significant differences in the distribution of values between the groups, no single index was able to effectively discriminate between groups using ROC curve analysis. Conclusions A prior threefold classification of clinically normal subjects according to epidemiological exposure to keratoconus was not sustained by significant differences in videokeratoscopic indices when comparing between groups.