Scheimpflug photography-based clinical characterization of the correlation of the corneal shape between the anterior and posterior corneal surfaces in the normal human eye

PURPOSE: To evaluate the correlation of the mean curvature and shape factors between both corneal surfaces for different corneal diameters measured with a Scheimpflug photography-based system. SETTING: Vissum Corporation, Alicante, Spain. DESIGN: Case series. METHODS: Randomly selected healthy normal eyes had a comprehensive ophthalmologic examination including anterior segment analysis with the Sirius system as follows: anterior and posterior mean corneal radius for 3.0 mm, 5.0 mm, and 7.0 mm; anterior and posterior mean shape factor for 4.5 mm and 8.0 mm; central (CCT) and minimum corneal thickness; and anterior chamber depth (ACD). RESULTS: The study enrolled 117 eyes (117 subjects; aged 7 to 80 years). The mean anterior mean corneal radius:posterior mean corneal radius ratio was 1.19 (range 1.12 to 1.27) for all corneal diameters (P = .86). The correlation coefficient between the anterior and posterior mean corneal radius was 0.85 or more for all corneal diameters. The anterior mean shape factor:posterior mean shape factor ratio for the 2 corneal diameters analyzed was approximately 1 (range 0.45 to 4.03). The correlations between anterior and posterior mean shape factors were extremely poor and not significant. Multiple regression analysis showed that the central posterior mean corneal radius was significantly correlated with the anterior mean corneal radius, CCT, and spherical equivalent (R-2 = 0.77, P<.01). CONCLUSIONS: Central posterior corneal curvature could be predicted from the anterior corneal curvature, pachymetry, and the refractive status of the eye but not from the corneal shape factor.