Changes in anterior and posterior corneal curvatures in keratoconus

Objective: To quantitatively evaluate the changes in anterior and posterior corneal curvatures of eyes with keratoconus. Design: Case-control retrospective and observational study. Participants: Thirty-one patients who were clinically diagnosed to have uni lateral or bilateral keratoconus and 18 normal subjects. Intervention: The anterior and posterior topographies were obtained using s canning-slit videokeratography and assessed by Fourier series harmonic anal ysis. Main Outcome Measures: Quantitative descriptors of the topography data, sph erical power, regular astigmatism, and irregular astigmatism (asymmetry and higher order irregularity) components were compared between the anterior a nd posterior surfaces and among groups of clinically diagnosed keratoconus (33 eyes), keratoconus suspect (13 eyes), and normal subjects (36 eyes). Results: Spherical power (P = 0.0003, Mann-Whitney U test with Bonferroni's correction of P values), regular astigmatism (P = 0.0166), and asymmetry ( P = 0.0031) of the anterior surface were significantly greater in the kerat oconus eyes than in the normal controls. For the posterior surface, spheric al power (P < 0.0001), regular astigmatism (P = 0.0143), asymmetry (P < 0.0 001), and higher order irregularity (P = 0.0032) of the keratoconus group w ere significantly greater than those of the control group. The keratoconus suspect eyes, when compared with the normal controls, showed a significantl y greater amount of spherical power (P = 0.0166) and asymmetry (P < 0.0001) in the anterior surface and spherical power (P < 0.0001), regular astigmat ism (P = 0.0244), asymmetry (P < 0.0001), and higher order irregularity (P = 0.0276) in the posterior surface. All refractive components demonstrated statistically significant correlations between the anterior and posterior s urfaces (P < 0.0001, Spearman's rank correlation). Conclusions: Not only the anterior but also the posterior corneal curvature is affected in keratoconus. These changes are observed from the early stag e of this disorder. (C) 2000 by the American Academy of Ophthalmology.