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 unilateral or bilateral keratoconus and 18 normal subjects. Intervention: The anterior and posterior topographies were obtained using scanning-slit videokeratography and assessed by Fourier series harmonic analysis. Main Outcome Measures: Quantitative descriptors of the topography data, spherical power, regular astigmatism, and irregular astigmatism (asymmetry and higher order irregularity) components were compared between the anterior and 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 keratoconus eyes than in the normal controls. For the posterior surface, spherical power (P < 0.0001), regular astigmatism (P = 0.0143), asymmetry (P < 0.0001), and higher order irregularity (P = 0.0032) of the keratoconus group were significantly greater than those of the control group. The keratoconus suspect eyes, when compared with the normal controls, showed a significantly greater amount of spherical power (P = 0.0166) and asymmetry (P < 0.0001) in the anterior surface and spherical power (P < 0.0001), regular astigmatism (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 surfaces (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 stage of this disorder. (C) 2000 by the American Academy of Ophthalmology.