Evaluation of relationships among refractive and topographic parameters

Purpose: To examine the relationships among several refractive and topographic parameters. Setting: Cullen Eye institute Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA. Methods: Using computerized videokeratography (EyeSys Corneal Analysis System(TM)), 287 corneas of 150 patients were retrospectively analyzed. The Holladay Diagnostic Summary (HDS) refractive maps were used to evaluate relationships among variables of the HDS and refractive error. Results: Myopic spherical equivalent refraction (P =.0003) and more negative asphericity (Q-values) (P =.0119) were correlated with steeper corneas. The Q-values were less negative in eyes with moderate myopia (2.0 to 6.0 diopters [D]) than in those with hyperopia (1.0 D or greater). The Q-values below -0.3 were correlated with less favorable values for predicted corneal acuity and corneal uniformity index a values. Mean corneal curvature measurements obtained by computerized videokeratography and standard keratometry showed a strong degree of correlation (P =.0001). Conclusion: As the degree of myopia and negative asphericity increased, the corneal radius of curvature decreased. Corneal Q-values less than -0.3 were associated with reduced optical performance of the cornea. J Cataract Refract Surg 1999; 25, 814-820 (C) 1999 ASCRS and ESCRS.