Evaluation of relationships among refractive and topographic parameters

Purpose: To examine the relationships among several refractive and topograp hic parameters. Setting: Cullen Eye institute Department of Ophthalmology, Baylor College o f Medicine, Houston, Texas, USA. Methods: Using computerized videokeratography (EyeSys Corneal Analysis Syst em(TM)), 287 corneas of 150 patients were retrospectively analyzed. The Hol laday Diagnostic Summary (HDS) refractive maps were used to evaluate relati onships among variables of the HDS and refractive error. Results: Myopic spherical equivalent refraction (P =.0003) and more negativ e asphericity (Q-values) (P =.0119) were correlated with steeper corneas. T he Q-values were less negative in eyes with moderate myopia (2.0 to 6.0 dio pters [D]) than in those with hyperopia (1.0 D or greater). The Q-values be low -0.3 were correlated with less favorable values for predicted corneal a cuity and corneal uniformity index a values. Mean corneal curvature measure ments obtained by computerized videokeratography and standard keratometry s howed 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 wer e associated with reduced optical performance of the cornea. J Cataract Ref ract Surg 1999; 25, 814-820 (C) 1999 ASCRS and ESCRS.