Prediction of letter contrast sensitivity using videokeratographic indices

PURPOSE: To analyze the relationship between corneal topography and letter contrast sensitivity. METHOD: Experiments were conducted on 59 eyes of 51 patients who had best s pectacle-corrected visual acuity of 20/20 or better and no ocular pathology except for the corneal shape. Thirty-nine eyes had an abnormal topographic pattern resulting from keratoconus, and the other 20 eyes showed a normal topographic pattern, Videokerarography was performed with the TMS-2 videoke ratoscoye, and the surface regularity index, sur face asymmetry index, and coefficient of variation of power were obtained for each subject. Letter co ntrast sensitivity was measured with the CSV-1000LV with spectacle correcti on. The correlation between the number of correct letters and topographic i ndices was calculated. RESULTS: The abnormal topography group had a significantly greater loss of letter contrast sensitivity (median = 20 letters) than the normal control ( median = 23 letters; P = .0001), There were statistically significant corre lations between number of correct letters and the coefficient of variation of power (r = -.77; P = .001), number of correct letters and surface regula rity index (r = -.76, P = .001), and the number of correct letters and surf ace asymmetry index: (r = -.64; P =.001), The linear regression equation be tween number of correct letters and the coefficient of variation of power w as the number of correct letters = -0.05 x the coefficient of variation of power + 23.2. CONCLUSIONS: Our results suggest that subtle visual deter;orations, which a re barely detected by contrast sensitivity resting, can be predicted object ively by the corneal topographic indices. (C) 2000 by Elsevier Science Inc. All rights reserved.