Original article
Prediction of letter contrast sensitivity using videokeratographic indices

This study was presented in part at the 1998 annual meeting of the Association for Research in Vision and Ophthalmology, Fort Lauderdale, Florida, May 15, 1998.
https://doi.org/10.1016/S0002-9394(00)00380-9Get rights and content

Abstract

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 spectacle-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. Videokeratography was performed with the TMS-2 videokeratoscope, and the surface regularity index, surface asymmetry index, and coefficient of variation of power were obtained for each subject. Letter contrast sensitivity was measured with the CSV-1000LV with spectacle correction. The correlation between the number of correct letters and topographic indices 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 correlations between number of correct letters and the coefficient of variation of power (r = −.77; P = .001), number of correct letters and surface regularity index (r = −.76, P = .001), and the number of correct letters and surface asymmetry index (r = −.64; P = .001). The linear regression equation between number of correct letters and the coefficient of variation of power was the number of correct letters = −0.05 × the coefficient of variation of power + 23.2.

CONCLUSIONS: Our results suggest that subtle visual deteriorations, which are barely detected by contrast sensitivity testing, can be predicted objectively by the corneal topographic indices.

Section snippets

Patients and methods

We studied 59 eyes of 51 patients (men, 29; women, 22). The eyes were divided into two groups: one group, with 20 eyes of 20 cases, had normal corneas and served as the controls (mean age, 28.3 ± 4.6 years). The second group, with 39 eyes of 31 cases, had abnormal corneal topography resulting from keratoconus (mean age, 27.4 ± 8.6 years). All the eyes had a best spectacle-corrected visual acuity 20/20 or better, and there were no abnormal ocular findings except for the refractive error and

Results

A comparison of letter contrast sensitivity in the normal control group and the abnormal topography group is shown in Figure 1. The abnormal topography group had a significantly greater loss of letter contrast sensitivity (number of correctly identified letters = 19.1 ± 2.5 letters, median 20.0 letters) than the normal control (number of correct letters = 22.6 ± 1.2 letters, median 23.0 letters, P = .0001, Mann-Whitney Rank Sum test). This was found despite the fact that all the subjects in

Discussion

Since Campbell and Gubisch24 first suggested that measurement of contrast sensitivity can provide a more comprehensive measure of spatial vision than the measurement of visual acuity, contrast sensitivity testing has become popular in clinical practice.25, 26 However, it has been argued that contrast sensitivity testing is mainly supplementary to Snellen acuity determination, and there is no benefit in the measurement of contrast sensitivity for clinical management, except where acuity is found

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    This work was supported in part by grant-in-aid No. 11671737 for scientific research from the Japanese Ministry of Education, Science, Sports, and Culture (Dr Maeda), and by a research grant from the Osaka Eye Bank, Suita, Japan (Dr Maeda).

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