The relative sensitivity of visual acuity and small letter contrast sensitivity in early cataract

Abstract

Purpose: To investigate the effects of early cataract on spatial frequency dependent contrast sensitivity (CS) measurement and log MAR visual acuity (VA) assessment.Methods: The relative sensitivity of two computer‐generated letter CS tests, 1/9.5 letter CS (1/9.5 LCS) (assessing low to medium spatial frequency CS) and 6/9.5 letter CS (6/9.5 LCS) (measuring high spatial frequencies), and a log MAR VA test were evaluated in 19 subjects with early cataract and 21 age‐matched controls.Results: Results indicate that these three tests decline with increasing cataract formation. The greatest visual reduction and the highest test discriminative ability were found with the 6/9.5 LCS test (Az score of 0.441 versus 0.408 for VA) and the lowest with the 1/9.5 LCS test (Az score of 0.383). However, measurement variability was greatest for 6/9.5 LCS. After correcting for this variability, the 6/9.5 LCS test still proved slightly more sensitive to early cataract and cataractous change than the other two measurements.Conclusion: The study suggests that 6/9.5 LCS or other size small letter CS tests are able to detect more subtle vision loss in cataract than visual acuity.