Influence of Cataract Morphology on Straylight and Contrast Sensitivity and Its Relevance to Fitness to Drive

Abstract

Aims: To evaluate straylight and contrast sensitivity in cataractous eyes of different morphologies, and to determine which type of cataract presents higher impairment of visual function, specifically compared to studies proposing new norms for European drivers. Methods: Best-corrected visual acuity (BCVA), contrast sensitivity and straylight were measured in 97 cataractous eyes using respectively a Snellen chart, a Pelli-Robson chart and the compensation comparison method (C-Quant Straylight Meter). Cataracts were graded using the Lens Opacities Classification System III (LOCS III) and divided into 4 groups: nuclear, cortical, nuclear-cortical and posterior subcapsular cataract. These results were compared to data from 38 cataract-free control subjects. Results: Contrast sensitivity was reduced and straylight increased in all cataract patients, most notably in posterior subcapsular and nuclear-cortical cataract. Contrast sensitivity and BCVA were correlated (r = 0.44), whereas straylight and BCVA were not. Applying cut-off values as proposed by European drivers studies of 1.25 log contrast sensitivity and 1.4 log straylight as safe margins for driving, 31% would be considered unfit to drive on the basis of contrast sensitivity and 78% on the basis of straylight, although their visual acuity was still above the current European visual acuity requirement for driving. Conclusions: Straylight and, to a lesser extent, contrast sensitivity are complementary to BCVA and should be taken into account when considering surgery or driving legality.