Comparative Assessment of Visual Acuity and Contrast Sensitivity in Drivers Presenting to Ophthalmologic Clinic of Hamadan Farshchian Hospital

Car accidents are the second leading cause of mortality in Iran. For safe driving, drivers require minimum acceptable visual acuity. In Iran, the accepted routine test to take driving license is Snellen vision chart, which is not adequate for visual acuity determination in real and natural environment. It seems that introducing a more sensitive and specific screening test is necessary. In this survey, we studied whether adding contrast sensitivity test to the present screening protocol is valuable or not.
A cross-sectional study of 200 drivers presenting to the ophthalmologic clinic of Farshchian Hospital in Hamadan, Iran, was performed during 2014-2016. The participants were chosen using the census sampling method. Complete ophthalmologic examination, visual acuity evaluation, and contrast sensitivity test were carried out. Data were analyzed using SPSS, version 20.
The mean age of the participants was 39.6 years. The patients were allocated to a group with normal visual acuity and a normal corrected visual acuity group. The most common refractive errors were concurrent myopia and astigmatism. In normal visual acuity group, the percentages of abnormal contrast sensitivity (in increasing order of frequency) in appropriate lighting condition were 0, 8.3, 13.8, and 22.2 in the right eye and 0, 10.8, 16.21, and 18.91 in the left eye, and in reduced lighting condition, they were 0, 13.8, 33.3, 33.3, and 41.6 in the right eye and 0, 21.62, 21.62, 27.02, and 27.02 in the left eye. With normal corrected visual acuity, the percentages of abnormal contrast sensitivity test in normal lighting condition were 0, 14.28, 35.71, 64.28, and 64.28 in the right eye and 0, 7.69, 46.15, 53.84, and 84.61 in the left eye and 0, 50, 85.71, 92.85, and 92.85 and 0, 61.53, 76.92, 76.92, and 84.61, respectively, in low light condition.
It seems that contrast sensitivity test is a better predictor of visual ability in comparison with visual acuity, thus, it is recommended to be added to the vision-related driving license requirements.