Impairment of contrast sensitivity function (CSF) as a measure of disability glare.

A method for quantitative measurements of disability glare in clinical practice is presented. Glare is induced by a circular fluorescent tube which surrounds a sinusoidal grating displayed on a monitor. The threshold contrast that is needed for detection of the grating is measured with and without presence of the glare light. This is repeated for several different spatial frequencies. The discrepancy between the contrast sensitivity function (CSF) obtained with and without glare light was used to calculate the glare score (n) as a measure of disability glare. This was done for normals and cataract patients. The results show that an increasing glare score is related to an increase in turbidity of the optic media, while visual acuity had a weak correlation to the glare score. We also studied the relation glare score versus luminance and found that normals had a glare score that was almost independent of luminance level, while the cataract patients had a marked decrease in glare sensitivity when the luminance decreased. Most patients had a glare score that corresponded to their glare problems. These findings indicate a potential for using this psychophysical disability glare test method in industry, transport, and clinical ophthalmology. Some sources of methodological error inherent in the test method are evaluated and discussed.