[Relation of visual acuity of test field luminance in glare sensitivity of various origin]

Intolerance to bright light is a nonspecific ophthalmological symptom, originating either in disturbances of the optic apparatus of the eye or caused by functional disturbances of the neuronal network of the retina. Disturbances in brightness and darkness adaptation can often cause considerable decrease in visual acuity, which is not evident in the standardized tests that measure photophobia in conjunction with visual function. If the test field is very bright and the patient has photophobia, the visual acuity is often reduced considerably. The relationship between visual acuity and luminance of the test field was determined in glare--sensitive patients using a relatively simple method and a large range of luminances (0.1-30,000 cd/m2). In contrast to previously used methods, visual acuity was determined in a range where neuronal mechanism can be expected to be responsible for adaptation to brightness. We found disturbances in the relationship between visual acuity and luminance in several diseases, and it was especially pronounced in cone dystrophies. Affections of the optic nerve and opacities of the optic media usually did not cause a marked decrease in visual acuity at high luminances. As a supplemental investigation to mesoptometry and nyctometry, the method described here primarily permits types of photophobia to be determined that are not caused by stray light. The dynamic nature of neuronal adaptation processes determined by this test has therefore considerable influence on visual acuity.