Contrast sensitivity function in evaluation of visual impairment due to retinitis pigmentosa

Spatial contrast sensitivity functions of 11 retinitis pigmentosa patients were studied. The patients represented 3 different stages of the disease: 1: in the very severely impaired patients the contrast sensitivity and grating resolution had decreased to a fraction of normal. 2: in severely impaired patients, who had lost peripheral field but had subjectively satisfactory vision in the central field, contrast sensitivity differed considerably from one patient to another, 3: some of the moderately impaired patients, who still had useful peripheral vision, had nearly normal contrast sensitivity in the central vision while they already had large ring scotomas. The severity of reduction in contrast sensitivity was poorly correlated with visual acuity, the size of the visual field and the age of the patient. Because contrast sensitivity function cannot be predicted by means of other clinical measurements, it should be included in evaluation of visual impairment due to retinitis pigmentosa. We also measured contrast sensitivity at low luminance levels: this procedure provided useful information for evaluation of vision in retinitis pigmentosa. The contrast sensitivity function of each patient agreed with the subjective view of the patient about his visual impairment and it also corresponded with the examiners' evaluation of the patient's performance in different visual and visuomotor tasks.