The psychometric function and reaction times of automated perimetry in normal and abnormal areas of the visual field in patients with glaucoma

Abstract

Purpose: To study the relationship of reaction time to the psychometric function in normal subjects, normal sensitivity test locations in patients with glaucoma, and test locations with 10 to 20 dB loss in patients with glaucoma.

Methods: The authors tested 10 patients with glaucoma and 10 age-matched normal volunteers with the Humphrey perimeter, first with program 24-2 and then with the method of constant stimuli to generate frequency of seeing curves. At two widely separated visual field locations on the program 24-2 grid, they presented stimuli in 2-dB intervals, 10 dB either side of the program 24-2 threshold, at 0 dB and 60 dB (15 repetitions per intensity). For the patients with glaucoma, they chose a visual field location with normal sensitivity and a location in an area of 10 to 20 dB loss.

Results: Analysis of variance with post hoc t-tests showed that reaction time (RT) at the 0-dB intensity was prolonged by approximately 90 msec in the abnormal sensitivity test location of patients with glaucoma compared to the control and the glaucoma normal sensitivity groups (P<0.0001). However, this difference was accounted for by only 4 of the 10 patients with glaucoma, reaching 100% of stimuli seen with the brightest stimulus at the moderately damaged test location. Reaction time at the frequency of seeing 50% estimated threshold showed no significant differences among the groups. Prolongation of RT from the 0-dB value was analyzed as a function of increasing attenuation of stimulus intensity. The results fit the equation RT = a + b(Intensity3) for all groups.

Conclusions: There is no significant difference in RT between normal subjects and patients with glaucoma either at threshold or to suprathreshold stimuli. Reaction time increases after a power function with increasing attenuation of stimulus intensity up to the threshold.