Variability in patients with glaucomatous visual field damage is reduced using size V stimuli

Abstract

Purpose: To test the hypothesis that variability of conventional automated perimetry can be reduced using size V stimuli for patients with glaucomatous visual field damage.

Methods: Ten patients with glaucoma and five age-matched control volunteers were tested with the Humphrey Field Analyzer program 24-2 or 30-2, after which the method of constant stimuli was used to measure frequency-of-seeing curves. This was done by controlling the perimeter with a custom program run by a personal computer. At two widely separated visual field locations on the program 24-2 or 30-2 grid, stimuli were presented in 2 dB intervals to at least 10 dB on either side of the estimated program 24-2 or 30-2 threshold. This protocol was performed for each of three stimulus sizes (Goldmann sizes I, III, and V). For the patients with glaucoma, one test location was chosen in an area of normal visual field sensitivity, the other in an area of 10 to 20 dB loss. Control subjects were tested at the (3 degrees, 3 degrees) and (-21 degrees, -9 degrees) test locations. Fifteen repetitions were performed at each intensity.

Results: Repeated measures analysis of variance showed that variability, as measured by the standard deviation of the cumulative Gaussian function of the fitted frequency-of-seeing curves, was lowest at the abnormal sensitivity test location in the subjects with glaucoma using a size V stimulus. Differences between the results from the V to III and V to I stimuli were statistically significant (size V = 2.9 dB, III = 10.1 dB, I = 10.1 dB). The same trend in estimated standard deviations was present in tests of the area of normal sensitivity (size V = 1.1 dB, III = 1.7 dB, I = 2.0 dB) in subjects with glaucoma and for the control subjects' peripheral test locations, but not for the central location. The smaller reduction in variability between estimated standard deviations of the size I and size III stimuli was not statistically significant at any test location.

Conclusions: Use of size V stimuli in conventional automated perimetry reduces variability in tests of moderately damaged and normal sensitivity test locations in subjects with glaucoma.