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

Purpose. To test the hypothesis, variability of conventional automated perimetry is reduced using size V stimuli in patients with glaucomatous visual field damage. Methods. We tested 10 glaucoma patients and 5 age-matched normal volunteers first with Humphrey program 24-2 and then measured frequency of seeing curves using the method of constant stimuli. This was done by controlling a Humphrey perimeter with a custom program run by a personal computer. At two widely separated visual field locations on the program 24-2 grid, stimuli were presented in 2 dB intervals, 10 dB either side of the estimated program 24-2 threshold and at 0 dB and 60 dB. This protocol was performed for each of three stimulus sizes (I, III, and V). For the glaucoma patients, one test location was chosen in an area of normal visual field sensitivity (by STATPAC analysis), the other in an area of 10 - 20 dB loss. Fifteen repetitions were performed at each intensity. Results. ANOVA with post-hoc t-tests showed variability as measured by the slope of the frequency of seeing curve was lowest at the abnormal sensitivity test location in the glaucoma subjects using a size V stimulus (size V=2.4, III=7.7, I=8.7), p = 0.005 for the V to III comparison. The same trend in slopes was present in the glaucoma subject's area of normal sensitivity (size V=1.0, III=1.9, I=2.3) and for the normal subject's test locations. The smaller reduction in variability between slopes of the size I and size III stimuli was not statistically significant at any test location. Conclusion. Size V stimuli of conventional automated perimetry reduce variability in moderately damaged test locations in glaucoma subjects.