Response variability in the visual field: Comparison of optic neuritis, glaucoma, ocular hypertension, and normal eyes

PURPOSE. To compare the relationship between rn sensitivity and response va riability in the visual field of normal eyes and eyes with optic neuritis ( ON), glaucoma (POAG), and ocular hypertension (OHT). METHODS. Frequency-of-seeing (FOS) data were collected from four visual fie ld locations in one eye of 71 subjects (12 ON, 25 POAG, 11 OHT, and 23 norm al), using a constant stimulus method on an Henson 4000 perimeter (Tinsley Instruments, Croydon, UK). At each location, at least 20 stimuli (subtendin g 0.5 degrees) were presented for 200 ms at six or more intensities above: and below the estimated threshold. The mean and SD of the probit fitted cum ulative Normal function were used to estimate sensitivity and response vari ability. Cluster regression analysis was carried out to determine whether t l;ere were differences in the sensitivity-log (variability) relationship be tween the four groups. RESULTS. Variability was found to increase with decreased sensitivity for a ll four groups. The combined data from the four groups was well represented (R-2 = 0.57) by the function log,(SD)= A sensitivity (dB) + B, where the c onstants A and B were -0.081 (SE, +/- 0.005) and 3.27 (SE, +/- 0.15), respe ctively. Including other statistically significant covariates (false-negati ve errors, P = 0.004) and factors (diagnosis, P = 0.005) into the model inc reased the proportion of explained variance to 62% (R-2 = 0.62). Stimulus e ccentricity (P = 0.34), patient age (P = 0.33), fixation loss rate (P = 0.1 0), and false-positive rate (P = 0.66) did not reach statistical significan ce as additional predictors of response variability. CONCLUSIONS. The relationship between response variability and sensitivity is similar for ON, POAG, OHT, and normal eyes. These results provide suppor ting evidence for the hypothesis that response variability is dependent on functional ganglion cell density.