Purpose: To compare the relationship between sensitivity and response variability 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 field locations in one eye of 71 subjects (12 ON, 25 POAG, 11 OHT, and 23 normal), using a constant stimulus method on an Henson 4000 perimeter (Tinsley Instruments, Croydon, UK). At each location, at least 20 stimuli (subtending 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 cumulative Normal function were used to estimate sensitivity and response variability. Cluster regression analysis was carried out to determine whether there were differences in the sensitivity-log (variability) relationship between the four groups.
Results: Variability was found to increase with decreased sensitivity for all four groups. The combined data from the four groups was well represented (R2 = 0.57) by the function log(e)(SD) = A.sensitivity (dB) + B, where the constants A and B were -0.081 (SE, +/-0.005) and 3.27 (SE, +/-0.15), respectively. Including other statistically significant covariates (false-negative errors, P = 0.004) and factors (diagnosis, P = 0.005) into the model increased the proportion of explained variance to 62% (R2 = 0.62). Stimulus eccentricity (P = 0.34), patient age (P = 0.33), fixation loss rate (P = 0.10), and false-positive rate (P = 0.66) did not reach statistical significance 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 supporting evidence for the hypothesis that response variability is dependent on functional ganglion cell density.