Purpose
Humphrey Field Analyzer (HFA) program 60-4 with stimulus size III has been used for monitoring peripheral visual field defects due to certain drug toxicities. Large threshold intersubject variability has been reported for PVF testing using this program. We tested the hypothesis that the smaller intersubject variability and higher threshold values may be achieved with stimulus size V for this program.
Methods
Peripheral visual field testing using HFA 60-4 program with stimulus III (n=33) and stimulus V (n=33) was performed in healthy volunteers (based on a normal visual acuity, slit lamp and fundus exam on comprehensive ophthalmic evaluation). Only reliable PVF tests were included (fixation loss, false positive and negative <30%). Each of the 60 measured threshold visual sensitivity (TVS) (decibels) locations was labeled with a NTSI (nasal/temporal/superior/inferior) coordinate system. Points were organized into inner, middle, and outer eccentricity rings and zones. Number of location points with low, middle, and high variability of the threshold sensitivities were calculated for both stimulus sizes. We defined variability as low for those test locations where the value of SD does not exceed 15% of its mean TVS value, middle if SD is in the range: >15% ≤ 40% of the mean, and high if SD is more than 40% of the mean value. Student’s t-test was used to compare individual and mean threshold visual sensitivity with stimulus size III and V. Chi-square test was used to compare proportions.
Results
Threshold visual sensitivities for individual location points as well as mean threshold sensitivities for inferior, superior, nasal, and temporal zones were higher with stimulus size V (p<0.01). The number of location points with high and middle variability of TVS was greater using stimulus size III vs. stimulus size V (p= 0.0296). More test locations with stimulus size V had low variability (Figure).
Conclusions
Since TVS is higher with stimulus V and variability is lower we believe PVF testing with stimulus V is a more efficient strategy when looking for peripheral change over time.