A comparison of Goldmann III, V and spatially equated test stimuli in visual field testing: the importance of complete and partial spatial summation

Abstract

PurposeGoldmann size V (GV) test stimuli are less variable with a greater dynamic range and have been proposed for measuring contrast sensitivity instead of size III (GIII). Since GIII and GV operate within partial summation, we hypothesise that actual GV (aGV) thresholds could predict GIII (pGIII) thresholds, facilitating comparisons between actual GIII (aGIII) thresholds with pGIII thresholds derived from smaller GV variances. We test the suitability of GV for detecting visual field (VF) loss in patients with early glaucoma, and examine eccentricity‐dependent effects of number and depth of defects. We also hypothesise that stimuli operating within complete spatial summation (‘spatially equated stimuli’) would detect more and deeper defects.MethodsSixty normal subjects and 20 glaucoma patients underwent VF testing on the Humphrey Field Analyzer using GI‐V sized stimuli on the 30‐2 test grid in full threshold mode. Point‐wise partial summation slope values were generated from GI‐V thresholds, and we subsequently derived pGIII thresholds using aGV. Difference plots between actual GIII (aGIII) and pGIII thresholds were used to compare the amount of discordance. In glaucoma patients, the number of ‘events’ (points below the 95% lower limit of normal), defect depth and global indices were compared between stimuli.Results90.5% of pGIII and aGIII points were within ±3 dB of each other in normal subjects. In the glaucoma cohort, there was less concordance (63.2% within ±3 dB), decreasing with increasing eccentricity. GIII found more defects compared to GV‐derived thresholds, but only at outermost test locations. Greater defect depth was found using aGIII compared to aGV and pGIII, which increased with eccentricity. Global indices revealed more severe loss when using GIII compared to GV. Spatially equated stimuli detected the greatest number of ‘events’ and largest defect depth.ConclusionsWhilst GV may be used to reliably predict GIII values in normal subjects, there was less concordance in glaucoma patients. Similarities in ‘event’ detection and defect depth in the central VF were consistent with the fact that GIII and GV operate within partial summation in this region. Eccentricity‐dependent effects in ‘events’ and defect depth were congruent with changes in spatial summation across the VF and the increase in critical area with disease. The spatially equated test stimuli showed the greatest number of defective locations and larger sensitivity loss.

Consistency of Structure-Function Correlation Between Spatially Scaled Visual Field Stimuli and In Vivo OCT Ganglion Cell Counts

“…21,[44][45][46] The age difference between individual subjects and the cohorts may therefore increase the variability within the dataset and confound the comparison of structure-function relationship between the normal and glaucomatous cohort. Hence, to minimize the variability imposed by intra-and intercohort age differences, the GCL thickness and DLS of all normal and glaucomatous subjects were age-corrected to the average age of the glaucomatous cohort using previously established regression analysis models as conducted in previous studies, 11,21,[24][25][26]31,32,45,47 including the commonly used SITAstandard algorithm of the HFA. 48 Specifically, for the GCL thickness, measurements from each normal and glaucomatous subjects were clustered into eight statistically separable classes and adjusted to match the average age of the glaucomatous cohort using a previously published conversion for all but the foveal area.…”

“…21 The difference imposed by age between these cohorts is within the test-retest variability range of the instruments, [44][45][46][47][48][49][50][51][52][53][54][55][56] and even before correction, there were notable overlaps between the prediction interval for the regression curves of the two cohorts (data not shown). Regardless, DLS and GCc for the normal and glaucomatous cohort were adjusted to a common age equivalent using a wellestablished age-correction method, frequently used in prior studies by different investigators 11,21,[24][25][26]31,32,45,47 and regularly utilized by clinical test algorithms for the Humphrey Field Analyzer; SITA. 48 A subanalysis was conducted to further confirm the validity of the age-correction technique, and good fidelity was demonstrated between the glaucomatous subgroup, and the normal age-corrected and age-matched cohorts ( Supplementary Fig.…”

“…15,[28][29][30][31][32] Within the central 308 of the field of vision, at which threshold visual field tests are most commonly conducted, the GIII target often exceeds spatial summation area, particularly for the central test locations. 24,25 Given the importance of test size in relation to the Ac to the fidelity of visual sensitivity, 15,[28][29][30]32 we hypothesize that the GC structure-function relationship will improve and approach 1:1 positive correlation by altering the test size within complete spatial summation. Similarly, as the summation characteristic is known to change with the disease process, 28 comparisons of the structure-function relationship between normal and glaucomatous cohorts need to be conducted.…”

Comparison of defect depths for sinusoidal and circular perimetric stimuli in patients with glaucoma

“…This study was conducted in the context of renewed research interest in revising perimetric stimuli. For circular stimuli as used in conventional perimetry, defects tend to be deeper with smaller stimuli . However, two studies (one from our lab) found that large flickered sinusoids can yield similar defect depths as the much smaller size III stimulus, with increased spread of the data in deeper defects .…”

The value of visual field testing in the era of advanced imaging: clinical and psychophysical perspectives

“…More recent studies have shown that equating for spatiotemporal summation characteristics can allow detection of functional losses in earlier stages of glaucoma . Simple modifications of test stimuli at different visual field test locations can specifically maximise defect detection, while maintaining the widest dynamic range of testing . Defects found with such stimuli have been shown to be commensurate with underlying, detectable structural loss, thereby potentially improving the structure‐function relationship (Figures and and see Figure A in Kalloniatis and Khuu) .…”