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Algis J Vingrys, Selwyn Marc Prea, Phillip A Bedggood, Yu Xiang George Kong; Scaled spots return fixed thresholds and reduced variability for better detection of peripheral visual field loss.. Invest. Ophthalmol. Vis. Sci. 2019;60(9):2466.
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The hill-of-vision arises from a fixed spot size and means that visual thresholds decrease whereas variability increases at peripheral locations. We test whether scaling spot size as a function of eccentricity stabilises thresholds as well as variability across the visual field.
We determine the spot size-scale needed to return fixed increment thresholds from published data. We apply this scale to a tablet perimeter and measure thresholds across the visual field to 30 deg in 10 young (24±2 yrs old) and 41 older (67±9 yrs old) controls. Variability was established by retest and data are expressed as mean ± sd. We consider the benefit of size-scaling for perimetry by obtaining Frequency-of-Seeing (FOS) curves in a sub-group of observers (n=6, young) from 1 to 30 deg using Goldman Size III targets and size-scaled spots. Thresholds were obtained on a 5 cd/sq.m background using 40 presentations at 9 luminance steps that span threshold (total 360 presentations per FOS: 10-12 mins). Response reliability was established by measuring false positive and negative rates. We parametrise performance in terms of equipment specific decibels with the mean and standard deviation of the best fitting cumulative normal returning threshold and variability.
As expected, observers gave a fixed threshold (Young, 29.9±0. 35 dB; Old, 29.1±0.86 dB) across the central visual field (0-30 degrees) using size-scaled spots. The older group gave a small age-related reduction in threshold (-0.8 dB). The FOS found similar thresholds at 1 and 27 deg in normal eyes using scaled spots but failed to return a constant FOS slope, being flatter at 27 deg (slope 0.46) than at 1 deg (slope 0.32). The size-scaled spot gave significantly lower variability at 27 deg than did a Goldman Size III target (slopes 0.46 vs 1.51, p<0.05). This reduced variability will yield better detection of early change at peripheral locations.
Perimetry pots can be scaled to return constant thresholds and reduced variability at peripheral locations compared with a Goldman Size III targets, affording better capacity to detect an early loss in sensitivity. We propose that size-scaling should be adopted in perimeters when testing increment thresholds in the central visual field.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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