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Anna Beata Zolubak, Luis Garcia-Suarez; Eccentricity Effect in Shape Discrimination Hyperacuity Compensated by Scaling Factors Lower than the Cortical Magnification Factor. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4942. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
SDH (Shape Discrimination Hyperacuity) is tested with Radial Frequency Patterns (RFP) and is used to monitor visual changes in Age-related Macular Degeneration (AMD). Little is known about peripheral processing of RFP, albeit it was found that the decline in sensitivity as a function of retinal eccentricity in SDH is compensated by scaling RFP with Cortical Magnification Factor (CMF). This procedure causes less precise identification of tested areas as enlarged stimuli subtend broader retinal field. We examined peripheral processing of RFP and whether scaling factors (SF) smaller than CMF compensate for the eccentricity effect in SDH
Sensitivity to radial deformations was measured in healthy observers (N=4) with a 2IFC 1up/2down staircase procedure. Achromatic RFP (peak spatial frequency 1cpd, frequency 6cpd) were displayed at 0° and at 5°,10°, 15°, 20° eccentrically to the fixation point on a calibrated CRT monitor. We presented RFP with fixed radii (1.2°) and RFP scaled with CMF and three SF derived from CMF by a factor of 0.5(SF1), 0.25(SF2) and 0.125(SF3).
Thresholds for the unscaled stimuli increased with eccentricity and decreased with cortical magnification following the power function t=0.0257E-1.244. All SF compensated for the peripheral performance falloff. Thresholds for SF1(M=0.0037, SD=0.001) were higher than for SF2(M=0.003, SD=0.001), SF3(M=0.0027, SD=0.006) and CMF(M=0.003, SD=0.001). ANOVA tests performed at each eccentricity showed no significant differences between the SF at 5° (F(3,12)=0.91, p=0.466), 10°(F(3,12)=2.97, p=0.074), 15°(F(3,12)=2.6, p=0.1) and significant difference at 20° (F(3,12)=6.42, p=0.008), where performance was worse for SF1 than SF3 and CMF.
Peripheral performance of SDH is inversely proportional to the eccentricity and the increase in the peripheral thresholds matches cortical magnification in V1. Performance for the RFP scaled with SF lower than CMF remains independent from eccentricity, although at eccentricities further than 15 deg, performance for the smallest SF differs from that for the largest SF. Spatial frequency and contrast of RFP were constant at all eccentricities, thus central and peripheral SDH can be equalised solely by RFP size scaling. Tests that aim to compare patients’ central and peripheral SDH may benefit from using smaller SF and target retinal areas more precisely.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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