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S. Demirel, R. Robinson; Upper vs. Lower Field Asymmetry in SAP and SWAP Thresholds: Comparison to Psychophysical Estimates of Ganglion Cell Density . Invest. Ophthalmol. Vis. Sci. 2003;44(13):69.
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Purpose: To test the hypothesis that upper vs. lower visual field sensitivity asymmetry for Standard Automated Perimetry (SAP) and Short Wavelength Automated Perimetry (SWAP) is determined by the density of retinal ganglion cells participating in these tasks. Methods: Upper and lower visual field sensitivity was measured at 20 degrees in the upper and lower mid peripheral visual field for five observers using SAP and SWAP on the Humphrey Visual Field Analyzer. SAP and SWAP sensitivities were measured using the standard stimulus and background configurations for these tests (G III for SAP, and GV for SWAP) the 'full threshold' algorithm and the 24-2 stimulus pattern. An average threshold was calculated using the four threshold locations nearest to 20 degrees directly above and 20 degrees directly below fixation. Resolution acuity was measured at the same locations assessed with threshold perimetry using drifting sinusoidal gratings that were either achromatic or S-cone isolating (blue gratings superimposed on a bright yellow background). Conditions employed have been shown previously to likely produce acuity endpoints that are limited by the density of retinal ganglion cells in peripheral vision. Resolution acuity for the different chromatic conditions and in upper and lower field was used to estimate the density of retinal ganglion cells participating in these tasks. Results: There was a significant upper vs. lower visual field sensitivity asymmetry for both SAP and SWAP (ANOVA: SWAP p=0.01, SAP p<0.01) with the inferior field being more sensitive than the upper field. There was also a significant upper vs. lower field asymmetry for S-cone isolating resolution acuity but not for achromatic resolution acuity (ANOVA: S-cone p<0.01, Achromatic p=0.26). Similar to the SAP and SWAP thresholds, resolution acuity was better in the inferior field for both S-cone isolating and achromatic gratings. Conclusion: Sampling limited resolution acuity estimates of retinal ganglion cell density generated from achromatic and S-cone isolating acuity measures mirror the asymmetry seen in differential light sensitivity as measured with SAP and SWAP.
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