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Padraig Mulholland, Tony Redmond, Margarita Zlatkova, David Garway-Heath, Roger Anderson; Temporal summation varies with visual field eccentricity for perimetric stimuli scaled to the area of complete spatial summation. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3924.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies have found the limit of complete temporal summation (critical duration) to remain constant across the visual field, but these studies did not account/control for changes in spatial summation with increasing visual field eccentricity. We wished to investigate temporal summation as a function of visual field eccentricity with a standard perimetric stimulus and a stimulus scaled to the area of complete spatial summation (Ricco’s area).
Achromatic temporal and spatial summation functions were generated for five healthy subjects (median age 29 years, range 24-47), at 5°, 10° and 15° eccentricity in four diagonal visual field meridians. A Goldmann III stimulus (0.43° diameter) was used for temporal summation experiments and a 200msec stimulus was used for spatial summation experiments. Temporal summation experiments were repeated with a stimulus equal in size to Ricco’s area at each test location. Ricco’s area and the critical duration were estimated from the respective functions using an iterative two-phase regression technique. All stimuli were presented on a gamma-corrected achromatic CRT monitor running at 121 Hz with an adapting field of luminance 10 cdm-2.
Ricco’s area was larger at greater visual field eccentricities (0.34 log units, x2(2) = 19.9, p<0.005). There were negligible differences in critical duration measurements across the range of eccentricities investigated with a Goldmann III stimulus (0.067 log units, x2(2) = 3.32, p = 0.19). Median (IQR) critical duration values at 5°, 10° and 15° eccentricity with the scaled stimulus were 35.4 msec (26.2, 44.3), 45.2 msec (34.6, 67.6) and 64 msec (42.8, 90) respectively. This increase was statistically significant (0.26 log units, x2(2) = 9.03, p = 0.011). Post-hoc Wilcoxon signed-rank analysis with Bonferroni correction reported a significant increase in critical duration estimates between 5° and 15° when examined using the scaled stimulus (z = -2.80, p = 0.005).
The critical duration increases with visual field eccentricity when the stimulus is scaled to the localized Ricco’s area. This may have implications for perimetric thresholds in regions where a Goldmann III stimulus equals or is smaller than Ricco’s area.
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