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Mitchell W. Dul, William H. Swanson, Tiffany Liu, Irene Tran; Developing CSP Stimuli For Resistance To Optical Defocus. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4809.
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© ARVO (1962-2015); The Authors (2016-present)
To model effects of blur on stimuli for use in Contrast Sensitivity Perimetry (CSP), and develop perimetric stimuli which are resistant to the effects of optical defocus yet small enough for testing near fixation.
Effects of blur at spatial frequencies of 0.1 to 2.0 cycles/degree (cpd) were calculated with geometrical optics, for pupil diameters from 2 - 8 mm. For each blur condition, effective contrast was computed by multiplying spatial frequency spectra of stimulus and blur conditions and computing the mean of absolute values. Predictions were tested on subjects free of eye disease who were refracted for testing distance and then had positive blur added. Stimuli were two-dimensional Gaussian windows multiplied by sinusoidal gratings. Stimulus size was determined by the standard deviation of the Gaussian window, and peak spatial frequency was determined by the spatial frequency grating. Expt 1 tested 10 people, using blur levels from 0 D to 3 D in steps of 1 D, for two stimuli (SD = 0.5°, spatial frequencies of 0.5 and 1.0 cpd) presented at sixteen locations along the diagonal meridians with eccentricities of 1.6°, 4.2°, 7.1°. Experiment 2 tested 12 people, using blur levels from 0 to 6 D in steps of 3 D, for three stimuli (0 cpd with SDs of 0.5° and 0.25°, and 0.5 cpd with SD 0.5°) presented at eight locations along the diagonal meridians with eccentricities of 4.2°, 7.1°. Experiment 3 tested 13 people, using four blur levels from 0 D to 6 D in steps of 1.5 D, for 56 stimuli at 56 locations throughout the central visual field; SD ranged from 0.5° to 1.8° and spatial frequency from 0.14 to 0.50 cpd.
Expt 1: 3 D of blur caused a greater decline (t = 7.7, p <0.0001) in log contrast sensitivity for the 1 cpd stimulus (-0.37 ± 0.13 log unit) than the 0.5 cpd stimulus (-0.09 ± 0.08 log unit). Expt 2: 3 D of blur caused less than an 0.1 log unit decline in contrast sensitivity for any of the stimuli; 6 D of blur caused similar declines for SD = 0.25°/SF=0.09 cpd (-0.33 ± 0.16 log unit) and for SD=0.5°/SF = 0.5 cpd (-0.36 ± 0.17 log unit), and less of a decline ( t >4.5 , p < 0.001) for SD = 0.5°/SD = 0.0 cpd (-0.17 ± 0.16 log unit). Expt III: 3 D of blur caused minimal losses in sensitivity: -0.06 ± 0.16 log unit for the smallest stimuli and -0.04 ± 0.10 log unit for the largest stimuli; 6 D of blur produced a decline in contrast sensitivity by -0.23 ± 0.16 log unit for the smallest stimuli and -0.08 ± 0.08 log unit for the largest stimuli.
Effects of blur were similar for model and data, and our optimized CSP stimuli should be sufficiently resistant to blur that perimetric sensitivities will be minimally affected by peripheral refractive error.
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