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Lenna E. Walker, Guido Maiello, Peter Bex, Fuensanta Vera-Diaz, Nancy J Coletta; Ability to perceive blur in central and near-peripheral retina in myopia. Invest. Ophthalmol. Vis. Sci. 2016;57(12):197.
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© ARVO (1962-2015); The Authors (2016-present)
Human and animal studies suggest that an ability to accurately detect and respond to blur is essential to emmetropization. Previous research has either evaluated sensitivity to blur indirectly, or has only examined sharp vs. blurred images (although real environments contain multiple blur levels). We evaluate sensitivity to blur differences across the visual field.
25 young (22-32yrs) healthy adults participated (n=18 myopes). Subjects had best corrected VA 0.0 LogMAR (20/20) or better in each eye and no binocular or accommodative dysfunction. Refractive error (Mean -3.87±4.15D) was determined by binocular subjective refraction.Blur discrimination thresholds were measured monocularly (dominant eye) and binocularly as a function of pedestal blur in an adaptive 4AFC task. Dead leaves stimuli were presented in a 50° diameter window @ 40cm. Gaussian blur pedestals (0.125, 0.5, 2, 8, or 32 arcmin) were confined to an annulus at 0°, 4°, 8° and 12° eccentricity, with a blur increment applied to one quadrant of the image. Blur discrimination thresholds were fit with a two-parameter (intrinsic blur and blur sensitivity) dipper function. MANOVA and Spearman correlations were used to evaluate the effects of refractive error, retinal eccentricity, and monocular vs. binocular conditions on intrinsic blur and blur sensitivity.
The level of intrinsic blur increased with retinal eccentricity (p<0.01) and was lower in binocular than monocular conditions (p<0.01). There was a significant correlation between the level of myopia and intrinsic blur at the fovea (ρ -0.52, p=0.03), but not at 4°, 8° or 12° eccentricity.Blur sensitivity decreased with retinal eccentricity (p<0.01). Blur sensitivity improved in binocular vs. monocular conditions at the fovea (p=0.04), not in the periphery. Blur sensitivity decreased with higher myopic refractive error in the peripheral retina, reaching significance at 12° eccentricity (ρ 0.60, p=0.02).
Sensitivity to blur decreases in the near periphery. Myopes experience a difficulty discriminating blur that is related to elevated levels of intrinsic blur at the fovea and a change in blur sensitivity in the periphery. Our data suggest that this difficulty is ameliorated in binocular viewing, but is still present in myopia. This is consistent with the hypothesis that excessive axial elongation is associated with spatial summation of retinal defocus that is eccentricity dependent.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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