Effect Of Blur Adaptation On Human Parafoveal Vision

PURPOSE. This study was conducted to investigate whether neural compensation for induced defocus can alter visual resolution in other areas of the human retina beyond the fovea. In certain circumstances, the blur adaptation response may be influenced by refractive status.METHODS. The effect of blur adaptation on the central 10 degrees of the retina was investigated in 20 normally sighted observers (10 emmetropes and 10 myopes; median age, 21 years). Visual acuity (VA) was measured at the fovea and at five locations of the parafoveal nasal visual field (2 degrees, 4 degrees, 6 degrees, 8 degrees, and 10 degrees) with best corrected distance vision. Myopic defocus of 1 D was introduced, and the same measurements were repeated immediately before and after a 30-minute adaptation.RESULTS. VA declined with increasing eccentricity in the clear, blurred, and blur-adapted viewing conditions. The rate of decline was quantified by the parameter E-2, which represents the amount of eccentricity dependence of the acuity task. Foveal and parafoveal VA decreased with the introduction of optical defocus and improved significantly after a period of blur adaptation. The consistent value of E-2 in each condition indicated that these changes in VA were not eccentricity dependent. Changes in VA under blurred and blur-adapted conditions were of similar magnitudes in myopic and emmetropic observers.CONCLUSIONS. Neural adaptation to blur improves VA under defocused conditions in the parafovea as well as the fovea, indicating that the underlying compensatory mechanism acts across a range of spatial scales and independently of retinal eccentricity. Foveal and parafoveal blur adaptation does not vary with refractive error. (Invest Ophthalmol Vis Sci. 2012;53: 1145-1150) DOI:10.1167/iovs.11-8477