Effect of blur adaptation on human parafoveal vision.
OBJECTIVE
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° 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°, 4°, 6°, 8°, and 10°) 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 E2, 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 E2 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.
Bradford School of Optometry and Vision Science, University of Bradford, Bradford, United Kingdom.
Aleksandra
A
Mankowska
Kiren
K
Aziz
Matthew P
MP
Cufflin
David
D
Whitaker
Edward A H
EA
Mallen
D000221:Adaptation, Ocular / Q000502:physiology*; D000328:Adult; D005260:Female; D005584:Fovea Centralis / Q000503:physiopathology*; D006801:Humans; D008297:Male; D011379:Prognosis; D012029:Refraction, Ocular; D012030:Refractive Errors / Q000503:physiopathology*; D014792:Visual Acuity; D014794:Visual Fields / Q000502:physiology*; D055815:Young Adult