Blur adaptation may occur in visual cortex

The improvement in visual resolution that results after sustained periods of retinal defocus may be due to an adaptation occurring in the central visual cortex, a recent study suggests.

Sini George, BS, MS and Mark Rosenfield, MCOptom, PhD, FAAO, attempted to determine whether this perceptual adaptation, which has been noted in previous studies, occurs in all individuals or only in certain subgroups. They examined the effects of prolonged defocus in 13 subjects with emmetropia and 18 with myopia. Subjects wore +2.5 D spherical lenses over their distance refractive correction for a continuous 2-hour period.

In both refractive groups, a significant improvement in Landolt C and grating visual acuity through the fogging lenses was measured. The mean change in grating visual acuity was significantly greater for the subjects with myopia, but the improvements in Landolt C acuity observed in the two groups was statistically equivalent.

The study is published in the July issue of Optometry and Vision Science.