Spatial contrast sensitivity in macular disorder

Spatial contrast sensitivity functions were evaluated in 30 patients with macular disorders and 16 age-matched control subjects. Eighteen of the affected eyes had macular holes and the rest had isolated macular problems. A loss in spatial contrast sensitivity in the central visual field indicated a relative scotoma resulting from macular dysfunctions. The nature and size of a localized scotoma such as the type caused by a macular lesion was estimated by measuring spatial contrast sensitivity as a function of retinal area centered on the fovea. Such spatial-contrast-threshold perimetry was found to be helpful in differential classification of macular holes. Spatial contrast sensitivity and visual resolution improved with increasing retinal area even in the eyes with macular holes, but never reached normal sensitivity for spatial frequencies above 5 cycles per degree (cpd) within our experimental conditions. The loss in sensitivity to low spatial frequencies (less than or equal to 5 cpd) was found to be apparent and a function of the retinal area stimulated. The summation curves (contrast sensitivity vs. stimulus size) were abnormal for all spatial frequencies. The 'critical' sizes (i.e. the stimulus size above which no increase in sensitivity occurred) were always larger in the affected eyes than those in the normal. Thus 'critical' areas of complete summation in the parafovea may be a better measure of functional integrity of central retina in the presence of a foveal lesion than the visual resolution that varies with the retinal area and location activated. Evaluation of contrast sensitivity of the parafoveal regions with nonfunctional fovea also indicated existence of similar mechanism of spatial vision in the fovea and the parafovea.