Visual acuity.

Visual acuity is the simplest and most utilized assessment of visual function. Reductions in acuity may result from many causes, including diseases of the macula and associated visual pathways and optical blur. Chart design and the psychophysical procedures employed to determine visual acuity impact measurement reliability and validity. Modern eye charts based on Bailey-Lovie design principles, used in conjunction with standardized psychophysical protocols, may minimize test-retest variability. Visual acuity improves rapidly during the first year of life, maturing more slowly until adult levels are reached at about 4-6 years of age or later. Thereafter, resolution acuity in healthy visual systems typically remains stable until the eighth decade of life, when reductions are most apparent for low-contrast stimuli. Standard measures of visual acuity do not assess the ability to resolve low-contrast stimuli. This is particularly important for elderly patients, who often suffer from conditions that reduce contrast sensitivity across the spatial frequency domain, potentially interfering with ambulation. Other forms of visual acuity, including minimal visible and the hyperacuities, may provide additional information regarding visual processing. Quantification of hyperacuity thresholds has demonstrated promise for the assessment of macular function.