Visual Acuity Overview

Study Notes

Visual Acuity

Visual acuity is a measure of the spatial resolution of the visual processing system. It is the ability of the eye to see fine details and is typically tested by requiring a person to identify optotypes, such as stylized letters or symbols, on a printed chart from a set viewing distance. Optotypes are represented as black symbols against a white background (i.e., at maximum contrast). The distance between the person's eyes and the testing chart is set so as to approximate "optical infinity" in the way the eye perceives it or at a defined reading distance (near acuity).

Visual acuity is measured in fractions, with the top number signifying the distance between the person and the chart, such as 20 feet for a standard Snellen chart. A result of "20/20" (or 6/6 when using meters) indicates normal visual acuity, meaning the person can read the line that those with normal vision can read. Visual acuity decreases as the bottom number gets larger, such as 20/40, which means the person can see at 20 feet what those with normal vision can see from 40 feet away.

Visual acuity is determined by various factors, including the viewing distance, the smallest feature or detail of the stimuli, refractive error, illumination, contrast, and the location of the retina being stimulated. Refractive errors such as myopia (nearsightedness), hyperopia (farsightedness), and astigmatism can cause blurry vision and affect visual acuity. Additionally, conditions like macular degeneration and retinal detachment can affect the retina, while issues like amblyopia (caused by the visual brain not developing properly) can affect the brain.

Visual acuity is typically tested as a measure of central or foveal vision, as it is highest in the very center of the visual field. However, acuity in peripheral vision can be of equal importance in everyday life. Acuity declines towards the periphery first steeply and then more gradually, in an inverse-linear fashion, following approximately a hyperbola. At 2 degrees eccentricity, for example, acuity is half the foveal value.

Visual acuity is just one facet of eye health, and with regular eye exams, an ophthalmologist can monitor the entire range of a person's visual function, including visual field testing, near acuity, and other aspects of visual health.

Description

Explore the concept of visual acuity, which measures the eye's ability to see fine details. Learn about how visual acuity is tested, factors affecting it, and its importance in eye health. Discover how conditions like myopia, macular degeneration, and amblyopia can impact visual acuity.