Visual Acuity

Harrison F. Daiber, David M. Gnugnoli, Harrison F. Daiber, David M. Gnugnoli

Excerpt

A visual acuity test is only one part of a comprehensive ophthalmologic examination. The goal of the visual acuity test is to determine clarity or sharpness of vision. Visual acuity testing examines a patient's ability to distinguish different optotypes (recognizable letters or symbols) at a standard distance. This process requires many functioning pathways, including light reaching the retina with appropriate refraction, the retina's health, and the downstream capacity to transfer and interpret the visual stimuli.

In the 1800s, there was a move to standardize visual testing, which led to the formation of several visual acuity charts with different optotypes. The first and still most widely used today is the Snellen chart. Other testing charts developed around that time include the Tumbling E chart, Landolt C chart, and Allen chart. More recently, the LogMAR chart (also known as ETDRS chart) has gained favor. The LogMAR chart provides more accurate results when compared to other visual acuity charts, and the results are more easily used in vision analysis, making it the preferred chart in clinical studies.

The results of visual acuity are classically reported using 20/20 (6/6 when using meters) for standard vision. The numerator describes the distance from the chart, typically 20 ft (6 m). The denominator describes the distance that an individual with normal vision (20/20 vision) can read the same line on the chart. For example, an individual with 20/60 vision would be able to distinguish the same optotype at 20 ft that another individual with normal (20/20) vision distinguishes at 60 ft. In the logMAR, visual acuity is reported as a single number where 0.0 is standard vision. Visual acuity decreases as the number increases and improves as the number decreases. Although 20/20 visual acuity has been referred to as "perfect vision," it is important to remember that this is only one aspect of vision and does not include other elements such as depth perception, peripheral vision, and colorblindness.

There are many reasons that an individual could have an altered visual acuity. One of the most common causes of altered vision is a refractive error, such as myopia (nearsightedness) and hyperopia (farsightedness). Additional causes of visual impairment include astigmatism, amblyopia, retinal detachment, macular degeneration, ischemia, cataracts, glaucoma, corneal abrasion, or other traumatic injuries. Visual acuity testing is essential as many of these factors can be benefited from early intervention. It is crucial to determine an individual's best-corrected visual acuity. The WHO describes individuals with low vision as having a best-corrected vision of 20/60 or worse, and blind as best corrected vision worse than 20/400, whereas legal blindness is identified as 20/200 in the United States. These formal definitions can have ramifications when it comes to accommodations and abilities to operate a motor vehicle.

Conflict of interest statement

Disclosure: Harrison Daiber declares no relevant financial relationships with ineligible companies.

Disclosure: David Gnugnoli declares no relevant financial relationships with ineligible companies.

Copyright © 2025, StatPearls Publishing LLC.

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Source: PubMed

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