Updated on 

December 14, 2021

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Visual Acuity Scores

What Does a Visual Acuity Score Mean?

Visual acuity, also known as clarity of vision or sharpness of vision, refers to a person's ability to see small details. A visual acuity score is the result of a vision test performed by an optometrist or ophthalmologist (opticians, technicians, and nurses can also perform a visual acuity measurement). It is usually expressed as a fraction that measures a patient's ability to see an object from 20 feet away compared to a person with normal vision who can see the object clearly from a longer distance.

For example, 20/20 vision means that you can see an object clearly from 20 feet away. 20/40 vision means that you need to be 20 feet away to see clearly what a person with normal vision can see from 40 feet away. Optometrists use your visual acuity to help determine your eyeglasses prescription.

Visual acuity is dependent on a combination of optical and neural elements, including:

  • The health and functionality of the retina
  • How sharply the retina forms images
  • How well your brain can interpret sensory inputs

Refractive errors or neural factors usually cause poor visual acuity. Refractive errors are visual impairments that affect the way light is bent, or refracted, in your eyeball, resulting in decreased visual acuity. Common refractive errors include:

  • Hyperopia (farsightedness)
  • Myopia (nearsightedness)
  • Astigmatism (irregular curvature of the cornea)

Neural factors that can decrease acuity occur in the retina, brain, or the pathway between the two. Examples include:

  • Age-related macular degeneration (AMD)
  • Detached retina
  • Amblyopia (lazy eye)
  • Brain injuries
  • Stroke

Most of the time, lower visual acuity can be corrected by eyeglasses, contact lenses, or refractive surgeries. 

What is a Visual Acuity Test?

Visual acuity is measured by charts, optical instruments, or computerized tests. Eye charts are the most common method of visual acuity testing. They show several rows of optotypes (letters, numbers, or symbols) that get progressively smaller towards the bottom. The most frequently used eye charts used are the Snellen Chart (left) and Tumbling E Chart (right).

Eye Charts for Visual Acuity

How is a Visual Acuity Test Performed?

An optometrist or ophthalmologist typically performs a visual acuity test. During the eye test, you'll be seated a certain distance from the visual acuity chart. Elements such as distance from the test chart and lighting conditions must be standardized.

The patient will cover their right or left eye and read the chart starting at the top and proceeding downwards until they can no longer distinguish the letters. They will then switch eyes and repeat the process from the same viewing distance. The doctor will use the line with the smallest visible letter size to give you your results.

How to Read the Results of a Visual Acuity Test

Visual acuity is typically measured in fractions or decimals. The first number in the fraction refers to the testing distance, and the second number refers to the distance someone with "normal" vision could see the same details from. Most vision testing in the United States uses the Snellen letter chart, which requires a test distance of 20 feet.

For example, 20/20 vision means that a person can see an object as well as anyone with "normal" vision from 20 feet. If you have 20/30 vision (a lower visual acuity score), it means the details you see from 20 feet away can be seen from 30 feet away by someone with "normal" visual abilities. Basically, the higher the second fraction number, the lower the visual function.

In most other countries, visual acuity is expressed using the metric system. Since 20 feet is equivalent to 6.096 meters, 20/20 vision is equal to 6/6 vision.

LogMAR Chart

The National Vision Research Institute of Australia developed the LogMAR chart (Logarithm of the Minimum Angle of Resolution) in 1976. The Bailey-Lovie chart and ETDRS chart (Early Treatment Diabetic Retinopathy Study) are two charts that use the LogMAR scale. Its design provides a more accurate visual acuity score than other charts. With a LogMAR chart, your visual acuity score is measured in reference to the minimum angle of resolution.

logmar chart

Visual Acuity Scales


Visual Acuity Score FAQs

What is the normal visual acuity?

20/20 is considered normal visual acuity. If you have 20/20 vision, it means that you can see objects clearly from 20 feet away. This is expressed as 6/6 in metric, 1.00 in decimal, and 0.0 in LogMAR measurement.

How is visual acuity measured?

An optometrist or ophthalmologist typically measures visual acuity. Although opticians, technicians, and nurses can also measure it. Your score will be in feet, meters, decimals, or the LogMAR scale.

What is 6/12 on the Snellen scale?

6/12 is a metric measurement on the Snellen scale. It is equivalent to 20/40 in feet, .50 in decimal, and .30 on the LogMAR scale.

What does a visual acuity score mean?

A visual acuity score is a measurement of a person’s ability to see small details with precision. It is also known as clarity of vision or sharpness of vision.

4 Cited Research Articles
  1. Kniestedt, Christoph, and Robert L Stamper. “Visual acuity and its measurement.” Ophthalmology clinics of North America vol. 16,2 : 155-70, v. doi:10.1016/s0896-154900013-0
  2. Bailey IL, Lovie JE. New design principles for visual acuity letter charts. American Journal of Optometry and Physiological Optics. 1976 Nov;53:740-745. DOI: 10.1097/00006324-197611000-00006.
  3. Raasch TW, Bailey IL, Bullimore MA. Repeatability of visual acuity measurement. Optometry and Vision Science : Official Publication of the American Academy of Optometry. 1998 May;75:342-348. DOI: 10.1097/00006324-199805000-00024.
  4. Rabbetts, R. B. . Validity and reliability of visual acuity measurements. Ophthalmic and Physiological Optics, 9, 458-458. doi:10.1111/j.1475-1313.1989.tb00957.
Melody Huang is an optometrist and freelance health writer. Through her writing, Dr. Huang enjoys educating patients on how to lead healthier and happier lives. She also has an interest in Eastern medicine practices and learning about integrative medicine. When she’s not working, Dr. Huang loves reviewing new skin care products, trying interesting food recipes, or hanging with her adopted cats.
Michael Bayba earned his B.A. in English and Linguistics from the University at Buffalo. Upon graduating, he began researching, writing, and editing full-time. His passion for promoting health and healing in communities around the world has led him to create evidence-based and research-backed content on vision and other health topics. His mission is to help individuals find quality and affordable treatment so they can live a healthy life.
Author: Michael Bayba  | UPDATED December 14, 2021
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Medical reviewer: Dr. Melody Huang, O.D.
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Dr. Melody Huang, O.D.
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