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Visual Acuity: Meaning, Tests & Scores Explained

Visual acuity is the ability of your eyes to distinguish between objects that you see when standing at a specific distance. It is also called visual sharpness, or clarity of vision. 

visual acuity testing

Acuity is the first thing eye doctors assess when examining a patient because it gives a baseline of the person’s eyesight.

Someone with normal visual acuity is measured to have 20/20 vision.

Introduction

Visual acuity is a determination of how strong your eyesight is. Eyecare professionals measure acuity by conducting various tests that designation how sharp, or clear, someone can see from 20 feet away.

Acuity is the first thing eye doctors assess when examining a patient because it gives a baseline of the person’s eyesight.

What Is a Visual Acuity Test? 

A visual acuity test is an eye examination that measures your eyes’ ability to read or see small details. In simple terms, a visual acuity test determines how sharp and clear your vision is.

The Snellen chart is the most common eye chart for the test. You can also use the jaeger and tumbling charts to perform visual acuity testing.

Who Performs Visual Acuity Testing?

There are four types of visual acuities, and each has its own test. Some acuity tests need you to go to the hospital, but some don’t.

In most cases, an ophthalmologist (eye doctor) is the one who performs the test. Other health professionals can also conduct the visual acuity test, including:

  • Nurses
  • Pediatricians (baby doctors)
  • Opticians
  • Medical technicians

You can also take a test at home, but you should visit the eye clinic for a thorough examination. 

How Visual Acuity Is Measured

Doctors measure visual acuity with two types of tests:

  • Snellen test
  • Random E test

Snellen test

Doctors use a Snellen chart that has letters written in different sizes, separated by green and red lines. They follow a set procedure when giving the test. It is:

  1. If you have glasses, the doctor will tell you to wear them before the test begins.
  2. Stand 6 meters (20 feet) from the Snellen chart.
  3. Cover one eye and leave the other open.
  4. Read the letters on the chart continuously up to a point where you can’t anymore.
  5. The optometrist will record the line with the smallest letter that you read.
  6. Repeat the procedure with the other eye.

Random E acuity test

This test is meant for children or adults who cannot read alphabetical letters. It uses an eye chart called a tumbling E chart. Unlike the Snellen chart, the tumbling E chart has only one letter: E.

It is written in different sizes and faces different directions. 

The procedure of doing the test is the same as that of Snellen. The only difference is that you need to identify the letters’ direction until you cannot see it anymore.

Understanding Your Results 

After administrating the tests, the doctor will give you the results. These results are usually in the form of fractions. The upper number represents the distance you stood at when viewing the chart. 

The lower digit is the distance in which a person with normal vision would see the object you read well. The results can show that you either have 20/20 vision or not.

Why Does Visual Acuity Matter?

Visual acuity matters because one’s eyesight affects so many aspects of daily life and work life. Taking an acuity test matters for the following reasons:

  • Eye treatment: The optometrist must do the test when checking for any eye complaints. Doing so will help avoid prescribing the wrong treatment for your eye disorder.
  • Legal functions: to have a driver’s license, some states will need you to have at least a 20/40 vision. You will thus need a visual acuity test before you start driving.
  • Monitoring diseases: Visual acuity helps monitor the progression of eye diseases. It also helps show if the doctor’s treatment for the affected eye is working.

What Does 20/20 Vision Mean?

If you have 20/20 vision, it means your eyesight is normal. That is, you can see objects clearly and distinctly when standing 20 feet away. However, 20/20 vision is not considered perfect vision because the reference of “perfect vision” encompasses other parts of your vision. 

What Does It Mean if You Don’t Have 20/20 Vision?

Your visual acuity test may show that you do not have 20/20 vision. For example, it may indicate that your eyesight is 20/30. (That means that you see objects clearly at 20 feet. But a person with normal vision can see the same thing when they are 30 feet away.) 

Not having 20/20 vision means you may be a candidate for visual correction, be it eyeglasses, contact lenses or vision surgery, such as LASIK. It may mean that you need glasses so that your eyes don’t have to work too hard when you drive or to read.

How Often Do You Need to Get a Visual Acuity Test?

Eye experts recommend people have comprehensive visual acuity tests regularly. Depending on your age, the American Optometric Association recommends the following examination frequency:

Children: Kids younger than 2 years should have an eye exam after six months and before their first birthday. Children who are 3 to 5 years old should have an exam least once more during that age. Kids who are ages 6 to 17 should have their first exam before their first birthday and then once a year after at 6.

Adults: People ages 18 to 64 should get eye tests at least every two years. Adults older than 65 should get tested at least once a year.

FAQs

What is normal visual acuity? 

Normal visual acuity is measured at 20/20. If you have 20/20 vision, it means you can see an object clearly at 20 feet, which you should see clearly at that distance. 

How is visual acuity measured?

The Snellen chart is the standard tool ophthalmologists use to measure visual acuity. During the test, you stand 20 feet from the chart and read the symbols written on it.

What does a visual acuity score mean?

It is a ratio that correlates to your vision performance to that of an individual with normal vision.

References

  1. Types of visual acuity. (Feb 2015). University of Minnesota Medical School Duluth.

  2. Visual Acuity. (January 2022). American Academy of Ophthalmology.

  3. Home Vision Tests for Children and Adults. (Feb 2021). American Academy of Ophthalmology.

  4. Clinical Examination of a Patient with Uveitis. (2020). Whitcuff and Nussenblatt’s Uveitis.

  5. Chapter 2 – Red Eye, Eye Pain, and Vision Loss. (2018). Urgent Care Medicine Secrets.

  6. Visual Acuity Testing. (October 2015). The University of Iowa Ophthalmology.

  7. Snellen Chart. (May 2021). StatPearls.

  8. Snellen Eye Chart to test visual acuity. Monroe Community College.

  9. Standards for Visual Acuity. (June 2006). National Institute for Standards and Technology.

  10. Visual acuity test. (January 2022). MedlinePlus. 

  11. 20/20 vision. (October 2018). Cleveland Clinic.

  12. Comprehensive eye exams. American Optometric Association. 

  13. Visual Acuity Measurement. Science Direct.

Last Updated March 1, 2022

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