Visual Acuity Tests: Types, Procedures, Benefits and Limitations

Published on March 22nd, 2024

Updated on January 21st, 2025

A visual acuity test measures the sharpness and clarity of a person’s vision and is performed by an optometrist as part of a standard eye test. A visual acuity test uses a letter chart and the results of the test will be read as a fraction or ratio such as 20/20 (6/6 in feet) vision, which is considered normal vision. The types of visual acuity tests include a Snellen visual acuity test, a children’s visual acuity test, and a pinhole visual acuity test. Keep reading to learn more about the different types of visual acuity tests and their benefits.

What is a Visual Acuity Test?

A visual acuity test is a common eye test performed by an optometrist as part of a comprehensive eye test. A visual acuity test examines a person’s visual acuity which is the measure of the sharpness and clarity of vision. This test is performed using an eye chart, most commonly a Snellan chart. Visual acuity is tested one eye at a time to measure the visual acuity individually and then tested with both eyes uncovered.

What is the Importance of a Visual Acuity Test?

A visual acuity test is very important as it helps determine if a person needs vision correction. Vision correction is important as, according to the Centres for Disease Control and Prevention, it contributes to a person’s overall well-being and independence. Clear vision is essential in performing everyday activities. At Oscar Wylee, we recommend everyone has an eye test at least once every two years. An eye test will include a visual acuity test.

How is a Visual Acuity Test Conducted?

A visual acuity test is conducted by an optometrist in an eye test using a letter chart. The letter chart typically used in a visual acuity test is a Snellen chart which is set at a testing distance of 6 metres, or 20 feet, away. The test will begin with the patient sitting across from the Snellen chart and the optometrist will get them to cover one eye and read letters that get progressively smaller until they cannot read the letters clearly. This will be repeated with the other eye covered and then with both eyes. The further down the chart a patient can see, the better their visual acuity is. Whatever the lowest line is they can read is then expressed as a fraction or ratio and can be used to describe the patient’s visual acuity.

A woman having a visual acuity test using a Snellen chart.

What are the Types of Visual Acuity Tests?

While a visual acuity test is most commonly performed using a Snellen chart, there are other types of visual acuity tests. According to the Cleveland Clinic, the other types of visual acuity tests include a children’s visual acuity test and a pinhole visual acuity test. These tests and their definitions are listed below.

Snellen visual acuity test: A visual acuity test using a Snellen chart is the most common form of this test which uses rows of letters that decrease in size to measure the sharpness and clarity of the patient’s vision.
Children’s visual acuity test: A children’s visual acuity test is slightly different from the standard adult test. A children’s visual acuity test may vary due to the optometrist and the age of the child but will most likely be conducted with a chart of symbols or pictures instead of letters.
Pinhole visual acuity test: A pinhole visual acuity test is used to help differentiate between blurry vision caused by an uncorrected refractive error and blurry vision caused by an eye disease.

How to Measure Visual Acuity?

Visual acuity is measured in a visual acuity test and represented as a fraction or ratio such as 6/6 (metres) or 20/20 (feet). Visual acuity is the measure of the sharpness and clarity of a person’s eyesight. Visual acuity measures your central vision only, not your peripheral vision, and can be tested for both distance and near vision. A visual acuity test is performed by an optometrist in a comprehensive eye test using a letter chart.

How to Read the Results of a Visual Acuity Test?

The results of a visual acuity test will be read as a fraction or ratio such as 6/6 or 6/12. The first number refers to the distance at which a person was tested and is shown in metres. The second number represents the line that contains the smallest letter they could read. This is known as the Snellen fraction. The results will be read by the optometrist to help them determine the vision correction the patient needs in their glasses or contact lenses.

Is Visual Acuity Measured Using a Snellen Chart?

Yes, visual acuity can be measured by a Snellen chart. A Snellen chart is a vision chart that is commonly used by an optometrist in an eye exam to test visual acuity. A Snellen chart contains rows of letters that decrease in size as you descend. It is meant to be read at a distance of 6 metres. According to the American Academy of Ophthalmology, the Snellen chart was first invented in 1862 by Dutch ophthalmologist Herman Snellen.

What are the Benefits of a Visual Acuity Test?

There are many benefits of a visual acuity test, some of which include it being quick and easy, detecting vision changes and also identifying vision problems. These benefits and their definitions are listed below.

Quick and easy: A visual acuity test is a quick procedure that checks a person’s sharpness and clarity of vision, typically taking 5 minutes. It is non-invasive and easy for the patient to understand and undergo.
Detect vision changes: A visual acuity test is a quick and simple way for an optometrist to see if there are any changes in the patient's vision. This will determine if a new glasses prescription is needed to give the person clear vision.
Identify vision problems: A visual acuity test is used to detect vision problems that make it difficult for a person to see at certain distances. These problems include refractive errors such as astigmatism, hyperopia and myopia.

The benefits of a visual acuity test which are they are quick and easy, they detect changes in vision and identify vision problems.

What are the Limitations of a Visual Acuity Test?

There are not many limitations of a visual acuity test, however, it is only a single part of checking a person’s vision and eye health, producing a measure of the sharpness and clarity of a person’s vision. Other tests performed in an eye test alongside a visual acuity test include a slit lamp exam, tonometry test, retinal exam and visual field test.

How do You Prepare for a Visual Acuity Test?

There is nothing specific you need to do to prepare for a visual acuity test. If you already have vision correction such as glasses or contact lenses, bring these to the appointment so the optometrist can determine if you require a change in prescription.

What to Expect During a Visual Acuity Test Procedure?

A person can expect a simple, easy procedure when they undergo a visual acuity test in a standard eye test. A visual acuity test is a non-invasive procedure that will usually take 5 minutes. Your optometrist will encourage you to relax and blink regularly while you are reading the letters. There is no preparation needed for a visual acuity test and the expectation during an eye test is you should feel no discomfort.

Can a Visual Acuity Test Identify Eye Problems?

Yes, a visual acuity test can identify eye problems such as refractive errors. Refractive errors are a type of vision issue that causes blurry vision due to the shape of the eye keeping light from focusing correctly on the retina. The four types of refractive errors are presbyopia, astigmatism, hyperopia and myopia.

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