What is visual acuity, how is it tested and more – Tips & Results

Visual acuity is a term used to describe the clarity or sharpness of your vision when measured at a distance of 20 feet.

Visual acuity is the most common clinical measure of how your eyes are functioning. It’s usually one of the first tests done during a comprehensive eye exam to determine how sharp your vision is.

If someone has 20/20 vision, it means they can see the same amount of detail as the average person from 20 feet away. If someone has 20/40 visual acuity, they can see the same amount of detail from 20 feet away that the average person would see from 40 feet away.

Why is visual acuity important?

Measuring your visual acuity is one of the first things you will likely do during a comprehensive eye exam at an optometrist.

This visual acuity test is a crucial part of detecting signs of vision problems. For example, it can detect ametropia, better known as farsightedness and nearsightedness. Hyperopia (farsightedness) occurs when you see clearly at a distance while your near vision is less clear. Myopia (short-sightedness) is the opposite – your near vision can be clear while your far vision is blurry.

20/20 eyesight doesn’t necessarily mean you have perfect vision. Visual acuity only measures the sharpness or clarity of your vision at a distance. Strength of your vision also includes eye coordination, depth perception, peripheral awareness, ability to focus, and color vision.

How is visual acuity tested?

A visual acuity test examines how well you can describe the details of a letter, picture or symbol from a certain distance.

Children often take visual acuity tests to track their developing vision. Identifying these issues early can prevent problems from getting worse.

As an adult, you may need an examination if you have problems with your vision or if you feel that the clarity of your vision has changed. It can also be part of any visual exams you may take to get your driver’s license.

There are two types of visual acuity tests.

Snellen‌

The Snellen test uses a chart that contains letters or symbols. These letters are arranged in rows – each row gets smaller and smaller in the chart.

To measure visual acuity, you will be asked to stand approximately 20 feet from this chart. If you cover one of your eyes, the optometrist or doctor will ask you to identify the letters in each row and read them aloud. Usually, they will ask you to go down each row, reading smaller and smaller letters – until you can no longer identify them. Then repeat the process with the other eye.

‌Random E

The randomized E test is commonly used with children or adults who have trouble recognizing letters. Instead of reading out different letters, the random E test uses only one capital letter E.

As you move down the chart, the capital E points in different directions and decreases in size. You will be asked to identify the direction the E is pointing (up, down, left, or right) until you can no longer see it clearly.

The random E test is calculated in the same way as the Snellen test – the line on which most Es can be correctly identified.

Understanding your test results

When you have completed a visual acuity test, you will get results as a fraction. The top number refers to the distance you are standing from the map. In most cases, this is 20 feet. The bottom number refers to the distance at which an average person with normal vision could read the same line you are reading.

Even if you omit a few letters from the smallest line you could read, that line will still be included in your results.

For example, 20/20 is considered normal. 20/40 indicates that the line you read correctly can be read by a person with normal vision from 40 feet away.

Someone with a visual acuity score of 20/200 is considered legally blind. Although it is possible to have even more advanced vision than 20/20 (without corrective lenses, such as binoculars), the limit is believed to be around 20/10.

If you don’t have 20/20 vision

It’s perfectly normal not to have 20/20 vision. Only about 35% of adults have 20/20 vision without using corrective lenses or surgery.

If your visual acuity isn’t 20/20, you may need contact lenses, glasses, or surgery. There may also be an underlying eye condition that needs treatment. Your doctor or optician can talk to you about any treatments or corrections you may need.

Many people can achieve 20/20 vision with the use of corrective lenses. However, you don’t have to have 20/20 vision to live a normal life. In most states, you need at least 20/60 or better to get a driver’s license.

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