Visual Acuity Test

What is a visual acuity test?

A visual acuity test is a test that checks your vision. Your “visual acuity” is the medical term for how well you can see.

You’ve experienced a visual acuity test if you’ve ever looked at a wall chart of letters or symbols during an eye exam or in your healthcare provider’s office.

Visual acuity tests are usually the quickest way for a provider or eye care specialist to tell that your vision has changed. After a visual acuity test, an eye care specialist might prescribe eyeglasses or contact lenses. If you already wear glasses or contacts, they might adjust your prescription to match your current visual acuity.

Visit an eye care specialist as soon as you notice any changes in your vision. Even if you only need your prescription adjusted, worsening vision can be the first sign of lots of conditions that can affect your eyes.

When is a visual acuity test performed?

You’ll receive a visual acuity test as part of your routine eye exam. Your eye care specialist will perform a visual acuity test each time you visit them to track any changes in your vision.

A visual acuity test can help diagnose common conditions that affect your vision, including:

• Nearsightedness (myopia).
• Farsightedness.
• Astigmatism.
• Presbyopia.
• Color blindness.

When should I have my eyes examined?

Having your eyes and vision checked regularly can help an eye care specialist identify problems right away. How often you should get your eyes checked usually depends on your age:

• Kids: A pediatrician should check your child’s eyes at every well-child visit until they’re old enough to start school, and then every one to two years.
• Adults younger than 40: Every five to 10 years.
• Adults between 40 and 54: Every two to four years.
• Adults older than 55: Every one to three years.

You might need your eyes checked more often than this if you wear glasses or contacts or need another type of visual aid. People with diabetes also need their eyes checked more often than what’s listed here.

Ask an eye care specialist how often you need an eye exam.

Who performs a visual acuity test?

Usually, your eye care specialist will perform a visual acuity test. An optometrist or ophthalmologist can also perform the test.

Your regular healthcare provider might perform a visual acuity test, too, especially if you visit them after you notice any symptoms in or around your eyes.

What are the types of visual acuity tests?

The most common types of visual acuity tests include:

• The Snellen eye chart: The Snellen visual acuity test is probably what you’re picturing if you think of a vision test. It’s a wall chart with rows of letters printed on it. The letters are big at the top, and each row gets increasingly smaller the farther down on the chart you look. Your eye care specialist will ask you to read rows until you can’t make out the letters. Some eye care specialists use Snellen charts projected on a wall or displayed on a screen.
• The random E chart: The random E visual acuity test is similar to the Snellen eye chart. It’s a wall chart, but instead of rows of different letters, it only has E printed on it. As the E gets smaller, it’s also rotated, flipped and positioned differently. You’ll read down the chart until you can’t tell which way the E is facing.
• Dynamic visual acuity test: Your eye care specialist will hold your head and move it back and forth while you perform a visual acuity test. This can test how well your eyes stabilize during motion without affecting your vision (your vestibulo-ocular reflex).
• Pinhole visual acuity test: Pinhole visual acuity tests are specifically for diagnosing myopia (nearsightedness). Your eye care specialist will ask you to cover one of your eyes with a paddle similar to one you’d use during a typical visual acuity test. However, the paddle for a pinhole test has one (or a few) tiny holes in it. Instead of using the uncovered eye to read a Snellen or random E chart, you’ll use the covered eye by looking through the pinhole.
• Visual acuity tests for children: There are few versions of pediatric visual acuity tests for kids of different ages. You might see a visual acuity for kids referred to as a Cardiff visual acuity test. Some tests use symbols or pictures instead of rows of letters. Your eye care specialist might also give your child a “cheat sheet” with the letters on a Snellen eye chart and ask them to match the letters they see on the sheet to their location on the wall chart.

How does a visual acuity test work?

Most visual acuity tests follow these steps:

• You’ll stand or sit 20 feet away from the chart or screen.
• Your eye care specialist will ask you to cover one of your eyes (usually with your hand or a paddle).
• Your eye care specialist will ask you to slowly read the chart, starting at the top with the biggest row of letters or symbols.
• You’ll keep reading smaller rows until you can’t see the letters or symbols clearly.
• After you finish with one eye, you’ll switch eyes and do the test again.

As the chart gets harder to read, it’s OK to guess at the letters or symbols, but tell your eye care specialist when the chart starts to get fuzzy or hard to read. Don’t squint or strain your eye to see. The point of a visual acuity test is to get an accurate assessment of your vision, so don’t worry about “failing” or trying your best to “pass.”

Your eye care specialist might perform a visual acuity test a few times if you already have a prescription for eyeglasses or contact lenses. They’ll check your vision while you’re not wearing your corrective lenses (this is called testing your uncorrected vision) and with them (your corrected vision).

How do I prepare for a visual acuity test?

You don’t need to do anything before a visual acuity test. If you wear glasses or contacts, make sure to wear them or bring them to your eye exam. Your eye care specialist will probably have you remove them to check your uncorrected vision.

What happens after a visual acuity test?

After you finish a visual acuity test, your eye care specialist will finish your eye exam. You might need other tests like a slit lamp exam to check for conditions that can affect your eyes, including:

• Cataracts.
• Glaucoma.
• Macular degeneration.

What are the risks of a visual acuity test?

There are no risks to a visual acuity test. You might feel uncomfortable while you’re not wearing your glasses or contacts, but that’s only temporary, and you’ll be able to wear them again as soon as your eye care specialist is done examining your eyes.

What type of results will I get from a visual acuity test?

The results of your visual acuity test will be a fraction that represents your uncorrected vision.

You’re probably heard of the most famous expression of vision — 20/20 vision. If you have 20/20 vision, you can see an object that is 20 feet away clearly. People sometimes think 20/20 vision means perfect vision. But it actually just means average or typical vision.

Most people don’t have 20/20 vision without wearing glasses or contacts. In fact, only around 35% of adults in the U.S. have natural 20/20 vision.

Your eye care specialist will tell you what you need to correct your vision after your visual acuity test. The most common way to correct your vision is by wearing glasses or contact lenses. If you already have a prescription, your eye care specialist might adjust it to match any changes in your vision they detected during the test.

When should I call my doctor?

Talk to your eye care specialist as soon as you notice any changes in your vision.

Go to the emergency room if your vision suddenly gets worse or you lose sight in one or both eyes.