Visual Acuity Test (Snellen Eye Test Chart)

A visual acuity test checks your vision. Visual acuity is the medical term for your eyesight and how well you can see. You’ve had a visual acuity test if you’ve ever looked at a wall chart of letters or symbols during an eye exam.

An eye doctor will check your ability to see and recognize shapes and details. It’s the quickest way to see if your vision has changed over time. It can be the first step to diagnosing the four most common types of refractive errors, including:

• Astigmatism
• Farsightedness
• Nearsightedness
• Presbyopia

Your eye care specialist may also use a visual acuity test to help diagnose color blindness.

Types of visual acuity tests

The Snellen eye test chart 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 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.

Other types of visual acuity tests include:

• 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 tests how well your eyes stabilize during motion without affecting your vision (your vestibulo-ocular reflex).
• Pinhole visual acuity test: Pinhole visual acuity tests diagnose nearsightedness. Your eye care specialist will ask you to look through a paddle that has one (or a few) tiny holes in it. Then, they’ll have you read an eye chart.
• Random E chart: This 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.
• Visual acuity tests for children: These are sometimes called Cardiff visual acuity tests. Some tests use symbols or pictures instead of letters. Your provider may give your child a “cheat sheet” to match letters they see to what’s printed on a Snellen 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 read the chart slowly, 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.

It’s OK to guess at the letters or symbols as they get smaller or harder to read. But make sure you tell your eye care specialist when the chart looks fuzzy. Don’t squint or strain your eye to see. The point of a visual acuity test is to check your current vision, so don’t worry about “failing.”

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

What happens after a visual acuity test?

After the 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 other eye conditions.

What type of results do you get and what do they mean?

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

You’ve probably heard of the most famous expression of vision — 20/20 vision. It means you can see an object that is 20 feet away clearly. Most people don’t have 20/20 vision without some correction.

Your eye care specialist will tell you what you’ll need to correct your vision after the test. The most common way to correct your vision is to wear glasses or contacts. If you already have a prescription, your provider might adjust it to match any changes they found.