A visual acuity test is an eye exam that checks how well you see the details of a letter or symbol from a specific distance.
Visual acuity refers to the ability to discern the shapes and details of the things you see. It’s just one factor in your overall vision. Others include color vision, peripheral vision, and depth perception.
There are several different types of visual acuity tests, most of which are very simple. Depending on the type of test and where it’s conducted, the exam can be performed by:
- an optometrist
- an ophthalmologist
- an optician
- a technician
- a nurse
No risks are associated with visual acuity tests, and you don’t need any special preparation.
You may need an eye exam if you feel you’re experiencing a vision problem or your vision has changed. A visual acuity test is one part of a comprehensive eye exam.
Children frequently take visual acuity tests. Early testing and detection of vision problems can prevent issues from getting worse.
Optometrists, driver’s license bureaus, and many other organizations use this test to check your ability to see.
Two commonly used tests are Snellen and random E.
The Snellen test uses a chart of letters or symbols. You’ve probably seen the chart in a school nurse’s office or eye doctor’s office. They’re different sizes and arranged in rows and columns. Viewed from 14 to 20 feet away, this chart helps determine how well you can see letters and shapes.
During the test, you'll sit or stand a specific distance from the chart and cover one eye. You’ll read out loud the letters you see with your uncovered eye. You’ll repeat this process with your other eye. Typically, your doctor will ask you to read smaller and smaller letters until you can no longer accurately distinguish letters.
In the random E test, you’ll identify the direction the letter “E” is facing. Looking at the letter on a chart or projection, you'll point in the direction the letter is facing: up, down, left, or right.
These tests tend to be more sophisticated when performed at an eye clinic than in a nurse’s office. At an eye doctor’s office, the chart might be projected or shown as a mirror reflection. You’ll look at the chart through a variety of different lenses. Your doctor will switch out the lenses until you can see the chart clearly. This helps determine your ideal eyeglass or contact lens prescription, if you need vision correction.
Visual acuity is expressed as a fraction, such as 20/20. Having 20/20 vision means that your visual acuity at 20 feet away from an object is normal. If you have 20/40 vision, for example, that means you need to be 20 feet away to see an object that people can normally see from 40 feet away.
If your visual acuity is not 20/20, you may need correction eyeglasses, contact lenses, or surgery. You might also have an eye condition, such as an eye infection or injury, that needs to be treated. You and your doctor will discuss your test results as well as any treatment or correction that might be necessary.