What does 20/20 Vision Mean?

20/20 vision

Have you ever wondered what those numbers on your eyeglass prescription actually mean? Although reading an eye chart is a fairly simple test, it provides a very accurate way to measure your visual acuity or the sharpness of your vision. You'll also need a few other tests, in addition to the results of your eye chart reading, before your optometrist hands you your eyeglass prescription.

Reading an Eye Chart Provides an Accurate Representation of Your Vision

Every eye exam includes a reading of the Snellen eye chart. The chart contains 11 lines of random letters, each line smaller than the preceding line. Patients were once required to stand exactly 20 feet away from the chart, but optometrists use mirrors today to approximate that distance.

The chart is read from the top to the bottom. Each line corresponds to a specific measurement, such as 20/20 or 20/80. If your vision is 20/60, you can read words clearly at 20 feet that people with normal vision can read at 60 feet. Although 20/20 is considered normal vision, some people can see even better than 20/20. If you can read the bottom line of the eye chart clearly, your vision is 20/10.

In addition to reading the Snellen eye chart, you may also be asked to read text on the small printed card that you'll hold in your hands. This test evaluates your near vision.

Other Eye Tests Augment Your Eye Chart Measurement

Your optometrist uses a variety of tests to determine your prescription, if needed, and assess the health of your eyes, including:

  • Refraction. Refraction helps your optometrist refine your prescription. You'll place your head against a phoropter, a device that contains multiple corrective lenses. While you look at a line on an eye chart, your optometrist will flip back and forth between two lenses and ask you to identify which lens provides the clearest image.
  • Autorefraction. Before your refraction, your optometrist or his staff may ask you to look into an autorefractor, a machine that does a very good job of estimating the prescription you'll need.
  • Cover Test. During this test, you'll cover one eye at a time and stare at a fixed point in the distance, then look at a near object. The test evaluates the ability of your eyes to work together to produce a single image. If you must move your eye in order to focus, you may have strabismus. Although the condition is commonly called "crossed eyes," it can still be an issue even if your eyes are only slightly misaligned. Strabismus is often detected during childhood and can be corrected with special eyeglasses, prism lenses, vision therapy or surgery if other treatment options aren't helpful.
  • Ocular Motility Test. The ocular motility test is a simple evaluation that assesses your ability to follow moving objects with your eyes. While you hold your head still, you'll use your eyes to follow a small beam of light that your optometrist moves in various directions.
  • Glaucoma Test. Glaucoma, a condition that occurs when the pressure inside your eyes rises to dangerous levels, can damage your optic nerve, resulting in vision loss. The test takes seconds and involves exposing each eye to a puff of air.
  • Color Blindness Test. Optometrists typically use the Ishihara Color Vision Test to determine if you can see colors normally. During the test, you'll look at a series of circles made up of colored dots. Each circle also contains a number in a lighter color. As you're shown the circles, you'll be asked to call out the numbers. If you can't see certain numbers, you may have color blindness.
  • Depth Perception Test: Eye exams also include a test of your depth perception. After you put on a pair of 3D glasses, you'll view a test booklet that contains several pages, each containing four circles. If your depth perception is normal, one of the circles will look as if it's closer to you than the others.
  • Slit Lamp Test. The slit lamp test takes advantage of the magnifying powers of a microscope to allow a thorough look at the individual structures that make up your eye. After you place your chin and forehead against the instrument, your optometrist will examine your corneas, whites of your eyes, eyelids, and irises. Your retinas can also be examined if dilating drops are used.

Is it time for your annual eye exam? Call us today to schedule your appointment.


American Optometric Association: Visual Acuity: What is 20/20 Vision?


All About Vision: Is 20/20 Vision Perfect Vision


American Academy of Ophthalmology: What Does 20/20 Vision Mean, 11/30/16


All About Vision: What to Expect During a Comprehensive Eye Exam



We look forward to hearing from you


Find us on the map


Reviews By Our Satisfied Patients

  • "Dr. Leek is very experienced and has a great kind, personality. I highly recommend him. His massage therapists are also great."
    Patricia K. / Grass Valley, CA

Featured Articles

Read about interesting topics

  • Fuchs' Corneal Dystrophy

    Fuchs' dystrophy (pronounced fooks DIS-truh-fee) is an eye disease characterized by degenerative changes to the cornea’s innermost layer of cells. The cause for Fuchs' dystrophy is not fully understood. If your mother or father has the disease, then there is roughly a 50 percent chance that you will ...

    Read More
  • Age-Related Macular Degeneration

    One of the leading causes of vision loss in people who are age 50 or older is age-related macular degeneration (AMD). This common eye condition leads to damage of a small spot near the center of the retina called the macula. The macula provides us with the ability to clearly see objects that are straight ...

    Read More
  • Diabetic Eye Diseases

    Diabetes is a condition that involves high blood sugar (glucose) levels. This can affect many parts of the body, including the eyes. One of the most common diabetic eye diseases is diabetic retinopathy, which is also a leading cause of blindness in American adults. Diabetic Retinopathy Diabetic retinopathy ...

    Read More
  • Presbyopia

    Somewhere around the age of 40, most people’s eyes lose the ability to focus on close-up objects. This condition is called presbyopia. You may start holding reading material farther away, because it is blurry up close. Reading suddenly gives you eyestrain. You might wonder when manufacturers started ...

    Read More
  • Laser Cataract Surgery

    The only way to correct the clouded vision caused by advanced cataracts is surgical intervention. If you find yourself pursuing cataract surgery to remove one or both cataract-disease lenses, you may be wondering what surgical approaches are available for treatment. Although eye surgeons have successfully ...

    Read More
  • Cataract Surgery

    With cataract surgery, your ophthalmologist removes the cataract-diseased lens of your eye. The ophthalmologist then replaces your natural lens with an artificial one. The Procedure This outpatient procedure is generally safe and takes less than an hour. Your ophthalmologist will dilate your pupil ...

    Read More
  • Peripheral Vision Loss

    Normal sight includes central vision (the field of view straight ahead) and peripheral vision (the field of view outside the circle of central vision). The inability to see within a normal range of view often indicates peripheral vision loss. In severe cases of peripheral vision loss, individuals only ...

    Read More
  • Presbyopia

    As we age, our eyes—like the rest of our bodies—begin to lose flexibility and strength. When this happens to the lens of the eye and its surrounding muscles, your lens will become stiff. This makes it harder to see close objects clearly because the eyes can't focus properly. It's a natural part of ...

    Read More
  • Patches

    Eye patches are used to strengthen muscle control in weak eyes. By placing a patch over the strong eye, the weaker eye is forced to do the heavy lifting. While it may be uncomfortable for the patient at first, the muscle controlling the weaker eye will become tougher and more resilient. This will allow ...

    Read More
  • Macular Hole

    The condition known as a macular hole refers to a tiny break in the macula that results in blurry or distorted vision. To fully understand the condition, one must understand eye anatomy. The macula is a spot located in the center of the retina (the back portion of the eye). Located where light comes ...

    Read More

Newsletter Sign Up