In the EBD Blog
Reviewed by Brian Boxer Wachler, MD on November 7, 2023
What is 20/20 Vision?
The phrase "20/20 vision" often describes perfect eyesight, but what does it actually mean? In eye care, 20/20 vision measures visual sharpness, indicating that you can see at 20 feet what someone with typical vision sees at that distance.
Doctors conduct vision tests using a Snellen chart to determine visual acuity. The chart features letters in various sizes. During an eye exam, you read these letters from a specific distance.
In "20/20 vision," the first number (20) represents the distance from the chart in feet, while the second number indicates how far a person with normal vision can read the same line. For instance, having 20/40 vision means you must be 20 feet away to see what someone with normal vision sees at 40 feet.
Eye care professionals use this metric to determine whether your eyes function properly or require correction.
Understanding 20/20 vision is crucial for eye health, as it aids in the early detection of issues for prompt treatment. Regular eye exams assess not just visual sharpness, but also aspects like depth and color vision, helping you maintain clear vision and healthy eyes.
The Science Behind Visual Acuity
Visual acuity enables us to see clearly, relying on the eye's functionality. The eye focuses light onto the retina using the cornea and lens. The retina, located at the back of the eye, converts this light into electrical signals, which travel to the brain through the optic nerve, producing sharp images.
Not everyone has perfect vision. Common issues like myopia and hyperopia can cause blurriness. Myopia, or nearsightedness, occurs when the eye is too long or the cornea is overly curved, causing distant objects to appear blurry. Hyperopia, or farsightedness, results from an eye that's too short or a cornea that's too flat, making close objects blurry.
Understanding these problems aids in resolving vision issues. Glasses are a common solution, and distinct types of lenses are available to adjust for different causes of blurry vision. There are even glasses with progressive lenses, which correct vision at both near and far distances in a single lens.
Learning about visual acuity helps us appreciate our vision's complexity. Keeping up with regular check-ups and corrective measures ensures clear sight.
When is a Visual Acuity Test Performed?
A visual acuity test is often performed during a comprehensive eye exam with an optometrist or ophthalmologist. These tests are provided for adults and children and may be recommended more frequently if you have risk factors such as a family history of eye diseases.
The American Optometric Association (AOA) recommends that adults have eye examinations on an annual basis. Children should receive an eye exam between the ages of 6-12 months and again between 3-5 years old. They should then undergo an exam before starting the first grade and once per year following that.
Types of Visual Acuity Charts
An eye chart is a tool used to assess visual acuity. These charts help your eye doctor evaluate your vision based on how well you can identify specific objects, patterns, or letters at a given distance. The most common eye charts include:
Snellen Chart
The Snellen eye chart is the most widely used chart to test visual acuity. It consists of several rows of uppercase letters that decrease in size as they go down the chart. The top row usually contains a single large letter "E.” The participant reads the letters out loud from the smallest row they can see clearly.
Random E Chart
The Random E chart is like the Snellen chart but consists of a series of capital "Es" arranged in different orientations. This chart allows an eye doctor to test visual acuity in people who can’t read letters, such as young children, or those unable to communicate verbally.
Tests for Children
Some charts are designed for children or toddlers who don’t know their letters yet. These charts feature pictures of familiar objects instead, making it easier for children to understand and participate in the exam.
One example is a Cardiff visual acuity test, which involves a set of cards with easily recognizable shapes (such as a fish, dog, or train) positioned at the top or bottom. During the test, the eye doctor watches the child’s eye movements to determine which part of the card they look toward. This can help the eye care professional assess the child’s visual acuity.
What Happens During a Visual Acuity Test?
During a visual acuity test, you’ll sit or stand a specific distance away from the eye chart. The standard for adults is 20 feet, while children may be tested at 10 feet. Some devices use mirrors so you can be tested by looking into the machine.
You’ll then cover one eye at a time and read the letters out loud from each row. You’ll be asked to start at the top and work your way down until the letters become too difficult to read. The smallest row of letters you can read is used to help determine your visual acuity.
An eye care professional may perform this test on a patient with and without glasses. Testing for "corrected" and "uncorrected" vision helps determine if your current prescription is still effective or if you might need a new one.
What Do Visual Acuity Numbers Mean?
Visual acuity results are expressed as a fraction, such as 20/20. The first number represents your distance from the eye chart in feet. The second number represents the distance (in feet) at which a person with normal vision can clearly see the same line of letters. Here are some examples of these measurements and what they mean.
20/20 Vision
20/20 is the standard for normal vision. If you have 20/20 vision, you can see clearly at 20 feet what a person is expected to see at that distance. Contrary to popular belief, 20/20 does not mean you have perfect vision. This is because visual acuity doesn’t include peripheral vision, depth perception, or color vision, among other aspects of vision.
20/40 Vision
If you have 20/40 vision, you can see at 20 feet what a person with normal vision can see at 40 feet. In other words, your vision is only slightly less than what is considered standard. In most states in the U.S., the minimum visual acuity score required for an unrestricted driver's license is 20/40.
20/60 Vision
A person with 20/60 vision can see at 20 feet what a person with normal vision can see at 60 feet. This is considered a moderate visual impairment. Individuals with 20/60 vision may need glasses or contact lenses to improve their sight.
20/100 Vision
People with 20/100 vision have significant visual difficulties. They can only see at 20 feet what a person with normal vision can see at 100 feet. People with 20/100 vision will need corrective measures like glasses, contact lenses, or surgery to achieve better sight.
20/200 Vision
20/200 vision means that a person must be 20 feet away to see an object that someone with normal vision can see clearly from 200 feet, indicating severe visual impairment.
Beyond 20/20: Achieving Better Vision
Many associate 20/20 with perfect vision, but we can surpass it. Vision therapy offers exercises to sharpen eyesight and enhance coordination. It's not just about seeing clearly—it's about seeing better.
Vision therapy serves as a workout for your eyes, incorporating exercises to enhance focus, eye movement, and depth perception. These exercises are tailored to address specific issues. For instance, if tracking moving objects is challenging, you might practice following a ball with your eyes. Over time, these exercises can significantly boost your vision skills.
Improving vision extends beyond eye exercises to include lifestyle changes. Consuming foods rich in vitamins A, C, and E supports eye health. Regular breaks from screen time can alleviate eye strain, while proper lighting prevents fatigue. These straightforward habits contribute to maintaining sharp eyesight.
Myths and Facts About 20/20 Vision
A common misconception is that 20/20 vision equates to perfect eyesight; however, it simply means seeing at 20 feet what most people see at that distance. It's about clarity, not perfection. Some individuals possess better than 20/20 vision, such as 20/15, indicating they see from 20 feet what others see from 15 feet.
Another myth suggests that wearing glasses weakens your eyes. In reality, glasses improve vision clarity without altering eye structure or weakening them.
Understanding these misconceptions reveals opportunities for improving vision. With the proper glasses prescription, achieving better than standard 20/20 vision is possible.