You’ve probably heard that 20/20 equals perfect vision. After all, this is the standard visual acuity your eye doctor aims for when prescribing glasses or contact lenses. But having 20/20 vision — with or without correction — doesn’t mean your eyes get a clean bill of health.  

“I get a lot of patients who come in with 20/20 vision and say, ‘Okay, I’m good,’ but there’s so much more to it than that,” says Katherine Tai, O.D., an optometrist with Bay Area Eye Care located inside America’s Best Eyesore + Eyewear in Fremont, California. “The eyes are a window to your whole health,” she adds. 

Here’s what the 20/20 vision test can and can’t tell you about your eyes. 

Has it been a while since your last eye exam? Now’s the time to book an appointment!   

What is visual acuity — and how is it measured? 

Visual acuity is how well you can see from a distance. In particular, visual acuity describes your ability to distinguish shapes and details of an object or printed material.  

A visual acuity test is used to determine how clearly you can see objects both near and far. And it is used to pick up vision changes from year to year, Dr. Tai explains. The test involves a standardized digital eye chart (the Snellen eye chart) with rows of letters of different sizes. (The test for young children usually features numbers or pictures of animals and familiar shapes.) 

You’ll sit or stand 20 feet away from the chart and read each row aloud until you no longer can make out the letters. 

This is just one part of a complete eye exam. Learn more about what to expect during your America’s Best eye exam here. 

What does it mean to have 20/20 vision? 

Having 20/20 vision means you can see what the average person can see while standing 20 feet away. In other words, 20/20 vision doesn’t mean perfect. 

• The top number is your distance from the chart as measured in feet.  
• The bottom number is the distance a person with average eyesight can read the same line in the eye chart.  

If your visual acuity is lower than average, the bottom number will be higher than 20. 

“So, if you have someone who’s 20/80, it means that what they can see at 20 feet is what a person with normal vision can see 80 feet away,” Dr. Tai explains. 

Your eye doctor will test your visual acuity during a comprehensive eye exam. While eye exams have traditionally been done in-person, you can also receive a digital eye exam at many America’s Best locations. These convenient exams take place in our stores with remote licensed optometrists. One of our on-site technicians will help you complete an on-screen appointment with an optometrist who is located elsewhere. 

Learn more and find a digital eye exam appointment. 

What can visual acuity tell you about your eye health? 

Visual acuity less than 20/20 can signal a refractive error. Common refractive errors include: 

• Nearsightedness (myopia), where close-up objects are clear, but distant objects are blurry. 
• Farsightedness (hyperopia), where distant objects are clear, but close-up objects are blurry. 
• Astigmatism, which is marked by a variation in the curvature of the eye that often causes blurry vision. 

Some refractive errors are mild and your eye doctor may simply want to monitor your vision to see how things progress. But most people with blurry vision will be prescribed glasses or contact lenses to help you see more clearly. Measuring your visual acuity helps your eye doctor determine the right prescription for you. 

Sometimes, having less than 20/20 vision can mean you have an eye disease or medical issue, Dr. Tai adds. However, it’ll take more than reading an eye chart to determine if that’s the case.  

 

What visual acuity can’t tell you about your eye health? 

Visual acuity is a helpful measurement of eye health. But it isn’t everything.  

Your eye doctor looks at many other factors to gauge your visual and overall health, including: 

• Peripheral (side) vision 
• Eye movement 
• Depth perception (ability to see objects in three dimensions) 
• Color vision 
• Health of the retina (back of the eye)  

These other factors help your doctor find various eye diseases that affect your health over time. 

For example, the 20/20 vision test can’t tell if you have glaucoma, which is a group of eye diseases that damage a nerve in the back of your eye. Glaucoma can lead to vision loss and blindness if left untreated. 

“Glaucoma actually has the nickname, The Silent Thief of Sight,” Dr. Tai says. The reason? You won’t notice any vision changes until 90% of the nerve is damaged.  

And, because glaucoma affects peripheral vision first, it can’t be detected in a 20/20 vision test. The only way to diagnose glaucoma is with a complete eye exam that measures your eye pressure, checks for nerve damage, and more. 

A comprehensive eye exam is also needed to diagnose diabetic retinopathy, a potentially serious complication in people with diabetes. When sugar levels get out of control, it creates wear and tear on the blood vessels in the body, often starting with the delicate blood vessels in the eye. This wear and tear damages the retina, or the light-sensing lining at the back of the eye, causing cloudy or blurred vision. 

Scoring less than average on the 20/20 test may indicate that you have an eye disease like diabetic retinopathy — but it’s not enough.  

“The 20/20 test can only tell us that something is not right,” Dr. Tai says. “It doesn’t show you the whole picture.” 

Therefore, don’t rely on visual acuity alone to measure your eye health. Even if you have 20/20 vision, it’s essential to get your eyes checked annually by an optometrist. 

Press play to learn more about the top reasons to get regular eye exams, even if you have 20/20 vision: 

 

Medically reviewed by Katherine Tai, O.D. 

See our sources:  
Visual acuity basics: American Academy of Ophthalmology 
Definition of 20/20 vision: American Academy of Ophthalmology 
Glaucoma basics: National Eye Institute and American Academy of Ophthalmology