What Is Visual Acuity?

Optometrists and ophthalmologists use the term “visual acuity” to describe what you can see at a distance. We consider 20/20 to be “perfect” vision, although some people can see even better than that (more on that below). 

Testing For Visual Acuity (VA)

Historically, the Snellen Eye Chart was the most common method used to determine general visual acuity here in the United States. The chart was designed so that a series of letters reduces in size from the top of the chart (which has one large letter) to the bottom (where there is a line of tiny letters) in a series of 11 rows. 

Today, the Snellen Eye Chart has made way for the LogMAR chart, considered the “gold standard.” It looks similar to the Snellen but is designed with a specific recurrence of letters, and a timer is implemented so that the time it takes for a patient to discern the letters accurately becomes part of a mathematical algorithm that determines VA. 

Other charts used to get a general assessment of visual acuity include the Tumbling (or Random) E chart, the Landolt C chart, and symbol charts. These are the ones used most often on patients who are not yet literate, who don’t speak English, or who may not be able to name letters for any number of reasons.

Using Eye Charts To Test Distance Vision

While you can technically use an eye chart at home to gain some sense of your visual acuity, results are only considered accurate when you receive a vision test from:

• Your optometrist or ophthalmologist
• A pediatrician or physician
• Medical technicians or medical assistants
• Nurses (including school nurses)

In almost all cases, if anyone other than an optometrist/ophthalmologist determines visual acuity issues, they’ll refer you to an eye doctor for official vision assessments, diagnostics, and prescriptions/treatments.

When we use eye charts, patients are standing or seated 20 feet away from the chart. People with 20/20 vision can see the last line of the chart with clarity. The larger the number there is on the bottom of the 20/XX equation, the less visual acuity you have.

If your visual acuity test results reveal that you have 20/60 vision, it means that someone with 20/20 vision can see what you can see when they are 60 feet away from the object(s). This would mean that you are nearsighted and we would begin assessing both the cause as well as determining which lens prescription would help you get as close to 20/20 vision as possible.

On the opposite end of the spectrum, if you have 20/10 vision, you are able to see things clearly from 20 feet away that those with 20/20 vision would only see if they are 10 feet away or closer. Once you reach a visual acuity of 20/200 or lower, that cannot be improved with glasses, contact lenses, or other refractive aids, you are considered legally blind.

Causes For Reduced Visual Acuity

There are many different causes of reduced visual acuity. Once your optometrist determines your visual acuity is less than 20/20, we want to find out why. From there, we can determine the best way to improve your vision (and - sometimes - your health if the cause is an underlying health issue).

Some of the most common causes for reduced visual acuity requiring eyeglasses, contacts, or surgery are:

• General nearsighted (myopia). Some people are genetically nearsighted. If your parents were born nearsighted or developed nearsightedness early in childhood or adolescence, you have a higher risk of being nearsighted, too.
• Farsighted. In some cases, you may do great with your eye chart test but not so great when we test for close visual acuity (reading or computer work). In this case, you’re diagnosed as farsighted, and you’ll need glasses for closer vision range.
• Astigmatism. People with astigmatism have eyes/lenses shaped more like a football (elliptical) than a basketball (sphere). This causes light to focus on two points, rather than one, on the retina. The result is blurred or smeared vision. 
• Presbyopia. This is caused by a hardening of the eye’s lens and is almost always an age-related condition. People 50+ almost always have some degree of presbyopia, so they need reading glasses.

Interestingly, vision charts testing for visual acuity are also color-coded, allowing us to detect color blindness, too. 

There are other conditions that cause vision loss, such as cataracts, macular degeneration, diabetic retinopathy, etc. However, these are all rooted in genetic or health-related causes and so are not considered part of the standard visual acuity lineup.

Can I Improve My Visual Acuity?

In most cases, there isn’t anything a patient can do to improve visual acuity other than take good care of your health, wear your glasses or contacts as needed, and visit your optometrist for annual eye exams.

In some cases, your optometrist may recommend vision therapy or a series of eye exercises to strengthen the eye muscles and the connection between the eyes, optic nerve, and brain. You can also support your eye health by practicing the 20/20/20 rule to prevent eye strain when working on a computer, using your phone, or reading for long periods of time. If you are prone to dry eye, you’ll also find that being proactive about eye lubrication and hydration (as well as avoiding eye strain) also supports visual acuity. 

Get Your Visual Acuity Test Results From Eye To Eye Family Vision Care

Do you feel like you squint more often than you used to when looking at a distance? Are headlights and other nighttime lighting developing halos these days? Do you have a hard time (blink blink blink) when looking back and forth between the book or post you’re reading and your kids’ ball games? 

All of those are signs you’re ready for an eye exam and accurate visual acuity testing. Contact Eye to Eye Family Vision Care and schedule an appointment.