What the eye test machine does and why you need it

The eye test machine at the DMV—officially called a vision screener or visual acuity tester—measures whether you can see well enough to drive safely. You look into the machine, focus on letters or symbols inside, and the operator records what you can read from a standard distance. It takes about one minute.

Every state requires this test before issuing or renewing a driver license. The machine doesn't diagnose eye disease or prescribe glasses. It straightforward checks: can you see a car, a traffic light, or a pedestrian from the distance a driver needs to react? If you can't, you either fail the test or pass it with restrictions—like "corrective lenses required."

You cannot skip this step. If you don't pass, you won't get a license, even if you pass the written knowledge test and the driving test.

Key Takeaways

  • The vision screener measures how clearly you can see letters or symbols at a distance, usually 20 feet, to confirm you meet the minimum standard for safe driving.
  • If you wear glasses or contacts, bring them with you—the machine tests your vision with correction if you normally use it.
  • Passing requires reading at least the 20/40 line on the chart; some states require 20/30 or better, and requirements vary by license type.
  • If you fail, you can usually retake the test the same day or schedule another appointment, and you may be referred to an eye doctor for a full exam.
  • Color blindness and peripheral vision are not tested by the machine, though some states conduct separate checks for these during the full vision exam.

How the machine works step by step

You sit in front of the screener and rest your forehead against the eyepiece. The operator will ask you to cover one eye at a time. Inside the machine, you see a chart with letters, numbers, or symbols that get smaller as you look down the rows—the same idea as an eye chart in a doctor's office, but automated.

You read aloud what you see, starting with the largest letters and moving down until the letters become too small to read clearly. The machine records the smallest line you can read with each eye. This measurement is your visual acuity, written as a fraction like 20/40 or 20/20.

The whole process takes about 60 seconds per eye. If you wear glasses or contacts, you wear them during the test—the machine is testing your vision as you actually use it to drive, not your uncorrected vision.

What the numbers mean and what you need to pass

Visual acuity is written as a fraction: the first number is always 20 (the distance in feet you stand from the chart), and the second number is the distance at which a person with normal vision could read that same line. So 20/40 means you can read at 20 feet what a person with normal vision reads at 40 feet—you need to be twice as close.

Most states require a minimum of 20/40 vision in each eye to pass. Some states require 20/30 or 20/25. A few states allow one eye to be weaker if the other eye is strong enough. The exact standard depends on your state and the type of license you are seeking—commercial driver licenses often have stricter requirements than regular passenger licenses.

If you have 20/20 vision, you pass easily. If you have 20/50 or worse, you will not pass and will need to see an eye doctor before you can retest. If you fall in the middle range, you pass but may be restricted to wearing corrective lenses while driving.

What happens if you fail the vision test

If you cannot read the required line, the DMV will not issue your license. You have two options: retake the test the same day (some DMVs allow this when ready; others require you to schedule another appointment), or visit an eye doctor first.

Many DMVs will refer you to an optometrist or ophthalmologist if you fail. The eye doctor performs a full vision exam, determines whether glasses or contacts will help you pass, and provides a report to the DMV. You then return to the DMV with the eye doctor's report and retake the vision screener.

If you already wear glasses or contacts and fail the test while wearing them, the problem is not correctable with a stronger prescription—it may be a medical eye condition. In that case, the eye doctor's report will determine whether you can drive at all, and the DMV may issue a license with severe restrictions or deny it entirely.

Preparing for the vision test

If you wear glasses or contacts, bring them with you to the DMV. Wear them during the test. If you have a new prescription and haven't picked up your glasses yet, do so before your DMV appointment—the test measures your vision with correction, and an outdated prescription may cause you to fail.

If you wear bifocals or progressive lenses, let the operator know. They may adjust how you position yourself at the machine to may support you are looking through the correct part of the lens.

If you have had recent eye surgery, cataract removal, or a change in your vision, schedule an eye exam with your doctor before going to the DMV. Vision can be unstable for weeks after certain procedures, and you may fail a test you would pass a few weeks later.

Get a good night's sleep before your appointment. Eye strain and fatigue can affect how clearly you read the chart, especially if you spend long hours on screens.

Differences between states and license types

Vision requirements vary by state. Some states use 20/40 as the minimum; others use 20/30. A few states test both eyes together and separately. Some states allow monovision (one eye corrected for distance, one for near) if each eye meets the standard individually.

Commercial driver licenses (CDLs) have stricter vision requirements than regular passenger licenses in all states. A CDL typically requires 20/25 vision in each eye, or 20/40 in one eye and 20/20 in the other, depending on the state. Passenger licenses are usually more lenient.

If you are renewing your license by mail or online, you may not need to retake the vision test if your previous test was recent enough. Check your state's DMV website for renewal rules.

What the vision test does not check

The vision screener measures only central visual acuity—how clearly you see straight ahead. It does not test peripheral vision (what you see to the sides), color blindness, night vision, or depth perception. Some states conduct separate tests for these during a full vision exam, but the machine itself does not.

If you have a medical eye condition—such as glaucoma, macular degeneration, or severe astigmatism—the machine may not detect it. You could pass the screener and still be unsafe to drive. If you are concerned about your vision beyond what the machine tests, see an eye doctor for a comprehensive exam.

The machine also does not test your ability to see in different lighting conditions, such as at night or in bright sunlight. These are real-world driving skills that the vision screener cannot measure.

Frequently Asked Questions

Can I wear sunglasses during the vision test?

No. You must remove sunglasses and any tinted eyewear. The machine needs to see your eyes clearly, and tinted lenses interfere with the test. If you have light-sensitive eyes, mention this to the operator—they may be able to dim the machine's light slightly.

What if I can read the chart but I'm not sure of a letter?

Guess. The operator is looking for the smallest line you can read with reasonable confidence. If you hesitate or squint, they will note that you cannot read that line clearly and move to the next one. Honesty matters more than trying to pass a line you are unsure about.

Do I have to pass the vision test on the same day as the written test?

The vision test is usually given on the same day as the written test, before you take the driving test. If you fail the vision test, you will not be allowed to take the driving test that day. You must pass vision first, then take the written and driving tests.

Can I retake the vision test when ready if I fail?

Some DMVs allow you to retake it the same day; others require you to schedule a new appointment. Call your local DMV or check their website to learn their policy. If you failed because you need glasses, you will need to see an eye doctor and return with a report before retesting.

What if I have one eye that is much weaker than the other?

The machine tests each eye separately. If one eye is significantly weaker, you may still pass if that eye meets the minimum standard (usually 20/40) and your other eye is normal. Some states allow one eye to be as weak as 20/70 if the other eye is 20/20 or better, but this varies. Check your state's specific rules.