A vision score of 20/20-1 means you read the 20/20 line on an eye chart but missed one letter. It’s essentially normal vision with a single error, placing you just a hair below perfect 20/20 acuity.
How the Minus Notation Works
During a standard eye exam, you read rows of letters that get progressively smaller. Each row corresponds to a visual acuity level: 20/40, 20/30, 20/20, and so on. The bottom number tells you the distance at which a person with normal sight could read that same line. If you can read the 20/20 line, you see at 20 feet what a normally-sighted person sees at 20 feet.
Most lines on the chart have five letters. When you get some but not all of them right, your examiner records the line you attempted along with a minus sign and the number you missed. Read four out of five letters on the 20/20 line, and your score is 20/20-1. Miss two on the 20/30 line, and it’s 20/30-2. This system works the same way on any line of the chart, regardless of how many letters that line contains.
You may also see a plus notation. If you read all of the 20/25 line and then correctly identify two letters on the smaller 20/20 line below it, that could be recorded as 20/25+2. The minus and plus signs simply capture the in-between scores that a single fraction can’t express on its own.
How 20/20-1 Compares to 20/20
The difference is minimal. Missing a single letter on the 20/20 line means your visual acuity is fractionally less sharp than someone who nails every letter, but in practical terms the two scores are nearly identical. You can still read standard-size text, recognize faces at normal distances, and handle everyday visual tasks without difficulty.
Some clinicians convert letter-by-letter scores into a more precise scale called logMAR, where each letter is worth 0.02 units. On that scale, perfect 20/20 equals 0.00, and 20/20-1 equals 0.02. That tiny gap is undetectable in daily life. Most eye care professionals consider 20/20-1 functionally equivalent to 20/20 for general purposes.
Does 20/20-1 Pass Vision Requirements?
This depends on who’s asking. For a driver’s license, it’s a non-issue. Every U.S. state sets its driving threshold at 20/40 or looser, so 20/20-1 clears that bar with room to spare.
Occupational standards can be stricter. The FAA requires 20/20 distant vision (with or without correction) for first- and second-class medical certificates, which cover commercial airline pilots and other professional aviators. Whether 20/20-1 satisfies that standard can come down to the individual aviation medical examiner. Some treat one missed letter as a pass; others may flag it for further testing. Third-class certificates, used by private pilots, only require 20/40, so 20/20-1 is well within range.
Military branches, law enforcement agencies, and certain federal jobs each set their own visual acuity thresholds. If your career hinges on a specific score, check the exact standard for that organization rather than assuming 20/20-1 will be treated the same as 20/20.
Why You Might Miss One Letter
A single missed letter doesn’t necessarily signal a vision problem. Several everyday factors can cause it:
- Fatigue or dry eyes. If your eyes are tired or your tear film is uneven, letters can blur intermittently. Blinking a few times might have been enough to read that last letter.
- Lighting and contrast. Exam room conditions, chart quality, and glare can all influence how sharply you perceive the smallest letters.
- Slight refractive error. A prescription that’s off by a tiny fraction of a diopter, or early changes in your lens, can cost you one letter at the threshold of your acuity.
- Letter difficulty. Not all letters are equally easy to distinguish. Confusing a “D” for an “O” or an “F” for a “P” at small sizes is common even with excellent vision.
If you scored 20/20-1 on one visit, you could easily score a clean 20/20 the next time, or vice versa. Day-to-day variation of one or two letters is normal and expected.
What 20/20 Doesn’t Measure
Visual acuity is only one piece of your overall vision. A 20/20 or 20/20-1 score tells you how well you resolve fine detail at a distance, but it says nothing about peripheral vision, depth perception, contrast sensitivity, color vision, or how well your eyes work together. You can score perfectly on a letter chart and still have trouble seeing in dim light or noticing objects off to the side. A comprehensive eye exam evaluates these other dimensions separately, which is why the letter chart is a starting point rather than the whole picture.