20/20 is the feet-based way of writing normal distance visual acuity, used mainly in the United States. It is the same as 6/6 in metric notation.
What the numbers mean
The test is done at 20 feet. 20/20 means you see at 20 feet what a person with standard vision sees at 20 feet. 20/40 means you need to be at 20 feet to see what someone with standard vision sees at 40 feet.
Converting between systems
| Feet | Metres | Decimal |
|---|---|---|
| 20/20 | 6/6 | 1.0 |
| 20/30 | 6/9 | 0.67 |
| 20/40 | 6/12 | 0.5 |
| 20/60 | 6/18 | 0.33 |
| 20/200 | 6/60 | 0.1 |
What 20/20 does not tell you
A 20/20 result says nothing about colour vision, peripheral vision, night vision, focusing at near distances or eye disease. That is why seafarer medicals assess more than one aspect of vision.
Sources
- International Maritime Organization — STCW Convention and Code — Regulation I/9, Section A-I/9 (opens in a new tab)
- World Health Organization — Blindness and vision impairment — fact sheet (opens in a new tab)
Links go to the original publishers. SeafarerFit is not affiliated with or endorsed by these organizations.
SeafarerFit provides educational information, health calculators, screening tools and medical-examination preparation resources. It does not provide diagnosis, treatment, medical certification or official determination of fitness for sea service.