The short answer6/6 vision means that from 6 metres away you can read the same line a normal eye reads from 6 metres. It is the normal standard for visual acuity, equal to 20/20 in US notation and 1.0 in decimal notation. The first number is the test distance and the second is the distance at which a normal eye reads the same line, so the bigger the second number, the weaker the vision.
How the eye test works
You sit 6 metres from a letter or number chart (a Snellen chart), cover one eye and read with the other. Each line is printed at a size a normal eye can read from a set distance: the big top letter from 60 metres, the normal line from 6 metres. The smallest line you can read clearly is your result.
So 6/12 means that from 6 metres you read the line a normal eye reads from 12 metres. You need to be half as far away to see what someone with normal vision sees.
Vision conversion chart
| Metric | US (feet) | Decimal | LogMAR | Meaning |
|---|---|---|---|---|
| 6/5 | 20/16 | 1.2 | -0.1 | Better than normal |
| 6/6 | 20/20 | 1.0 | 0.0 | Normal vision |
| 6/7.5 | 20/25 | 0.8 | 0.1 | Close to normal |
| 6/9 | 20/30 | 0.67 | 0.2 | Mild reduction |
| 6/12 | 20/40 | 0.5 | 0.3 | Mild to moderate reduction |
| 6/18 | 20/60 | 0.33 | 0.5 | Moderate reduction |
| 6/24 | 20/80 | 0.25 | 0.6 | Moderate reduction |
| 6/36 | 20/120 | 0.17 | 0.8 | Severe reduction |
| 6/60 | 20/200 | 0.1 | 1.0 | Only the biggest letter |
Is 6/6 perfect vision?
No. 6/6 is the normal threshold, not the maximum. Many young people with healthy eyes read 6/5 or even 6/4. And 6/6 only measures sharp central vision at distance. It says nothing about side vision, near vision, colour vision or the health of the optic nerve.
With or without glasses?
An eye test report usually gives two numbers for each eye: vision without glasses, and the best vision with the right glasses or lens. The second number matters most. If it reaches 6/6 with glasses, the eye most likely just needs correction. If it does not reach 6/6 even with the best glasses, something else in the cornea, lens or retina needs looking into.
You may also see PH (pinhole). If vision improves when reading through a tiny hole, the problem is usually how the eye focuses light, and glasses can fix it.
WHO categories of vision impairment
| Category | Vision in the better eye |
|---|---|
| Mild | Worse than 6/12, down to 6/18 |
| Moderate | Worse than 6/18, down to 6/60 |
| Severe | Worse than 6/60, down to 3/60 |
| Blindness | Worse than 3/60 |
Frequently asked questions
Is 6/9 vision bad?
6/9 is a mild reduction. Many people never notice it day to day, but it can show when reading distant signs or driving at night. A light pair of glasses usually corrects it.
If I see 6/6, do I not need glasses?
Not always. Young people with long-sightedness can read 6/6 because the eye's focusing muscles compensate, but they tire with reading and screens. After 40, distance vision can be 6/6 while near vision needs reading glasses.
Is 6/6 the same as a zero prescription?
No. 6/6 is a result from reading the chart. A prescription is the lens power that corrects your vision. Someone with a -3.00 prescription may read 6/6 with glasses and 6/60 without them.
What does 6/60 mean?
From 6 metres you can only see the biggest letter on the chart, which a normal eye sees from 60 metres. Without glasses this is often strong short-sightedness that glasses correct. With glasses it needs a full eye exam soon.