Boots WebMD Partners in Health
Return To Boots

Eye health centre

Select a topic to explore more.
Select An Article

Visual acuity

Visual acuity describes how well you see detail with your central vision.

This is usually measured using a special chart with rows of letters that start with one big one at the top and get smaller row by row - called a Snellen scale.

It is named after Dutch ophthalmologist Herman Snellen who invented it in 1862.

During a routine eye test, the optician or ophthalmologist will sit a person 6 metres from the chart. If glasses or contact lenses are worn, these should be used for the test.

Each eye is tested while the other one is covered. Eyes may also be tested together.

The rows of letters correspond to the minimum size of letter that could be seen by someone with normal vision from 6m up to 60m.

A score on the test is given for each eye.

Each eye is assessed with two numbers, such as having 6/6 vision.

The first number is the distance the chart is viewed from.

The second is the distance at which the person being tested can see a letter clearly.

This used to be in the form 20/20 when the distance was measured in feet not metres.

The result of the Snellen test is just one aspect of vision tests an optician or ophthalmologist may carry out, others include checking reading distance (near vision), peripheral vision or colour vision.

If you can only read the big letter on the top line, that's recorded as 6/60 - you can see at 6m what can usually be seen from 60m with normal vision.

If you can identify 2 letters from the second row, that's 6/36

Three letters from the third row is 6/24

This continues down to the seventh row, where around 7 letters corresponds to 6/6 vision.

Snellen scale test scores for each eye and both - called binocular vision - might be:

 

Left eyeRight eyeBinocular vision
6/66/66/6
6/126/66/6
6/12No vision6/12

 

 

Visual acuity and driving

For driving, the Department of Work and Pensions says a person needs to be able to read the third line up from the bottom of the chart with just their eyes, or with glasses or contacts - so 6/9 vision also sometimes expressed as 0.5.

Standards are higher for lorry drivers and bus drivers.

Next Article:

WebMD Medical Reference

Stay informed

Sign up for BootsWebMD's free newsletters.
Sign Up Now!

Popular slideshows & tools on BootsWebMD

woman blowing nose
How to tell the difference
smiling baby
Causes and remedies
bowl of soup
Small changes that lead to weight loss
boy looking at broccoli
Simple tips for feeding fussy eaters
cold sore
How to cope with cold sores
boy coughing
Treatments for cold and fever
bain illustration
Best foods for your brain
bucket with cleaning supplies in it
Cleaning for a healthy home
avacado on whole wheat crackers
Plenty to choose from
woman looking at hair
What your hair says about your health