Understand the vision chart
What is an eye chart?
An eye chart contains rows with letters that get smaller and smaller on each line. For younger children, there are instead symbols, such as an apple or a house, on the chart.
The eye doctor or optician will ask you to say what you can see on the chart – row by row – in order to determine your visual acuity. Visual acuity is an indication of how much you can see after your vision has been corrected with glasses or contact lenses. Visual acuity should not be confused with visual strength. You can read about the difference between the two concepts on the page ‘Difference between visual strength and visual acuity’.
What does visual acuity indicate?
Ideally, you should be able to see 100% (with glasses or contact lenses). This means that you can read the bottom row on the chart at a distance of six meters. This is called 6/6. 6/6 means that you have to stand six meters away to be able to see what a person with good natural vision can see at six meters i.e., the same distance.
If you have a visual acuity of 6/18, it is the equivalent of standing six meters away from something in order to see something than a normal-sighted person would be able to see at a distance of 18 meters.
These fractions can be converted to a decimal number or percentage, which describes the same visual acuity in a different form.
A visual acuity of 6/18 as a fraction can be converted to a decimal by dividing 6 by 18. So, see it as a calculation. 6/18 = 0.33. In doing so, you convert the fraction to a decimal.
If you want to understand the visual acuity score in terms of percentage, you do the following calculation instead. 6/18 * 100 = 33%.
So based on how many lines you can read on the eye chart, you can understand the visual acuity score in a number of different ways: as a fraction, a decimal, and a percentage.
Categorising visual acuity
There are different ways to understand a visual acuity score: as a percentage, decimal, or fraction, bit it can mean the same thing. Below is a summary of common groupings used to differentiate between visual acuity scores.
Severely visually impaired can also be called ‘social blindness’.
The requirement to drive a car is visual acuity of minimum 50%. An eye with 50% vision is sufficient. This does not mean that you have to have 50% in both eyes.