Visual impairment is when a person has sight loss that cannot be fully corrected using glasses or contact lenses.
It's estimated that as many as two million people in the UK may be living with this sort of sight problem. Of these, around 365,000 are registered as blind or partially sighted.
It's important to visit an optometrist (optician) for an eye test at least every two years so they can check for signs of vision loss.
If you already have visual impairment, it is still important to have a regular eye test, as your optometrist can monitor for further changes in the eyes and advise on making best use of your vision.
Find an optician near you.
How vision is tested and measured
There are two main areas that are assessed when your vision is tested:
- visual acuity – central vision used to look at objects in detail, such as reading a book or watching television
- visual field – ability to see around the edge of your vision while looking straight ahead
The main tests used to assess your visual acuity and field are described below.
Visual acuity testing
A test called the Snellen test is often used to measure your visual acuity. It involves reading letters off a chart on which the letters become progressively smaller. This chart is used during a routine eye test.
After the test you are given a score for your visual acuity. A Snellen score consists of two numbers. The first number represents how far away from the chart you were able to successfully read the letters on the chart. The second number represents how far away a person with healthy vision should be able to read the chart.
So if you were given a visual acuity score of 6/60, it means you can only read at 6 metres away what a person with healthy eyesight can read at 60 metres away.
Visual field testing
There are a number of different tests that can be used to assess your visual field.
One test involves looking straight ahead at a device while lights are flashed on and off at the edges of your vision. You will be asked to press a button every time you see a light. This shows any gaps in your field of vision.
Alternatively, you may be asked to follow an object (or the tester's hand) with your eyes as it is moved across your field of vision. You will be asked to say when you first see the object and when you can no longer see it.
Types of visual impairment
Visual impairment is usually classified as either ’sight impaired’ or ‘severely sight impaired’. These classifications are based on the results of the tests described above.
Sight impairment, previously called ‘partial sight’, is usually defined as:
- having poor visual acuity (3/60 to 6/60) but having a full field of vision, or
- having a combination of slightly reduced visual acuity (up to 6/24) and a reduced field of vision or having blurriness or cloudiness in your central vision, or
- having relatively good visual acuity (up to 6/18) but a significantly reduced field of vision
Severely sight impaired
The legal definition of severe sight impairment (which was previously called ‘blindness’) is when ‘a person is so blind that they cannot do any work for which eyesight is essential’.
This usually falls into one of three categories:
- having very poor visual acuity (less than 3/60), but having a full field of vision
- having poor visual acuity (between 3/60 and 6/60) and a severe reduction in your field of vision
- having slightly reduced visual acuity (6/60 or better) and a significantly reduced field of vision
Causes of visual impairment
Most causes of visual impairment in the UK are conditions that develop as you get older. About 8 in every 10 people with visual impairment are over 65.
However, losing your vision is not an inevitable part of ageing. It is often the result of a condition that can either be treated or sometimes even prevented. This is why it's so important to have regular check-ups with your optometrist.
Some of the most common causes of visual impairment include:
- age-related macular degeneration (AMD) – where the central part of the back of the eye (the macula, which plays an important role in central vision) stops working properly
- cataracts – where cloudy patches can form within the lenses of the eyes
- glaucoma – where fluid builds up inside the eye, damaging the optic nerve (which relays information from the eye to the brain)
- diabetic retinopathy – where blood vessels that supply the eye become damaged from a build-up of glucose
In some of these cases, such as cataracts, treatment can at least partially restore your vision.
Vision loss caused by AMD, glaucoma and diabetic retinopathy cannot usually be reversed. However, there are several treatments that can prevent further damage to vision, or at least slow down the progression of these conditions.
Getting help and support
There are support services, charities and devices that can all help make life easier if your vision is impaired.
Just because you have low vision, it does not mean you are no longer able to work or live independently.
With the help of assistive technology, training and support, many people who are either partially sighted or blind can continue to live full lives and work in demanding roles.
Read more about getting help and support if you are living with a visual impairment.
Registering as visually impaired
If you are visually impaired, it is important to register this with your local authority. This is not compulsory, but it can entitle you to a range of benefits, such as:
To register, your visual acuity and visual field will have to be tested by an ophthalmologist (a doctor who specialises in diagnosing and treating eye conditions).
If the results show you are sight impaired or severely sight impaired, you will be issued with what is known as a Certificate of Visual Impairment (CVI) and a copy will also be sent to your local social services who can offer practical support.
Speak to your optometrist, GP or ophthalmologist for more information on registration. You can also read more about registering vision impairment on the Gov.uk website.