An Overview of Visual Impairment

What is Visual Impairment?

Visual impairment is when a person has sight loss that cannot be corrected using glasses or contact lenses.

There are two main categories of visual impairment:

  • being partially sighted or sight impaired – where the level of sight loss is moderate.
  • severe sight impairment (blindness) – where the level of sight loss is so severe that activities that rely on eyesight become impossible.

How vision is measured

There are two main areas that are looked at when someone’s vision is measured:

  • visual acuity – which is your central vision and is used to look at objects in detail, such as reading a book or watching television
  • visual field – which is your ability to see around the edge of your vision while looking straight ahead

The Snellen test

A Snellen test measures 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 made up 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 6 metres away what a person with healthy eyesight can read 60 metres away.

Visual field testing

During visual field testing you will be instructed to look straight ahead at a device while lights are flashed on and off in your peripheral vision. You will be asked to press a button every time you see a light. This shows any gaps in your field of vision.

Partial sight

Partial sight, or sight impairment, is usually defined as:

  • having very poor visual acuity (3/60 to 6/60) but having a full field of vision, or
  • having a combination of moderate 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 lot of your field of vision is missing

Severe sight impairment (blindness)

The legal definition of severe sight impairment (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 extremely 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 average visual acuity (6/60 or better) and an extremely reduced field of vision

Getting help

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. With the help of assistive technology, training and support, many people who are either partially sighted or blind can continue to work in often very demanding roles. Probably the most well known example is the politician David Blunkett.

Registering as visually impaired

It is also important that you register as visually impaired. To register, your visual acuity and visual field will have to be tested by an ophthalmologist (a doctor who specialises in treating eye conditions).

If the results show you are partially sighted or blind, 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.

Being registered as visually impaired can entitle you to a range of benefits, such as:

  • Disability Living Allowance (DLA) – a tax-free benefit to help with any costs a person has relating to their disability
  • a 50% reduction in the TV licence fee
  • tax allowance
  • a disabled person’s card

Your GP or ophthalmologist can provide more information on registration.


If you are diagnosed with a condition known to cause low vision, you have a legal obligation to inform the Driver and Vehicle Licensing Agency (DVLA). Failure to do so is a crime and can result in a £1,000 fine.

The Directgov website has advice about how to tell the DVLA about a medical condition.

If you are registered as having a sight impairment or a severe sight impairment, the DVLA will assume that your driving licence is no longer valid and you will no longer be able to drive.

Occasionally, exceptions are made in people with mild sight impairment. If you think this applies to you, then your doctor will need to fill in a questionnaire for the DVLA.

You are only legally allowed to drive if you can read a number plate from a distance of 20 metres (65 feet). You are allowed to wear glasses or contact lenses when reading the plate.

Who is affected

There are around 360,000 people who are registered as visually impaired in England. As many as 2 million people in the UK may be living with some degree of visual impairment.

Most cases of visual impairment in this country are caused by ageing. It is estimated that around 1 in 5 people over the age of 75 have some degree of visual impairment.

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 macular, which plays an important role in central vision) stops working properly
  • cataracts – where cloudy patches can form on 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 due to a build-up of glucose

Can vision be restored?

It depends on the underlying cause.

Cataracts can be treated with surgery that usually leads to at least a partial improvement in vision.

In cases of AMD, glaucoma and diabetic retinopathy, it is usually not possible to restore vision. However, there are several treatments that can prevent further damage to vision, or at least slow down the progression of these conditions.

This information comes from the NHS Choices Website