Understanding sight loss

Almost 2 million people in the UK have some sort of sight loss and 360,000 are registered as visually impaired. Sight loss can affect us at any age but it is common for our vision to get worse as we get older.

There are two types of sight loss; visual acuity and loss of peripheral vision. It is possible to have a loss of acuity and peripheral vision at the same time.


Snellan Chart

Acuity means the clarity and sharpness of our vision, it is our ability to recognise details, such as faces, to read text and watch television. This can also be referred to as the sharpness of our vision.

Most of us will recognise the Snellen chart; the capital letters we are asked to read during sight tests at the opticians or ophthalmologist. This chart is used to test our visual acuity, whilst we are looking at the letters of the chart using our central vision.

The test is an important part of any sight loss exam and can be used to determine whether you need glasses.

Some common acuity sight loss conditions are Age-Related Macular DegenerationCataracts, and both long and short sightedness.

Peripheral vision

Our peripheral vision is what we can see to the side of us without turning our head.  This vision helps us with mobility, locating things and depth perception. It has a big affect on our balance. If you have a loss of peripheral vision, you will be able to see things straight ahead of you but not to either side, above or below the eye level. This is often known as ‘tunnel vision’.

Your optician or ophthalmologist will test your peripheral vision as part of your routine sight test. Any loss to your peripheral vision can be measured in degrees of remaining visual field.

Some common causes of peripheral sight loss are Retinitis Pigmentosa (RP), Glaucoma, and Retinal Detachment.

Some common causes of peripheral sight loss are Retinitis Pigmentosa (RP), Glaucoma, and Retinal Detachment.