Monocular vision (sight in one eye)

3-Dimensional (3D) vision

When we look at something, both eyes point towards it and focus on the same spot. Each eye sends a slightly different image to the brain. The brain combines the images coming from each eye into one image, which lets us see in 3D. This is called depth perception or stereopsis, and it helps us judge distance.

Using only one eye instead of both together can affect your 3D vision. This can cause problems judging speed, depth and direction. At first, this can make everyday tasks harder, such as judging the height of steps or pouring liquid into a cup accurately. Ball sports or judging oncoming traffic can also be affected. With time, this will improve. Your visual system begins to use other clues, such as the size and position of objects, as well as light, shadow and texture, to judge distance.

Field of vision

Your field of vision is everything you can see when looking straight ahead, including above, below, and to the sides. With sight in only one eye, your field of vision will be reduced on the affected side. Therefore, you may not notice people or objects there, especially in new places or busy environments. With time, most people naturally learn to turn their head more towards the affected side when needed. It can help to ask people to sit or approach you on your good side where it is easier for you to notice them.

‘Altered’ vision in unaffected eye

If the sight loss in one eye is not complete, it may also cause things to appear less clear in the affected (good) eye. This is because the brain is used to receiving similar pictures from both eyes (binocular vision). Therefore initially, it struggles to adjust to suddenly receiving a picture from just one eye (monocular vision). The poor sight in the affected eye can "interfere" with vision from your good eye. With time, this usually improves as the brain learns to rely more on the unaffected eye. As this happens, the good eye usually “takes over”.

Tired eyes

When you have sight in only one eye, the eyes have to work harder to make the most of the vision you still have. Because of this extra effort, you may find that your eyes become tired more quickly, even after doing simple tasks. You may find you need to take more breaks regularly.

You can continue using your good eye for activities such as reading or watching television; this won’t damage your eyes. However, you may find it helpful to take regular breaks from these tasks to prevent your eyes from becoming tired. When you have sight in only one eye, this eye has to work harder to make the most of the vision you still have. Because of this extra effort, you may find that your eyes become tired more quickly, even after doing simple tasks.

In most cases, people naturally adjust over time. The brain is very good at adjusting to changes in vision. When you lose sight in one eye the brain gradually learns to rely more on the unaffected eye. As this happens, the stronger eye usually “takes over,” and tasks that once felt difficult often become easier.

Everyone adjusts at their own pace and it’s difficult to say how long it may take for someone. It can take longer if the sight loss happened suddenly rather than gradually. Give yourself time to adapt. The practical tips below might help. Once someone has adapted, they are usually able to read, get around and carry out everyday activities without any problems.

Here are some simple ideas that may help in everyday life:

• When putting a drink down, place the other hand on the surface first, then put the drink next to it.
• When pouring a drink, rest the lip of the container on the edge of the cup or glass to guide you.
• Take care on stairs - move slowly, feel for each step, and hold the handrail.
• When crossing the road, pause at the kerb to judge the height of the kerb and the distance of traffic. Use controlled road crossings like red light crossings or zebra crossings.
• Ask friends and family to sit or approach you on your seeing side, where it is easier for you to notice them.
• In crowded places, walk with someone or keep a wall on your affected side to avoid bumping into things.
• You may need to turn your head more to see on your affected side. This will feel more natural with time.
• Making things bigger, using brighter lighting or using colour to make things easier to see may help while adapting.

You may still be able to drive a car or motorcycle if you have vision in one eye. However, your other eye must meet the Driver and Vehicle Licensing Agency (DVLA) legal eyesight standard, and you must have adapted to the change.

Judging distances may be harder and you may be less aware of things on the side where you have lost vision. Using your wing mirrors more can often help. You should remember that blind spots may feel bigger when you only have vision in one eye.

For complete loss of vision in one eye (where there is no perception of light in the affected eye), the driver:

• must meet the same visual acuity and visual field standards as binocular drivers (drivers with sight in both eyes). This means that with your unaffected eye you must be able to read a number plate from 20 metres and read down to the 6/12 line (or better) on the eye test letter chart with any glasses or contact lenses you need. Your unaffected eye must also have good all-round field of vision of at least 120 degrees wide.
• may drive only after clinical advice of successful adaptation to the condition. This means that you should not drive until you have been advised by your doctor, orthoptist or optometrist (optician) that you have fully adapted to monocular vision.

Telling the DVLA (or DVA)

You do not need to tell the DVLA if you have sight in only one eye and your other eye:

• meets the DVLA vision standard, and
• has no eye conditions.

You must tell the DVLA if you have vision in one eye and your other eye:

• does not meet the DVLA vision standard, or
• has another eye condition.

If you live in Northern Ireland, you must contact the DVA.

Your ophthalmologist (hospital eye doctor), orthoptist or optometrist can explain the rules and tell you if you need to inform the DVLA or the DVA.

If you have have a lorry or bus licence (HGV or PSV), the rules are different. You must tell the DVLA or DVA about your monocular vision.

You may need to fill in a V1V form, which you can find on the DVLA website. If you live in Northern Ireland, you can find contact details for the DVA on their website.

RNIB cannot decide if you can continue driving. If you’re unsure whether your vision meets the requirements, ask your GP, optometrist, orthoptist or ophthalmologist for advice.

If you only have useful vision in one eye, you may feel that you are partially sighted. However, you would not usually meet the criteria to be formally certified and registered as sight impaired unless both eyes have significant loss of vision.

This is because certification is based on how well you can see with your better eye. So, if your other eye still has good or useful vision, an eye consultant would not usually be able to certify you as sight impaired.

The criteria for certification and registration are set nationally by the Department of Health. A consultant eye doctor will decide whether someone can be certified based on these criteria and their professional judgement.

If you have some loss of sight in your other eye as well then it is worth discussing the possibility of certification and registration with your ophthalmologist.

If you have useful vision in only one eye, it is important that you protect and monitor the health of your good eye.

Regular eye examinations

Continue with eye clinic appointments if you are under the care of an ophthalmologist at your hospital.

You should have regular eye tests with your optometrist so they can:

• Check the health of your eye
• Monitor any changes in your vision
• Detect any problems early as the sooner any eye conditions can be detected, the better the outcome for your sight.

Your optometrist will advise you on how often you should have your eyes examined based on your individual situation.

Protecting your eye

To reduce the risk of injury to your good eye, it is recommended that you use protective eyewear or sports goggles when doing activities such as:

• Sports (especially ball or contact sports)
• Gardening
• DIY or home improvements.

Protective eyewear can help prevent serious injury or loss of vision.

A dispensing optician can help you choose suitable protective eyewear. They are qualified to:

• Fit glasses and protective frames
• Recommend appropriate lenses and materials
• Provide advice on eyewear for specific activities.

Protect your eyes from UV light by wearing sunglasses that provide 100% UV protection when outdoors. This may help reduce damage to the eyes over time.

You can speak to a dispensing optician at your local optician’s practice for advice.

General health

Taking care of your general health can help protect the sight in your unaffected eye:

• Do not smoke. Smoking increases the risk of several eye conditions that can affect sight.
• Eat a healthy, balanced diet with plenty of fresh fruit and colourful and leafy vegetables, and oily fish.
• Maintain a healthy weight. This can support overall eye health and reduce the risk of conditions such as diabetes and high blood pressure, which can affect vision.

If you have further questions about monocular vision, please get in touch with our Helpline by calling 0303 123 9999.

Artificial Eyes provides some useful information on adapting to monocular vision which may be helpful for people who have lost sight in one eye.