The retina is the light-sensitive layer that lines the inside of your eye. Coats disease can make these blood vessels weak and grow incorrectly, causing them to leak fluid and blood under the retina. This means that the cells of the retina can’t work properly and this can cause sight to be affected.
Coats disease usually occurs in children or teenagers under the age of 18, but most often before the age of 10. It affects boys more than girls, and generally it only affects one eye. It’s quite a rare condition, affecting only around 1 in 100,000 people.
– How does the eye work?
– What causes Coats disease?
– How does Coats disease affect the eye?
– How does Coats disease affect sight?
– How is Coats disease diagnosed?
– How is Coats disease treated?
– In the long term for people with Coats disease
– Managing with sight in only one eye
When you look at something, light is focused onto your retina. The retina is a delicate tissue, made up of light-sensitive cells, that lines the inside of your eye. Your retina converts the light into electrical signals that travel along the optic nerve to our brain. The brain then interprets these signals so we can "see" the world around us.
The retina is supplied with blood by a network of blood vessels on its surface and by a layer of blood vessels underneath the retina.
Light is focused onto a tiny area of your retina called the macula. This highly specialised part of your retina is vital, because it enables you to see fine detail when you are looking directly at something such as words, photos or the television. The macula also gives you much of your ability to see colours. The rest of your retina, gives you side vision (peripheral vision).
The cause of Coats disease isn't fully known (this is medically known as idiopathic) and there are no known risk factors. It doesn't appear to be hereditary (passed through families) so it’s extremely unusual for it to affect more than one child or person in the same family.
Some studies have suggested that in some people it may be caused by a fault in a particular gene. However, more research needs to be done to confirm whether this may be the case and to find out what role this faulty gene may play in the development of Coats disease.
Coats disease only affects the eye and does not affect any other parts of the body, so people with Coats disease are otherwise generally healthy.
Coats disease affects the smaller blood vessels (capillaries) in the retina. Retinal capillaries are important in supplying the retina with blood which carries nutrients to the cells of the retina, so that they work correctly. The cells of the retina need to remain healthy for you to be able to see clearly.
Coats disease causes retinal capillaries to develop incorrectly. They become wider (dilated) and twisted, which make them more noticeable when the inside of the eye is examined. The medical term for these changes is telangiectasia.
As well as the retinal capillaries becoming dilated, they also become weak and leaky. This causes some of the fluid from the blood to leak out of the vessels and into the retina. This fluid builds up in the retina and causes it to become waterlogged (swollen). Eventually, exudates (lipids which have leaked out of the vessels) build up underneath the retina, causing a yellow appearance in the affected area.
Where there are areas of exudates and telangiectasia, the retina won’t be able to work properly. This in turn will mean sight in this part of vision won’t be clear.
Coats disease has different stages depending on how it is affecting the retinal capillaries and retina:
Stage 1: Telangiectasia (dilated and twisted capillaries) which is causing minimal change to the retina and to vision.
Stage 2: Telangiectasia and exudates which cause increased changes to the retina and some changes in vision.
Stage 3: Large areas of swelling with retinal detachment. Vision is likely to be poor at this stage.
Stage 5: The eye has no sight and no treatment is available to improve sight. In most cases the eye isn’t painful, but if it were, treatment may be needed to prevent any pain or further damage to the eye.
In the early stages of Coats disease peripheral (side) vision is most likely to be affected.
Coats disease may progress, and as more of the retina is involved or damaged, more of the vision can become affected. If Coats disease affects the macula then your central, detailed vision will be affected.
In the advanced stages of Coats disease, more vision will have been lost because more of the retina has been affected. When a large area of retina has become swollen due to leaking fluid, it can cause the retina to detach from the back of the eye, which can cause loss of sight.
For the majority of people, Coats disease only affects one eye, so people with Coats disease will have good sight in the other eye.
Coats disease is a condition which can get worse over time. However, it can stop getting worse on its own, so not everyone progresses to stage 5. It’s not known why the condition can stop getting worse in some people, so it’s not possible to predict how the condition may progress in someone. Generally, the outcomes for sight are poorer in children who are at a more advanced stage of the condition when they are first diagnosed.
Most children with Coats disease don’t have any symptoms – the eye doesn’t look unusual, isn’t painful or red, and young children won’t usually be aware that there is a problem with their vision. Often children are diagnosed following an unusual finding at an optician’s appointment or after failing a school vision screening test. Older children may be able to tell that the vision in one eye has worsened.
Sometimes, the eye may have an odd appearance on photographs like a white/pale pupil rather than a red pupil when a flash photograph is taken. A white pupil is known as leukocoria. If you notice that your child has the appearance of leukocoria at any time, it’s important that their eyes are examined by an optometrist (also known as an optician) or ophthalmologist (hospital eye doctor) urgently, because there are other serious eye conditions that can give a similar appearance.
Some children who have Coats disease may develop a squint. This is where the eye with Coats disease doesn’t point in the same direction as the other eye. You can find more information about squint here.
Often, an eye examination is the only way to tell if your child has an eye condition. Children can adapt very quickly to a change in their vision and there can be very few signs that they have any problems especially if only one eye is affected. All children should have their eyes screened when they start full time at school.
If you are concerned about your child's vision or their eyes it’s important to have them checked by an optometrist. An optometrist is able to check for any changes in the level of vision and the health of the eyes. If the optometrist is concerned by anything they find during the eye examination, they can make a referral to a hospital eye clinic.
At the eye clinic, the ophthalmologist will check the eyes by putting in drops to make the pupils larger. This allows them to get a better view when examining the retina. They will then shine a bright light into the eye to look at the retina.
Sometimes the ophthalmologist may want to perform another test known as a fluorescein angiogram. This is where a dye is injected into a blood vessel in the arm, which travels through the bloodstream to the eye. Alternatively, the dye may be given with fruit juice as a drink. When the dye reaches the eye, a series of photographs are taken which will show the blood vessels of the retina filling with the dye. From these photographs, the ophthalmologist will be able to see if any of these capillaries are leaking and be able to diagnose Coats disease.
The aim of treatment for Coats disease is to stabilise any changes that have occurred on the retina and to prevent sight from getting worse.
In the early stages of Coats disease, there may be no effect to vision. If the disease is very mild, treatment may not be needed straight away and the ophthalmologist may decide to monitor the eyes at regular appointments. In some people Coats disease doesn't develop any further than stage 1.
However where there are a lot of changes to the retina, even when the vision remains good, the ophthalmologist may decide to carry out some treatment to help prevent damage to the vision.
The treatment depends on where and how much of the retina has been affected. The treatments used for Coats disease are laser photocoagulation and cryotherapy (freezing treatment). The aim of both these treatments is to stop the retinal capillaries from leaking. The treatment is targeted at leaking blood vessels to help them to seal up and prevent further leakage. Most children would have these treatments carried out under a general anaesthetic.
In more advanced stages of Coats disease, where the retinal capillaries have leaked a lot and large areas of swelling have caused the retina to detach from the back of the eye, the treatment will be aimed at re-attaching the retina. The type of treatment may vary depending upon how large the detachment is and how long the retina has been detached for, but may include surgery to re-attach the retina.
Occasionally, in certain circumstances, a drug called anti-VEGF may be injected into the eye as part of the treatment of severe Coats disease.
The effect that Coats disease has on sight will vary from person to person. Generally, the condition will gradually progress and affect more of the retina. This can be minimised or halted with treatment. For younger children, especially those under three years old, the changes to their retina tend to progress more quickly, are difficult to control and are more likely to have a long-term effect on vision. In older children and young adults, Coats disease can have a much milder and slower effect on the retina.
The effect that Coats disease will have on sight will depend on the age at which it is first diagnosed. Being diagnosed early, when the capillaries are only showing slight changes would mean that there are more treatments available, such as laser photocoagulation or cryotherapy. In very occasional cases, treatment can improve vision, but in most cases the aim of treatment is to prevent further worsening of vision.
If you or your child has been diagnosed in the later stages of Coats disease, where large areas of the retina have already been affected, then laser photocoagulation alone may not be effective. It may be necessary to consider surgery to the retina.
Sometimes despite all treatment, the eye doesn’t respond and all sight in that eye may be lost. Late complications such as cataract (cloudy lens) or glaucoma (raised pressure) may also need treatment.
Typically, the eye feels comfortable during these late complications. Very rarely, uncontrolled glaucoma can cause the eye to become painful. If this is the case and the eye remains painful, it could be removed and replaced with an artificial eye, but this would be a last resort and is very uncommon.
Most people with Coats disease do not have their eye removed.
The amount of vision lost will vary between individuals. Coats disease usually only affects one eye. This is known as monocular vision, where someone has good sight in only one eye.
Children tend to adapt very well to using their better eye. This doesn’t mean that they will be overusing their better eye or causing any damage to the better eye as this adaptation is a natural process. It’s unusual for children with good vision in one eye to need additional support in their education. People with monocular vision are not considered partially sighted.
Having monocular vision can affect depth perception and hand-eye coordination. With some tasks, your child may appear clumsy and uncoordinated at first, for example when they throw and catch a ball. However, this generally improves as your child gets older and adapts to being monocular.
Even with good vision in their better eye, someone with monocular vision doesn't have as much peripheral vision as someone with two eyes. With time they will adapt to this without realising by turning their head more to see things in their peripheral vision. Other people can help by sitting or approaching someone with monocular vision on the same side as their good eye, to make it easier for them to see you.
It’s important for people who have good sight in only one eye to have regular eye tests with an optometrist so that the health of their good eye can be monitored. Your optometrist should let you know how often you need to have your eyes examined.
For people who have sight in only one eye, it may be a good idea to consider the use of protective eyewear or sports goggles for certain sports or activities to help prevent injury to the good eye. You can speak to a dispensing optician at your local opticians practice for more advice about this. Dispensing opticians are qualified in the dispensing and fitting of spectacles and can give professional advice about suitable frames and lenses.
People with monocular vision are still able to drive a private vehicle (Group 1) as long as the vision in their remaining eye is unaffected by other eye conditions, and their good eye is able to achieve the visual requirements for driving. However, monocular vision would mean you couldn't hold a heavy good vehicle (HGV) or public service vehicle (PSV) licence (Group 2). Some professions, such as being a pilot, police officer or certain roles within the Armed Forces require a specific level of vision to be reached in both eyes. Keeping this in mind can help with planning a career choice for the future.
It’s completely natural to be upset when your child has been diagnosed with Coats’ disease and it’s normal to find yourself worrying about the future and how your child will manage with a change in their vision. We’re here to support you every step of the way, and to answer any questions you may have – just get in touch with our Sight Loss Advice Service.