Coats Disease

What is Coats Disease?

Coats disease (also known as exudative retinues) is a rare eye disorder affecting 1 in 100,000 people. Coats disease is associated with the development of abnormal retinal blood vessels. The role of these blood vessels is to send blood and oxygen to the retina. In Coats disease, the blood vessels become tangled and allow a fatty fluid (lipid) to leak into the retina. The fatty build-up gradually disconnects the retina away from the eye, eventually causing blindness.^[1] 

Coats disease is an idiopathic disease, meaning the reason why people develop this condition is still unknown. This condition is 69% more likely to be seen in males. Coats disease usually starts in childhood around the age of 8-16. Although it has the potential to develop later in adolescence.

Coats disease usually presents in one eye. However, if it is diagnosed in both eyes, one eye is likely to be more affected than the other.

Signs and symptoms of Coats disease are often variable in levels of severity. The symptoms gradually become more prominent as the disease progresses. The earlier Coats disease is diagnosed, the likelier it is for it to be treated successfully. 

Among the research community, it is generally agreed that Coats disease is not genetic, but some cases have been linked to a faulty gene. It is thought that Coats disease could be triggered by a deficiency in a protein called Norrin. Further investigation on what causes this disease to manifest has yet to be researched.^[2] 

Patients with Coats Disease generally do not have any other health conditions.

How does Coats Disease affect the eye?

Coats disease is a progressive disease that usually worsens over time.^[3] Fluid buildup leaks into the back of the eye, causing the retina to gradually become disconnected. This means that the connection between the eye and how light is transmitted is damaged. The more fluid that is leaked into the eye, the more profound vision loss is experienced. Coats disease-derived vision loss potentially leads to blindness, although this is rare. Additionally, the younger the child, the more likely Coats disease will progress at a faster rate.^[4]

Signs and Symptoms

Signs and symptoms of Coats disease are often variable in terms of severity, which is dictated by the speed at which the disease progresses.^[5] The majority of diagnoses, however, are not made until later in progression.

Early symptoms^[6]

• Feeling eye pressure/pain behind the eye/s (glaucoma)
• Reduced vision
• Reduced ability to see colours
• Reduced peripheral vision
• Visual acuity
• Leukocoria
• Misalignment of the eyes (strabismus) – eyes not lining up in the same direction, sometimes described as being ‘cross-eyed’
• Yellow eye (leukocoria)
• Lack of depth perception – struggling to judge how close or far away an object is
• Inflammation of the eye
• Reddening of the eye

Later symptoms

• Glaucoma
• Eyeball atrophy
• Cataracts
• Retinal detachment
• Further pain/pressure behind the eyes
• Discoloured iris (usually red)
• Further difficulty of being able to see

Stages of Coats Disease

Stage 1

Only slight changes to your eyesight and feelings of pressure from behind the eyes. This is because the damaged and dilated capillaries (telangiectasia) are beginning to affect the retina and eyesight. In some cases, Coats disease does not progress any further than stage 1 symptoms.

Stage 2

Continued and further loss of vision. Fluids begin to leak behind the eyes (lipid exudate). The retina starts to become detached.

Stage 3

Swelling and inflammation of the eyes are likely. The retina has become more disconnected or completely detached. At this stage, surgery is recommended.

Stage 4

Complete retinal detachment has occurred. Eye surgery can treat and prevent any further problems, although eyesight is likely to remain poor long-term. 

Stage 5

At the final stage of Coats Disease, extreme pain, complete vision loss, cataracts and glaucoma may be seen.^[7]

Diagnosis

Coats disease is usually diagnosed by an ophthalmologist. It is not always easy to diagnose this condition, especially in young children who are not always able to explain and express the discomfort in their eyes (and other symptoms) to their care providers.

One of the first signs of Coats disease is ‘yellow eye’ (similar to red-eye flash). This phenomenon happens when a photo is taken and yellow eye(s) are noticed in the photo.^[8]

Treatment

The treatment of Coats disease depends on what stage it is diagnosed at, and what is best for the patient. The main goal will be to preserve and maintain eyesight as much as possible. Combined treatments are often effective, depending on the individual's stage of the disease.

Laser Surgery (photocoagulation)

Laser treatment is usually the best option in the early stages of the disease. This is used to reduce, or completely take away, any abnormal blood vessels by burning them away.^[9] 

Laser surgery usually works best during the early stages of Coats disease along with cryosurgery and other therapies (see below). This treatment is likely to be performed by an eye doctor under a general anaesthetic.

Cryosurgery

Cryosurgery is used to freeze any faulty blood vessels and also to seal the eye back together. This protects the eyes from any further leakage. Cryosurgery is likely to be performed under a general anaesthetic. Cryosurgery is used for Coats disease at the stages where the retina starts to become more unattached.

Intravitreal Injections

Intravitreal injections (anti-VEGF therapy) is usually used at the more advanced stages of Coats disease when the retina has become more disconnected. The intravitreal fluid is administered into the back of the eye near the retina to help reduce inflammation. 

Surgical Interventions

In the later stages of Coats disease, more invasive interventions, such as eye surgery, may be needed. This aims to repair the retinal detachment and also prevent further leakage. Below are a couple of examples of treatments for the later stage of Coats disease. The main aim at this stage is to prevent any further damage.^[10]

Retinopexy

Retinopexy is a non-invasive therapy that may be considered alongside other treatments. This is where a bubble of gas is injected into the back of the eye to help weld the retina together. You are likely to see flashes of bright lights during the process and it may feel slightly uncomfortable. You may need more than one session to situate the retina in the correct position.

Scleral Buckling

Scleral buckling is a more complex procedure that is usually conducted in the final stages of Coats disease. This is where the surgeon stitches a sponge-like substance into the sclera (the white part of the eye), in hopes of sealing the retina back together permanently. Scleral buckling has a 90% success rate.^[11]

Vitrectomy

Vitrectomy is a surgery that helps to repair a detached retina and to fix it back into place.^[12] This procedure includes taking part or all of the vitreous humour away from the eye and replacing it with a solution of salt water, bubble oil or gas. The surgery usually takes from one to several hours to complete. It is usually done under a local or general anaesthetic.^[13]

Similar or Related Eye Diseases

Here is a list of some eye diseases with similar signs and symptoms to Coats disease:

Coats Plus Syndrome

Unlike Coats disease, Coats Plus Syndrome is an extremely rare inherited disorder that is associated with Coats disease. To be diagnosed with this, you should already have the diagnosis of Coats disease. It is associated with abnormalities of the brain, gastrointestinal disorders, and liver failure. Unlike Coats disease, Coat Plus Syndrome is a life-threatening condition. Unfortunately, the life expectancy of people diagnosed with this disease is expected to be limited to around 30 years.^[14]

Symptoms of Coats Plus Syndrome

• Brain abnormalities: seizures, and a loss in intellectual functioning, including affecting the way you move
• Fluid-filled cysts and abscesses
• Loss of brain tissue (leukodystrophy)
• Low bone density
• Shortage of red blood cells (anaemia)
• Abnormal gastrointestinal bleeding
• Liver failure

Less Common Symptoms

• Prematurely grey hair
• Abnormal skin pigmentation
• Abnormalities in fingernails and toenails

Coats Plus Syndrome has also been associated with another condition called leukoencephalopathy, which presents with similar symptoms but is triggered by different genetic causes.

Retinoblastoma

A retinoblastoma is a form of eye cancer, which exhibits similar symptoms to Coats disease. Retinoblastoma causes similar symptoms in the eyes such as: 

• Inflammation of the eyes
• Eyes not lining up in the same direction (strabismus)
• White colour shows up in the middle of the eye, during flash photography
• Red and puffy eyes
• Eyesight limitations
• Irregular dilation of vessels

In 2015, eye expert Shields JA, MD reported that the difference between Coats disease and retinoblastoma is the presentation of the pupillary reflex. In retinoblastoma, the appearance is more white than yellow, and the vitreous part of the eye appears hazy. Like Coats disease, retinoblastoma is common in children.

Age-related Macular Degeneration

Even though age-related macular degeneration is common and Coats disease is rare, it still presents with a lot of similar signs and symptoms, such as:

• Blurred/reduced eyesight
• Progressive disease
• Cuts off oxygen to the eye
• Fluid leakage in the retina

Turner's Disease

Turner's disease is a disease related to chromosome abnormalities, which genetically affect female individuals. One of its major symptoms is the eyes not lining up correctly (strabimus). This is seen in one-third of its cases. Research has suggested that Coats disease should be considered a rare eye disorder, occasionally linked to Turner syndrome.^[15]

Summary

Coats disease is a progressive disease that is more successfully treated during the early stages. Being aware of any changes in your eyesight or a child's is key to the best possible outcome. If you have any concerns, please see a healthcare provider and attend regular eye tests at your ophthalmologist.