Coats’ disease is a rare, non-hereditary eye disorder characterized by abnormal development of blood vessels in the retina. The retina is the delicate, light-sensing layer of tissue that lines the back of the eye. Its job is to act like the film in a camera or the sensor in a digital camera, capturing light and converting it into neural signals that are sent to the brain.

To function properly, the retina is nourished by a network of tiny blood vessels. In a healthy eye, these vessels are perfectly formed and sealed. In Coats’ disease, some of the retinal blood vessels, particularly the arteries and capillaries, are abnormally dilated, twisted, and weak. These faulty vessels are called telangiectasias.

A helpful analogy is to think of the retina as a delicate, high-tech movie screen at the back of the eye.

• It is nourished by a network of perfectly sealed, microscopic irrigation pipes (the blood vessels).
• In Coats’ disease, it is as if sections of these pipes were manufactured incorrectly. They are weak, bulging, and have tiny leaks.
• These faulty pipes constantly ooze a sticky, fatty, yellowish fluid, called exudate, into and behind the movie screen.
• This leakage makes the screen “waterlogged.” As the fluid and fatty deposits build up, they can cause the retina to blister and lift away from the back wall of the eye. This is a retinal detachment, and it is the primary cause of vision loss in Coats’ disease.

In my experience, Coats disease often presents as sudden vision changes in a child, which understandably alarms parents especially when the condition affects only one eye and progresses without pain.

The exact cause of Coats’ disease is unknown. It is not linked to any specific illness, injury, or environmental exposure during pregnancy. The current leading theory is that most cases of Coats’ disease are caused by a somatic genetic mutation.

• Somatic mutation is a random genetic error that occurs in a single cell after conception.
• This mutation is then passed down to all the cells that descend from that original faulty cell, but it is not present in the other cells of the body.
• In Coats’ disease, a somatic mutation is believed to occur in a gene that is critical for the normal, stable development of retinal blood vessels. One gene that has been implicated is the NDP gene, though this does not account for all cases.
• This “on-the-spot” genetic error is what leads to the formation of the abnormal, leaky vessels in the retina.

Clinically, Coats disease is considered idiopathic meaning the exact cause is unknown but it’s not inherited or linked to infection.

Coats’ disease is a congenital disorder, meaning the predisposition for the blood vessels to develop abnormally is present at birth, even if the signs do not become apparent until later in childhood.

• It is not contagious.
• It is not hereditary in the vast majority of cases. Because it is caused by a somatic mutation that is not present in the parent’s reproductive cells, a parent with Coats’ disease will not pass it on to their children, and the parents of an affected child are not at an increased risk of having another child with the condition.

Demographics and Characteristics

Coats’ disease has a very distinct clinical profile:

• It almost always affects only one eye (unilateral).
• It overwhelmingly affects males more than females, at a ratio of about 3 to 1.
• The diagnosis is typically made in childhood, with the average age of diagnosis being around 8 to 10 years old, although it can be diagnosed in infants and, more rarely, in adults.

In my experience, I’ve had to reassure families that it’s not due to anything they did or didn’t do, it’s a spontaneous condition involving malformed retinal vessels.

In the very early stages, Coats’ disease often causes no symptoms, and a child is completely unaware of any problem with their vision. The disease is often first detected during a routine vision screening at school or when a parent notices an abnormality.

The two most common presenting signs are:

• Leukocoria: This is a term for an abnormal white or yellowish glow from the pupil. A parent often notices it first in a flash photograph. Instead of the usual “red eye” reflex, the pupil of the affected eye may appear white or yellow. Any child with leukocoria requires an immediate and urgent examination by an ophthalmologist.
• Strabismus: A misalignment of the eyes, often called a “lazy eye.” The affected eye may turn inward or, more commonly, outward. This often occurs because the brain is starting to ignore the blurry, distorted image coming from the eye with the diseased retina.

As the leakage and retinal detachment progress, other symptoms will develop in the affected eye:

• Decreased vision, which can be gradual or sudden.
• Loss of depth perception.
• In very advanced and untreated stages, the eye can become painful, red, and blind due to complications like neovascular glaucoma (very high pressure in the eye) or cataracts.

Clinically, I look for signs like reduced visual acuity, strabismus (eye misalignment), or a retinal detachment on a fundoscopic exam, sometimes mimicking retinoblastoma in early stages.

If a parent or pediatrician suspects a problem, they will refer the child to a pediatric ophthalmologist or a retinal specialist for a comprehensive evaluation.

The Critical Differential Diagnosis: Retinoblastoma

The number one priority during the diagnostic workup is to definitively differentiate Coats’ disease from retinoblastoma. Retinoblastoma is a life-threatening childhood eye cancer that can also present with leukocoria and strabismus. While retinoblastoma is a cancer and Coats’ disease is a benign vascular condition, their appearance can sometimes be similar.

The diagnostic process includes:

1. Dilated Fundus Examination: This is the key to diagnosis. The ophthalmologist will use special eye drops to dilate the pupil. This allows them to use a magnifying instrument called an indirect ophthalmoscope to get a clear, panoramic view of the entire retina at the back of the eye. The doctor will look for the classic signs of Coats’ disease: the abnormal, twisted blood vessels (telangiectasias) and the characteristic yellow, waxy lipid exudates.
2. Ocular Ultrasound (B-scan): This is a simple, non-invasive ultrasound of the eye. It is crucial for differentiating Coats’ from retinoblastoma. In retinoblastoma, calcium deposits within the tumor are almost always present and are easily seen on an ultrasound. In Coats’ disease, there is no calcification.
3. Fluorescein Angiography: This is a specialized photographic test that provides a detailed map of the retinal blood vessels. A harmless vegetable-based dye (fluorescein) is injected into a vein in the arm. As the dye circulates through the eye, a special camera takes a rapid series of photographs. This test will clearly highlight the specific “light-bulb” shape of the abnormal vessels and will show exactly where they are leaking fluid.
4. Optical Coherence Tomography (OCT): This is a non-invasive scan that provides a high-resolution, cross-sectional image of the retina, allowing the doctor to see the fluid and exudates under the retina.
5. CT or MRI Scan: These imaging studies of the eye and brain may be performed if the diagnosis is still uncertain after the initial examination.

In my experience, differentiating Coats disease from retinoblastoma is critical, especially in younger patients, sometimes requiring an ocular oncologist’s input.

There is no treatment to “cure” the underlying genetic defect that causes the blood vessels in Coats’ disease to be abnormal. The goal of treatment is to stop the leakage from these faulty vessels to preserve as much vision as possible, resolve any retinal detachment, and prevent the progression to blindness and a painful eye.

Treatment is dependent on the stage and severity of the disease.

1. Observation

For very mild, peripheral cases of Coats’ disease that are not progressing and are not affecting the central vision, a doctor may recommend a period of careful observation with regular follow-up exams.

2. Ablative Therapy

This is the mainstay of treatment for active, leaking Coats’ disease. The goal is to “ablate” or destroy the abnormal, leaky blood vessels to create a scar that seals the leak.

• Laser Photocoagulation: A high-energy laser beam is focused directly onto the abnormal vessels to create tiny burns, which effectively cauterizes and closes them.
• Cryotherapy: A freezing probe is applied to the outside of the eyeball (the sclera) over the area of the abnormal vessels. Extreme cold destroys leaky vessels. This technique is often used for vessels that are located in the far periphery of the retina where a laser cannot easily reach.

3. Anti-VEGF Injections

In recent years, injections of medications that block a chemical called Vascular Endothelial Growth Factor (VEGF) have been used as an adjunct treatment. These drugs, like bevacizumab, are injected directly into the eye and can help reduce fluid leakage and swelling.

4. Surgery for Advanced Disease

If the disease has progressed to a total retinal detachment, more complex surgery performed by a vitreoretinal surgeon is required.

• Vitrectomy: The surgeon removes vitreous gel from the eye.
• Scleral Buckle: A silicone band is often placed around the eye to support the retina.
• During the surgery, the surgeon will drain the fluid from under the retina and use laser or cryotherapy to treat the abnormal vessels.
• While surgery can be successful at reattaching the retina, the visual prognosis for eyes with advanced, chronic detachments is often poor.

5. Enucleation (Eye Removal)

In the very end-stage of the disease, if the eye is blind, painful due to high pressure (neovascular glaucoma), and has a poor cosmetic appearance, the removal of the eye may be recommended to relieve the patient’s pain. This is a last resort for the most severe, untreated cases.

Clinically, I monitor closely for recurrence, especially in children, regular follow-up is essential even after initial treatment, as the disease can re-activate.

Coats’ disease is a rare, non-hereditary childhood eye disorder that causes the development of leaky blood vessels in the retina. While the diagnosis can be frightening for parents, it is important to remember that it is not cancer and does not affect the child’s general health. The most critical first step is a prompt and thorough evaluation by an ophthalmologist for any child who develops a “lazy eye” or a white or yellow reflex in their pupil. This is essential to rule out the more dangerous condition of retinoblastoma. While there is no cure for Coats’ disease, treatment is aimed at saving sight. Clinically, I’ve found that parental awareness and routine eye exams in childhood make a real difference in detecting conditions like Coats disease early enough for effective treatment.

American Academy of Ophthalmology (AAO). (2023). What is Coats’ Disease? Retrieved from https://www.aao.org/eye-health/diseases/what-is-coats-disease

National Organization for Rare Disorders (NORD). (2021). Coats Disease. Retrieved from https://rarediseases.org/rare-diseases/coats-disease/

National Institutes of Health, Genetic and Rare Diseases Information Center (GARD). (2021). Coats disease. Retrieved from https://rarediseases.info.nih.gov/diseases/6112/coats-disease