Coats’ disease, also known as exudative retinitis, is a rare congenital condition (congenital means that one is born with it), which causes tiny blood vessels called capillaries to develop abnormally in the retina. The capillaries become abnormally dilated and twisted. This interferes with normal blood flow and eventually causes the capillaries to weaken and become leaky.
Coats’ disease is named after Dr. George Coats, who first described the condition in 1908. It generally affects young children—the average age at which symptoms first become noticeable is six to eight, although it is possible for symptoms of Coats’ disease to manifest in patients as young as five months or as old as seventy. About a third of Coats’ disease sufferers are over the age of thirty at the time of diagnosis.
Coats’ disease affects males three times more than females (although the American Academy of Ophthalmology puts the ratio closer to 10:1). In 90 percent of cases the condition is unilateral, meaning that it affects only one eye.
What Are the Causes of Coats’ Disease?
The exact cause of Coats’ disease is not known, but the condition is believed to result from a genetic mutation. Although Coats’ disease is congenital, it is not hereditary.
The symptoms of Coats’ disease result from the abnormal dilation of the blood vessels in the retina, the medical term for which is telangiectasia. (The roots of this word are Greek: tele means end; angio means blood vessel; and ectasia means dilation.)
The telangiectasia of the retinal blood vessels weakens them, causing blood—and proteins and lipids (fatty material) from the blood—to leak into the eye. When this leakage affects the retina, it causes a condition known as exudative retinopathy. This fluid, which is called exudate, builds up on and in the retina, causing swelling and interfering with its function.
What Are the Signs and Symptoms of Coats’ disease?
In its early stages, Coats’ disease tends to affect peripheral vision. The affected person will begin to experience blurred vision.
The appearance of the affected eye in flash photography can also be an early warning sign suggesting Coats’ disease. Indoor flash photography often produces a familiar effect commonly known as “red-eye”; this effect is caused by the reflection of the flash off the retina. If Coats’ disease is present, however, the affected eye will appear to glow yellow or white rather than red. This effect is caused by the reflection of the flash off the cholesterol deposits that have formed on the retina due to the leakage of lipids.
Eventually the buildup of cholesterol deposits that causes the photographic “yellow-eye” phenomenon will become visible to the naked eye as leukocoria, a strange white reflection from the retina (leukocoria can also be a sign of retinoblastoma—a dangerous, life-threatening tumor in the eye).
As Coats’ disease progresses, eye flashes and eye floaters may also begin to appear in the affected person’s vision. Cataracts, a condition in which the lens of the eye becomes cloudy, may also form. The gradual buildup of pressure within the eye can cause pain if the fluid does not drain properly, and can result in glaucoma.
A person affected by advanced Coats’ disease may also develop strabismus (an inward or outward turn in the affected eye), since only the unaffected eye is being used to see properly.
Finally, the abnormal growth of blood vessels in the iris—the colored part of the eye—may cause the iris to become discolored and take on a reddish appearance. This is called rubeosis iridis.
The Stages of Coats’ disease
Coats’ disease progresses in stages, and the signs and symptoms of the disease tend to track those stages:
Stage 1: Telangiectasia. At this early stage of Coats’ disease, the patient has not yet experienced any symptoms. A retinal examination conducted by an eye doctor will reveal abnormally twisted and dilated blood vessels in the retina, but the blood vessels are all intact and have not leaked.
Stage 2: Exudation. This is the stage at which the dilated and stressed blood vessels begin to weaken, and blood and other fluids begin to leak into the retina.
At stage 2, the degree to which the leakage of blood and lipids into the retina affects vision will depend on how aggressive the disease is and how quickly the leakage begins to develop. Vision may remain normal for much of this stage if the leakage is not severe. As the condition approaches its third stage, however, the leakage will begin to affect the center of the retina, and vision loss will become more pronounced.
Stage 3: Retinal Detachment. At this stage the buildup of intraocular pressure (eye pressure) will cause the retina to detach and begin to peel away from the back of the eye. Retinal detachment is a sight-threatening condition and a medical emergency. At this point, failure to seek immediate medical attention can result in permanent vision loss or blindness.
Stage 4: Total Retinal Detachment Accompanied by Glaucoma. At this stage the retinal detachment that began during stage 3 has become quite severe, and the affected person’s loss of vision is nearly total. Glaucoma—damage to the optic nerve due to elevated eye pressure—occurs at this stage. (As a matter of definition, it is the presence of glaucoma in addition to severe retinal detachment that distinguishes stage 4 from stage 3.)
Stage 5: End-Stage Coats’ disease. At this stage the affected eye is blind, and sight has been irretrievably lost. At stage 5, many sufferers will experience phthisis bulbi—a shrinking of the affected eyeball.
Other Conditions that Can Be Caused by Coats’ Disease
As noted above, secondary conditions resulting from Coats’ disease include retinal detachment, cataracts, glaucoma, and strabismus. Amblyopia (a condition in which the eyes and brain fail to work properly together) and uveitis (eye inflammation) are also common secondary conditions.
Diagnosis of Coats’ disease
Unfortunately, diagnosis of Coats’ disease is often not made until the condition has advanced at least to stage 2, and in young children the disease tends to be very aggressive. Children often adapt easily to reduced visual acuity, and may not realize that anything is wrong with their vision.
Diagnosis is often made only after the child performs poorly in vision tests conducted at school. (This is why it is essential for all parents to bring their children in for an eye exam before the age of 4 even if no symptoms or signs are apparent.)
Coats’ disease is diagnosed through a combination of careful ophthalmic examination, careful study of the patient’s medical history, and a number of testing methods, including CT scans and a procedure called a fluorescein angiogram. This procedure involves injecting a fluorescent dye into the patient’s arm. This dye travels through the patient’s blood stream, and when it reaches the eye a series of photographs are taken that enable the ophthalmologist to see whether any of the blood vessels in the eye are leaking.
Ultrasound can also be used to detect calcium, which would point to a diagnosis of retinoblastoma rather than Coats’ disease.
Treatment of Coats’ disease
Early-stage treatment of Coats’ disease may involve using either laser treatment or cryotherapy (freezing), either to destroy the abnormal blood vessels or to constrict them and stop the fluid leakage. If the leaky vessels are close to the optic nerve, however, this approach is not recommended, as it runs the risk of damaging the nerve.
Other procedures that may be necessary for a patient suffering from Coats’ disease include vitrectomy (removal of some of the vitreous humor, the gel that fills the eyeball), or surgery to repair a detached retina.
Prognosis for Coats’ disease
The prognosis for Coats’ disease depends on a number of different factors, including how early the condition is diagnosed and how quickly it develops—i.e., how aggressive it is. Coats’ disease tends to be less aggressive when it is detected in older children or in young adults.
Patients who have been treated for Coats’ disease will need to be monitored for recurrence, and may need additional treatment for amblyopia. This happens because even after treatment, Coats’ disease patients tend to have poor vision in the affected eye. Amblyopia may be treated with corrective lenses or an eye patch.
Although Coats’ disease tends to result in blindness, some cases spontaneously halt without treatment. This remission is sometimes only temporary, but in some cases it is permanent. There have even been documented cases in which the condition has reversed itself.
Once Coats’ disease reaches stage 4, however, blindness is a likely outcome, and it is permanent in most cases. In about 25 percent of cases, enucleation (removal of the eye) is necessary at stage 5 to relieve pain or to prevent further complications.
What Is Coats Plus Syndrome?
There is another condition, even more rare than Coats’ disease, known as Coats’ Plus syndrome. Like Coats’ disease, Coats Plus syndrome is genetic. In addition to having all the symptoms of Coats’ disease, however, people affected by Coats Plus syndrome also suffer brain abnormalities:
- Abnormal calcium deposits in the brain
- Fluid-filled brain cysts
- Leukodystrophy, the loss of a type of brain tissue called white matter
These abnormalities gradually become worse, causing seizures, problems with motor control, and a loss of cognitive function. Coats Plus syndrome also causes low bone density and anemia.