Coats disease is a rare, non-inherited eye disorder involving the abnormal development of blood vessels in the retina. Classified as an idiopathic retinal vascular disorder, its cause is unknown. Coats disease primarily affects young males and is typically diagnosed in childhood or adolescence, often before age 10. The condition usually affects only one eye, making it a unilateral disorder. It is characterized by leaky vessels, which can lead to vision loss and, in severe cases, blindness.
The Underlying Pathology
The core mechanism involves a defect in the retinal blood vessels, known as retinal telangiectasia. This condition is characterized by the malformation and dilation of small retinal capillaries, which can resemble tiny aneurysms. These abnormal, fragile vessels become highly permeable and begin to leak fluid, proteins, and lipids.
This leakage, called exudation, causes the retina to swell and separate from the underlying tissue. This separation is termed exudative retinal detachment and is a serious complication of the disease.
The progressive buildup of fluid and cholesterol-rich deposits beneath the retina leads to the yellow appearance seen in advanced cases. Extensive fluid accumulation can lift the entire retina away from its nutrient supply. The extent of this detachment, especially if it involves the macula, determines the severity of vision loss.
Identifying the Symptoms
Coats disease usually develops without pain in the affected eye. The most common initial sign is unilateral vision loss, which may be gradual and often overlooked, especially in young children who rely on their unaffected eye. This reliance on one eye can also lead to a loss of depth perception.
A more noticeable symptom is leukocoria, a white or yellowish reflection in the pupil. Often called a “cat’s eye reflex,” this is caused by light reflecting off the subretinal exudate or the detached retina. Leukocoria requires immediate investigation by a specialist to differentiate Coats disease from other serious conditions.
Another secondary sign is strabismus, or eye misalignment, where the affected eye may wander inward or outward. This can occur because the affected eye has poor vision and cannot maintain proper alignment with the healthy eye. While symptoms manifest in childhood, the condition is progressive for most patients.
Diagnosis and Staging
Diagnosis of Coats disease begins with a comprehensive eye examination by an ophthalmologist, including indirect ophthalmoscopy. The doctor dilates the pupil to get a detailed view of the retina, looking for abnormal, dilated blood vessels and lipid deposits. The presence of these telangiectatic vessels and associated exudation is usually sufficient for a clinical diagnosis.
To confirm the diagnosis and map the extent of vascular abnormalities, fluorescein angiography (FA) is frequently used. A fluorescent dye is injected into the bloodstream, allowing the doctor to photograph the retina as the dye travels through the vessels. This clearly highlights the leaky vessels and areas of non-perfusion where blood supply is absent.
Ultrasound imaging is also an important tool, particularly in advanced stages. It can detect the degree of retinal detachment when the retina is obscured by dense exudates. Following these diagnostic procedures, the disease is typically assigned a stage to guide treatment and prognosis. The Shields classification system categorizes the disease from Stage 1 (abnormal vessels only) up to Stage 5 (total retinal detachment and vision loss).
Treatment and Visual Outcomes
The primary goal of treating Coats disease is to destroy the abnormal, leaky blood vessels to stop exudation and prevent further retinal detachment. For early to moderate stages, the most common treatments are laser photocoagulation and cryotherapy. Laser photocoagulation uses heat to seal telangiectatic vessels located centrally in the retina.
Cryotherapy involves applying intense cold to the outer surface of the eye to destroy abnormal vessels in the peripheral retina. These treatments aim to cause the exudate to reabsorb, which can lead to retinal reattachment and preservation of remaining vision. Multiple treatment sessions are often required to achieve complete closure of all abnormal vessels.
For advanced stages involving extensive or total retinal detachment, complex surgical interventions may be necessary. These include vitrectomy (removing the vitreous gel to access the retina directly) and scleral buckling (a procedure used to push the eye wall closer to the detached retina).
Visual outcomes depend heavily on the stage of diagnosis and treatment. Early detection provides the best chance for maintaining usable vision, especially if the central macula is unaffected by the exudate. In severe, late-stage cases where the eye is blind and painful, enucleation (surgical removal of the eye) may be considered.