Coats disease is a rare, non-hereditary eye disorder that affects the retina, the light-sensitive tissue at the back of the eye. It is characterized by the abnormal development of retinal blood vessels, which leads to vision impairment. The disease predominantly affects males, typically presenting in children and young adults. It is almost always unilateral, meaning it affects only one eye. If left untreated, the resulting vision loss can be progressive and severe, making Coats disease a significant cause of monocular vision loss in the pediatric population.
Defining Coats Disease and Its Underlying Pathology
Coats disease is classified as an idiopathic condition, meaning its exact origin is uncertain. The core pathology involves a distinct breakdown of blood vessels within the retina, known as telangiectasia. In this condition, small retinal capillaries become abnormally dilated, twisted, and irregular. These malformed vessels are weak and lose their normal barrier function.
This breakdown causes the vessels to leak fluid and lipids into and under the retinal tissue, a process called exudation. The accumulation of this lipid-rich fluid is toxic to the retina and causes it to swell. If the leakage is persistent and massive, the fluid builds up beneath the retina, resulting in an exudative retinal detachment. This detachment prevents the retina from receiving oxygen and nutrients, leading to progressive and often permanent vision loss in the affected eye.
Research suggests a possible link to a somatic mutation in the NDP gene, which occurs spontaneously in the retinal cells and is not inherited. This gene produces the norrin protein, which is involved in the normal development of retinal blood vessels. A defect in the norrin signaling pathway explains the abnormal vascular growth characteristic of Coats disease and accounts for its non-hereditary, unilateral presentation.
Recognizing the Signs
The signs of Coats disease often become noticeable in childhood, frequently before the age of 10. Because the condition is usually unilateral, a child may not complain of vision problems as the unaffected eye compensates, making observation by a parent or doctor important. One of the most common presenting signs is leukocoria, which is a white or yellowish reflection in the pupil instead of the normal red reflex. This white pupil, sometimes noticed in flash photography, is caused by the reflection off the exudates or the detached retina.
Another frequent sign is strabismus, or the misalignment of the eyes, which can occur when the affected eye has lost significant vision. Older children and adults may instead notice a progressive blurring or deterioration of vision in one eye. As the disease advances, symptoms can include pain or redness if the internal eye pressure rises due to secondary complications like glaucoma. Recognizing these early signs is important because prompt intervention can significantly alter the visual outcome.
Diagnosis and Staging
Diagnosis begins with a comprehensive eye examination, requiring the pupil to be fully dilated for a clear view of the retina. The ophthalmologist looks for characteristic telangiectatic vessels, yellow lipid exudates, and evidence of retinal detachment. Specialized imaging tests confirm the diagnosis, determine the disease extent, and differentiate it from serious conditions like retinoblastoma.
The most informative diagnostic tool is fluorescein angiography (FA). A fluorescent dye is injected into a vein and tracked as it flows through the retinal blood vessels. This technique clearly highlights the abnormal, leaky vessels and telangiectasias, confirming the diagnosis and identifying areas requiring treatment. Once diagnosed, the disease is classified using the standardized Shields staging system, which uses five stages to categorize severity.
The Shields system categorizes severity into five stages, which directly guides the choice of treatment and helps predict the visual prognosis.
- Stage 1: Mildest stage, showing only telangiectasias without leakage.
- Stage 2: Telangiectasias with exudation, sub-classified based on fovea involvement.
- Stage 3: Exudative retinal detachment (subtotal or total).
- Stage 4: Total retinal detachment along with secondary glaucoma.
- Stage 5: Advanced end-stage disease and potential blindness.
Treatment Approaches
The primary objective of treatment for Coats disease is to destroy the abnormal, leaky blood vessels and prevent further exudation and retinal detachment. For less severe cases, specifically Stages 2A or less, the intervention of choice is laser photocoagulation. This procedure uses a focused thermal laser to obliterate the telangiectatic vessels and aneurysms, stopping the leakage of fluid and lipids. The treatment is often guided by fluorescein angiography to ensure all affected areas are treated, and the use of yellow-spectrum laser wavelengths is sometimes preferred.
Cryotherapy, or freezing the affected area, is another intervention used, particularly for peripheral vessels that are difficult to reach with a laser or in cases where there is already significant subretinal fluid. The freezing causes inflammation and scarring, which destroys the abnormal vessels and promotes the reabsorption of the fluid.
For advanced cases, specifically Stages 3 and higher with total retinal detachment, surgical options become necessary. Procedures like pars plana vitrectomy are performed to drain the subretinal fluid and reattach the retina. In these complex cases, the surgeon may also use endolaser photocoagulation during the surgery to treat the vessels directly. In the most advanced, end-stage disease (Stage 5), where the eye is blind and painful due to complications like neovascular glaucoma, the removal of the eye, known as enucleation, may be required to alleviate pain.