Coats disease is an eye disorder characterized by abnormal development of the blood vessels in the retina (retinal telangiectasia). Most people begin showing symptoms in childhood. Early signs and symptoms vary but may include vision loss, "crossed eyes" (strabismus), and a white mass in the pupil behind the lens of the eye (leukocoria). Over time, Coats disease may also lead to retinal detachment, glaucoma, and clouding of the lens of the eye (cataracts). In most cases, only one eye is affected. Coats disease is not inherited and the underlying cause is not known. It has been theorized that some cases may be due to somatic mutations (acquired, not inherited) in the NDP gene. Treatment depends on the symptoms present and may include cryotherapy and laser photocoagulation (alone or in combination), steroids for inflammation, and/or surgery for retinal detachment.

The cause of Coats disease is not currently known. It has been theorized that somatic mutations (acquired, not inherited) in the NDP gene may lead to isolated cases of Coats disease. However, this has not been proven. Coats disease has been reported as one feature of several genetic syndromes. In these cases, the underlying cause of each syndrome may be responsible for Coats disease. When Coats disease occurs with additional abnormalities that affect the brain, bones, gastrointestinal system, and other parts of the body, it is called Coats plus syndrome and is caused by mutations in the CTC1 gene.

The signs and symptoms of Coats disease typically begin at an early age (between ages 6 and 8). The disorder may occur at any age, but the majority of people with Coats disease are diagnosed in the first two decades of life. Some people may have few or no symptoms, while others are very severely affected. The condition is almost always progressive (symptoms get worse over time), although alternating periods of sudden worsening with periods of no apparent progression are common. Early signs and symptoms may include loss of vision, misalignment of the eyes (strabismus), and/or the development of a white mass in the pupil behind the lens of the eye (leukocoria). As the disease progresses, affected people may develop glaucoma, cataracts, reddish discoloration in the iris (rubeosis iridis or neovascular glaucoma), shrinking of the affected eyeball (phthisis bulbi), and/or swelling and irritation of the middle layer of the eye (uveitis). Over time, Coats disease may cause detachment of the retina and substantial loss of vision. When Coats disease occurs with additional abnormalities that affect the brain, bones, gastrointestinal system, and other parts of the body, it is called Coats plus syndrome.

Treatment for Coats disease depends on the severity in each person. The following treatments (used alone or in combination) may be tried:

• Laser photocoagulation (uses a laser to shrink or destroy blood vessels)
• Cryotherapy (a procedure that uses extreme cold to destroy abnormal blood vessels)
• Intravitreal corticosteroid injections to control inflammation
• Anti-vascular endothelial growth factor (anti-VEGF) injections

More advanced disease with extensive retinal detachment may also require surgical interventions such as vitrectomy, scleral buckling to correct a detached retina, and external drainage of fluids.

The prognosis varies in each case. Factors that effect the prognosis include the stage of disease at the time of diagnosis, the age at diagnosis, the rate of disease progression, and the effectiveness of treatment. In some older children and young adults, spontaneous regression (improvement of symptoms) has been reported. Younger children typically have more aggressive disease and often have a total retinal detachment by the time they are diagnosed; these children usually have a poor visual outcome. Some people present with advanced disease which does not benefit from treatment, while others show disease progression despite treatment. While most people respond well to treatment, approximately 25% will become worse and require removal of the eye. An ophthalmologist with knowledge about Coats disease may be able to make a general prediction about the chances of retaining the eye and preserving vision.  The extent of visual impairment varies considerably from person to person. Favorable visual outcomes are more likely to be achieved with early detection and treatment, with combined therapies as needed. Even when treatment is not able to restore sight, it is beneficial in saving the eye.

A diagnosis of Coats disease is often suspected based on the presence of signs and symptoms, and findings on a thorough eye examination. Specialized tests to confirm the diagnosis and rule out other conditions may include retinal fluorescein angiography, diagnostic echography, and in some cases, a CT scan of the orbits, and/or MRI.

Isolated Coats disease is not an inherited condition. Rarely, Coats disease can be a feature of an underlying, inherited genetic syndrome. For example, it is a key feature of a condition called Coats plus syndrome, which is characterized by Coats disease plus abnormalities of the brain, bones, gastrointestinal system, and other parts of the body. Coats plus syndrome is inherited in an autosomal recessive manner.