Coats’ disease was first described by George Coats in 1908, as unilateral retinal vascular abnormality [1]. It was followed by Leber reporting a different syndrome showing multiple retinal aneurysms, associated with retinal degeneration [2]. In 1955, Reese elaborated on the features described by Coats and Leber and concluded that they were varying presentations of the same disease complex with retinal telangiectasia being the underlying pathology, eventually leading to progressive exudation and retinal detachment [3]. The most noteworthy and assertive account of Coats’ Disease came from Shields et al., in 2000 Sanford Gifford Memorial Lecture, who used strict guidelines to diagnose Coats disease and differentiate from other simulating conditions [4]. Earlier Coats’ Disease was used as an umbrella term to describe an array of exudative retinal vasculopathy. However, the Shields study defined Coats disease as idiopathic retinal telangiectasia with intraretinal and/or subretinal exudation without appreciable retinal or vitreal traction [4]. Retinal telangiectasia was defined as dilated, irregular caliber, small- to medium-sized retinal blood vessels. The term exudative retinopathy was used for yellow exudation in the sensory retina or subretinal space [5].

Coats’ disease typically occurs in young males and is diagnosed in the first or second decades of life. Patients can present with a range of symptoms and signs, with the most common being decreased visual acuity, strabismus, and leukocoria. The three classical features that are pathognomonic of Coats’ are exudative retinal detachment, telangiectatic vessels, and peripheral retinal ischemia. There are various modalities to confirm the clinical suspicion of Coats' disease. Although it is possible to reach to diagnosis from clinical examination alone, in the majority of cases, some form of ancillary testing such as fluorescein angiography, Optical Coherence Tomography(OCT), B-Scan, computerized tomography (CT), and magnetic resonance imaging (MRI) is needed.

A 10-year-old male patient came to the Ophthalmology OPD at Dr. D. Y. Patil Medical College, Hospital & Research Institute, Kolhapur with unilateral gradual painless diminution of vision in the left eye which progressed over years to current visual acuity.

Fig-2: Right eye Fundus is within normal limits.

(image was taken with Optomed Smartscope M5 fundus camera)

Fig-3: Left eye fundus showing aneurysmal dilatation.

Telangiectasia, intraretinal and subretinal exudates involving the macula and lipid deposits.

(images were taken with Optomed Smartscope M5 fundus camera)

Systemic examination: Cardio-vascular, central nervous system, respiratory system, and per abdominal system were all within normal limits.

Because of the substantial and intensifying nature of the disease, laser photocoagulation was scheduled,532 nm laser photocoagulation, using a laser indirect ophthalmoscope delivery system, was performed to the telangiectatic vessels and peripheral capillary non-perfusion areas in the left eye.

A staging classification of Coats disease was put forward by Shields et al. based on their observations. An updated classification has been suggested with stage 2B being subdivided into stage 2B1 without subfoveal nodule and stage 2B2 with subfoveal nodule since the presence of a subfoveal nodule significantly affects the visual outcome.¹⁰

Two pathological processes are known to occur in Coats’ disease [11,12].

• Endothelial level changes of the retinal vasculature cause breakdown of the blood-retinal barrier. Following this, plasma leaks into the vessel wall causing thickening and “sausage-like” shape of vessels.
• Damaged endothelium along with abnormal pericytes leads to bulging of the vessels and the characteristic telangiectasia.

This pathogenic vasculature causes retinal hypoxia and exudation of lipids from these vessels is responsible for retinal detachment, retinal thickening, and retinal cyst formation.

Most commonly seen complications of Coats’ are caused by chronic retinal detachment. Patients may present with a painful blind eye due to neovascular glaucoma as a result of iris and angle neovascularisation. Although there are marked retinal ischemia, retinal neovascularisation is infrequent and so is the occurrence of vitreous and retinal hemorrhage. Retinal macrocysts occur as degenerative changes and are seen often as the duration of retinal detachment increases.

Anterior chamber cholesterolosis is an unusual complication that develops most likely as a result of the migration of cholesterol crystals from the exudates in the subretinal space into the anterior chamber possibly through retinal dialysis [13].

The most important differential diagnosis of Coats’ is retinoblastoma and may often lead to unnecessary enucleation in patients. Other differentials include- Persistent hyperplastic primary vitreous (PHPV), toxocariasis.

Other diseases showing exudative detachment are retinopathy of prematurity, familial exudative retinopathy, and Norrie disease. Some disease entities showing leukocoria include retinal hemorrhage, hemangioblastoma, choroidal hemangioma, coloboma, endophthalmitis, cytomegalovirus retinitis, and toxoplasmosis.

However, contrary to young patients, adult presentation of Coats’ shows stable visual acuity and slower progression, and more local involvement. Young patients with macular involvement with diffuse retinal detachment show poor visual prognosis. Since there is a lacunae in the universal guidelines for the treatment of Coats’ disease, we aimed our therapy towards the telangiectatic vessels and non-perfusion areas. We preferred photocoagulation as the treatment of choice, as the presentation was still timely with the presence of localized exudation and detachment. Other higher modalities for treatment that can be used are Anti VEGF agents with or without argon laser photocoagulation and cryotherapy. The patient was eventually lost to follow up, however, other studies suggest a fair prognosis with such a line of treatment and substantial improvement in visual acuity.

Coats’ is a nonhereditary, sporadic disease presenting with vascular telangiectasia with intraretinal and subretinal exudation with no racial preponderance and systemic associations. The three classical features that are pathognomonic of Coats’ are exudative retinal detachment, telangiectatic vessels, and peripheral retinal ischemia.

The modalities for treatment of Coats disease that can be used are laser photocoagulation, anti-VEGF agents, or a combination of both, cryotherapy, and surgery for retinal detachment. Greater knowledge about the typical features, diagnosing the disease at an early stage, and initiating appropriate treatment can greatly improve the visual outcomes and reduce the rate of enucleation in Coats disease.