Coats Disease: An Overview

George Riding

Coats disease is a rare unilateral idiopathic retinal vascular disorder of childhood characterised by abnormal retinal telangiectasia and progressive intraretinal and subretinal exudation (1–3). Coats disease may clinically mimic retinoblastoma and can progress to exudative retinal detachment, neovascular glaucoma, and phthisis bulbi (2, 5). An understanding and recognition of Coats disease is essential for all trainee and aspiring ophthalmologists.

This overview aims to provide a concise introduction to the aetiology, diagnosis, classification and management of Coats disease.  

Aetiology

Coats disease pathogenesis involves the breakdown of the blood-retinal barrier through the loss of pericytes and endothelial cells at the vascular endothelium, resulting in vascular leakage, exudation and areas of hypoperfusion (2).

Coats disease or Coats “response” has historically been used inconsistently to describe a broad range of exudative vitreopathies (3, 5). The term Coats-like phenotype is now preferred to describe conditions with similar exudative retinopathy and sequelae, including Coats plus syndrome, Leber miliary aneurysm, and bilateral or familial cases, which are not considered true Coats disease (2).

Coats disease is classically sporadic and non-hereditary, and molecular genetic screening is therefore generally reserved for syndromic or bilateral presentations, which are more likely to represent Coats-like phenotypes with an underlying genetic basis (2).

Epidemiology 

The incidence of Coats disease in the UK is approximately 0.09 per 100,000 (6). Coats disease typically affects young males and is most commonly diagnosed in the first or second decades of life, with a reported median age at diagnosis of 5–6 years (range 1 month to 63 years) and a male predominance of 76%–84% across case series (3–5). Coats disease can present in later adulthood, where it is typically diagnosed at an earlier stage and is less advanced (7). 

Clinical Features 

The most common presenting symptoms include gradually worsening unilateral visual acuity, strabismus, and xanthocoria – a yellow-orange hued pupil secondary to underlying telangiectatic vessels and lipid-rich exudation – which may be mistaken for the grey-white leukocoria associated with retinoblastoma (3).  Although patients with early–stage disease may be asymptomatic and diagnosed incidentally, most referred patients have significant visual impairment, with 76% having visual acuity of 20/200 or worse at presentation in a case series (3).

Indirect ophthalmoscopic fundus examination findings are stage dependent. The hallmark of Coats disease is telangiectasia with fusiform “lightbulb” aneurysms, named to reflect the bulging vessels surrounded by yellow exudate, most commonly found in the peripheral retina with a temporal and inferior predilection (3). With advancing disease, intraretinal and subretinal exudation may migrate towards the macula, whilst fibroglial subfoveal nodules, exudative retinal detachment, and retinal haemorrhage may develop (2). Retinal macrocysts, vitreous haemorrhage and vasoproliferative tumours may arise in longstanding detachments (2). In advanced disease, rubeosis iridis may occur, with neovascular glaucoma a late-stage complication(5).

Patients with Coats disease are frequently referred for investigation of retinoblastoma, owing to shared presenting features of leukocoria in young children and possibility of retinal detachment (3). Table 1 highlights key features to differentiate Coats disease from retinoblastoma, with accurate diagnosis reliant on specialist clinical assessment and interpretation of imaging (2, 8). Other important differential diagnoses in children with leukocoria include stage V retinopathy of prematurity, persistent fetal vasculature, toxocariasis, familial exudative vitreoretinopathy, endophthalmitis and others (2–5).

 Coats diseaseRetinoblastoma
PresentationUnilateral; Male predominanceUnilateral or bilateral
Fundus reflexXanthocoriaLeukocoria
TelangiectasiaHallmark lightbulb telangiectasia; can be tracedDip into mass
Vitreous SeedingAbsentCan be present
CalcificationAbsentPresent on CT and US
MassSub-retinal clump exudatesLesion can be throughout and obscures vessels

Investigations 

The mainstay of imaging in Coats disease is fundus fluorescein angiography (FFA), which is used to identify leaking anomalous vessels and delineate the extent and location of telangiectasia (2). FFA typically demonstrates hyperfluorescence of the telangiectatic vessels in the venous phase, areas of capillary non-perfusion, dye leakage from abnormal vessels, and hypofluorescence along areas of exudation (8).  FFA can also demonstrate “lightbulb” aneurysms, cystoid macular oedema and optic disc or iris neovascularisation (8).

Optical coherence tomography can aid in the identification of macular oedema, vitreomacular traction, intraretinal and subretinal fluid, epiretinal membrane and subfoveal nodules (8). B-Scan ultrasonography can detect subretinal exudation and exudative retinal detachment, and is utilised to exclude an intraocular mass or calcification, as seen in retinoblastoma (9). Cross-sectional imaging with CT or MRI scan may be utilised to rule out retinoblastoma. CT typically demonstrates intraocular calcification with retinoblastoma, whilst MRI demonstrates characteristic differences in T1- and T2-weighted signal intensity that aid differentiation from Coats disease (2, 9).

Classification 

Multiple classification systems have been proposed with considerable overlap, although the classification system proposed by Shields et al. (4) is most widely adopted and preferred by experts (2) (Table 1). Of note, Daruich et al. (10) proposed splitting Stage 2B into Stage 2B1 (without subfoveal nodule) and Stage 2B2 (with subfoveal nodule), as the presence of a subfoveal nodule is a strong predictor of subsequent macular fibrosis and poor visual acuity.

StageFundus features
1Retinal telangiectasia only 
2Telangiectasia with exudation 
2AExtrafoveal exudation 
2BFoveal exudation 
3Exudative retinal detachment 
3ASubtotal detachment
3A1Subtotal, extrafoveal
3A2Subtotal, foveal
3BTotal retinal detachment 
4Total retinal detachment with glaucoma 
5Advanced end-stage disease e.g. phthisis, no light perception

Management 

Management strategies aim to prevent disease progression by ablating telangiectatic vessels, resolving the intra and sub-retinal exudation, with outcomes more favourable when treatment is initiated at earlier stages (4, 5). Table 3 demonstrates the preferred modalities of treatment highlighted by Ghorbanian et al. (11) and adapted by Sen et al. (5).

StageTreatment
Stage 1, 2Laser photocoagulation or cryotherapy
Stage 3Laser photocoagulation or cryotherapy; external drainage of total retinal detachment considered
Stage 4External drainage of total retinal detachment, vitreoretinal surgery, or glaucoma surgery considered
Stage 5 asymptomaticObservation
Stage 5 symptomaticEnucleation
Adjuvant therapyAnti-VEGF, intravitreal or periocular steroids

Patients with stage 1–2 disease are usually observed if there is little exudation and no threat to vision (12).If disease progresses but remains stages 1 – 3A, laser photocoagulation or cryotherapy can be used to cauterise defective vessels (13). Laser photocoagulation is preferred over cryotherapy in early stage disease as it provides direct coagulation to problematic leaking vessels whilst being less invasive (13, 14). Cryotherapy tends to be used to treat peripheral vascular malformations or stage 3A and 3B disease as it is effective at producing burns in the detached retina (2, 14).

Vitreoretinal surgery techniques such as pars plana vitrectomy, scleral buckling, drainage of subretinal fluid and silicone oil injection may be required in retinal detachment cases (2, 14). Enucleation is carried out in cases of a painful, blind eye whereas a painless blind eye can be monitored (4, 15).

Adjuvant therapies may be used to reduce exudation and macular oedema (5). Intravitreal steroids can be used to reduce central retinal thickness and exudates (5). Anti-VEGF medications have also been studied as an adjunctive treatment in Coats disease with favourable findings (16).

References

  1. Coats G. Forms of retinal diseases with massive exudation. Royal London Ophthalmic Hospital Reports. 1908;17:440–525.
  2. Mahesh M, Radke NV, Agrawal R, Balaratnasingam C, Biswas J, Gupta V, Ho M, Kim M, Kumar V, Kusaka S, Lam WC, Lee VYW, Lu H, Munier FL, Rojanaporn D, Tsang CW, Wu WC, Yonekawa Y, Zhao P, Shanmugam MP, Lam DSC. International consensuses and guidelines on diagnosing and managing Coats disease by the Academia Retina Internationalis, the Asia-Pacific Vitreo-retina Society, and the Academy of the Asia-Pacific Professors of Ophthalmology. Am J Ophthalmol. 2025;282:162–86.
  3. Shields JA, Shields CL, Honavar SG, Demirci H. Clinical variations and complications of Coats disease in 150 cases: the 2000 Sanford Gifford Memorial Lecture. Am J Ophthalmol. 2001;131(5):561–71.
  4. Shields CL, Udyaver S, Dalvin LA, Lim LS, Atalay HT, Khoo CTL, Mazloumi M, Shields JA. Coats disease in 351 eyes: analysis of features and outcomes over 45 years at a single center. Indian J Ophthalmol. 2019;67(6):772–83.
  5. Sen M, Shields CL, Honavar SG, Shields JA. Coats disease: an overview of classification, management and outcomes. Indian J Ophthalmol. 2019;67(6):763–71.
  6. Morris B, Foot B, Mulvihill A. A population-based study of Coats disease in the United Kingdom: epidemiology and clinical features at diagnosis. Eye. 2010;24:1797–801.
  7. Daruich A, Matet A, Munier FL. Younger age at presentation in children with Coats disease is associated with more advanced stage and worse visual prognosis: a retrospective study. Retina. 2018;38(11):2239–46.
  8. Shields JA, Shields CL. Differentiation of Coats disease and retinoblastoma. J Pediatr Ophthalmol Strabismus. 2001;38:262–6.
  9. Shields CL, Schoenberg E, Kocher K, Shukla SY, Kaliki S, Shields JA. Lesions simulating retinoblastoma (pseudoretinoblastoma) in 604 cases: results based on age at presentation. Ophthalmology. 2013;120(2):311–6.
  10. Daruich AL, Moulin AP, Tran HV, Matet A, Munier FL. Subfoveal nodule in Coats disease: toward an updated classification predicting visual prognosis. Retina. 2017;37(8):1591–8.
  11. Ghorbanian S, Jaulim A, Chatziralli IP. Diagnosis and treatment of Coats disease: a review of the literature. Ophthalmologica. 2012;227(4):175–82.
  12. Kanski JJ, Bowling B. Clinical Ophthalmology: A Systematic Approach. 8th ed. Edinburgh: Elsevier; 2016.
  13. Shields JA, Shields CL, Honavar SG, Demirci H, Cater J. Classification and management of Coats disease: the 2000 Proctor Lecture. Am J Ophthalmol. 2001;131(5):572–83.
  14. Kusaka S. Surgical Management of Coats Disease. Asia-Pacific Journal of Ophthalmology (Phila). 2018 May-Jun;7(3):156–159. doi:10.22608/APO.201867.
  15. Udyaver S, Dalvin LA, Lim LS, Mazloumi M, Atalay HT, Khoo CTL, Shields JA, Shields CL. Predictors of enucleation in Coats disease: analysis of 259 eyes of 259 patients at a single center. J AAPOS. 2019 Oct;23(5):266.e1-266.e9.
  16. Lin CJ, Hwang JF, Chen YT, Chen SN. Effect of intravitreal bevacizumab in the treatment of Coats disease in children. Retina. 2010;30(4):617–22.

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