Coats' Disease

Coats' disease is a rare, idiopathic, typically unilateral retinal vascular disorder characterised by abnormal telangiectatic and aneurysmal retinal blood vessels with progressive intraretinal and subretinal exudation of cholesterol-rich lipid. First described by George Coats in 1908, it affects predominantly young males in the first two decades of life, though adult-onset forms exist. The hallmark is massive accumulation of yellow lipid beneath and within the retina, ultimately producing exudative retinal detachment and severe, often irreversible, vision loss if left untreated.

Unlike retinoblastoma — which it may closely mimic clinically — Coats' disease is non-hereditary, non-neoplastic, and not associated with systemic malignancy. The condition is overwhelmingly unilateral (approximately 90–95% of cases) with a strong male predominance (male-to-female ratio approximately 3:1 to 5:1). Annual incidence is estimated at approximately 0.09 per 100,000 individuals. Most cases present in childhood, with a median age of around 5 years, but adult-onset Coats' disease — typically more indolent — also occurs.

Early detection and appropriate ablative treatment (laser photocoagulation or cryotherapy) can stabilise the disease and preserve vision, particularly in Shields Stage 1–2 disease. Advanced disease with total exudative retinal detachment (Stage 3B–5) carries a guarded to poor visual prognosis despite intervention, and globe-preservation rather than functional vision becomes the primary goal. Optometrists play a critical role in detecting leukocoria and other early signs and initiating urgent ophthalmology referral.

The aetiology of Coats' disease is incompletely understood. The vast majority of cases are considered idiopathic and sporadic, with no consistent germline mutation identified in isolated Coats' disease.

Somatic NDP Gene Mutation

Black et al. (1999) identified somatic mutations in the NDP gene — encoding norrin, a cystine-knot growth factor critical for retinal vascular development via the Wnt/β-catenin pathway — in a subset of Coats' disease cases. These somatic (non-heritable) mutations are restricted to ocular tissue. Norrin is essential for the development and maintenance of retinal capillaries; disruption leads to abnormal retinal angiogenesis, telangiectatic vessel formation, and blood-retinal barrier incompetence. This distinguishes somatic NDP mutation from germline NDP mutation, the latter causing X-linked Norrie disease with severe bilateral retinal dysplasia.

Vascular Endothelial Dysfunction

Primary breakdown of the inner blood-retinal barrier at the level of retinal vascular endothelium is central to disease pathogenesis. Defective tight junctions between endothelial cells — resulting from developmental dysgenesis of the retinal vasculature — permit passive transudation of lipoprotein-rich plasma into the retinal parenchyma and subretinal space. Elevated concentrations of vascular endothelial growth factor (VEGF) are found in the aqueous humour and subretinal fluid of affected eyes, implicating angiogenic dysregulation in the chronic cycle of vascular leakage and ischaemia.

Associated Conditions

Bilateral or atypical Coats' disease should prompt evaluation for the following:

• Facioscapulohumeral muscular dystrophy (FSHD): Coats-like exudative retinopathy in up to 60% of severe early-onset FSHD; caused by DUX4 expression from D4Z4 repeat contraction
• Coats' Plus syndrome (CTC1 mutation): bilateral Coats-like retinopathy with intracranial calcifications, leukoencephalopathy, bone marrow failure, and gastrointestinal telangiectasia
• Turner syndrome (45,X): bilateral Coats-like exudation described; mechanism uncertain
• Senior-Løken syndrome: nephronophthisis with retinal dystrophy and Coats-like features
• Norrie disease (germline NDP): distinct from Coats' disease; bilateral; severe; associated with hearing loss and intellectual disability
• Parry-Romberg syndrome: ipsilateral Coats-like exudation in a minority of cases

1. Primary Retinal Vascular Dysgenesis

The initiating event is a developmental abnormality of retinal vasculature. Telangiectatic, saccular, and fusiform aneurysmal dilatations arise from structurally abnormal retinal capillaries and larger vessels, predominantly in the temporal periphery. These vessels lack competent endothelial tight junctions, rendering them constitutively leaky.

2. Inner Blood-Retinal Barrier Breakdown

Defective endothelial junctions permit the passive transudation of plasma and lipoprotein-rich fluid across the vessel wall — constituting a breakdown of the inner blood-retinal barrier (iBRB). Leaked fluid accumulates first within the retinal layers (intraretinal oedema and exudate) and then in the subretinal space (subretinal exudate), separating the sensory retina from the retinal pigment epithelium (RPE).

3. Lipid and Cholesterol Accumulation

Extravasated plasma undergoes concentration within the retinal outer nuclear and outer plexiform layers, depositing lipid and cholesterol — forming the characteristic yellow hard exudates seen clinically. In the subretinal space, accumulated cholesterol crystals, lipid-laden macrophages (foam cells), and erythrocytes form a viscous, cream-coloured exudate. This lipid accumulation is toxic to photoreceptors and RPE cells, accelerating irreversible retinal degeneration.

4. VEGF Upregulation and Self-Amplifying Cycle

Retinal ischaemia distal to telangiectatic and non-perfused vessel segments upregulates VEGF, which further increases vascular permeability and promotes additional leakage — creating a self-reinforcing cycle. VEGF also drives iris neovascularisation (rubeosis iridis) and disc/retinal neovascularisation in advanced disease, precipitating neovascular glaucoma.

5. Progressive Exudative Retinal Detachment

Accumulation of subretinal fluid causes progressive, bullous, serous (exudative) retinal detachment — without retinal break or vitreoretinal traction. In Stage 3 disease, the detachment may become subtotal or total, with the retina folded in a funnel-shaped configuration. Chronically detached photoreceptors undergo irreversible atrophy and degeneration. Subretinal macrophages phagocytose extravasated lipid and cholesterol, leading to foam cell accumulation.

6. End-Stage Disease

In Stage 4–5 disease, total retinal detachment, neovascular glaucoma, hyphaema, and anterior segment ischaemia ensue. Anterior migration of subretinal cholesterol can enter the anterior chamber, simulating mass lesions. Chronic inflammation from lipid extravasation may produce a uveitic picture. Ultimately, untreated or refractory disease progresses to phthisis bulbi.

Demographic Factors

• Male sex: approximately 75% of cases occur in males; male-to-female ratio ranges from 3:1 to 5:1 across published series
• Young age: peak onset in the first decade; median age at presentation approximately 5 years in childhood-onset disease; adult-onset is less aggressive but not uncommon
• Unilateral involvement: bilateral disease is rare (<5–10%) and strongly suggests an underlying systemic condition (FSHD, Coats' Plus, Turner syndrome, Senior-Løken syndrome)
• Race: no consistent racial predilection reported; global distribution

Systemic Conditions Associated with Coats-Like Retinopathy

• Facioscapulohumeral muscular dystrophy (FSHD): Coats-like exudative retinopathy in up to 60% of severe FSHD; bilateral; correlates with D4Z4 repeat contraction severity
• Turner syndrome (45,X): bilateral Coats-like exudation reported; chromosomal aneuploidy may predispose to retinal vascular dysgenesis
• Senior-Løken syndrome: nephronophthisis with retinal involvement; Coats-like retinal findings in a subset
• Coats' Plus syndrome (CTC1 gene mutation): bilateral retinopathy with multisystem involvement; telomere maintenance defect
• Norrie disease (germline NDP mutation): bilateral; distinct from Coats' disease but sharing NDP pathway dysregulation

Prognostic Risk Factors for Worse Outcomes

• Age <4 years at diagnosis (more aggressive disease course)
• Advanced stage (3B–5) at presentation
• Foveal exudate involvement (Stage 2B onward)
• Total retinal detachment
• Rubeosis iridis at presentation
• Delayed diagnosis or treatment
• Massive subretinal exudate volume

Anterior Segment Signs

• Leukocoria: white or yellow-white pupillary reflex from subretinal cholesterol-laden exudate reflecting behind the lens; the most common presenting sign in children and the most important sign to detect and act on urgently
• Strabismus: typically exotropia secondary to unilateral visual deprivation and poor fixation in the affected eye
• Rubeosis iridis: iris neovascularisation in Stage 4 disease, driven by VEGF from retinal ischaemia
• Elevated IOP: secondary to neovascular angle closure in Stage 4
• Anterior chamber cholesterol: rare; anterior migration of subretinal cholesterol can produce crystalline deposits or simulate mass in the anterior chamber
• Hyphaema: in advanced neovascular disease

Posterior Segment Signs

• Retinal telangiectasia: irregularly dilated, tortuous, aneurysmal retinal vessels — light-bulb aneurysms, fusiform dilatations, and saccular outpouchings — predominantly in the temporal periphery; may also involve posterior pole in severe cases
• Intraretinal hard exudates: yellow-white lipid deposits in the outer plexiform layer; may form circinate rings around leaking vessels or a partial or complete macular star pattern
• Subretinal exudate: creamy-yellow, cholesterol-rich fluid beneath the sensory retina; in advanced disease, massive and distinctive; the hallmark of Coats' disease
• Glistening cholesterol crystals: golden-refractile deposits within subretinal fluid; pathognomonic when present in quantity
• Exudative (serous) retinal detachment: bullous, shifting, dome-shaped elevation without retinal break or vitreoretinal traction; may be subtotal or total
• Retinal haemorrhages: may occur from rupture of fragile telangiectatic vessels; less prominent than exudation
• Neovascularisation of the disc or retina: in advanced ischaemic cases (Stage 3B–4)
• Optic disc: generally normal in early disease; disc oedema or neovascularisation possible in advanced stages
• Vitreous: typically clear; haemorrhage uncommon

Imaging Signs

• FFA: early hyperfluorescence of telangiectatic vessels with late profuse leakage; areas of capillary non-perfusion in ischaemic zones
• OCT: intraretinal and subretinal fluid; disruption of ellipsoid zone and outer nuclear layer; outer plexiform layer lipid deposits; intact vitreoretinal interface
• B-scan ultrasound: dome-shaped exudative detachment with high internal reflectivity; critically, no acoustic shadowing or calcification (distinguishing feature from retinoblastoma)
• MRI: subretinal fluid shows T1 hyperintensity (protein/cholesterol-rich); no calcified mass

Symptoms vary markedly with disease stage and age. Unilateral early-stage disease in children is frequently asymptomatic, as the fellow eye maintains binocular visual function. Most childhood cases are detected by parents, teachers, or healthcare providers noting leukocoria or squint.

Presenting Symptoms (Children)

• Leukocoria: white or yellow pupillary reflex, commonly first noticed by parents in photographs with flash; the most common presenting complaint in children
• Strabismus / squint: secondary to unilateral vision loss; often the triggering reason for optometry or paediatric review
• Reduced visual acuity (unilateral): often only detected when the fellow eye is occluded during formal vision assessment or screening
• Visual field loss: corresponding to the extent of retinal detachment; young children are unlikely to report this directly

Presenting Symptoms (Adults)

• Gradually reduced central vision: from macular exudate accumulation or subretinal fluid under the fovea
• Metamorphopsia: distortion of straight lines from macular exudate deforming the photoreceptor layer
• Central or paracentral scotoma: corresponding to areas of foveal exudate or detachment
• Floaters: rare; may occur if vitreous haemorrhage develops

Advanced Disease Symptoms

• Ocular pain: in Stage 4 neovascular glaucoma; aching, pressure-like pain; may be severe with high IOP
• Conjunctival redness: from raised IOP or anterior uveitis in late disease
• Complete vision loss: Stage 3B–5; no perception of light in end-stage disease

• Progressive exudative retinal detachment: the primary disease complication; subtotal or total detachment leads to irreversible photoreceptor loss and blindness
• Foveal exudate and photoreceptor atrophy: lipid deposition in the foveal and parafoveal outer plexiform layer causes permanent displacement and atrophy of cones; irreversible central vision loss even after structural resolution
• Neovascular (rubeotic) glaucoma: VEGF-mediated iris and angle neovascularisation obstructs aqueous outflow; painful, vision-threatening; may require surgical intervention (Stage 4)
• Vitreous haemorrhage: from rupture of friable telangiectatic or neovascular vessels; reduces view of posterior segment
• Tractional retinal detachment: fibrovascular proliferation post-treatment or in advanced disease may add a tractional component to the primarily exudative detachment
• Anterior chamber cholesterol: migration of subretinal lipid anteriorly through the pupil; may simulate intraocular tumour
• Phthisis bulbi: end-stage atrophic shrunken globe from chronic hypotony and retinal degeneration (Stage 5)
• Amblyopia (children): visual deprivation from unilateral early-onset disease causes profound amblyopia even in the absence of structural progression; must be actively treated alongside structural disease management
• Enucleation: may be unavoidable in Stage 4–5 disease with a painful blind eye or when retinoblastoma cannot be definitively excluded

Coats' disease in the typical unilateral sporadic form is a purely ocular condition without systemic complications. However, bilateral or atypical presentations should prompt a broader systemic evaluation, as several hereditary conditions present with Coats-like retinopathy as one component of a multisystem disorder.

Facioscapulohumeral Muscular Dystrophy (FSHD)

The most clinically important systemic association. FSHD is caused by aberrant expression of the DUX4 transcription factor from contracted D4Z4 repeat arrays at chromosome 4q35. Coats-like exudative retinopathy occurs in up to 60% of severe, early-onset FSHD and may be bilateral. Severity of retinal involvement correlates with repeat array size and systemic disease severity. Clinicians should screen for facial weakness (inability to fully close eyes, smile weakness), scapular winging, and proximal upper limb weakness in any patient with bilateral Coats-like retinopathy.

Coats' Plus Syndrome (CTC1 Mutation)

A rare autosomal recessive multisystem syndrome caused by mutations in CTC1, encoding a component of the CST telomere maintenance complex. Coats' Plus (also termed cerebroretinal microangiopathy with calcifications and cysts, CRMCC) features:

• Bilateral Coats-like exudative retinopathy (the retinal phenotype)
• Intracranial calcifications (predominantly basal ganglia) and white matter cysts
• Leukoencephalopathy with progressive neurological deterioration
• Bone marrow failure (aplastic anaemia / pancytopenia)
• Gastrointestinal telangiectasia and bleeding
• Osteoporosis, growth retardation, and short stature

Turner Syndrome (45,X)

Bilateral Coats-like exudative retinopathy has been reported in Turner syndrome. The mechanism is uncertain but may relate to retinal vascular dysgenesis in the setting of chromosomal haploinsufficiency. Girls diagnosed with bilateral Coats-like retinopathy should be assessed for features of Turner syndrome (short stature, primary amenorrhoea, webbed neck, lymphoedema, cardiac defects).

Senior-Løken Syndrome

An autosomal recessive nephronophthisis-retinal dystrophy syndrome. Children with nephronophthisis (progressive renal failure with polyuria/polydipsia) and retinal involvement — including Coats-like exudation — should be evaluated by nephrology. Causative genes include NPHP1 and related ciliopathy genes.

Other Reported Associations

• Parry-Romberg syndrome (progressive hemifacial atrophy): ipsilateral Coats-like changes described; rare
• Epidermal naevus syndrome: rare ocular involvement including Coats-like exudation
• Hypomelanosis of Ito: rare; Coats-like retinopathy reported

Diagnosis is primarily clinical, supported by multimodal retinal imaging. The critical first step is urgent exclusion of retinoblastoma in any child presenting with leukocoria.

Clinical Assessment

• Red reflex assessment (Brückner test): detection of asymmetric or absent red reflex; the primary screening tool for leukocoria in all paediatric eye examinations
• Visual acuity: unilateral reduction common; use appropriate age-adjusted tests (Kay Pictures, Cardiff Cards, Snellen)
• Cover test: evaluate for strabismus (exotropia common)
• Anterior segment slit-lamp examination: rubeosis iridis, anterior chamber cholesterol, lens changes
• IOP measurement: for Stage 4 glaucoma detection

Fundus Camera Imaging

• Wide-field colour fundus photography: documents telangiectatic vessel morphology, extent of lipid exudation, and detachment; Optos or Clarus-type ultra-widefield imaging is particularly useful for peripheral lesions
• Fluorescein angiography (FFA): gold standard for detecting and mapping telangiectatic lesions; early hyperfluorescence of telangiectatic vessels with late-phase leakage; identifies areas of capillary non-perfusion and zones requiring ablation; guides laser treatment planning

OCT (Optical Coherence Tomography)

• Macular OCT: intraretinal and subretinal fluid; outer nuclear layer and ellipsoid zone disruption; hard exudate at the outer plexiform layer; intact vitreoretinal interface (no traction — distinguishing feature from tractional RD)
• Swept-source OCT / enhanced depth imaging: subretinal cholesterol visualisation and detachment morphology
• OCT-angiography (OCTA): demonstrates telangiectatic flow in the superficial and deep capillary plexuses; useful adjunct to FFA, particularly for monitoring

B-Scan Ultrasonography

• Essential when fundal view is obscured by media opacity; demonstrates dome-shaped exudative detachment with high internal reflectivity
• Critical differentiating feature: absence of acoustic calcification — retinoblastoma shows characteristic posterior acoustic shadowing from calcification; Coats' disease does not

MRI / CT

• MRI orbits: subretinal fluid shows T1 hyperintensity (high protein and cholesterol content); no enhancing intraocular mass; no calcification — distinguishes from retinoblastoma (T1 hypointense mass with calcification)
• CT: rarely indicated (radiation); confirms absence of calcification when B-scan is equivocal; calcification on CT is highly suspicious for retinoblastoma

Management is stage-guided and aims to ablate leaking telangiectatic vessels, resolve subretinal exudation, reattach the retina, and preserve functional vision. Treatment cannot restore vision already lost from foveal exudate damage or photoreceptor atrophy. Multiple treatment sessions are typically required, and long-term surveillance is essential given the risk of recurrence.

Stage 1: Observation or Early Ablation

• Stage 1 without exudation may be observed with 3–6 monthly fundus imaging
• Some centres advocate early laser photocoagulation of telangiectatic lesions to prevent progression to exudative disease

Laser Photocoagulation

• First-line treatment for Stage 1–2 and accessible Stage 3A disease
• Targets the walls of leaking telangiectatic vessels directly; typically using an argon (532 nm green) or diode laser
• Ablation causes endothelial closure of abnormal vessels, reducing exudation; exudate absorption occurs over weeks to months
• Multiple sessions often required; serial FFA guides retreatment targeting residual leaking lesions
• Limited by peripheral location of lesions — may require indirect laser delivery

Cryotherapy

• Indicated for peripheral telangiectatic lesions inaccessible to laser, or in Stage 3A with accompanying subretinal fluid that limits laser effectiveness
• Transconjunctival cryotherapy applied directly over lesion segments under indirect ophthalmoscopic visualisation
• Can be combined with laser in a single session; effective at ablating peripheral telangiectasia
• May induce temporary exacerbation of exudation; monitor closely after treatment

Anti-VEGF Therapy (Adjunct)

• Intravitreal anti-VEGF agents (bevacizumab, ranibizumab) used as adjunctive therapy to reduce vascular permeability and assist exudate resolution
• Anti-VEGF is not recommended as monotherapy; used in combination with or prior to laser/cryotherapy to reduce macular oedema and facilitate better ablative outcomes
• Particularly useful in Stage 2B–3A disease with macular oedema, and in eyes with massive exudation obscuring the laser view
• Evidence is based on retrospective series and small case reports; no randomised controlled trial data yet available
• Intravitreal anti-VEGF also used for rubeosis iridis in Stage 4 as an adjunct to definitive glaucoma management

Surgical Management

• Pars plana vitrectomy with subretinal fluid drainage: for Stage 3B total exudative detachment; removes subretinal cholesterol-rich fluid to facilitate retinal reattachment; combined with intraoperative laser and cryotherapy
• Scleral buckling: adjunct in selected Stage 3B cases to bring the peripheral retina within reach of ablative treatment
• Glaucoma management (Stage 4): intravitreal anti-VEGF for rubeosis; cycloablation (laser or cryo-cyclodestruction) or glaucoma drainage devices for refractory IOP elevation
• Enucleation: reserved for painful blind eyes (Stage 4–5), refractory neovascular glaucoma, or when retinoblastoma cannot be definitively excluded; a prosthetic eye provides cosmesis post-enucleation

Amblyopia Management (Children)

• Patching (occlusion) therapy of the fellow eye and optical correction of refractive error must be initiated alongside structural treatment
• Duration and intensity guided by age and depth of amblyopia
• Prognosis for amblyopia reversal depends critically on age of initiation; earlier treatment yields better outcomes

Prognosis is strongly stage-dependent and is also influenced by age at diagnosis, foveal involvement, rapidity of intervention, and amblyopia management in children.

Visual Prognosis by Stage

• Stage 1–2A: excellent anatomical and functional prognosis with timely laser treatment; most eyes achieve stable or improved visual acuity; exudate resolution occurs over weeks to months post-ablation
• Stage 2B: guarded; foveal exudate causes photoreceptor disruption and may result in permanent central vision impairment even after structural success; hard exudate beneath the fovea limits visual recovery
• Stage 3A (extrafoveal): moderate; anatomical reattachment rates of 70–80% with combined laser and cryotherapy; functional vision depends on whether the fovea was involved at any point
• Stage 3A2 and 3B: poor visual prognosis; retinal reattachment may be achievable surgically but functional vision is typically limited to hand motions or light perception; goal shifts to globe preservation
• Stage 4–5: extremely poor; vision loss is complete; management aims at pain relief and cosmesis; enucleation may be necessary

Recurrence and Long-Term Monitoring

• Telangiectatic vessels may reactivate after initially successful treatment; recurrence rates of 20–30% are reported at long-term follow-up, requiring retreatment
• Serial FFA-guided surveillance every 3–6 months is standard following initial treatment
• Lifelong ophthalmic follow-up is recommended, even in stabilised early-stage disease
• The fellow eye in sporadic unilateral Coats' disease is at low but non-zero risk and should be periodically examined; FFA of the fellow eye in childhood-onset cases is recommended by some centres

Adult-Onset Coats' Disease

Adult-onset disease typically follows a more indolent natural history with slower progression, less aggressive exudation, and better response to treatment than childhood-onset disease. Visual prognosis in adults is generally more favourable, particularly when diagnosed before total foveal exudate accumulation.

Functional vs. Anatomical Success in Children

Structural success (retinal reattachment, exudate resolution) does not guarantee functional visual recovery in children. Concurrent amblyopia from prolonged visual deprivation, photoreceptor loss from chronic subretinal fluid, and foveal lipid damage all independently limit visual outcomes. Patching therapy must be maintained even after anatomically successful retinal treatment.