Retinal Vessel Occlusion

Retinal vessel occlusion covers occlusion of the retinal arteries (central, branch, cilioretinal) and veins (central, branch, hemiretinal). Both are vascular emergencies of the eye and markers of systemic vascular disease.

Retinal artery occlusion

• Incidence is about 1 to 2 per 100,000 per year, with a mean age near 60 and a male predominance.
• Central retinal artery occlusion accounts for about 55 to 60% of cases, branch occlusion for about 35 to 40%, and cilioretinal artery occlusion for the remainder.
• The inner retina tolerates complete ischaemia for roughly 90 to 100 minutes in experimental models, with irreversible damage after about 4 hours.
• Causes:
• Embolism from carotid atheroma (cholesterol, Hollenhorst plaque), cardiac sources (valvular vegetations, atrial fibrillation, myxoma, patent foramen ovale) or calcific emboli.
• Giant cell arteritis (about 5 to 10% of central retinal artery occlusions in patients over 50).
• Thrombosis, vasculitis (polyarteritis nodosa, lupus, Susac syndrome), hypercoagulability, sickle cell disease, pregnancy, oral contraceptives, trauma, and migraine.
• Retrobulbar injection and filler injection to the face.
• About 25% of patients with central retinal artery occlusion have an associated acute ischaemic stroke on MRI, and cardiovascular risk is raised for years afterward.

Retinal vein occlusion

• It is the second commonest retinal vascular disease after diabetic retinopathy. Prevalence is about 0.5 to 1% in adults over 40, rising with age.
• Branch retinal vein occlusion is about four times as frequent as central retinal vein occlusion.
• Pathophysiology: compression of the vein at an arteriovenous crossing or at the lamina cribrosa by a stiffened artery, with turbulent flow, endothelial damage and thrombosis.
• Risk factors: hypertension (in over 50%), diabetes, hyperlipidaemia, age, glaucoma and ocular hypertension, smoking, obesity, sleep apnoea, hyperviscosity (myeloma, Waldenström macroglobulinaemia, polycythaemia), thrombophilia (antiphospholipid syndrome, factor V Leiden, hyperhomocysteinaemia), oestrogen use, inflammatory disease (sarcoidosis, Behçet disease, vasculitis), and medications including the combined oral contraceptive pill.
• Classification:
• Non-ischaemic (perfused) central retinal vein occlusion has about 10% risk of conversion to ischaemic disease.
• Ischaemic central retinal vein occlusion is defined by 10 or more disc areas of capillary non-perfusion on fluorescein angiography, with relative afferent pupillary defect, visual acuity under 20/200, and a high risk of neovascularisation.
• Branch occlusion in the macular region causes macular oedema, while non-perfusion over 5 disc areas can induce neovascularisation.
• Complications: macular oedema (the commonest cause of vision loss), neovascularisation of the iris and angle (100-day glaucoma, appearing at about 3 months after ischaemic central vein occlusion), vitreous haemorrhage, tractional retinal detachment, and macular ischaemia.

Central retinal artery occlusion

• Sudden, painless, profound monocular vision loss (counting fingers to light perception in about 90%), sometimes preceded by amaurosis fugax.
• Relative afferent pupillary defect is present.
• Fundus findings: retinal whitening and oedema with a cherry-red spot at the fovea, narrowed arterioles with "boxcarring" (segmentation of the blood column), and an embolus in about 20% of patients. In the first hours the fundus may look normal.
• Cilioretinal artery sparing (15 to 30% of eyes) preserves central vision.

Branch retinal artery occlusion

• Sudden sectoral field loss (altitudinal), with whitening of the retinal territory.

Retinal vein occlusion

• Painless blurring or visual loss over hours to days, varying from mild to severe. Some patients note floaters.
• Fundus findings: dilated tortuous veins, diffuse "blood and thunder" flame and blot haemorrhages in all four quadrants (central vein occlusion) or in one sector with the apex at the crossing site (branch occlusion), cotton wool spots, disc swelling and macular oedema.
• Hemiretinal occlusion affects the superior or inferior half of the retina.

Giant cell arteritis features to ask about: new headache, scalp tenderness, jaw claudication, polymyalgia, weight loss, fever, and transient visual loss. Arteritic anterior ischaemic optic neuropathy and "chalky white" disc oedema may coexist.

Differential diagnosis: ophthalmic artery occlusion (no cherry-red spot, complete loss), anterior ischaemic optic neuropathy, retinal detachment, vitreous haemorrhage, ocular ischaemic syndrome, diabetic retinopathy, hypertensive retinopathy, papilloedema, radiation retinopathy, and Purtscher retinopathy.

Retinal artery occlusion

• Clinical diagnosis on dilated fundus examination, confirmed by optical coherence tomography showing inner retinal hyperreflectivity and thickening in the acute phase, then thinning.
• Fluorescein angiography shows delayed arterial filling and arteriovenous transit time, and is not essential acutely.
• Urgent stroke work-up, within hours, as for a transient ischaemic attack or stroke:
• MRI brain with diffusion-weighted imaging.
• CT or MR angiography of the head and neck, or carotid duplex.
• ECG, prolonged rhythm monitoring, and transthoracic and transoesophageal echocardiography.
• ESR, CRP and platelet count immediately in anyone over 50. A raised value in the right clinical setting calls for treatment before biopsy or imaging confirmation. Temporal artery ultrasound, MRI or biopsy follow.
• Blood tests: CBC, glucose or HbA1c, lipids, renal function, blood cultures if endocarditis is a concern, and in younger patients thrombophilia screen, antiphospholipid antibodies, ANA, ANCA, haemoglobin electrophoresis, homocysteine, and syphilis serology.

Retinal vein occlusion

• Dilated fundus examination, optical coherence tomography for macular oedema thickness, and widefield fluorescein angiography for non-perfusion and neovascularisation.
• Gonioscopy and iris examination at every visit for the first 6 months in ischaemic central vein occlusion.
• Systemic evaluation: blood pressure, HbA1c or glucose, fasting lipids, CBC, ESR, creatinine and renal function, ECG, and urinalysis.
• Younger patients (under 50) or those with bilateral, recurrent or atypical occlusion: thrombophilia and antiphospholipid testing, serum protein electrophoresis, homocysteine, ACE, ANA, ANCA, syphilis, and HIV.
• Assess for glaucoma and measure intraocular pressure in both eyes.

Central retinal artery occlusion (emergency, treat within hours)

• Immediate referral to an emergency department with stroke capability, and manage as an acute stroke equivalent.
• Intravenous thrombolysis within 4.5 hours of onset in selected patients: alteplase 0.9 mg/kg (maximum 90 mg, 10% bolus and the rest over 60 minutes) or tenecteplase 0.25 mg/kg (maximum 25 mg). Benefit is greatest within 4.5 hours and falls thereafter, with uncertain benefit beyond 6 hours. Exclude giant cell arteritis-related occlusion when planning thrombolysis, though coexisting disease does not forbid it.
• Intra-arterial thrombolysis has not shown clear benefit and is reserved for trial settings.
• Conservative manoeuvres are of unproven benefit but are low risk: lie flat, ocular massage (digital pressure for 5 seconds with release, repeated for 15 minutes), paracentesis of the anterior chamber, topical timolol 0.5% twice daily, IV acetazolamide 500 mg or oral 250 to 500 mg, and breathing a carbogen mixture. Sublingual isosorbide dinitrate 5 mg has been used. None is a replacement for stroke pathways.
• Antithrombotics: aspirin 300 mg then 75 to 100 mg daily, unless thrombolysed (then delay for 24 hours), and a short course of dual antiplatelet therapy with clopidogrel 75 mg after loading when a minor stroke is present.
• Giant cell arteritis: methylprednisolone 500 to 1000 mg IV daily for 3 days, then prednisolone 1 mg/kg daily (maximum 60 to 80 mg), with tocilizumab 162 mg SC weekly as a steroid-sparing agent. Begin without waiting for biopsy.
• Secondary prevention: atorvastatin 40 to 80 mg daily, blood pressure below 130/80 mmHg, treat carotid stenosis (endarterectomy within 2 weeks for symptomatic stenosis of 70 to 99%), anticoagulation for atrial fibrillation (apixaban 5 mg twice daily), closure of patent foramen ovale in selected patients, smoking cessation, and glycaemic control.
• Monitor for neovascularisation of the iris (2 to 18% at 4 to 5 weeks), treated with panretinal photocoagulation and anti-VEGF.

Retinal vein occlusion

• Treat systemic risk factors: blood pressure, diabetes, lipids (atorvastatin 20 to 40 mg), antiplatelet therapy only when otherwise indicated (aspirin does not improve outcomes and anticoagulation is not recommended routinely), stop oestrogen-containing contraceptives, treat hyperviscosity (plasmapheresis or venesection for polycythaemia), and manage glaucoma.
• Macular oedema with visual acuity of 20/40 or worse:
• Intravitreal anti-VEGF is first line: ranibizumab 0.5 mg monthly, aflibercept 2 mg monthly for 3 to 5 injections then every 8 weeks or treat-and-extend, bevacizumab 1.25 mg monthly (off-label), or faricimab 6 mg. Typically 6 to 12 injections over the first year, with visual gains of 15 or more letters in over half of patients.
• Intravitreal dexamethasone implant 0.7 mg every 4 to 6 months, or triamcinolone, for patients with poor response or who cannot attend monthly visits. Cataract and raised intraocular pressure are the main adverse effects, and must be monitored.
• Macular grid laser for persistent branch occlusion oedema in selected cases.
• Observation is appropriate for mild oedema with good vision, since some resolve spontaneously (about 30% in branch occlusion at 12 months).
• Neovascularisation or ischaemic central vein occlusion: panretinal photocoagulation (1200 to 1600 burns in one to three sessions), with anti-VEGF as an adjunct, particularly for iris or angle neovascularisation (bevacizumab 1.25 mg). Sectoral photocoagulation for branch occlusion with neovascularisation.
• Neovascular glaucoma: anti-VEGF, panretinal photocoagulation, topical timolol 0.5% twice daily, brimonidine 0.2% three times daily, dorzolamide 2% three times daily, atropine 1% twice daily, prednisolone acetate 1%, and glaucoma drainage device or cyclodestruction for refractory cases. Avoid prostaglandin analogues and miotics.
• Vitreous haemorrhage and tractional detachment: vitrectomy.
• Follow-up monthly for the first 6 months in central vein occlusion, then at extending intervals, with monitoring for rubeosis at each visit.

Prognosis

• Central retinal artery occlusion: final acuity of counting fingers or worse in about 80%, spontaneous improvement to 20/40 or better in under 10%. Branch artery occlusion retains acuity of 20/40 or better in over 80%.
• Central retinal vein occlusion: non-ischaemic disease often retains acuity better than 20/200, whereas ischaemic disease usually remains 20/200 or worse. Branch occlusion regains 20/40 or better in about 50 to 60% with treatment.