Central Retinal Vein Occlusion

Central retinal vein occlusion is obstruction of the central retinal vein at or behind the lamina cribrosa, causing venous congestion, retinal hemorrhage and macular edema. Prevalence is about 0.8 in 1000 people, rising steeply after age 60.

Classification:

• Non-ischemic (about 75 to 80%): perfused, good prognosis, 15 to 30% convert to ischemic
• Ischemic: 10 or more disc areas of capillary nonperfusion on fluorescein angiography, poor acuity, relative afferent pupillary defect

Risk factors: hypertension in most patients, diabetes, hyperlipidemia, glaucoma, age over 50. In patients under 50, think of thrombophilia, hyperviscosity (myeloma, Waldenström macroglobulinemia, polycythemia), vasculitis, sarcoidosis, oral contraceptive use and orbital compression.

The causes of poor vision are macular edema, macular ischemia and neovascular complications. Iris neovascularization develops in about 45% of ischemic eyes, typically within 3 months (the "hundred day glaucoma"), and can cause neovascular glaucoma. The fellow eye is affected in about 7% over 5 years.

• Sudden painless unilateral loss of vision, ranging from mild blurring to counting fingers
• Dilated tortuous veins in all four quadrants
• Diffuse flame and blot hemorrhages ("blood and thunder")
• Optic disc swelling, cotton wool spots, macular edema
• Relative afferent pupillary defect in ischemic disease
• Rubeosis iridis and raised intraocular pressure in late ischemic disease

Red flags: acuity worse than counting fingers, afferent pupillary defect, any iris vessels, young age, bilateral disease.

• Dilated fundus examination. Perform gonioscopy and iris examination before dilating if rubeosis is suspected.
• OCT: central subfield thickness above about 300 micrometres indicates macular edema, with cystic spaces and subretinal fluid.
• Widefield fluorescein angiography: prolonged venous filling, leakage, capillary dropout (above 10 disc areas defines ischemic disease).
• Intraocular pressure at every visit.
• Systemic screen: blood pressure, glucose and HbA1c, lipids, full blood count, ESR, urea and electrolytes, ECG. In patients under 50 or with bilateral or recurrent disease: thrombophilia screen, serum protein electrophoresis, ANA, ANCA, ACE, syphilis serology.

Differentials: ocular ischemic syndrome (peripheral hemorrhages, carotid stenosis), diabetic retinopathy, hypertensive retinopathy, radiation retinopathy, papilledema, hyperviscosity retinopathy.

Treat systemic disease first: blood pressure below 130/80 mmHg, diabetes control, lipid lowering with atorvastatin 40 mg at night. Treat hyperviscosity (plasmapheresis, chemotherapy) and polycythemia (venesection to hematocrit below 45%, aspirin 75 mg daily). Aspirin has no proven ocular benefit.

Macular edema (acuity 20/40 or worse with central thickening):

• Intravitreal aflibercept 2 mg (0.05 mL) monthly for 3 to 6 doses, then treat and extend. Alternatives: ranibizumab 0.5 mg monthly, bevacizumab 1.25 mg in 0.05 mL (off label).
• Dexamethasone implant 0.7 mg every 4 to 6 months when anti-VEGF is unsuitable. Adverse effects: cataract, raised intraocular pressure (about 25 to 30%).
• Injection technique: povidone iodine 5% to the conjunctival sac, eyelid speculum, 30-gauge needle 3.5 mm (pseudophakic) to 4.0 mm (phakic) behind the limbus. Complications: endophthalmitis (about 0.02 to 0.05% of injections), raised pressure, cataract, retinal tear and detachment.

Neovascularization: panretinal photocoagulation with 1200 to 2000 burns (spot 200 to 500 micrometres, 0.1 second) once rubeosis or angle vessels appear, with intravitreal anti-VEGF as a bridge. Monthly review for 6 months in ischemic disease.

Neovascular glaucoma: timolol 0.5% twice daily, dorzolamide 2% three times daily, brimonidine 0.2% twice daily, atropine 1% twice daily, prednisolone 1% four times daily. Acetazolamide 500 mg orally twice daily short term. Avoid prostaglandin analogues. Refractory pressure needs a drainage device or cyclodestruction.

Vitrectomy is for nonclearing vitreous hemorrhage over 3 months or tractional detachment.

Follow up: monthly while injecting, then every 2 to 3 months. Counsel on warning signs of rubeosis and pain. Isovolemic hemodilution and radial optic neurotomy are not recommended.