central retinal vein occlusion

**Pathophysiology** - The central retinal artery and vein share a common adventitial sheath as they pass through the lamina cribrosa. Atherosclerotic thickening of the artery compresses the vein, which causes turbulent flow, endothelial damage, and thrombosis (Virchow triad). - Venous outflow obstruction raises venous and capillary pressure. This leads to hemorrhage, exudation, macular edema, and retinal ischemia. - Ischemia upregulates VEGF. VEGF drives neovascularization of the iris (rubeosis iridis) and the angle, which can cause neovascular (secondary angle-closure) glaucoma. This is the "100-day glaucoma" seen with ischemic CRVO.

**Risk factors** - Age >50 (most common), hypertension (most common systemic association), hyperlipidemia, diabetes mellitus, and atherosclerotic disease. - Open-angle glaucoma or elevated intraocular pressure. - Hypercoagulable states, especially in young patients: antiphospholipid syndrome, factor V Leiden, protein C/S or antithrombin deficiency, and hyperhomocysteinemia. - Hyperviscosity states (multiple myeloma, Waldenström macroglobulinemia, polycythemia vera, leukemia). - Oral contraceptives, vasculitis, sarcoidosis.

**Clinical presentation** - Sudden, painless, unilateral vision loss, which ranges from mild to severe. - A relative afferent pupillary defect (RAPD) is present in ischemic CRVO.

**Fundoscopy** - "Blood and thunder" or "tomato splashed" retina: diffuse flame-shaped and dot-blot hemorrhages in all four quadrants. - Dilated, tortuous retinal veins. - Cotton-wool spots, optic disc swelling, and macular edema.

**Classification** - Non-ischemic (perfused, ~70–80%): better prognosis, and some cases resolve. - Ischemic (non-perfused): severe vision loss, RAPD, and high risk of neovascularization.

**Diagnosis** - Clinical diagnosis from fundoscopy. - Fluorescein angiography shows delayed venous filling and areas of capillary non-perfusion. - OCT assesses macular edema. - Workup for systemic risk factors: BP, glucose/HbA1c, lipids, and IOP. Consider a thrombophilia and hyperviscosity workup in young patients or those without risk factors.

**Treatment** - Treat underlying systemic conditions and reduce cardiovascular risk. - Intravitreal anti-VEGF (ranibizumab, aflibercept, bevacizumab) is first-line for macular edema. Intravitreal corticosteroid implants (dexamethasone) are an alternative. - Panretinal photocoagulation (PRP) for neovascularization (rubeosis iridis or retinal neovascularization). - Monitor closely for neovascular glaucoma, especially in the first 3–6 months.

**High-yield comparisons** - Central retinal ARTERY occlusion (CRAO): sudden painless vision loss, pale retina with a cherry-red spot, usually from an embolus (carotid atherosclerosis, cardiac source), and associated with giant cell arteritis. Treat as an emergency. Look for a carotid or cardiac source. - Branch retinal vein occlusion (BRVO): occurs at arteriovenous crossings, causes sectoral hemorrhages, and is strongly associated with hypertension. - Retinal detachment: painless, with floaters, flashes, and a "curtain" over the visual field. - Vitreous hemorrhage: floaters and painless vision loss, often from proliferative diabetic retinopathy. - Ocular ischemic syndrome (carotid stenosis) can mimic CRVO with a "venous stasis retinopathy" pattern, but the hemorrhages are mid-peripheral and the veins are dilated but not tortuous.

**Board pearls** - Painless sudden monocular vision loss with diffuse hemorrhages is CRVO until proven otherwise. - The main complication to remember is neovascular glaucoma, mediated by VEGF. - Young patient with CRVO: think hypercoagulable or hyperviscosity state.