A i.e. Dilated Retinal Vein Central Retinal Vein Occlusion and Ocular Ischemic Syndrome due to carotid aery stenosis are both associated with dilated retinal veins and hence this feature cannot be used to distinguish these conditions. However, ophthalmic aery pressure (measured by ophthalmo dynamometry) and retinal aery pressure is usually normal in CRVO and decreased (low) in carotid aery obstruction. And to differentiate both conditions other features include presence of swollen optic disc & touous retinal veins in CRVOQ. Ophthalmodynamometry is a non invasive method of estimating ophthalmic aery pressure. Features Ocular Ishemic Syndrome (Carotid Aery Obstruction) CRVO (Non Ischaemic) (Central Retinal Vein Obstruction) Definition Ocular Ischemic Syndrome is a condition with variable spectrum of sign and symptoms resulting from chronic ocular hypoperfusion usually secondary to severe carotid aery obstruction. Pathogenesis of this syndrome is decreased aerial inflow on a chronic basis CRVO is an ocular syndromes with ocular signs and symptoms resulting from an occlusion of the central retinal vein - Ischemic : Complete obstruction (20? 25% of cases) - Non ischaemic : Incomplete obstruction (70-75% of cases) Laterality Unilateral (80%) Unilateral Age (years) 50-80 50-80 Fundus signs Veins Dilated, nontouous Dilated, touous Optic disc Normal Swollen Retinal aery perfusion pressure Decreased Normal Retinal hemorrhages Mild Mild to severe Microaneurysms Mid-periphery Variable Hard exhudates Absent unless in association with diabetes Rare Fluorescein Angiography Choroidal filling Delayed, patchy Normal Aeriovenous transit time Prolonged Prolonged Retinal vessel staining Prominent aerial staining Prominent venous staining Ophthalmodynamometry (non invasive) Ophthalmic aery pressure is usually lowQ Ophthalmic aery pressure is usually normal or elevated