Retinal vein occlusion includes vascular occlusions of either the branch or central retinal vein, resulting in potential vision changes and long term sequelae. It is the second most common retinal vascular disease after diabetic retinopathy. Retinal vein thrombosis is strongly associated with age-related local and systemic factors. The central retinal artery and the branch retinal arteriole share common adventitial sheath at arteriovenous crossings with their respective venous counterparts, and therefore atherosclerotic changes in the arteries may precipitate occlusion of the veins.
In central RVO (CRVO), the occlusion is at or proximal to the lamina cribrosa of the optic nerve, where the central retinal vein exits the eye. CRVO is further divided into the categories of perfused (nonischemic) and nonperfused (ischemic).
Non ischaemic CRVO (sometimes called ‘venous stasis retinopathy’) is the more common form. 1/3rd of patients will progress to ischaemic CRVO.
Ischaemic CRVO is characterized by substantially decreased retinal perfusion with capillary closure and retinal hypoxia. Macular ischaemia and neovascular glaucoma following this are the major causes of visual morbidity.
| Non-Ischaemic CRVO (Perfused) | Ischaemic CRVO (Nonperfused) |
|---|---|
| Most common type | Less common |
| Mild to moderate loss of acuity, usually 20/200 or better | Severe visual loss, usually less than 20/200 |
| Mild afferent pupillary defect | Marked afferent pupillary defect |
| Field defect is uncommon | Field defect is common |
| Milder features of haemorrhage, cotton-wool spots, disc or macular oedema, and mild venous tortuosity and dilation | More severe features of haemorrhage, cotton-wool spots, disc or macular oedema, and mild venous tortuosity and dilation |
| FA showing delayed AV transit time, usually good retinal capillary perfusion, and some late leakage | FA showing marked delay in AV transit time, extensive areas of capillary non-perfusion and vessel wall staining and leakage |
| Normal ERG | Depressed ERG |
| Good prognosis with less chance of anterior segment neovascularization/neovascular glaucoma | Poor prognosis. High risk of neovascular glaucoma. Rubeosis iridis develops in 50% of eyes between 2-4 months. |
The management of non-ischaemic CRVO is generally much less aggressive than ischaemic CRVO.
Color fundus photograph showing the presence of venous tortuosity with distension in CRVO. There are moderate intraretinal hemorrhages throughout the posterior pole with a greater amount of hemorrhages in a peripapillary region. Mild disk oedema appears to be present. Image Courtesy of Alasil et al.
BRVO is a venous occlusion at any branch of the central retinal vein. Occlusions occurring at the proximal part of the central retinal vein trunk results in an hemi retinal vein occlusion (HRVO), which is considered a subtype of either CRVO or BRVO.
BRVO can be anatomically classified into ‘major’ or ‘macular’. Major BRVO refers to occlusion of a retinal vein draining one of the quadrants, whereas macular BRVO refers to occlusion of a venule within the macula. BRVO is most common in the superotemporal quadrant, felt to be due to the increase arteriovenous crossings here.
BRVO can be further classified into non-ischaemic and ischaemic ( > 5 disc diameters of nonperfusion on FA ).