Arterial And Venous Occlusions

Retinal Artery or Vein Occlusions not only are responsible for a sizeable percentage of vision loss but also are indicative of significant systemic vascular disease. The retinal circulation, though complex, may be thought of as like a tree, with various branches progressively smaller. Obstruction of flow may involve any of the branches or the central ‘trunk’. The cause is seldom clear-cut, though association with various other conditions is inescapable. Branch retinal artery occlusion (BRAO), presenting as loss of vision in a portion of the visual field, occurs virtually always in patients with atherosclerotic disease or secondary to blockage from emboli (platelets, calcium, cholesterol). Central retinal artery occlusion (CRAO) most commonly is caused by atherosclerosis or emboli similar to BRAO; however, vision loss is more severe, involving the entire visual field. A rarer cause of abrupt vision loss is Giant Cell Arteritis (GCA)or Temporal Arteritis (TA). It is an auto-immune inflammation of the arteries that may affect one eye and then the other and lead to total blindness in a matter of days. In BRAO and CRAO, the diagnostic evaluation focusing on the carotid arteries and the heart may be performed over a few days, but in suspected giant cell arteritis it must be done in hours. Blood tests-sedimentation rate and C-reactive protein are helpful in establishing the diagnosis, but the ‘gold standard’ is a temporal artery biopsy. Treatment with high dose steroids is instituted even before the test results are obtained.
Vision loss from retinal vein occlusion may be less abrupt than what occurs with arterial occlusion and generally less severe. Branch retinal vein occlusion is virtually always associated with elevated blood pressure. The resultant partial visual loss, corresponding to the segment of retina affected, is explained by the retinal hemorrhages, edema and possibly ischemia in the involved retina. The latter may be documented with fundus fluorescein angiography (FFA) and optical coherence tomography (OCT). If edema is documented and does not clear within 4-6 months, laser may be of some help in decreasing it. Visual loss from central retinal vein occlusion (CRVO) is a general obscuration of the entire visual field. The appearance of the retina is described as “pizza-pie” or “blood and thunder”. Though the cause is not known, frequently associated conditions include: atherosclerosis, glaucoma, diabetes, hypertension, and a variety of blood diseases which increase its viscosity. In addition to visual loss, a significant complication of all vascular occlusions is the development of new blood vessels (neovascularization) which grow out of the retina into the vitreous cavity, where they can bleed and further aggravate visual loss. A more devastating complication is neovascular glaucoma, caused by growth of new blood vessels over the iris and the angle between it and the cornea, thus closing the channels through which aqueous fluid normally flows out of the eye. Neovascular glaucoma can be so painful and disfiguring as to require enucleation (removal of the eye). With timely intervention with laser or cryotherapy, such a radical procedure is now extremely rare.