Retinal Vascular Occlusive Disease

Retinal vascular occlusion is one of the most devastating ophthalmic vascular diseases. It is often associated with systemic illnesses such as hypertension, diabetes and atherosclerosis. It is a common occurrence among elderly patients who experience a sudden, painless loss of vision and visual field. Due to a combination of late diagnosis, complications secondary to the occlusion and limited available treatments, a reversal of an occlusion is problematic. The etiology of retinal occlusion is unknown; however, thrombus formation and the resulting alteration of blood flow, blood constituents or the vessel wall injury have been implicated. Currently, there is an incomplete understanding of how the alteration in blood flow due to thrombosis causes defects in visual function. The mammalian retina is a complex system made up of multiple cell types. The retina is supplied by two blood circulations:   retinal and choroidal. The outer retina, mainly the photoreceptors, is supplied by the choroidal circulation. The inner retina, including bipolar cells and ganglion cells, is supplied by the retinal circulation.

There are two types of retinal vascular occlusion: arterial and venous occlusion. The thrombus formation can occur either in a central artery (vein) or in a branch artery (vein). Compare the normal fundus photo to both arterial and venous occlusion.

Normal Fundus

Central retinal artery occlusion (CRAO): The ophthalmoscopic appearance consists of superficial whitening of the posterior retina, a cherry red spot, and, in approximately 20% of affected eyes, thrombosis/emboli can be observed.

CRAO

Central retinal vein occlusion (CRVO):The fundus of an eye with CRVO shows dilated, tortuous retinal veins, intra-retinal hemorrhages, macular edema, swollen optic disc and in severe cases, cotton-wool spots.

CRVO

Occlusions are the most dramatic ophthalmic problems clinically because of the painless, rapid onset of symptoms that generally lead to permanent vision loss. Previous clinical studies of retinal vascular occlusion have been primarily limited to the pathophysiology of the disease and there are limited experimental animal models that mimic the human form of the retinal occlusion.The current understanding of retinal vascular occlusion lacks an in-depth examination of visual function and its association with changes in blood flow.