Vascular occlusions – classification

Description

Retinal vascular occlusions are the second most common vascular disease affecting the retina, after diabetic retinopathy. They show a strong association with systemic diseases, such as atherosclerosis and carotid artery disease, hypertension, diabetes, hyperlipidemia, temporal arteritis, and hypercoagulation or vasculitis disorders. Occlusions affecting the retinal arteries tend to result from emboli, whether due to atheromatous plaques breaking free into the blood stream, or from cholesterol (Hollenhorst plaques), calcifications, impurities injected into the blood from IV drug use, or many other factors. Venous occlusions tend to relate to formation of a thrombus at arteriovenous crossings, where there is narrowing of the vessel lumen, blood turbulence and platelet aggregation. Central retinal vein occlusions also have an association with primary open-angle glaucoma.

Symptoms

Visual symptoms are more likely in retinal vascular occlusions if a large area of retina is affected or is in close proximity to the macula. A sudden painless loss of vision may be reported with a central retinal vascular occlusion. There may be a history of previous brief loss of vision (amaurosis fugax), transient ischemic attack (TIA), or stroke (cerebrovascular accident).

Signs And Classification

• Branch Retinal Vein Occlusion (BRVO). Initial signs are dilated and tortuous veins, flame, dot and blot haemorrhages, retinal edema and cotton wool spots. Later signs may include hard exudates, macula edema and neovascularization. BRVOs may be characterized in terms of the occlusion location – distance from the disk and proximity to the macula. The occlusion location dictates the size of the affected area of retina and the likelihood of macula edema, which in turn affect the visual prognosis.
• Branch Retinal Artery Occlusion (BRAO). Arterial occlusions cause retinal infarction (whitening) rather than the hemorrhagic signs associated with venous occlusions. The arterioles and venules are narrowed and the retinal tissue whitens due to ischemia. BRAO’s may be characterized in the same way as BRVO’s.
• Central Retinal Vein Occlusion (CRVO). Venous occlusion affecting the entire retina, attributed to a blockage in the central retinal vein at the level of the lamina cribrosa within the optic disk or perhaps due to atherosclerosis of the adjacent central retinal artery. A complete blockage is termed an ischemic CRVO. If the vein bifurcates posterior to the lamina cribrosa, then a hemi-retinal vein occlusion may occur.
• Central Retinal Artery Occlusion (CRAO). CRAO has superficial whitening of the retina due to the retinal nerve fiber ischemia and infarction. There is a characteristic cherry-red spot at the macula, since the nerve fiber layer is thin and the choroidal circulation is more visible. A positive relative afferent pupil defect (RAPD, Marcus Gunn pupil) is present, and vision loss is usually severe.
• Venous stasis retinopathy, a partial occlusion of the retinal veins leading to a slowing of the blood flow but not a complete blockage.
• Cilio-retinal artery occlusion. Present in only some patients, the small cilio-retinal artery supplies the posterior pole retina and derives from the posterior ciliary circulation.
• Ophthalmic artery occlusion, where both retinal and choroidal circulation is obstructed.

Prevalence

Whilst overall vascular occlusions are uncommon (1:1000), they are relatively common (1:100) in specific at-risk groups such as people over 50 years.

Significance

Vascular disease kills 60% of Australians, particularly via cerebral and cardiac events (stroke and heart attack). Retinal vascular occlusions are not only vision threatening, but indicate increased risk for systemic vascular disease.

Differential Diagnosis

Retinal vascular occlusions are usually unilateral, unlike Hypertensive or Diabetic retinopathy.

Management

While the mainstay of management is systemic in nature, local urgent treatment may be required for CRAO, and laser treatment may be required for BRVO and CRVO. For details, see the individual conditions listed above under Signs And Classification.