What is retinal artery occlusion?
This is a blockage of a retinal artery that causes a varying amount of visual loss, depending on the type of artery occlusion.
What are the types of retinal artery occlusion?
There are 3 main types:
- Branch Retinal Artery Occlusion (BRAO) – a branch retinal artery supplies a quadrant of the retina, and occlusion of one of these vessels produces an area of the vision that is missing (visual field defect) that can usually be demonstrated with automated perimetry.
- Central Retinal Artery Occlusion (CRAO) – the central retinal artery supplies the whole retina – if this becomes blocked, the patient usually loses all vision in the affected eye (unless the eye has a cilio-retinal artery – see below)
- Cilio-Retinal Artery Occlusion – the cilio-retinal artery is only present in a small number of people. It supplies blood to part of the retina responsible for central vision (the macula) but its supply is derived from the choroidal rather than the retinal blood supply. If an eye has a cilio-retinal artery, it can either become blocked itself (causing an area of visual loss near or affecting the main central vision) or alternatively its presence can be responsible for “sparing” of the central vision in cases of central retinal artery occlusion that would otherwise have caused profound loss of vision.
What causes retinal artery occlusions?
The arteries can become blocked with different types of material – these are called ’emboli’ and can be made of either cholesterol, calcium, or clots of blood called thrombus. Rarely, retinal artery occlusions are associated with inflammation of the arteries in the head (a condition called giant cell arteritis).
What eye tests are done?
Depending on the type of retinal artery occlusion present, different tests may be done to document or confirm the relevant abnormalities, including visual field testing to show the area of field missing, fluorescein angiography to confirm the lack of blood flow in the affected vessel, OCT scanning which (after the acute phase) normally shows thinning of the inner retina in the affected area, and/or colour fundus photography which may for example document a visible embolus.
What other tests are needed?
The significance of retinal artery occlusion is that it may be a predictor for stroke, so patients are normally referred for other tests including ultrasound of the carotid arteries in the neck, echocardiography, and often blood tests (eg for cholesterol levels) to see if anything can be done to minimise the risk of stroke. Patients will usually also have an inflammatory marker called CRP (C-reactive protein) checked in their blood in order to help exclude giant cell arteritis (see above).
What complications of retinal artery occlusion can occur in the eye?
Usually, the visual deficit from retinal artery occlusion is instantly apparent, does not evolve, and is not associated with any further complications. In a very small number of cases of CRAO, new vessels can grow at the front of the eye (rubeosis iridis) and this can cause secondary glaucoma. This is however much more common with central retinal vein occlusion.