At the top of this photograph is a white patch in a retinal artery. This is an embolus that has lodged at a branching point in the artery and has cut off the circulation beyond it. This retinal artery occlusion has happened beyond the branch of the artery that supplies blood to the centre of the macula so the central vision has been preserved.
When a retinal artery occlusion occurs, it is usually a sudden event and can have a devastating and permanent effect on vision. This is an ophthalmic emergency.
If a central retinal artery occlusion occurs patients experience almost complete loss of vision in that eye. Patients should be seen as soon as possible after noticing this and may require emergency treatment. This generally consists of reducing the pressure in the eye (IOP) and increasing blood flow to the retina.
Similar treatment is also possible for a blockage of a branch retinal artery, which may only affect a part of the vision, typically either the top or bottom half of the vision. Whether this includes the central vision is simply a matter of luck and depends on whether the artery affected usually supplies blood to the fovea.
The blockage in the artery can rarely be due to sudden a drop in a patient’s blood pressure following major vascular surgery or after severe blood loss.The commonest cause, though, is an embolus. This is a small solid object (cholesterol, plaque or clot) that has been dislodged from the wall of the heart or blood vessel in the neck (carotid artery). In addition to this being a serious condition for the eye, it can sometimes be a serious threat to the brain if the source of the embolus releases more into the circulation of the brain.
Apart from the immediate eye treatment, daily low-dose aspirin is usually started as a precaution and urgent investigation of the heart and carotid arteries is important.