This is when the main artery to the retina, or one of its branches, becomes blocked. This can lead to irreversible loss of sight. The usual cause for this is that a small fragment of cholesterol plaque from the inner wall of the carotid artery (main artery in neck) becomes dislodged and travels down the arteries until it can go no further (end artery), this happens to be the retinal artery in this case.
This occurs when the internal carotid artery has become partially blocked by plaque and the blood flow past it is turbulent. As well as bits of cholesterol, the embolus (blocking fragment) may be some clotted blood cells triggered by the turbulent flow. Sometimes people have some warning of the blockage in the form of “amaurosis fugax”; this is a condition where there are transient episodes of visual loss, which generally recover after a minute or so. The retinal artery can become blocked when there is a vasculitis such as in temporal arteritis.
Risk factors for atheromatous vascular disease include:
- Hypertension (raised blood pressure)
- Diabetes
- Smoking
- Raised cholesterol or abnormal lipid levels
- Rare clotting disorders
Symptoms
- Sudden painless loss of vision; this may either be the whole field of vision or a defect above or below the horizontal mid line.
- Rarely, this may be associated with a headache. Sometimes the headache is associated with inflammation of the blood vessels (cranial or temporal arteritis).
Investigation
- Scanning of the carotid vessels with ultrasound or less commonly arteriogram (where dye is injected into the blood vessels) possibly in combination with a CT or MRI scan.
- Fluorescein angiography may be ordered.
- Blood tests will be taken to help exclude the risk factors above.
- If arteritis is suspected a temporal artery biopsy may be arranged.
Treatment
- Immediate management may include massage of the eye in an attempt to dislodge the clot.
- Sometimes paracentesis (draining of aqueous fluid) from the eye may help.
- Drugs to reduce the pressure in the eye may be tried.
- If arteritis is diagnosed, steroids will be commenced immediately.
- A platelet-inhibiting drug such as aspirin will be commenced.
- If a“critical stenosis” (generally above 70% blockage) is identified an operation (endarterectomy) may be offered in order to relieve the blockage.
Prognosis
- If the central vision is spared there may just be a permanent blind patch.
- If the central vision is affected the prognosis is unfortunately rather poor.
Note the pale top half of the
retina and the white spot of plaque
blocking the vessel.
This angiogram shows exactly where
the blockage lies.
