The eye is the only part of the body where blood vessels can be viewed in their normal state without surgery. The state of the vessels within the eye can give a good indication as to the state of blood vessels elsewhere in the head and also in the body. There are currently studies to investigate if it is possible to predict with accuracy those who might be at risk of heart attacks and strokes, even dementia, solely by looking at the retinal vessels.
The retina of the eye has blood supplied by the central retinal artery, and drainage by the central retinal vein. Any interruption in either of these parts will cause problems- the retina, like the brain has a very high demand for blood to function properly.
The blood supply and its drainage divides into an upper and lower branch, which then is further divided into a nasal and temporal branch, so that each quadrant has its own blood supply and drainage, but all are subdivisions of the same central source. There is also a central Macular Branch, which supplies the central specialised part of the retina.
Symptoms of a vascular occlusion in the eye are a sudden painless loss, or blurring of vision. This may affect the entirety of the eye, or only an area, depending on the blood vessel division affected.
This is less common than venous occlusion
The Ophthalmic artery arises from the Internal Carotid Artery, one of main sources of blood to the brain, and it is the first branch of this artery after the carotid splits into its external and internal parts. The first branch of the ophthalmic artery is then the central retinal artery.
Blockage of an artery may be caused by a blood clot, a fat embolism, or an atheromatous plaque becoming detached from the inner wall of a blood vessel. These materials tend to travel until the artery diameter is too small to allow their passage, and a blockage occurs.
Most causes of retinal artery occlusion are from the heart or more commonly the carotid artery.
Risk factors include;
- Carotid artery disease, a condition in which one or both of the two large blood vessels in the neck become narrowed or blocked
- Heart rhythm problem (atrial fibrillation)
- Heart valve problem
- High levels of fat in the blood (hyperlipidemia)
- High blood pressure
- Intravenous drug abuse
- Vascular Spasm
- Temporal arteritis (damage to arteries due to an immune response)
Treatment for an arterial occlusion is usually ineffective, but any attempt must be started as soon as possible- within hours.
If the type of blockage can be determined, treatment may include massage of the eye, to try to dislodge the blockage, carbon dioxide therapy (CO2 causes the arteries to dilate, which may allow the blockage to move- if not away then at least into a smaller, less important artery) and “clot busting” injections, to attempt to break up the blockage.
Regardless to the outcome of the ocular problem, there will be various tests required of the blood, arteries and the heart, to try to determine what the cause of the blockage was, and to attempt to ensure that the risk factors can be reduced- it that clot had not gone into the ophthalmic artery it would have traveled up the internal carotid and likely lodged somewhere in the brain, possibly causing a stroke.
This most often occurs because of Atherosclerosis – hardening of the arteries. The artery walls become stiffer and thicker, which causes an increased pressure upon the veins where they cross, as they share a common outer layer. This can cause a partial or total occlusion of the vein. High Blood Pressure, high Eye Pressure and Diabetes are risk factors, as are any blood disorders which may make the blood thicker or stickier (more likely to clot), and the condition becomes more likely with age.
There is little effective treatment for venous occlusion, though, unless the sight is extremely poor at the onset of the problem, it is likely that there will be a significant improvement in the vision. There are two types of venous occlusion- ischaemic and non ischaemic. Ischaemic venous occlusions mean that the retina is starved of oxygen, and it is this type which causes a more profound visual loss, and a poorer chance of resolution.
Longer term consequences of an ischaemic vein occlusion are the possibility of new blood vessels growing, both on the retina and also on the iris, which can cause secondary Glaucoma. This so called “90 day Glaucoma” usually occurs approximately 3 months after the initial occlusion, and any eyes at risk must be monitored, as laser treatment may be used to arrest this vessel growth, should it occur.
Anterior Ischaemic Optic Neuropathy
This occurs because of a blockage in the Posterior Ciliary Arteries which supply the optic nerve head (the optic nerve as it leaves the eye). Because of the way the blood vessels here subdivide and then reconnect, there may be a complete failure of the optic nerve, or there may be an altitudinal defect, where only the upper or lower half of the visual field is affected.
Again treatment is usually ineffective, and any investigation is aimed at preventing the other eye suffering the same fate, or worse consequences.
This often occurs through the night- the person noticing the problem immediately on waking- this is thought to be because the blood pressure normally decreases when asleep.
Transient Ischaemic Attack
Some people have experienced a condition called Amaurosis Fugax, or fleeting vision loss. This is caused by a Transient Ischamic Attack or TIA, where a blockage occurs, but then can quickly clear. A TIA can resolve without leaving any residual damage, but again this should be promptly investigated, as it may indicate an increased risk of a more permanent loss.
Although there are few effective treatments for any of the above conditions, prompt investigation should be sought- Anterior Ischaemic Optic Neuropathy, as described above can often affect both eyes, but not at the same time. For Artery Occlusions, even if medics could break the blockage and restore blood flow, there would be little chance of recovery of vision after 24 hours, and vision would be seriously compromised after 4 to 6 hours, so speed is of the essence. Tests to assess the risk of another episode, and treatment to try to reduce this risk can save the sight of the fellow eye. It is particularly important to rule out as soon as possible a condition called Arteritis.
Arteritis, also called Giant Cell Arteritis (if it affect the neck, upper body and arms) or Temporal Arteritis if it affects the head only (often it is detectable in the artery that runs over the temple), is an auto immune disorder which usually affects people over age 55, it is three times more common in females than males. It causes the middle layer of the arteries to become profoundly thickened, which in turn reduces the capacity to carry blood- the “pipe” becomes narrowed. It is often accompanied by a general malaise (tiredness and feeling unwell), but can come on so slowly that, until treatment is commenced, the individual was unaware just how bad they were feeling! Symptoms may include jaw pain that comes and goes or occurs when chewing, dull throbbing in the temple, weight loss, fever, painful or tender scalp- sore to brush or comb hair
Arteritis is so serious that if this was considered a possibility in the hospital, it would usually be treated until or unless proven otherwise- treatment is with high dose steroids, which reduce the inflammation within the arteries, and many patients report a massive increase in how well they feel very soon after treatment is started.
Tests for Arteritis include an ESR (Erythrocyte Sedimendation Rate), where a small amount of blood is taken and put into a test tube. A High ESR will be displayed if the red cells separate from the blood plasma and fall to the bottom of the test tube faster than normal. The only sure diagnostic technique is to take a biopsy of the temporal artery, where it is cut and the two ends rejoined. Microscopic examination of the artery can confirm if the condition is present.