By Ike Schouten, ophthalmologist
Blood Supply to the Eye
Blood is pumped from the heart; the eye is supplied via a branch of the carotid artery. The eye is a sphere with a small opening at the back; through this opening, the optic nerve exits the eye and travels to the brain, and through the same opening, the arterial (arterial; inflow) blood supply to the retina enters, and the venous (venous; outflow) central blood vessel exits the eye through the same opening.
Blood Vessels in the Retina
The retina is the inner lining of the eyeball that contains light-sensitive cells. Once the ophthalmologist has administered eye drops to dilate the pupil, the retina and its blood vessels can be visualized using light and a special lens. The central retinal artery, which enters the eye, branches into four branches that continue to branch into smaller and smaller vessels until they form such a fine network that it cannot be seen without special imaging techniques; these are the capillaries. These capillaries then merge into progressively larger vessels that converge into the central vein, which exits the eye through the same opening.
Ocular infarction = retinal infarction
The blockage of a retinal artery is called an arterial occlusion or an ocular infarction; this is comparable to a heart attack or a stroke. It can occur in the central artery entering the eye or in one of its branches. All the small blood vessels located downstream from the blocked vessel no longer receive blood, causing the retinal tissue in that area to be deprived of oxygen. Retinal circulation supplies the inner part of the retina with oxygen; if this does not occur, the retina swells and takes on a whitish appearance (Figure 4). These retinal abnormalities can also be clearly observed on an OCT scan of the retina.
Symptoms When the retina is deprived of oxygen, this causes a painless, acute loss of vision. In the case of a central retinal artery infarction, vision is often so impaired that the patient can only perceive light or, for example, see hand movements or fingers held up at close range. In the case of a retinal artery branch occlusion, a dark spot is seen. The retina cannot survive for long without oxygen, and irreversible damage occurs as early as 4 hours. The occlusion usually resolves spontaneously; the blood vessels then return to normal, but irreversible damage to the retina has already occurred. In about 20% of people, some vision returns within the first three days; after that, vision does not improve any further.
Causes of an ocular infarction
A central arterial occlusion is caused by an embolus—a clot containing cholesterol, calcium, or platelets—which usually originates from atherosclerosis (hardening of the arteries) in the carotid artery or the heart, but can actually come from anywhere along the entire blood supply pathway. In the case of an ocular infarction, the patient is therefore referred to the TIA clinic, an internist, or a cardiologist for further evaluation. Major risk factors include high blood pressure, diabetes, smoking, elevated cholesterol, and cardiac arrhythmias. In some cases, vasculitis underlies the infarction; blood tests are performed to confirm this. If this is the case, treatment with steroids is initiated to prevent further complications, including in the other eye.
Treatment In the first few hours after the infarction, an ophthalmologist may attempt to improve blood flow—for example, by massaging the eyeball—but this usually has no effect. Since there are no other effective treatments, an ocular infarction is a very dramatic and life-altering condition. The medical course of action following diagnosis focuses primarily on identifying underlying causes and addressing risk factors to prevent other cardiovascular problems in the future. Psychological counseling may be necessary to assist with adjusting to the new visual situation, as well as with processing and accepting the condition.
Additional Eye Problems
In a small percentage of people with central retinal artery occlusion, the damaged retina produces substances that stimulate new blood vessel growth. Although this may sound like a good thing, unfortunately these blood vessels do not grow where they are needed. They can grow on the iris and near the drainage system for the eye’s internal fluid, obstructing the drainage of this fluid and causing very high intraocular pressure; This condition is called neovascular glaucoma and must be treated with laser therapy and injections to prevent a painful, blind eye.
Other types of blood vessel blockages in the eye
A venous occlusion can also occur in the retina; in this case, the blockage is in the draining vessels, the veins. Blood can still enter the eye but can no longer drain properly; this is also known as an ocular thrombosis (CRVO or BRVO). Furthermore, an infarction of the small blood vessels of the optic nerve can occur, preventing the proper transmission of information from the retina to the brain via the optic nerve (AION). More information on this topic can be found at oogziekenhuis.nl and oogartsen.nl.
