Central Retinal Artery Occlusion (CRAO)

What is CRAO?

CRAO is an ischemic stroke of the part of eye known as inner retina, caused by blockage in the central retinal artery or one of its main branches.

 

What is inner retina?

Eyeball is a hollow globe-like structure and is filled with clear fluid. In its front is a small opening or the pupil through which light rays enter. Inside of the eyeball, especially on its sides away from the pupil, is lined by a special tissue, the retina. Retina acts as a receiver for the incoming light signals. Electrochemical processes convert light into electrical signals that are sent to the occipital brain region for interpretation.  The section of the retina that faces inward toward the clear fluid is referred to as the inner retina or the inner side of retina, while the surrounding or the outer side is known as the outer retina. Each layer receives blood supply from different vessels. The inner retina is supplied by branches of the retinal artery. The retinal artery is a branch of ophthalmic artery, which is a direct branch of the carotid artery.

 

What are symptoms of CRAO?

CRAO typically causes sudden, painless vision loss in one eye.

 

Who usually gets affected by CRAO?

This type of stroke occurs in 2–10 out of every 100,000 individuals. The average patient age is in the mid-60s, with people over 80 years experiencing higher incidence rates. Men have a slightly greater risk than women.

 

What are other risk factors for CRAO?

Probably the strongest risk factor is the stenosis or tightening of the carotid artery on that side. Other risk factors include age, heart disease (such as atrial fibrillation or heart failure), aortic arch disease, obesity, high blood pressure, high cholesterol, tobacco use and diabetes.  

 

What exactly happens in CRAO?

The retinal artery may lose its capacity to supply blood to the inner retina due either to gradual accumulation of deposits within the vessel wall or occlusion by an embolus originating elsewhere. Rarely, it can also happen from inflammation of the vessel wall. While the retina can tolerate brief periods of reduced blood flow, prolonged obstruction may lead to irreversible damage and permanent loss of vision. Damage to retina may lead to permanent blindness. The extent of damage and type of blindness is influenced by the presence of collateral or alternate circulation. In certain cases, patients with sufficient or efficient alternate circulation may experience limited visual impairment.

 

What is arteritic type of CRAO?

This type of CRAO is caused by inflammation of the vessel wall, most often due to Giant cell arteritis. This condition may be considered in individuals over 50 years old who present with symptoms such as jaw pain, polymyalgia rheumatica, diffuse posterior neck pain, scalp tenderness, or a new headache. Patients may exhibit increased inflammatory markers, including ESR and CRP.

 

How is CRAO diagnosed?

Sudden, painless vision loss in one eye—especially peripheral vision—is typical and aids diagnosis. On exam, the affected pupil often appears dilated and does not fully or promptly constrict when exposed to bright light, though it constricts normally with light in the unaffected eye (provided it is otherwise healthy)—this is known as afferent pupillary defect. CT or MRI may offer indirect support but not direct confirmation. Fundoscopy is most useful; the retina may appear pale or white from loss of blood supply. A common finding on fundoscopy is referred to as the cherry-red spot. Occasionally, an embolus—such as a blood clot, cholesterol debris, or a foreign body from cosmetic eye procedures—may become lodged in the retinal artery or its branches. Fundoscopy also help to rule out other similar causes of visual loss.

 

What conditions may look like CRAO?

Many conditions that may lead to relatively quick loss of vision may look like CRAO. Some of those conditions are as follows:

1. Central retinal vein occlusion
2. Vitreous hemorrhage
3. Retinal detachment
4. Glaucoma
5. Optic neuritis
6. Ischemic optic neuropathy
7. Migraine
8. Brain stroke

What are the chances of recovery from CRAO?

In most cases, CRAO leads to permanent visual loss. Even if recovery happens, it usually is partial. This type of visual loss cannot be corrected with eyeglasses.

 

How is CRAO treated?

If CRAO is suspected and the time of onset is less than 4.5 hours, the patient is referred to an emergency room equipped to treated acute strokes. In ER, if not done before, fundoscopy is performed to rule out alternate ocular causes of visual loss. Other initial testing may include head CT to r/o bleed, ESR and CRP to rule out vasculitis, and other standard tests before considering treatment with a blood thinner like tPA or TNK. The risk of bleeding from tPA or TNK while treating CRAO is quite low. The benefit, even if modest, may significantly improve patient’s vision, which may help avoid permanent disability.

 

Is there a catheter-based treatment for CRAO?

Yes, there is an option of taking a small catheter to the ophthalmic artery and delivering a smaller dose of tPA or TNK. This may be an option for patients who cannot have full dose of these drugs, like patients on a blood thinner or with recent surgery. However, unlike the option of intravenous tPA or TNK administration, this method involves a risk of complications associated with catheterization. Because of multiple complexities, this type of treatment is unavailable in routine settings, as it requires highly specialized level of care.

 

Are there other means of treatment?

Researching online, one may find many other potential treatments such as anterior chamber paracentesis (removing fluid from the eye), eye massage, eye pressure lowering agents, isosorbide dinitrate, beta blockers, oxygen/carbon-dioxide therapy, or breathing in a paper bag. None of these therapies have been proven to work and some carry potential risks.

Hyperbaric oxygen therapy, on the other hand has some value. It is mildly effective but is only available in specialized settings.

 

What can I do to prevent CRAO?

The approach is same as any stroke prevention. Modifiable risks, especially high blood pressure, should be controlled. Please read the article of stroke for details on stroke prevention.

 

Where may I find more information about CRAO?

American Academy of Neurology

American Academy of Ophthalmology