WHAT IS RETINAL ARTERY OCCLUSION

Retinal Artery Occlusion: An Overview

Retinal artery occlusion (RAO) is a critical vascular condition characterized by a blockage in the arteries that carry blood to the retina. This condition is typically associated with a sudden, painless loss of vision in one eye. The severity and extent of the visual impairment are directly determined by which specific vessels are obstructed and the area of the retina affected.

Understanding CRAO and BRAO

The ophthalmic artery is the primary vessel supplying blood to the eye, and its blockage causes the most significant damage. Medical professionals categorize these blockages into two main types:

• Central Retinal Artery Occlusion (CRAO): A blockage in the main retinal artery, often resulting in severe vision loss. Interestingly, approximately 25% of the population possesses an extra vessel called a cilioretinal artery, which can preserve central vision if it remains unaffected during a CRAO event.
• Branch Retinal Artery Occlusion (BRAO): A blockage in a smaller branch artery. This may cause a loss of a specific section of the visual field. If the affected area is small or not central, a BRAO might even go unnoticed by the patient.

Primary Causes and Risk Factors

Retinal artery occlusion occurs when the retinal artery is blocked by an embolus (a small piece of cholesterol) or a thrombus (blood clot). While some occlusions are transient—lasting only seconds or minutes if the blockage breaks up—others can lead to permanent damage. Most patients are in their 60s, and the condition is more prevalent in men, with bilateral involvement occurring in only 1% to 2% of cases.

Common Risk Factors

Several systemic conditions increase the risk of developing a retinal artery occlusion:

Diagnostic Testing and Procedures

To accurately diagnose CRAO, specialists perform a dilated eye examination. A hallmark sign is the "cherry red spot," where the center of the macula appears red against a pale, blood-deprived retina. In cases of BRAO, the retina appears whitened along the blocked vessel, a sign that typically lasts 4 to 6 weeks.

Advanced diagnostic tools include:

• Fluorescein Angiography (FA): This test highlights delays in the filling of retinal arteries.
• Optical Coherence Tomography (OCT): This provides detailed images showing swelling in the inner retinal layers, which may eventually lead to atrophy.

Treatment and Emergency Management

Currently, there is no clinically proven treatment that predictably alters the natural history of CRAO. However, several emergency therapies may be attempted to dislodge the blockage, provided they are administered within a 4 to 6-hour window after symptoms begin:

1. Hyperventilation: Inhaling carbogen (95% oxygen, 5% carbon dioxide) to dilate arteries.
2. Paracentesis: Removing a small amount of fluid from the front of the eye to lower intraocular pressure.
3. Medication: Using drugs to reduce pressure within the eye.
4. Ocular Massage: Manual pressure applied to the eye to help move the clot.

Note: Patients with acute onset CRAO or BRAO must be referred immediately to an emergency room to evaluate the risk of a stroke.

Prognosis and Long-term Complications

The visual prognosis for CRAO is generally severe, though patients with a cilioretinal artery have an 80% chance of recovering vision to 20/50 or better. For BRAO, while visual field loss is often permanent, central visual acuity recovers to 20/40 or better in approximately 80% of cases.

A rare but serious complication is the growth of abnormal new blood vessels (neovascularization), which can lead to vitreous hemorrhage or glaucoma. In such instances, laser photocoagulation therapy is utilized to reduce the retina's oxygen demand and halt the growth of these damaging vessels.

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Op. Dr. Ahmet Umay
NICOSIA / CYPRUS
Resource: The Foundation of the American Society of Retina Specialists