Definition

Retinal artery occlusion, also known as central retinal artery occlusion (CRAO), is a sudden blockage of the retinal arteries. The retina, a thin layer at the back of the eye, converts light into nerve signals for the brain. It has two main blood vessels: the central retinal artery and the central retinal vein. The arteries deliver oxygen-rich blood to the retina, and any blockage to the main artery or the branches can deprive retinal cells of oxygen, causing progressive damage. Sudden blockage of retinal arteries can lead to a sudden loss of vision. Immediate treatment is crucial, as delays can result in permanent blindness.

Causes

Several factors can cause retinal artery occlusion, including uncontrolled hypertension, diabetes mellitus, heart valve disease, congenital heart disease, injected drug use, and blood clotting disorders. Other causes include a history of eye injury, congenital abnormalities of the central retinal artery, reduced blood flow due to increased intraocular pressure, and arterial stenosis. Plaque-blocking retinal arteries can originate from calcium, cholesterol, heart surgery, or bacterial sources.

Risk Factor

Retinal artery occlusion is more prevalent in men than women and typically affects individuals over 60, though it can occur in younger people as young as 30. It usually affects one eye, but 1-2% of cases involve both eyes. Both the right and left eyes are equally susceptible. Retinal artery occlusion is less common than retinal vein occlusion.

Symptoms

The primary symptoms of retinal artery occlusion include:

• Sudden and significant decrease in visual acuity.
• Sudden darkening of vision without visible external eye abnormalities, typically affecting only one eye.
• Visual disturbances without accompanying itchiness or pain.
• Blurred vision that may be intermittent.
• Weak pupillary reaction with asymmetrical pupils.
• Severe visual impairment.

Patients with retinal artery occlusion should be aware of the risk of sudden blood vessel blockages in other organs, such as the heart (leading to heart attacks) or the brain (leading to strokes).

Diagnosis

The diagnosis of retinal artery occlusion involves a comprehensive process, including anamnesis (in-depth interviews), visual examination, and fundoscopy. Patients typically present with sudden, painless loss or impairment of vision in one eye, often reporting severe and rapid onset. Many have a history of transient visual function loss or impairment that resolves within seconds to minutes on its own. Symptoms indicating arterial occlusion, such as headache, neck pain, and scalp discomfort, may occur simultaneously or precede the visual impairment.

A thorough patient history to identify systemic diseases that can cause embolisms is crucial in finding the diagnosis. Essential diagnostic evaluations include blood pressure measurement, electrocardiography, and examining blood sugar levels and lipid profiles to identify conditions like hypertension, atherosclerosis, or diabetes.

During a pupillary reflex test, an abnormal response will be observed in the affected eye, though the forepart of the eye may appear normal unless complications arise. Funduscopic examination often reveals a unique "cherry red spot," but the eye may appear normal in the early stages of retinal artery occlusion. Additional diagnostic tools, such as electroretinography and color Doppler ultrasound, are used to detect decreased or absent blood flow velocity in the central retinal artery.

Management

Currently, effective treatments to restore vision after retinal artery occlusion are still under research. It is recommended to begin treatment within 24 hours of the onset of symptoms. Several treatment options are available:

• Press the eyeball for 5-15 seconds and then release the pressure multiple times. This aims to release the arterial blockage and increase retinal perfusion.
• Paracentesis. Removing some fluid from the eyeball rapidly decrease intraocular pressure, helping the arterial perfusion pressure to push the emboli to the periphery.
• Timolol eye drops and systemic medication such as acetazolamide can help lower intraocular pressure.
• Nd: YAG Laser Therapy. Aiming to break down the retinal artery blockages. However, this procedure can lead to complications like aneurysms and vitreous hemorrhage.
• Hyperbaric Therapy. Administering 100% oxygen at high pressure, which is effective if initiated within 12 hours of occlusion.

Complications

Retinal artery occlusion can lead to complications like iris neovascularization and optic disc neovascularization, both of which involve the growth of new, fragile blood vessels in response to a lack of oxygen caused by retinal artery occlusion. Patients with this condition should have regular check-ups during the first three months to monitor for complications. Additionally, retinal artery occlusion patients have a 10% risk of stroke within the first year, and this risk increases over time.

Prevention

Preventive measures for retinal artery occlusion include maintaining blood pressure below 140/90 mmHg, keeping LDL cholesterol levels normal, consuming a high-fiber, low-fat diet, and exercising regularly. Diabetic patients should adhere to their medication regimen and have regular check-ups to monitor blood sugar levels.

When to see a doctor?

Immediate medical attention is necessary for sudden, painless decreases in visual acuity. Since these visual disturbances can be transient, prompt evaluation is essential for early treatment. Regular eye examinations are recommended for individuals with risk factors such as high blood pressure, uncontrolled cholesterol, diabetes, blood clot history, and prior ocular injuries.