Retinal Arterial Occlusions
The central retinal artery is the main blood vessel that supplies blood to the retina.
This artery can become completely blocked due to an embolism (obstruction of a blood vessel by material traveling within it) or a thrombosis (formation of a clot directly within the artery).
The obstruction may involve the main artery or one of its branches.
Causes
The most common cause of arterial occlusion is an embolus originating from the heart or the carotid arteries.
Other frequent risk factors include advanced age, high blood pressure, diabetes, obesity, a sedentary lifestyle, smoking, high cholesterol, and hyperhomocysteinemia.
Symptoms
Patients experience sudden, severe, and painless vision loss.
In central retinal artery occlusion (CRAO), vision loss is more profound.
In branch retinal artery occlusion (BRAO), the sudden vision loss affects only part of the visual field.
The degree of vision loss and visual field defects depend on the size and location of the obstructed area.
In both cases, patients may report previous episodes of temporary vision loss that resolved within a few minutes.
Diagnosis
Diagnosis is made by an ophthalmologist. Useful tests include:
- Fluorescein angiography: Primarily used to detect retinal neovascularization (new blood vessels that attempt to compensate for blocked ones).
- Optical coherence tomography (OCT): Allows visualization of retinal edema (fluid accumulation), especially in the central area.
- Systemic evaluation: Once arterial obstruction is diagnosed, the underlying cause must be investigated. This includes monitoring blood pressure and heart rate, coagulation tests, blood glucose and lipid levels, Doppler ultrasound of the supra-aortic trunks (carotid arteries), and screening for cardiac arrhythmias.
Evaluation should always involve Internal Medicine, Cardiology, Hematology, and Vascular Surgery specialists.
Treatment
No treatment has proven clearly superior in restoring vision. Therefore, prevention through control of risk factors (such as hypertension, diabetes, and other atherosclerosis risk factors) is essential.
Treatment aims to increase blood flow in the occluded artery (by lowering intraocular pressure or promoting arteriolar vasodilation) and to remove the embolus.
Up to 20% of patients may develop neovascularization (formation of new blood vessels), mainly within the first three months. In such cases, panretinal laser photocoagulation is effective in preventing secondary neovascular glaucoma (increased intraocular pressure) resulting from the obstruction.