RETINAL ARTERY OCCLUSION

Overview of branch retinal artery occlusion and central retinal artery occlusion.

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A retinal artery occlusion (RAO) is a medical condition in which blood flow to the retina is blocked, leading to a sudden and often severe loss of vision in the affected eye. The retina is the light-sensitive tissue at the back of the eye responsible for converting light into nerve signals that are sent to the brain, allowing us to see.

There are two main types of retinal artery occlusion: central retinal artery occlusion (CRAO) and branch retinal artery occlusion (BRAO).

  1. Central Retinal Artery Occlusion (CRAO):
    • CRAO occurs when the central retinal artery, which supplies blood to a significant portion of the retina, becomes blocked. This can happen due to a blood clot or embolism that travels from another part of the body and lodges in the artery, blocking the flow of blood.
    • The sudden interruption of blood supply to the central retina can cause a rapid and severe loss of vision in the affected eye. Patients often describe it as a curtain or veil descending over their vision.
    • CRAO is considered a medical emergency, and immediate evaluation and intervention are crucial to attempt to restore blood flow and minimize vision loss. Unfortunately, the prognosis for vision recovery in CRAO is often guarded.
  2. Branch Retinal Artery Occlusion (BRAO):
    • BRAO occurs when one of the smaller branches of the central retinal artery becomes blocked. Unlike CRAO, where the entire blood supply to the central retina is affected, BRAO only affects a portion of the retina supplied by the blocked branch.
    • The symptoms of BRAO vary depending on the location and extent of the blockage. Patients may experience a sudden, painless loss of vision in one part of their visual field, often described as a “missing” or “blacked-out” area.
    • While BRAO is also a serious condition, the visual outcome can be more variable than in CRAO. Some patients may experience partial recovery of vision, especially if the blockage is limited to a smaller area of the retina.

Risk factors for both CRAO and BRAO include a history of cardiovascular disease, hypertension, diabetes, and other vascular conditions. Management involves identifying and addressing the underlying causes and, in some cases, attempting interventions to improve blood flow.

It’s essential for individuals experiencing sudden vision loss to seek immediate medical attention, as prompt medical attention may be necessary for patients with retinal artery occlusion because they they have a high risk of stroke.

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Although no treatment has been shown beneficial for central retinal artery occlusion, the evaluation and management of this disorder is still important.

Evaluation:

  1. Clinical Examination:
    • A thorough eye examination by an ophthalmologist is the primary step in diagnosing CRAO. The sudden, painless loss of vision is a key symptom.
    • The doctor will assess visual acuity, pupillary reactions, and examine the retina to look for signs of ischemia (lack of blood flow) such as a pale retina and the presence of a cherry-red spot in the macula (a small area in the center of the retina).
  2. Ancillary Testing:
    • Fluorescein angiography: This test involves injecting a dye into the bloodstream and taking photographs to visualize the blood flow in the retina. In CRAO, the affected area may show delayed or absent blood flow.
    • Optical Coherence Tomography (OCT): This imaging technique provides detailed cross-sectional images of the retina, helping to assess the thickness of retinal layers and identify any swelling.
  3. Systemic Evaluation:
    • Since CRAO is a type of stroke, patients who have had a CRAO need to be urgently evaluated to see if they also have had a stroke.  This may require an urgent visit to their primary care doctor or an emergency room.  In addition, CRAO is often associated with systemic vascular diseases, additional evaluations may be needed to assess the patient’s cardiovascular health. This may include blood pressure measurement, blood tests, and other cardiovascular assessments.

Management:

  1. Immediate Intervention:
    • Some interventions have been attempted to dislodge the embolism causing the blockage, but none have been shown to be effective.
    • Sometimes an anterior chamber tap is done to lower the intraocular pressure and attempt to dislodge the embolism.
  2. Medical Management:
    • Currently, no established medical treatments have consistently demonstrated benefits in the management of CRAO.
    • Some medications, such as intra-arterial thrombolytics or hyperbaric oxygen therapy, have been investigated, but their effectiveness remains uncertain.
  3. Prognosis:
    • Unfortunately, the visual prognosis in cases of CRAO is often guarded. Even with prompt intervention, vision recovery is limited, and some individuals may experience permanent visual impairment.  There is a small risk of neovascular glaucoma in patients with CRAO and therefore it is common for people with CRAO to be checked regularly for several months after the onset of the vision loss. About 10 percent of patients with CRAO regain useful vision in the eye.
  4. Prevention:
    • Managing systemic risk factors is crucial to prevent recurrence or the occurrence of other vascular events. This may involve lifestyle modifications, medications, and close monitoring of cardiovascular health.

It’s important to note that while various treatments have been studied, the overall consensus in the medical community is that the evidence supporting their efficacy is limited, and the management of CRAO remains challenging.

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Evaluation:

  1. Clinical Examination:
    • Similar to CRAO, an ophthalmologist will conduct a comprehensive eye examination to assess visual acuity, pupillary reactions, and examine the retina. In BRAO, the symptoms are often localized to a specific part of the visual field.
  2. Ancillary Testing:
    • Fluorescein angiography may be performed to visualize blood flow and identify the specific branch affected. Optical Coherence Tomography (OCT) can help assess the extent of retinal damage and identify any swelling.
  3. Systemic Evaluation:
    • As with CRAO, a broader systemic evaluation may be conducted to identify and manage underlying risk factors such as hypertension, diabetes, or cardiovascular disease. In addition, since about 20 percent of patients with a BRAO also have a stroke, most patients with BRAO require urgent medical evaluation with their primary care physician or at the emergency room to rule out a stroke.

Management:

  1. Natural Course:
    • One notable aspect of BRAO is that, in some cases, patients may experience spontaneous improvement in vision over time as the eye heals.
  2. Monitoring and Supportive Care:
    • In cases where there is no immediate threat to the patient’s overall health, a conservative approach may be taken. The patient may be monitored regularly, and supportive measures may be implemented to manage associated symptoms, such as addressing any swelling or edema.
  3. Antiplatelet Therapy:
    • While the evidence is not robust, some physicians may consider antiplatelet therapy (such as aspirin) to reduce the risk of further thromboembolic events. The decision to use antiplatelet therapy is often made on a case-by-case basis, weighing potential benefits against risks.

Prognosis:

  • The visual prognosis in BRAO is generally more favorable than in CRAO. Improvement in vision can occur over weeks to months as the retina heals and collateral circulation develops.
  • The extent of visual recovery depends on factors such as the location and size of the affected branch, the speed of onset, and the presence of underlying systemic conditions.

Important Note:

  • Unlike CRAO, where the entire blood supply to the central retina is affected, BRAO only involves a portion of the retina. This localized nature of the occlusion contributes to the potential for spontaneous improvement and better visual outcomes.

It’s crucial for individuals experiencing sudden vision changes to seek prompt medical attention. While no specific treatment has been shown to be consistently effective for BRAO, monitoring and management of underlying risk factors are essential. The variability in outcomes highlights the importance of individualized care and ongoing follow-up with healthcare professionals. Regular eye examinations and systemic health management can contribute to the overall well-being and visual health of individuals affected by BRAO.