Retinal Vessel Occlusion

A retinal vessel occlusion is a blockage in a major artery or vein of the retina. Depending on the location, the occlusion can be classified as central retinal artery occlusion (CRAO), branch retinal artery occlusion (BRAO), central retinal vein occlusion (CRVO), or branch retinal vein occlusion (BRVO). Typically, a retinal vessel occlusion is a thromboembolic event. Risk factors include hypertension, diabetes mellitus, and cardiac valvular disease. Central retinal artery occlusion is characterized by sudden, unilateral, painless loss of vision and/or transient vision loss (amaurosis fugax). Treatment options are limited in all cases and usually ineffective. When the macula is involved, prognosis is especially poor, leading to permanent vision loss.

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Anatomy

  • The internal carotid artery enters the skull through the carotid foramen and branches into the ophthalmic artery, which further divides into:
    • The central retinal artery (occlusion (CRAO); supplies the inner ⅔ of the retina) 
    • The posterior ciliary arteries (branch retinal vein occlusion (BRAO); supply the outer ⅓ of the retina)
  • The central retinal vein (occlusion (CRVO)) 
    • Drains either into the superior ophthalmic vein or the cavernous sinus directly

Etiology

Central retinal artery occlusion/branch retinal artery occlusion

  • Embolism (most common cause of ipsilateral CRAO) 
    • Cardiogenic or atherosclerotic (most commonly of carotid origin) 
      • Risk factors include:  
        • Hypertension
        • Diabetes mellitus
        • Atrial fibrillation
        • Cardiac valvular problems/patent foramen ovale (leads to clots breaking off) 
    • Cholesterol embolism; usually occurs after vessel catheterization
    • Septic embolism, as a consequence of infective endocarditis
  • Inflammatory conditions such as temporal arteritis and other forms of vasculitis

Central retinal vein occlusion/branch retinal vein occlusion

Exact causes are not known, although there is an association with the following conditions:

  • Atherosclerotic conditions
    • Hypertension
    • Hypercholesterolemia
    • Smoking
    • Diabetes mellitus
    • Obesity
  • Hypercoagulable state
    • Sickle cell anemia
    • Antiphospholipid syndrome
    • Multiple myeloma
  • Inflammatory (e.g., systemic lupus erythematosus (SLE))
  • Pharmacological (e.g., oral contraceptive pills)
  • CRVO is categorized into 2 types based on etiology: ischemic (hemorrhagic retinopathy) and nonischemic (venous stasis retinopathy)

Clinical Presentation and Diagnosis

Clinical presentation

Central retinal artery occlusion

  • Sudden, painless, complete monocular vision loss
  • Patients may recall transient similar episodes (e.g., amaurosis fugax)
  • Fundoscopic examination reveals:
    • Pallor of optic disc due to narrowed arteries
    • Cherry red” spot in the macula (at the fovea centralis)

Central retinal vein occlusion

  • May be sudden or gradual, painless, monocular vision loss
  • Fundoscopic examination reveals
    • Swollen optic disc (papilledema) and engorged retinal veins with hemorrhage
    • Blood and thunder” appearance due to extensive hemorrhage (ischemic type) 
    • Cotton-wool” spots: white deposits on the retina due to swelling of the retinal nerve (ischemic type)

Diagnosis

Diagnosis of both conditions is usually clinical but additional investigations may be ordered.

  • Fluorescein angiography (to differentiate ischemic from non-ischemic forms of CRVO)
  • Optical coherence tomography (used to assess the progression of retinal vein occlusion or response to treatment)
  • Carotid doppler 
  • Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP): to rule out vasculitides

Differential Diagnosis

  • Vitreous hemorrhage: intraocular bleeding in or around the vitreous body usually from trauma, a retinal tear, or any disease causing neovascularization. Patients present with floaters and cloudy vision. Treatment includes surgery and avoiding anticoagulants. Vitreous hemorrhage is differentiated from a vessel occlusion due to a more gradual onset and the presence of floaters. 
  • Retinal detachment: separation of the neurosensory retina from the retinal pigment epithelium. Classically, the condtion presents as a curtain descending over the eye causing painless vision loss, but can also cause floaters and flashes early on. Most common causes are aging and trauma. Diagnosis is with direct eye exam and ultrasound. Treatment is surgery by laser or freezing. 
  • Cataracts: opacification of the lens in the eye, which leads to a decrease in vision. Cataracts often develop slowly and can affect 1 or both eyes. Risk factors are age and eye injury. Symptoms may include faded colors, blurry or double vision, halos around light, trouble with bright lights, and trouble seeing at night. Cataracts can be visualized as a cloudy lens on eye exam. Curative treatment is surgical replacement of the lens.

References

  1. Hedges III, T. R. (2018). Central and branch retinal artery occlusion. UpToDate. Retrieved September 24, 2020, from https://www.uptodate.com/contents/central-and-branch-retinal-artery-occlusion?search=retinal%20vascular%20occlusion&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1#H17
  2. Covert, D. J. , & Han, D. P. (2019). Retinal vein occlusion: Epidemiology, clinical manifestations, and diagnosis. UpToDate. Retrieved September 24, 2020, from https://www.uptodate.com/contents/retinal-vein-occlusion-epidemiology-clinical-manifestations-and-diagnosis?search=retinal%20vascular%20occlusion&source=search_result&selectedTitle=2~150&usage_type=default&display_rank=2#H7614371
  3. Hayreh SS, Podhajsky PA, Zimmerman MB. (2009). Retinal Artery Occlusion Associated Systemic and Ophthalmic Abnormalities. Ophthalmology.

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