Retinal vessel occlusion

Retinal artery occlusion refers to occlusion of the central retinal artery and/or its branches, usually as a result of thromboembolic phenomena. Central retinal artery occlusion (CRAO) is characterized by sudden, painless loss of vision and a relative afferent pupillary defect. Ophthalmoscopy reveals a pale, edematous retina and a cherry-red spot in the foveal region. Branch retinal artery occlusion (BRAO) presents with specific patterns of visual field defects depending on which branch is involved. Treatment is usually ineffective because of irreversible ischemic damage to the retina. The prognosis is especially poor if the macula is involved. Retinal vein occlusion is more common than retinal artery occlusion and follows a less fulminant course. Branched retinal vein occlusion (BRVO), which is more common than central retinal vein occlusion (CRVO), is usually asymptomatic unless the macula is involved. CRVO may be either non-ischemic or ischemic. Fluorescein angiography is required in order to differentiate between ischemic and non-ischemic retinal vein occlusion. The prognosis of ischemic CRVO is less favorable since it is associated with neovascular glaucoma and retinal detachment. While BRVO and non-ischemic CRVO usually do not require any treatment, ischemic CRVO requires laser therapy.

Retinal vessel occlusion causing retinal ischemia. Based on the site of occlusion, retinal vessel occlusion can be classified into the following entities:

• Central retinal artery occlusion (CRAO)
• Branch retinal artery occlusion (BRAO)
• Central retinal vein occlusion (CRVO), assuming one of two forms:
  • Non-ischemic CRVO (venous stasis retinopathy)
  • Ischemic CRVO (hemorrhagic retinopathy)
• Branch retinal vein occlusion (BRVO)

Retinal artery occlusion

• Age of onset: > 60 years
• Sex: ♂ > ♀

Retinal vein occlusion

• Age of onset: > 80 years
• Sex: ♂ = ♀

Retinal vein occlusion is much more common than retinal artery occlusion. Retinal vein occlusion is the second most common vascular disease of the retina (after diabetic retinopathy).

Epidemiological data refers to the US, unless otherwise specified.

Retinal artery occlusion

• Embolism
  • Release of thrombotic emboli as a result of carotid artery atherosclerosis (most common)
  • Emboli from the atria (usually as a result of atrial fibrillation)
• Thrombosis
  • Usually as a result of atherosclerosis
  • Most common site of thrombosis: lamina cribrosa (site where the optic nerve pierces the sclera)
• Rare causes
  • Vasculitis (e.g., temporal arteritis)
  • Arterial vasospasm
  • Fibromuscular dysplasia

Retinal vein occlusion

The exact cause of thromboembolic retinal vein occlusion is unknown, but risk factors include:

• Systemic diseases
  • Atherosclerosis
  • Hypertension
  • Diabetes mellitus
• Hypercoagulable/prothrombotic states
  • Polycythemia vera
  • Oral contraceptive use
• Ocular diseases
  • Atherosclerosis of the retinal artery (may cause compression of the adjacent retinal vein and lead to turbulent blood flow)
  • Glaucoma
  • Vasculitis of the retinal artery

Retinal artery occlusion

Retinal vein occlusion

• Definition: sudden, painless loss of vision that lasts for seconds to minutes and is followed by spontaneous recovery (mostly unilateral)
• Cause: retinal ischemia following transient occlusion of the central retinal artery by microemboli
  • Cardiovascular causes (atherosclerosis, carotid artery stenosis, cardiac thrombi)
  • Vasculitis (e.g., temporal arteritis, lupus erythematosus, polyarteritis nodosa)
• Treatment
  • Although amaurosis fugax is self-limiting, it is a harbinger of more serious conditions. Therefore, perimetry and treatment of the underlying cause are essential:
    • Reduction of cardiovascular risk factors (e.g., low-dose aspirin therapy)
    • In the case of temporal arteritis: high-dose glucocorticoid therapy
• Complications
  • Retinal artery occlusion
  • Transient ischemic attacks (TIA)
  • Stroke

Retinal vessel occlusion is primarily a clinical diagnosis; (based on the patient's history and fundus examination). Additional investigations are usually performed to identify underlying risk factors, to differentiate between subtypes (e.g., in the case of CRVO).

Retinal artery occlusion

• Evaluation for cardiovascular risk factors:
  • Carotid doppler (to look for atherosclerotic plaques)
  • Echocardiography (to identify potential sources of emboli, e.g. cardiac vegetations, patent foramen ovale)
• Tests to rule out temporal arteritis:
  • Inflammatory markers (e.g., ↑ ESR)
  • Temporal artery biopsy

Retinal vein occlusion

• Fluorescein angiography: in order to differentiate ischemic from non-ischemic forms of retinal vein occlusion
• Optical coherence tomography may be performed to look for macular edema. ^[2]

References:^[1]

Retinal artery occlusion ^[3][4]

Retinal artery occlusion is an ophthalmologic emergency.

• Eyeball massage
• Carbogen therapy: inhaling a mixture of 5% CO₂ and 95% O₂
• Decrease intraocular pressure; with drugs and/or surgical therapy (e.g., paracentesis of the anterior chamber)
• Hemodilution
• Vasodilators (e.g., calcium channel blockers, sublingual nitroglycerine)
• High-dose glucocorticoid therapy if temporal arteritis is suspected
• Intra-arterial thrombolysis (IAT)
• Hyperbaric oxygen therapy

Treatment should be initiated as soon as possible, as permanent retinal damage occurs within 1.5 hours of central retinal artery occlusion.

Retinal vein occlusion ^[1][3]

• Ischemic CRVO must be treated with: ^[5][6]
  • Panretinal photocoagulation
    • Corrects ischemic hypoxia and thereby minimizes neovascularization.
    • A technique that uses a laser to cause thermal burns to retinal tissue.
  • If macular edema is present: intravitreal injection of VEGF inhibitors and/or steroids
• BRVO and non-ischemic CRVO usually do not require treatment.

Release of vasoproliferative substances (e.g., VEGF) from the ischemic retina causes:

• Neovascularization of the iris (rubeosis iridis) → neovascular glaucoma
• Neovascularization of the retina → vitreous hemorrhage → retinal detachment

Of all types of retinal vessel occlusion, ischemic CRVO is most commonly associated with neovascularization.

We list the most important complications. The selection is not exhaustive.

Retinal artery occlusion

• Central retinal artery occlusion: severe loss of vision
• Branch retinal artery occlusion: loss of vision and/or visual field defects (depending on which branch of the retinal artery is affected)

Retinal vein occlusion

• Rule of thirds: Visual acuity improves in one-third of cases, remains the same in another third, and worsens in the remaining third.
• The prognosis is especially poor in the case of ischemic CRVO.

References:^[1]