Retinal vessel occlusion

Retinal vessel occlusion is the complete or partial obstruction of retinal arteries or veins, most commonly due to thromboembolism. Depending on the extent and site of occlusion (central vessel or its branches), retinal vessel occlusion may be asymptomatic or manifest as sudden painless loss of vision in the affected eye. Retinal artery occlusion (RAO) is the blockage of the central retinal artery or its branches and is a form of ischemic stroke. Central retinal artery occlusion is characterized by sudden, painless unilateral loss of vision and a relative afferent pupillary defect. On fundoscopy, the ischemic retina appears pale and edematous with a cherry-red spot at the fovea centralis. Branch retinal artery occlusion manifests with visual field defects corresponding to the affected artery branch; fundoscopic findings of retinal ischemia are limited to the territory of the affected artery branch. Patients with acute, symptomatic RAO require urgent referral for stroke evaluation, possible thrombolysis, and assessment and treatment of underlying systemic disease (e.g., acute stroke, carotid stenosis, giant cell arteritis). Retinal vein occlusion (RVO), categorized as either central retinal vein occlusion or branch retinal vein occlusion, is more common than RAO and follows a milder course. Typical fundoscopic findings include retinal hemorrhages, cotton wool spots, macular edema, and papilledema, which result from increased venous pressure in the retina. Management of RVO focuses on treating complications (e.g., macular edema, neovascularization) to minimize vision loss and optimizing modifiable risk factors. Patients with RAO often experience irreversible loss of vision, while the prognosis is more favorable for RVO.

Definition ^[1]

• RAO is the partial or complete obstruction of retinal arteries causing retinal ischemia.
• Classification of RAO is based on the site of the occlusion.
  • Central retinal artery occlusion (CRAO): obstruction of the central retinal artery after it branches from the ophthalmic artery
  • Branch retinal artery occlusion (BRAO): obstruction of one of the four branches (superior, inferior, nasal, or temporal) of the central retinal artery

RAO is a form of acute ischemic stroke. ^[2]

Epidemiology

• Age of onset: : > 60 years ^[1]
• Sex: ♂ > ♀ ^[1]
• Incidence of CRAO: rare ^[2]

BRAO is more common than CRAO. However, symptomatic CRAO is more common than symptomatic BRAO. ^[2]

Risk factors ^[1]

Risk factors for thromboembolic RAO are similar to ASCVD risk factors and include:

• Cigarette smoking
• Hypertension
• Hyperlipidemia
• Obesity
• Diabetes mellitus
• Cardiac disease (e.g., atrial fibrillation)
• History of amaurosis fugax or other transient ischemic neurological symptoms

Etiology ^[1][2][3]

• Thromboembolism (95% of cases)
  • Carotid artery atherosclerosis (most common)
  • Cardiogenic embolism (e.g., due to atrial fibrillation, valvular heart disease, infective endocarditis)
  • Retinal artery thrombosis due to atherosclerosis
• Vasculitis: (5% of cases): e.g., giant cell arteritis (GCA) ^[1][2]
• Rare causes
  • Hypercoagulable state
  • Retinal artery vasospasm
  • Fibromuscular dysplasia
  • Complication of cosmetic facial injection

Thromboembolic occlusion most commonly occurs at the lamina cribrosa, where the central retinal artery narrows as it pierces the dural sheath of the optic nerve. ^[4][5]

Clinical features ^[1]

• Sudden, painless unilateral loss of vision
• Features of cerebral stroke may be present. ^[1][6]
• Features of the underlying etiology may be present.

Management

• Refer all patients with suspected RAO to an emergency department or a stroke center immediately. ^[1][2]
• Confirm the diagnosis with comprehensive eye examination; consider retinal imaging.
• Perform concurrent assessment for underlying serious underlying etiologies (ischemic stroke, GCA).
• Treat underlying causes and optimize modifiable risk factors.
• Follow up patients regularly to assess for complications.

Acute, symptomatic RAO is an ophthalmologic and medical emergency. Do not delay management as permanent retinal damage occurs quickly and there is a high risk of serious comorbid illness (e.g., cerebral stroke, cardiovascular disease). ^[1][2][6]

Diagnostics ^[1][2]

Comprehensive eye examination

The classic CRAO findings of a gray-white, edematous retina and a cherry-red spot may take several hours to develop. CRAO should be suspected if a patient presents with sudden, painless vision loss and a relative afferent pupillary defect, even if the initial fundoscopic examination appears normal. ^[1][2]

Retinal imaging ^[1][2]

• Indications
  • Diagnostic uncertainty
  • Assessment of severity ^[8]
• Options
  • Optical coherence tomography
  • Fundus fluorescein angiography
  • Electroretinogram

Assessment for underlying etiology ^[2][4][8]

• Further assessment depends on patient age and clinical features.
• For patients ≥ 50 years of age, assess for:
  • Thromboembolism ^[2]
  • Symptoms of giant cell arteritis; if present, initiate treatment of GCA with high-dose steroids before obtaining diagnostic studies.
• For patients < 50 years of age:
  • Risk factors for vascular disease: Assess for suspected thromboembolism.
  • No risk factors for vascular disease: Assess for hypercoagulability.

Treatment ^[1][2]

• Management is aimed at identifying and treating the underlying cause.
• Specialists may consider thrombolysis. ^[2][10]
• To prevent recurrence of CRAO or other forms of ischemic stroke: ^[1]
  • Start primary prevention of stroke to optimize modifiable risk factors.
  • Educate patients on symptoms of stroke and the importance of seeking early treatment.
• Arrange regular follow-up with ophthalmology to optimize vision and assess for complications (e.g., neovascularization). ^[2]

Conservative measures such as ocular massage, anterior chamber paracentesis, IOP-lowering medications (e.g., timolol and acetazolamide), and vasodilation are controversial, as studies show no evidence of efficacy but some evidence of harm. ^[1][2]

Differential diagnoses ^[2]

• Other causes of sudden, painless, unilateral vision loss, e.g.:
  • Retinal detachment
  • Intraocular hemorrhage
  • Optic neuropathy
• Other causes of a cherry-red spot on fundoscopy, e.g.:
  • Tay-Sachs disease
  • Niemann-Pick disease

Prognosis

• CRAO: severe, often irreversible loss of vision ^[2]
• BRAO: often irreversible visual field defects (depending on which branch of the retinal artery is affected)
• Individuals with RAO are at increased risk for subsequent stroke, myocardial infarction, and death. ^[6]

Definition ^[11]

• RVO is the partial or complete obstruction of a retinal vein.
• Classification of RVO is based on the site of the obstruction. ^[11]
  • Central retinal vein occlusion (CRVO): obstruction of the central retinal vein at or proximal to the lamina cribrosa
  • Branch retinal vein occlusion (BRVO): obstruction of a branch or tributary of the central retinal vein

The terms "ischemic RVO" and "nonischemic RVO" are no longer preferred because all forms of RVO show signs of ischemia. ^[11]

Epidemiology

• Age of onset: > 40 years ^[11]
• Sex: ♂ = ♀ ^[12]

RVO is the second most common vascular disease of the retina (after diabetic retinopathy) and is much more common than RAO. ^[11][13]

Etiology ^[11][13]

RVO is typically caused by thrombosis within a retinal vein. Risk factors for RVO include conditions associated with atherosclerosis and thrombogenesis, e.g.:

• Major risk factors
  • History of RVO
  • Older age
  • Hypertension
  • Atherosclerosis (systemic and/or retinal artery) ^[11][13]
  • Hyperlipidemia
  • Diabetes mellitus
• Minor risk factors
  • Hypercoagulable states
  • Glaucoma
  • Vasculitides

Clinical features ^[11]

• CRVO: sudden, painless unilateral loss or blurring of vision
• BRVO: variable presentation
  • May be asymptomatic if the macula is spared
  • Floaters
  • Sudden, painless visual field defect

Diagnostics ^[11]

• RVO is a clinical diagnosis based on history and findings on a comprehensive eye examination.
• Refer to ophthalmology for diagnostic confirmation and management.
• Assess for underlying etiology (e.g., screening for modifiable ASCVD risk factors, thrombophilia, vasculitis). ^[11][14]

Eye examination

Features on fundoscopy in acute RVO result from increased venous pressure. In CRVO, these features affect the whole retina, while in BRVO, they are segmented and restricted to the affected retinal area.

Retinal imaging ^[11]

The following modalities can be used to determine the extent of retinal ischemia and macular edema, and to assess response to therapy.

• Fluorescein angiography
• Optical coherence tomography
• Fundus photography

Management ^[11]

• There are currently no established treatments to reverse RVO; treatment is that of underlying etiology. ^[11][17]
• Treat associated macular edema with:
  • Preferred: intravitreal anti-VEGF therapy
  • Alternative: intravitreal steroids (e.g., dexamethasone)
• Ongoing management is shared between ophthalmology and internal medicine and/or primary care. ^[11]
  • Internal medicine and/or primary care optimize modifiable risk factors to prevent recurrence.
  • Ophthalmology screens for and manages complications (e.g., provides peripheral panretinal photocoagulation for neovascularization). ^[11][18]

Complications ^[11]

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

25% of patients with CRVO develop neovascularization. ^[11]

Prognosis

• Depends on the site of occlusion (distal better than proximal) and degree of occlusion (partial occlusion better than complete occlusion, BRVO better than CRVO) ^[11]
• Patients with RVO have an increased risk of all-cause mortality and cardiovascular events. ^[19]

• 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)
• Diagnostics: see “Diagnostics for TIA.”
• 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
  • RAO
  • Transient ischemic attacks (TIAs)
  • Stroke