Anatomy

• The internal carotid artery enters the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. 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 Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries (branch retinal artery 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 Atrial fibrillation Atrial fibrillation (AF or Afib) is a supraventricular tachyarrhythmia and the most common kind of arrhythmia. It is caused by rapid, uncontrolled atrial contractions and uncoordinated ventricular responses. Atrial Fibrillation
      • Cardiac valvular problems/ patent foramen ovale Patent Foramen Ovale A patent foramen ovale (PFO) is an abnormal communication between the atria that persists after birth. The condition results from incomplete closure of the foramen ovale. Small, isolated, and asymptomatic PFOs are a common incidental finding on echocardiography and require no treatment. Patent Foramen Ovale (leads to clots breaking off) 
  • Cholesterol embolism; usually occurs after vessel catheterization
  • Septic embolism, as a consequence of infective endocarditis Endocarditis Endocarditis is an inflammatory disease involving the inner lining (endometrium) of the heart, most commonly affecting the cardiac valves. Both infectious and noninfectious etiologies lead to vegetations on the valve leaflets. Patients may present with nonspecific symptoms such as fever and fatigue. Endocarditis
• Inflammatory conditions such as temporal arteritis Temporal arteritis Giant cell arteritis (GCA), also known as temporal arteritis, is a type of large-vessel vasculitis that predominantly affects the aorta and its major branches, with a predilection for the branches of the carotid (including the temporal artery). Giant cell arteritis is defined by inflammatory leukocytes in the vessel walls leading to reactive damage, ischemia, and necrosis. Giant Cell 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 Hypercoagulable Hypercoagulable states (also referred to as thrombophilias) are a group of hematologic diseases defined by an increased risk of clot formation (i.e., thrombosis) due to either an increase in procoagulants, a decrease in anticoagulants, or a decrease in fibrinolysis. Hypercoagulable States state
  • Sickle cell anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview
  • Antiphospholipid syndrome Antiphospholipid syndrome Antiphospholipid syndrome (APLS) is an acquired autoimmune disorder characterized by the persistent presence of antiphospholipid antibodies, which create a hypercoagulable state. These antibodies are most commonly discovered during a workup for a thrombotic event or recurrent pregnancy loss, which are the 2 most common clinical manifestations. Antiphospholipid Syndrome
  • Multiple myeloma Multiple myeloma Multiple myeloma (MM) is a malignant condition of plasma cells (activated B lymphocytes) primarily seen in the elderly. Monoclonal proliferation of plasma cells results in cytokine-driven osteoclastic activity and excessive secretion of IgG antibodies. Multiple Myeloma
• Inflammatory (e.g., systemic lupus erythematosus Systemic lupus erythematosus Systemic lupus erythematosus (SLE) is a chronic autoimmune, inflammatory condition that causes immune-complex deposition in organs, resulting in systemic manifestations. Women, particularly those of African American descent, are more commonly affected. Systemic Lupus Erythematosus ( SLE SLE Systemic lupus erythematosus (SLE) is a chronic autoimmune, inflammatory condition that causes immune-complex deposition in organs, resulting in systemic manifestations. Women, particularly those of African American descent, are more commonly affected. Systemic Lupus Erythematosus))
• 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 Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. 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 Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. 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 Vasculitides Vasculitides are a group of conditions characterized by vasculitis, ischemia, and damage to the organs supplied by the affected vessels. The affected arteries are of different sizes and locations and vary by the type of vasculitis. 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 Anticoagulants Anticoagulants are drugs that retard or interrupt the coagulation cascade. The primary classes of available anticoagulants include heparins, vitamin K-dependent antagonists (e.g., warfarin), direct thrombin inhibitors, and factor Xa inhibitors. Anticoagulants. Vitreous hemorrhage is differentiated from a vessel occlusion due to a more gradual onset and the presence of floaters. 
• Retinal detachment Retinal detachment Retinal detachment is the separation of the neurosensory retina from the retinal pigmented epithelium and choroid. Rhegmatogenous retinal detachment, the most common type, stems from a break in the retina, allowing fluid to accumulate in the subretinal space. Retinal Detachment: separation of the neurosensory retina from the retinal pigment epithelium Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface 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 in one or both eyes. Risk factors are age and eye injury. Symptoms may include blurry or double vision, trouble with bright lights, halos around light, faded colors, and trouble seeing at night. Cataracts can be visualized as a cloudy lens on eye exam. Curative treatment is surgical replacement of the lens.