A. Characteristics

1. Patient can pinpoint at one moment visual acuity loss WITHOUT first covering one eye
2. Sudden monocular visual loss
   1. Usually vascular occlusion to optic nerve or retina
   2. Most often due to embolism; thrombus rare
3. Classification of Syndromes
   1. Retinal Artery Occlusion
   2. Retinal Vein Occlusion
   3. Carotid Artery Insufficiency
4. Hypertensive Retinopathy [5]

B. Retinal Arterial Occlusion [10]

1. Similar to stroke in pathophysiology
2. Etiology
   1. Associated with hypertension (HTN), diabetes, carotid atheroscerlosis, cardiac valve disease
   2. Visible emboli in ~20% of cases, often at arterial bifurcation
   3. Hollenhorst plaque - refractile, choleesterol, suggest carotid origin
   4. Calcific plaque - dull, white, suggest cardiac origin
   5. Thrombosis of or hemorrhage into atheromatous plaque is also common
   6. Vasculitis, vasospasm and trauma are less common
   7. Acute retinal cholesterol emboli occur after invasive aorta procedures [8]
   8. In patients with acute renal failure after instrumentation, rule out cholesterol emboli
3. Branch Retinal Artery cclusion
   1. Retinal whitening due to edema from infarction
   2. Edema resolves leaving permanent visual field deficit
4. Central Retinal Artery Occlusion
   1. Sudden painles visual loss (20/100 to LP)
   2. Central scotoma and peripheral field loss
   3. Afferent pupillary defect
   4. Milky white retina in posterior pole - sgementation ("box-carring") of blood flow
   5. Disc becomes pale over one month
   6. Irreversible damage to retina occurs after 90 minutes of occlusion
   7. Therefore, need to treat quickly
   8. ~10% of patients retain central vision due to patent cilioretinal artery perfusing fovea
5. Treatment of Retinal Artery Occlusion
   1. Intermittent digital pressure on globe - propel obstruction down stream
   2. Lower intraocular pressure acutely via paracentesis and/or IV acetazolamide 500mg
   3. Use of carbogen (95% oxygen/5% carbon dioxide) investigation - increase vasodilation
   4. Use of calcium channel blocking agent is investigational
   5. Treatment usually unsuccessful in restoring vision
6. Evaluation
   1. Treatment is usually instituted before evaluation (due to time pressure)
   2. Evaluate for cardiovascular and cerebrovascular disease
   3. Blood pressure
   4. Vasculitis - ESR (Giant cell arteritis), serologies, MR angiography
   5. Thorough search for source of embolism - carotid doppler, echocardiogram
   6. Hypercoagulability screen (including antiphospholipid antibdies) if indicated
   7. Consider prophylactic qd aspirin to reduce platelet aggregation
7. Asymptomatic retinal cholesterol emboli is a 10X risk factor for stroke [1]

C. Venous Occlusion

1. Types
   1. Central Retinal Vein Occlusion (CRVO)
   2. Branch Retinal Vein Occlusion
2. Risk Factors for Venous Occlusion
   1. Systemic HTN
   2. Glaucoma - both
   3. Diabetes (due to vascular disease)
   4. Hyperopia
   5. Young Patients: mitral valve disease, collagen vascular disease
3. Ischemic Type Central Vein Occlusion
   1. Patients usually >60 years of age
   2. Visual loss is usually severe, 20/100 or worse
   3. About 1/3 of all CRVO are ischemic
   4. Extensive hemorrhage throughout retinal layers, cotton-wool spots, tortuous veins
   5. Non-perfusion of retinal capillaries leads to retinal ischemia
   6. Complications: iris neovascularization (50%), glaucoma, macular edema and ischemia
   7. Vitreous hemorrhage can also occur, particularly after neovascularization
4. Non-Ischemic Type Central Vein Occlusion
   1. Iris neovascularization is uncommon compared with ischemic type
   2. Characteristic macular edema late in course
   3. Visual acuity usually in 20/40-20/100 range; may be worse due to macular edema
   4. ~10% of non-ischemic CRVO convert to ischemic CRVO at 6 months
5. Ischemic versus Non-Ischemic CRVO
   1. Fluorescein angiogram reveals degree of nonperfusion
   2. Ischemic CRVO tends to have afferent pupilary defect
   3. Electroretinography reveals reduced b:a ratio in ischemic CRVO
6. Treatment [4]
   1. CRVO study has altered management though findings controversial
   2. Ischemic CRVO with neovascular glaucoma should be monitored monthly
   3. Panretinal photocoagulation with laser is no longer recommended prophylactically
   4. Macular edema - macular grid laser not found to be effective in CRVO study
   5. Tissue Plasminogen Activator (TPA) studies ongoing
   6. High rates of intravitreous hemorrhage have been found with streptokinase
   7. Ranibizumab (Lucentis®) is an anti-VEGF monoclonal antibody Fab fragment
   8. Early data indicate that ranizibumab monthly intravitreous injections are associated with improved visual acuity at 3 months in CRVO and BRVO
7. Branch Retinal Vein Occlusion (BRVO)
   1. Visual loss acutely only if macula involved
   2. Occurs at sight of A-V crossing (A pulsations block venous flow)
   3. A-V crossings most common at superotemporal region (visual loss inferonasal)
   4. Edema, hemorrhage (exudates if chronic)
   5. Associated diseases - predispositions as for CRVO
   6. Complications: retinal neovascularization, macular edema, macular ischemia
   7. Treatment
   8. Macular edema treated with grid laser
      1. Scatter laser photocoagulation) for neovascularization
   9. Rinibizumab (see above) has also shown early efficacy here

D. Ocular Ischemic Syndromes

1. Presentations of Carotid Artery Insufficiency
   1. Venous stasis retinopathy / hypoperfusion retinopathy
   2. Idiopathic iris neovascularization
   3. Anterior segment inflammation, idiopathic
2. Significant carotid occlusive disease may be treatable
   1. Carotid doppler study
   2. Echocardiogram
   3. Check retinal artery pressure (low in carotid disease, normal in CRVO)
   4. Patients with carotid disease should be evaluated for endarterectomy
3. Anterior ischemic optic neuropathy [2,3]
4. Retinal arteriolar narrowing is a 1.4X risk factor for coronary artery disease in women but not in men [9]

E. Amaurosis Fugax [6,7]

1. Transient Monocular Blindness
   1. Often described as "shade drawn upward or downward over the eye"
   2. Attacks can be single or multiple
2. Caused by abrupt, temporary reduction in blood flow to single eye
   1. Occlusive Arterial Disease: atherosclerosis, thromboemboli, vasculitis (arteritis)
   2. Low Perfusion Pressure: hypotension, AV Fistula, Glaucoma, intracranial HTN
   3. Poor Retinal Perfusion: malignant hypertension, vasospasm, increased blood viscosity
   4. Other: cold sensitivity, malaria, pregnancy, Interleukin-2, paraneoplastic disease
   5. Amaurosis with migraine is often linked to vasospastic disease
3. Treatment
   1. Evaluate for carotid disease with doppler ultrasound or MRI angiography
   2. Strongly consider endarterectomy if >70% stenosis
   3. Evaluate for thromboembolic disease (from heart) with echocardiography
   4. Erythrocyte Sedimentation Rate (ESR)
   5. Biopsy to rule out giant cell arteritis (GCA)
   6. Consider vasospasm; empiric trial of Calcium blockers if above causes are ruled out

References

1. Bruno A, Jones WL, Austin JK, et al. 1995. Ann Intern Med. 122(4):249
2. IOND Trial Research Group. 1995. JAMA. 273(8):625
3. Levin LA. 1995. JAMA. 273(8):666
4. CVOS Group. 1995. Ophthalmology. 102:1425
5. Wong TY and Mitchell P. 2004. NEJM. 351(22):2310
6. Gautier JC. 1993. NEJM. 329(6):426
7. Winterkorn JMS, Kupersmith MJ, Wirtschafter JD, Forman S. 1993. NEJM. 329(6):396
8. Gittinger JW and Kershaw GR. 1998. Arch Intern Med. 158(11):1265
9. Wong TY, Klein R, Sharrett AR, et al. 2002. JAMA. 287(9):1153
10. Miller NR and Newman NJ. 2004. Lancet. 364(9450):2045