Central Retinal Artery Occlusion

Central retinal artery occlusion is acute interruption of blood flow in the central retinal artery, causing infarction of the inner retina. It is an emergency equivalent to ischemic stroke of the eye. Incidence is about 1 to 2 in 100,000 people a year, with mean age near 60 and slight male predominance.

Classification:

• Non-arteritic permanent (about two thirds)
• Non-arteritic transient (about 15%)
• Non-arteritic with cilioretinal artery sparing (about 15%)
• Arteritic, from giant cell arteritis (under 5%)

Causes:

• Embolic: carotid atheroma, calcific aortic or mitral valve, atrial myxoma, endocarditis
• Thrombotic atherosclerosis
• Vasculitis, hypercoagulable states, sickle cell disease
• Trauma, cocaine, and periocular filler injection

Experimental data indicate that irreversible damage begins after roughly 100 minutes of complete ischemia, with limited recovery possible up to about 240 minutes. Final acuity is counting fingers or worse in about 80% of eyes. Within weeks, 2 to 18% develop neovascular glaucoma. Systemic complications dominate prognosis: concurrent silent cerebral infarction on MRI in 25 to 30%, with a high short term risk of stroke and myocardial infarction.

• Sudden painless monocular visual loss, usually counting fingers to light perception
• Relative afferent pupillary defect
• Retinal whitening with a cherry red spot at the fovea
• Arteriolar attenuation and segmentation of the blood column (box carting)
• Visible emboli in 20 to 40%
• A cilioretinal artery, present in 15 to 30% of eyes, preserves a central island of vision
• Preceding amaurosis fugax in 10 to 15%

Giant cell arteritis features in patients over 50: jaw claudication, scalp tenderness, new headache, polymyalgia, weight loss, diplopia. Red flags are any of these, plus bilateral or sequential visual loss and focal neurological signs.

• Clinical diagnosis from history and dilated fundus examination.
• ESR, CRP and platelet count at once in every patient over 50. Temporal artery biopsy within 2 weeks if giant cell arteritis is suspected, without delaying steroids.
• OCT: acute inner retinal thickening and hyperreflectivity, later thinning. Fluorescein angiography shows delayed arm-to-retina time and slow arteriovenous filling.
• Vascular imaging: carotid duplex or CT/MR angiography of head and neck, ECG, prolonged rhythm monitoring (24 to 72 hours or longer), transthoracic then transesophageal echocardiography.
• MRI brain with diffusion weighted imaging for silent infarcts.
• Blood tests: glucose, HbA1c, lipids, full blood count, clotting. In patients under 50, thrombophilia screen, ANA, ANCA, syphilis serology and blood cultures when endocarditis is possible.

Differentials: ophthalmic artery occlusion (no cherry red spot, choroidal ischemia), central retinal vein occlusion, retinal detachment, vitreous hemorrhage, optic neuropathy, nonorganic loss.

Time is critical. No therapy has proven benefit, but treatment should start immediately.

Acute measures (within the first hours):

• Refer to a stroke centre without delay. Treat as an acute stroke pathway.
• Intravenous thrombolysis within 4.5 hours in selected patients without contraindications: alteplase 0.9 mg/kg (maximum 90 mg), 10% as a bolus over 1 minute, the remainder over 60 minutes. Evidence is limited and it is not universal practice.
• Ocular massage: firm digital pressure over the closed globe for 10 to 15 seconds, then release, repeated for 5 minutes.
• Anterior chamber paracentesis: sterile technique at the slit lamp, 30-gauge needle at the limbus, remove 0.1 to 0.2 mL of aqueous. Risks are infection, lens injury and hyphema.
• Timolol 0.5% one drop topically once, and acetazolamide 500 mg IV once (contraindicated in sulfonamide allergy).

Giant cell arteritis:

• Methylprednisolone 1 g IV daily for 3 days, then prednisolone 1 mg/kg/day orally (maximum 60 to 80 mg), reducing by 10 mg every 2 weeks to 20 mg, then 2.5 mg every 2 to 4 weeks to 10 mg, then 1 mg monthly. Total course 12 to 24 months.
• Give omeprazole 20 mg daily, calcium 1000 mg, vitamin D 800 IU daily and alendronate 70 mg weekly.
• Tocilizumab 162 mg SC weekly as a steroid sparing agent.

Secondary prevention (all non-arteritic cases):

• Aspirin 300 mg once daily for 2 weeks, then clopidogrel 75 mg once daily long term.
• Atorvastatin 80 mg at night, targeting LDL below 1.8 mmol/L (70 mg/dL).
• Blood pressure below 130/80 mmHg. Diabetes control. Smoking cessation.
• Carotid endarterectomy within 2 weeks for symptomatic stenosis of 70 to 99% (50 to 69% in selected patients).
• Atrial fibrillation: apixaban 5 mg twice daily (2.5 mg twice daily if two of: age 80 or above, weight 60 kg or below, creatinine 133 micromol/L or above).

Neovascular glaucoma surveillance: gonioscopy and iris examination at 2 to 4 weeks and monthly for 3 months. If rubeosis appears, panretinal photocoagulation (1200 to 1600 burns of 500 micrometre spot size, 0.1 to 0.2 second) with intravitreal bevacizumab 1.25 mg in 0.05 mL. Lower pressure with timolol 0.5% twice daily, dorzolamide 2% three times daily and brimonidine 0.2% twice daily, then drainage device or cycloablation.

Follow up includes visual field, OCT and vascular risk review. The fellow eye and cerebral circulation remain at risk, so counsel on stroke symptoms.