central retinal artery occlusion

**Anatomy/Pathophysiology:** The central retinal artery is a branch of the ophthalmic artery (from the internal carotid). It supplies the inner retina (inner two-thirds). The fovea/macula is thin and gets its blood supply from the underlying choroid (via ciliary arteries), so it remains perfused. When the CRA is blocked, the inner retina becomes ischemic and edematous (opaque, whitened), while the fovea stays red, which produces the classic "cherry-red spot." Irreversible retinal damage occurs after roughly 90-100 minutes of complete occlusion in experimental models, so time matters.

**Etiology:** - Embolism (most common): carotid atherosclerotic plaque (Hollenhorst plaque = cholesterol embolus seen at arteriolar bifurcations), cardiac emboli (atrial fibrillation, endocarditis, valvular disease, atrial myxoma), and paradoxical emboli. - Giant cell (temporal) arteritis: must always be considered in patients >50 years. Look for jaw claudication, scalp tenderness, headache, PMR symptoms, elevated ESR/CRP. Treat with immediate high-dose IV steroids to protect the other eye. - Other: hypercoagulable states, vasculitis, sickle cell disease, trauma, and hypotension or increased intraocular pressure.

**Clinical Presentation:** - Sudden, painless, severe monocular vision loss (often counting fingers or light perception only). - Relative afferent pupillary defect (Marcus Gunn pupil). - Fundoscopy: diffuse retinal whitening/pallor, cherry-red spot at the macula, narrowed arterioles, and "boxcarring" (segmentation) of blood in vessels. Emboli may be visible. - Amaurosis fugax (transient monocular vision loss, "curtain coming down") may precede it as a TIA of the eye. - A cilioretinal artery, present in about 20% of people, may spare part of the macula and preserve some central vision.

**Diagnosis:** Clinical diagnosis with fundoscopy, supported by OCT, fluorescein angiography (delayed arterial filling), and ESR/CRP in older patients. Because CRAO is an ocular stroke, perform urgent stroke workup: carotid imaging (duplex US/CTA/MRA), ECG/telemetry, echocardiography, and lipid/glucose evaluation. Brain MRI frequently shows concurrent silent infarcts.

**Management:** - Treat as an acute stroke. Refer emergently to a stroke center or ophthalmology. - Conservative measures with limited evidence: ocular massage, lowering IOP (acetazolamide, anterior chamber paracentesis), and rebreathing/carbogen. - IV thrombolysis (alteplase/tenecteplase) within about 4.5 hours of onset may be considered, and this is an area of active evidence development. - Treat the underlying cause: antiplatelets/statin, carotid endarterectomy or stenting for significant stenosis, anticoagulation for AF, and steroids for GCA. - Visual prognosis is generally poor. Complications include neovascularization (rubeosis iridis) and neovascular glaucoma.

**High-yield Comparisons:** - CRAO: painless, sudden, cherry-red spot, pale retina. - Central retinal vein occlusion (CRVO): painless, "blood and thunder" fundus with diffuse hemorrhages, dilated tortuous veins, and disc edema. Risk factors include HTN, hypercoagulability, and glaucoma. - Retinal detachment: flashes, floaters, "curtain" with a visible detached retina. - Other cherry-red spot causes: Tay-Sachs, Niemann-Pick, and Sandhoff disease (lysosomal storage disorders with macular ganglion cell accumulation, where the fovea lacks ganglion cells so it appears red against the pale surrounding retina). - Anterior ischemic optic neuropathy: giant cell arteritis causing arteritic form with pale swollen disc.

**Board Pearls:** Sudden painless monocular vision loss + cherry-red spot = CRAO. Think carotid atheroma first, cardiac embolus next, and GCA in elderly patients with systemic symptoms. Always work up like a stroke.