What is the most likely diagnosis for a 65-year-old woman with hypertension (high blood pressure), hyperlipidemia (elevated lipid levels), type 2 diabetes mellitus (T2DM), and a history of cigarette smoking who presents with sudden, painless loss of vision in one eye?

Right Central Retinal Artery Occlusion

The most likely diagnosis is right central retinal artery occlusion (CRAO). This patient's presentation of sudden, painless monocular vision loss with complete visual field loss (no light perception) in the setting of multiple vascular risk factors is pathognomonic for CRAO.

Clinical Reasoning

This patient's clinical profile perfectly matches CRAO based on multiple converging factors:

• Sudden, painless monocular vision loss is the hallmark presentation of CRAO, occurring over seconds and representing an ophthalmologic emergency 1

• Complete visual field loss (no light perception throughout all fields) indicates central rather than branch retinal artery occlusion, as branch occlusions would cause sectoral visual field defects 1

• The patient's age (65 years) and vascular risk factor profile (hypertension, hyperlipidemia, diabetes, smoking) are classic for CRAO, with incidence peaking around age 60-80 and increasing dramatically with these exact risk factors 1

• In over 80% of CRAO cases, initial visual acuity is "count fingers" or worse, consistent with this patient's no light perception 1

Why Other Diagnoses Are Excluded

Branch retinal artery occlusion is ruled out because it causes sectoral (not complete) visual field loss corresponding to the affected arterial distribution 1

Optic neuritis is excluded because it typically presents with pain on eye movement, occurs in younger patients (20-40s), and has a different time course with gradual vision loss over hours to days rather than seconds 1

Migraine visual aura is incompatible with this presentation because auras are transient (lasting 5-60 minutes), typically have positive visual phenomena (scintillations, fortification spectra), and resolve completely without permanent vision loss 1

Critical Immediate Actions Required

This patient requires emergency triage to a stroke center immediately because:

• CRAO is now recognized as an acute ischemic stroke equivalent by the American Heart Association 1

• The risk of concurrent or subsequent cerebral stroke is 3-6% within the first 1-4 weeks, with 20-24% having concurrent acute brain infarction on MRI 1

• In 95% of cases, CRAO results from thromboembolic disease, requiring urgent stroke workup including carotid imaging and cardiac evaluation 1

The natural history without intervention is devastating, with only 17% of patients achieving functional visual recovery 1

Essential Diagnostic Confirmation

Funduscopic examination would reveal classic findings:

• Retinal whitening with cherry red spot at the fovea 1
• Attenuated retinal arteries with "boxcar" segmentation of blood flow 1
• Relative afferent pupillary defect (Marcus Gunn pupil) 1

Urgent evaluation for giant cell arteritis (GCA) is mandatory in this age group, as 5% of CRAOs are arteritic, requiring immediate high-dose corticosteroids to prevent fellow eye involvement 1