What is the differential diagnosis for a patient with dimmed vision?

Differential Diagnosis of Dimmed Vision

The differential diagnosis for dimmed vision depends critically on whether the onset is acute or gradual, unilateral or bilateral, and whether it is associated with pain, as these features distinguish between sight-threatening emergencies requiring immediate intervention versus chronic conditions amenable to outpatient management.

Acute Unilateral Painless Vision Loss

Retinal Vascular Occlusions

• Central retinal artery occlusion (CRAO) presents with sudden, painless vision loss over seconds, typically reducing acuity to 20/200 to counting fingers, with classic fundoscopic findings of retinal whitening and cherry-red spot developing within hours 1
• Branch retinal artery occlusion (BRAO) causes sectoral vision loss corresponding to the affected arterial distribution 1
• Patients with CRAO or BRAO require immediate emergency department referral to a certified stroke center within hours, as the risk of subsequent stroke is highest in the first few days after onset 1
• Boxcar segmentation of blood flow in retinal vessels is a key finding visible on slit-lamp biomicroscopy 1

Posterior Vitreous Detachment and Retinal Breaks

• Acute PVD typically occurs between ages 45-65 and presents with photopsias (light flashes) and floaters, with 8-22% having retinal tears at initial examination 1
• The presence of vitreous hemorrhage strongly correlates with retinal tears—two-thirds of patients with vitreous hemorrhage have at least one retinal break 1
• Patients with acute PVD symptoms require urgent dilated fundus examination to detect retinal breaks, as untreated tears can progress to rhegmatogenous retinal detachment 1

Transient Monocular Vision Loss (TMVL)

• TMVL represents a retinal arterial TIA and mandates same-day evaluation with immediate referral to an emergency department or rapid-access TIA clinic 1
• The differential diagnosis requires distinguishing vascular TMVL from other causes of transient visual loss through comprehensive ophthalmic examination 1

Binocular Vision Disturbances

Convergence Insufficiency

• Presents with eyestrain, headaches, blurred vision at near, horizontal diplopia, or need to close one eye while reading 1
• Sensorimotor examination demonstrates exophoria greater at near than distance, insufficient positive fusional vergence (<20 prism diopters), and distant near point of convergence (>6 cm) 1
• Associated with concussion history, Parkinson's disease, and recurrent sub-concussive events 1

Macular Distortion with Binocular Diplopia

• Epiretinal membranes or subretinal neovascular membranes cause dissimilar foveal images that cannot fuse binocularly, though peripheral fusion remains intact 2
• The lights on/off test is pathognomonic: in complete darkness, a test letter appears single, but when room lights are turned on, peripheral fusion reasserts and the letter becomes double 2
• Prevalence increases with age: 2% under age 60, up to 12% over age 70, with 16-37% of patients with these maculopathies developing binocular retinal diplopia 2

Vitreomacular Interface Disorders

Vitreomacular Traction (VMT)

• Occurs when portions of posterior cortical vitreous remain adherent to the macula during PVD, causing tractional changes 1
• Patients report impaired visual function, metamorphopsia, and may experience acute or chronic symptoms depending on severity 1
• Spectral domain OCT is the gold standard for diagnosis and characterization of VMT and associated retinal changes 1

Epiretinal Membrane (ERM)

• Appears as thin, translucent cellophane-like membrane on retinal surface, though thicker white fibrotic membranes are more likely to become symptomatic 1
• Patients experience stable vision with few symptoms or progressive loss with metamorphopsia and diplopia, often closing one eye while reading to eliminate distortion 1

Critical Diagnostic Pitfalls

Ophthalmic Artery Occlusion

• Presents with hand motions vision or worse due to severe ischemia of the globe and associated ocular tissues, distinguishing it from CRAO 1
• Requires differentiation between arteritic (giant cell arteritis) and nonarteritic causes, as arteritic RAO demands immediate high-dose corticosteroids 1

Bilateral Presentations

• Bilateral simultaneous acute vision loss is rare (1-2% of CRAO cases) but when present suggests systemic embolic source or bilateral carotid disease 1
• Requires comprehensive cardiovascular and neurologic workup including brain MRI with diffusion-weighted imaging, carotid imaging, and cardiac evaluation 1

Immediate Triage Algorithm

For acute onset (hours to days):

• Unilateral painless vision loss → Emergency ophthalmology evaluation within 24 hours to rule out CRAO, BRAO, or retinal detachment 1
• Transient vision loss → Immediate stroke center referral for vascular imaging and cardiac workup 1
• Floaters with flashes → Urgent dilated examination for retinal tears 1

For subacute/chronic onset (weeks to months):

• Binocular blur at near with asthenopia → Evaluate for convergence insufficiency with sensorimotor examination 1
• Metamorphopsia with diplopia → OCT imaging for macular pathology and vitreomacular interface disorders 1, 2