What is the differential diagnosis for a patient presenting with unilateral partial visual field disturbance?

Differential Diagnosis of Unilateral Partial Visual Field Disturbance

The differential diagnosis for unilateral partial visual field disturbance must systematically distinguish between ocular pathology (affecting the eye itself), optic nerve disease, and neurological causes (affecting the visual pathways or brain), with the pattern and location of field loss being the critical diagnostic feature.

Anatomic Localization by Field Defect Pattern

Ocular Causes (Pre-Chiasmal, Unilateral Eye)

Altitudinal defects (respecting the horizontal meridian) strongly suggest ocular pathology rather than neurological disease 1:

• Glaucoma: Progressive optic neuropathy causing characteristic arcuate scotomas, nasal steps, or altitudinal defects; may present initially in one eye before becoming bilateral 2
• Retinal vascular occlusion: Branch retinal artery or vein occlusion causing sectoral field loss corresponding to vascular distribution 1
• Retinal detachment: Peripheral field loss corresponding to area of detached retina
• Idiopathic intracranial hypertension: Causes blind spot enlargement, nasal field loss (especially inferonasal), and isopter constriction; visual loss becomes irreversible once chronic papilledema develops 3

Optic Nerve Disease (Pre-Chiasmal, Unilateral)

Central scotomas are characteristic of optic nerve or macular disease 1:

• Optic neuritis: Central or cecocentral scotoma with pain on eye movement, afferent pupillary defect
• Ischemic optic neuropathy: Sudden altitudinal field loss, often inferior, with disc edema
• Compressive optic neuropathy: Progressive field loss with optic disc changes
• CMV retinitis (in immunocompromised): Peripheral scotomas or central field defects depending on lesion location; presents with floaters and characteristic fluffy yellow-white retinal lesions 4

Neurological Causes (Post-Chiasmal)

Homonymous field defects (same side affected in both eyes) indicate retrochiasmal pathology, though may appear unilateral if patient only notices deficit in one eye 4:

• Stroke: Most common cause of homonymous hemianopia or quadrantanopia; right hemisphere strokes commonly cause left-sided neglect 4, 5
• Visual neglect: Patient ignores visual stimuli on one side despite intact visual ability; caused by brain damage, usually right hemisphere stroke; differs from true field cut as visual system is intact but brain fails to process information 5, 6
• Tumor or mass lesion: Progressive homonymous field defect
• Traumatic brain injury: Can cause various patterns of field loss 5

Critical Distinguishing Features

Visual Neglect vs. True Field Defect

Visual neglect must be distinguished from hemianopia as they require different management approaches 4, 5:

• Neglect characteristics: Patient unaware of failing to attend to one side; can coexist with hemianopia; diagnosed by line bisection, cancellation tests, and drawing evaluations 5
• True hemianopia: Patient aware of visual loss; consistent field defect on perimetry

Functional (Medically Unexplained) Visual Loss

Consider functional visual loss when findings are inconsistent or anatomically implausible 7, 8:

• More common in females (79% in one series) 7
• Frequently associated with unexplained symptoms in other medical specialties (36% of cases) 7
• Bilateral cases often show identical acuities in each eye; concentric (tubular) field constriction is characteristic 7, 8
• Complaints of glare or pain common (60%) 7
• Should not be diagnosis of exclusion; requires positive inconsistent findings on examination 7

Diagnostic Approach

Immediate Assessment

Perform targeted examination to localize pathology 6, 9:

• Visual acuity testing: Unilateral reduction suggests ocular or optic nerve disease
• Pupillary examination: Afferent pupillary defect indicates optic nerve or severe retinal disease 6, 9
• Intraocular pressure: Exclude acute glaucoma 9
• Confrontation visual fields: Determine pattern (altitudinal, central scotoma, homonymous)
• Fundoscopy: Look for disc edema, pallor, retinal lesions, or vascular occlusion

Formal Visual Field Testing

Automated perimetry is essential for documenting and characterizing field defects 4:

• Distinguishes between ocular patterns (altitudinal, arcuate) and neurological patterns (homonymous)
• Documents central scotomas characteristic of optic nerve disease 4
• Identifies inconsistent patterns suggesting functional loss 7, 8

Neuroimaging Indications

Urgent neuroimaging (CT or MRI) is required for suspected stroke, mass lesion, or unexplained neurological field defects 6:

• Homonymous field defects require brain imaging to exclude stroke or tumor 6
• Avoid MRI if metallic foreign body suspected 6, 9
• Bilateral vision loss or signs of increased intracranial pressure warrant urgent imaging 6

Common Pitfalls

• Assuming unilateral complaint means unilateral pathology: Homonymous hemianopia affects both eyes but patient may only notice deficit in one eye
• Missing visual neglect: Patient appears to have field cut but actually has intact visual fields with attentional deficit; requires specific testing 4, 5
• Delaying treatment in glaucoma: Fellow eye in unilateral glaucoma is at high risk (26% developed field loss in one study); female sex and greater damage in affected eye predict faster progression 2
• Missing reversible causes: Idiopathic intracranial hypertension field loss is reversible only before chronic papilledema develops 3
• Dismissing functional visual loss: Requires thorough workup to exclude organic disease; one patient in a series developed organic pathology after 18 months 7