What causes unilateral central visual field loss?

Unilateral Central Visual Field Loss: Causes and Differential Diagnosis

Unilateral central visual field loss (central scotoma) is most commonly caused by macular pathology, particularly age-related macular degeneration, or optic nerve disease such as optic neuritis, with the pattern of field loss being critical for anatomic localization. 1

Primary Ocular Causes

Macular Disease

• Age-related macular degeneration (AMD) with choroidal neovascularization is a leading cause of central scotoma in older adults, presenting with metamorphopsia and progressive central vision loss 2
• Patients with unilateral retinal pigment epithelial tears face a 37% risk of fellow eye visual loss in the first year, 59% by two years, and 80% by three years 3
• Central retinal artery occlusion causes sudden, painless, profound unilateral vision loss and can result from paradoxical emboli, including those from patent foramen ovale 4

Optic Nerve Pathology

• Optic neuritis characteristically presents with central or cecocentral scotoma, pain on eye movement, and an afferent pupillary defect 1
• Compressive optic neuropathy from vascular structures (such as sclerotic internal carotid artery) can cause nasal field defects, though this is rare and requires surgical decompression if diagnosed early before optic atrophy occurs 5

Glaucoma

• While glaucoma typically causes arcuate scotomas and peripheral defects, it can present initially in one eye before becoming bilateral 1
• Patients with initially unilateral glaucomatous field loss have only a 7.2% risk of fellow eye progression at 5 years, though first-affected eyes show 25% progression risk 6

Refractive and Developmental Causes

Amblyopia

• Anisometropic amblyopia develops from unequal refractive error causing asymmetric image focus, resulting in unilateral vision reduction that may include central field involvement 2
• Visual deprivation amblyopia from congenital cataracts, corneal opacities, or ptosis causes severe unilateral vision loss, often 20/200 or worse, and is most severe when unilateral due to interocular competition 2
• Strabismic amblyopia from constant, non-alternating tropias results from competitive inhibition between the two eyes at cortical level 2

Infectious/Inflammatory Causes

• CMV retinitis in immunocompromised patients presents with peripheral or central scotomas depending on lesion location, accompanied by floaters and characteristic fluffy yellow-white retinal lesions 1

Critical Diagnostic Approach

Initial Examination Elements

• Measure visual acuity with best correction, perform pupillary examination for afferent pupillary defect, and measure intraocular pressure 1
• Distinguish between true field defects and visual neglect: the latter involves intact visual pathways but failed cortical processing, typically from right hemisphere stroke causing left-sided neglect 1, 7

Perimetry and Imaging

• Automated perimetry is essential to document the pattern of field loss and distinguish ocular patterns (altitudinal, arcuate) from neurological patterns (homonymous defects) 1
• Optical coherence tomography (OCT) is critical for evaluating macular pathology and detecting subretinal or intraretinal fluid in AMD 2
• Urgent neuroimaging (CT or MRI) is required for suspected stroke, mass lesion, or unexplained neurological field defects 1

Key Clinical Pitfalls

• Do not confuse visual neglect with true hemianopia: neglect patients have normal visual fields on formal testing but fail to attend to stimuli on the affected side, requiring line bisection and cancellation tests for diagnosis 7
• Altitudinal defects strongly suggest ocular rather than neurological pathology 1
• Central scotomas from structural retinal abnormalities (optic nerve hypoplasia, macular dragging) may have a treatable amblyopic component that should not be overlooked 2
• In AMD patients presenting with new symptoms (metamorphopsia, scotoma), prompt examination is critical as early anti-VEGF treatment optimizes outcomes 2