OcuLearning › Neuro

Nonphysiologic Visual Loss

ROUTINE — Neuro

Symptoms

  • loss of vision without organic explanation
  • malingering: intentional feigning for secondary gain (financial/legal)
  • psychogenic (conversion): patient truly believes vision is lost due to psychological stress

Clinical Findings

Clinical examination

  • normal pupillary light reactions and normal dilated fundus exam
  • no ocular or neuro-ophthalmic findings explain the deficit
  • behavior: saccades to command, glancing at new people, or reaching accurately for objects

Bedside testing

  • stereopsis (titmus/randot): identifying the "fly" requires ≥20/70 acuity
  • mirror test: involuntary tracking of reflection proves vision is present
  • optokinetic (okn) drum: reflex nystagmus confirms vision better than counting fingers
  • base-out 4pd prism: convergent refixation proves foveal vision

Visual fields

  • tubular ("tunnel") field: pathognomonic if area stays same size at 1m and 2m
  • goldmann patterns: star-shaped, spiraling, or crossing isopters

Objective testing

  • normal pattern vep, multifocal erg, and full-field erg
  • normal oct and fundus autofluorescence (faf)

Etiology

Psychogenic (conversion)

  • unconscious production of symptoms triggered by trauma, school failure, or abuse

Malingering

  • intentional feigning for disability claims, litigation, or military avoidance

Factitious (Munchausen)

  • intentional production to assume the sick role (primary gain)

Red Flags

  • organic mimics: occult maculopathy (azoor, mewds), cone dystrophy, or early compressive neuropathy
  • pediatric triggers: bullying, parental conflict, or munchausen-by-proxy
  • adult secondary gain: requires meticulous documentation for legal/insurance purposes

Investigations

Total blindness claims (NLP/HM)

  • pupillary testing: absence of rapd in unilateral nlp is impossible
  • mirror and okn drum tests to elicit involuntary tracking

Subnormal vision claims (20/40 to 20/400)

  • fogging test: add +4.00 to "good" eye while testing binocularly in phoropter
  • distance-near discrepancy: 20/100 at 20ft should be 20/50 at 10ft
  • vertical prism dissociation: seeing two images with prism proves near-symmetric vision

Imaging & electrophysiology

  • oct macula and rnfl to exclude subtle organic disease
  • full-field and multifocal erg to rule out outer retinal dystrophies
  • pattern vep to objectively assess optic nerve pathways

Treatment

Communication strategy

  • do not confront the patient; avoids destroying the therapeutic relationship
  • provide a "way out": e.g., "these drops will help your vision return to normal"

Management

  • reassurance once organic disease is excluded
  • multidisciplinary care: coordinate with primary care, neurology, and psychiatry
  • positive reinforcement of objective improvements

Clinical Pearl

in functional visual loss, never confront — offer "tests that will help us figure this out" and let the exam prove normal function while the patient saves face.

Differential Diagnosis

  • • amblyopia (check for strabismus/anisometropia)
  • • occult maculopathy (e.g., azoor, cone dystrophy, solar retinopathy)
  • • cancer-associated or melanoma-associated retinopathy (car/mar)
  • • early compressive or infiltrative optic neuropathy
  • • toxic retinopathies (e.g., hydroxychloroquine)

Related Neuro Conditions