Relative Afferent Pupillary Defect (Marcus-Gunn Pupil)

///Relative Afferent Pupillary Defect (Marcus-Gunn Pupil)
Relative Afferent Pupillary Defect (Marcus-Gunn Pupil) 2018-01-30T16:37:19+00:00

Relevant physical signs

  • Testing for an RAPD
    • RAPD demonstrates an ipsilateral partially-injured optic nerve
    • For a right-sided RAPD:
      • At rest, both pupils are of equal size in dim light
      • When light is shone into the left eye, both pupils constrict normally
      • When the light is swung over to the right side one second later, both pupils dilate, although they remain smaller than at rest.
      • When the light is swung back to the left side, both pupils constrict again
      • Pupils always remain equal
    • RAPD is shown by weaker bilateral pupil constriction in the affected eye compared with the other
  • Red desaturation
    • Test visual acuity to finger counting
    • Hold up a red hat pin an ask the patient what colour it is
  • Eye movements
    • Internuclear ophthalmoplegia
    • Complex ophthalmoplegias
    • Nystagmus
  • Other cranial nerves
    • Jaw jerk (pseudobulbar palsy)
    • Look for facial weakness
    • Look for pseudobulbar palsy
      • Increased gag reflex
      • Absent palatal movement
      • Spastic tongue (cannot be protruded)
  • Cerebellar
    • Assess for cerebellar / bulbar / pseudobulbar speech
    • Intention tremor / dysmetria
    • Dysdiadochokinesis
    • Assess gait if possible
  • Others
    • Pronator drift

Differential diagnosis

  • Optic neuropathies
    • Optic neuritis
      • Multiple sclerosis
      • Neuromyelitis optica
    • Giant cell arteritis
    • Glaucoma
    • Traumatic optic nerve injury
    • Optic nerve glioma
    • Sarcoidosis
    • Systemic lupus erythematosus
    • Sjögren’s syndrome
    • Wegner’s granulomatosis
  • Orbital disease
    • Thyroid eye disease
    • Orbital cellulitis
    • Orbital tumour
  • Infection
    • Cryptococcus
    • Lyme disease
    • West Nile virus
    • Cytomegalovirus
    • Toxoplasmosis
    • Herpes simplex virus
    • Syphilis
  • Iatrogenic
    • Ethambutol
    • Infliximab
    • Radiation-induced optic nerve damage
  • Leber’s optic neuropathy
  • Retinal disease
    • Retinal detachment
    • Central retinal vein occlusion
    • Central retinal artery occlusion
    • Severe macular degeneration

Investigations

  • Visual evoked potentials
  • Consider aquaporin-4 antibodies (neuromyelitis optica)
  • Lumbar puncture looking for unpaired oligoclonal bands
  • Magnetic resonance imaging of the brain and spinal cord looking for lesions disseminated in space
  • Consider temporal artery biopsy
  • Consider auto-antibody panel
  • Thyroid function tests if clinically-indicated

Management

  • See section on Multiple Sclerosis
  • For giant cell arteritis: prednisolone 1mg/kg for two weeks, then tail

Relative Afferent Pupillary Defect

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