title: Pupillographic investigation of the relative afferent pupillary defect associated with a midbrain lesion.
abstract: OBJECTIVE
  To identify clinical and pupillographic features of patients with a relative afferent pupillary defect (RAPD) without visual acuity or visual field loss caused by a lesion in the dorsal midbrain.
  
  
  METHODS
  Experimental study.
  
  
  METHODS
  Four patients with a dorsal midbrain lesion who had normal visual fields and a clinically detectable RAPD.
  
  
  METHODS
  The pupil response from full-field and hemifield light stimulation over a range of light intensities was measured by computerized binocular pupillography.
  
  
  METHODS
  The mean of the direct and consensual pupil response to full-field and hemifield light stimulation was plotted as a function of stimulus light intensity.
  
  
  RESULTS
  All 4 subjects showed decreased pupillographic responses at all intensities to full-field light stimulation in the eye with the clinical RAPD. The pupillographic responses to hemifield stimulation showed a homonymous pattern of deficit on the side ipsilateral to the RAPD, similar to that observed in a previously reported patient with an optic tract lesion.
  
  
  CONCLUSIONS
  The basis of a midbrain RAPD is the nasal-temporal asymmetry of pupillomotor input that becomes manifest when a unilateral postchiasmal lesion interrupts homonymously paired fibers traveling in the contralateral optic tract or midbrain pathway to the pupillomotor center, respectively. The pupillographic characteristics of an RAPD resulting from a dorsal midbrain lesion thus resemble those of an RAPD resulting from a unilateral optic tract lesion, but without the homonymous visual field defect.
  
  
  BACKGROUND
  The author(s) have no proprietary or commercial interest in any materials discussed in this article.
authors.affiliation: Hôpital Ophtalmique Jules Gonin, Lausanne, Switzerland.
authors.forename: Aki
authors.initials: A
authors.lastname: Kawasaki
authors.forename: Neil R
authors.initials: NR
authors.lastname: Miller
authors.forename: Randy
authors.initials: R
authors.lastname: Kardon
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001254:Astrocytoma / Q000150:complications* / Q000175:diagnosis; D001930:Brain Injuries / Q000150:complications* / Q000175:diagnosis; D020526:Brain Stem Infarctions / Q000150:complications* / Q000175:diagnosis; D003941:Diagnostic Techniques, Ophthalmological; D006801:Humans; D008027:Light; D008875:Middle Aged; D010775:Photic Stimulation; D010871:Pinealoma / Q000150:complications* / Q000175:diagnosis; D011680:Pupil / Q000528:radiation effects*; D011681:Pupil Disorders / Q000175:diagnosis* / Q000209:etiology*; D014792:Visual Acuity; D014794:Visual Fields