title: A comparison of the Marcus Gunn and alternating light tests for afferent pupillary defects.
abstract: OBJECTIVE
  The authors compared two methods, the Marcus Gunn test and the alternating light test, for detecting a relative afferent pupillary defect.
  
  
  METHODS
  A randomized, prospective clinical trial.
  
  
  METHODS
  Fourteen patients with unilateral optic neuropathy.
  
  
  METHODS
  The Marcus Gunn and alternating light tests were performed on each patient.
  
  
  METHODS
  The results of the Marcus Gunn and altemating light tests for detecting a relative afferent pupillary defect on the affected side.
  
  
  RESULTS
  The Marcus Gunn test was able to identify the affected eye in only 8 of 14 patients, whereas the alternating light test correctly identified the affected eye in 13 of 14 patients. Results of the Marcus Gunn test were indeterminate in 4 of 14 patients and were incorrect in 2 of 14 patients. Results of the alternating light test were indeterminate in one patient and never incorrectly identified the affected eye.
  
  
  CONCLUSIONS
  The alternating light test is superior to the Marcus Gunn test for detecting relative afferent pupillary defects.
authors.affiliation: Department of Ophthalmology, Duke University Eye Center, Durham, North Carolina 27710, USA.
authors.forename: L B
authors.initials: LB
authors.lastname: Enyedi
authors.forename: S
authors.initials: S
authors.lastname: Dev
authors.forename: T A
authors.initials: TA
authors.lastname: Cox
mesh_terms: D003941:Diagnostic Techniques, Ophthalmological; D006801:Humans; D008027:Light; D009901:Optic Nerve Diseases / Q000150:complications; D011446:Prospective Studies; D011681:Pupil Disorders / Q000175:diagnosis*; D015203:Reproducibility of Results