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A comparison of the Marcus Gunn and alternating light tests for afferent pupillary defects
1Department of Ophthalmology, Duke University Eye Center, Durham, North Carolina 27710, USA.
Objective:
The authors compared two methods, the Marcus Gunn test and the alternating light test, for detecting a relative afferent pupillary defect.
Design:
A randomized, prospective clinical trial.
Participants:
Fourteen patients with unilateral optic neuropathy.
Intervention:
The Marcus Gunn and alternating light tests were performed on each patient.
Main Outcome Measures:
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.
Conclusion:
The alternating light test is superior to the Marcus Gunn test for detecting relative afferent pupillary defects.