A comparison of the Marcus Gunn and alternating light tests for afferent pupillary defects.

Abstract

The authors compared two methods, the Marcus Gunn test and the alternating light test, for detecting a relative afferent pupillary defect. A randomized, prospective clinical trial. Fourteen patients with unilateral optic neuropathy. The Marcus Gunn and alternating light tests were performed on each patient. The results of the Marcus Gunn and altemating light tests for detecting a relative afferent pupillary defect on the affected side. 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. The alternating light test is superior to the Marcus Gunn test for detecting relative afferent pupillary defects.