Pupillographic characteristics of simulated relative afferent pupillary defects.

Relative afferent pupillary defects were simulated in normal individuals by performing the alternating light test while dimming the light in front of one eye with neutral density filters. Pupillary responses were elicited using a binocular photostimulator and recorded using a binocular television pupillometer. In five subjects, four spatial variables of the pupillary response--contraction amplitude, minimum size, final size, and redilatation amplitude--were measured and compared. Contraction amplitude was found to be the best indicator of small pupil defects. In eight other subjects, the contraction amplitude elicited by using filters from 0.3 to 3.0 log units in density was plotted. Amplitude of consensual responses increased as direct responses decreased, and initial constrictions were visible in many subjects at the 1.8 log unit level. The best method for detecting relative afferent pupillary defects using the alternating light test is to compare contraction amplitudes, looking for consensual responses that are greater than direct responses.