VARIABILITY OF THE RELATIVE AFFERENT PUPILLARY DEFECT

PURPOSE: Afferent asymmetry of visual function is detectable in both n ormal and pathologic conditions. With a computerized test, we assessed the variability in measuring afferent asymmetry of the pupillary ligh t reflex, that is, the relative afferent pupillary defect. METHODS: In ten normal subjects, pupillary responses to an alternating light stim ulus were recorded with computerized infrared pupillography, The relat ive afferent pupillary defect for each test was determined by using a new computer analysis. The 95% confidence interval of each determinati on of relative afferent pupillary defect was used to represent the sho rt-term fluctuation in its measurement. To optimize the test for clini cal use, we studied the influence of stimulus intensity, duration, and number on the variability of the relative afferent pupillary defect. RESULTS: When the relative afferent pupillary defect was based on only a few light alternations (stimulus pairs), there was excessive variab ility in its measurement (95% confidence interval > 0.5 log units). Wi th approximately 200 stimulus pairs, the 95% confidence interval was r educed to less than 0.1 log unit (relative afferent pupillary defect /- 0.05 log unit). Also, there was less variability when the dark inte rval between alternating light stimulation was less than one second. C ONCLUSIONS: Computerized infrared pupillography can standardize the al ternating light test and minimize the error in quantifying a relative afferent pupillary defect. A reproducible relative afferent pupillary defect measurement is desirable for defining afferent injury and follo wing the course of disease.