Computerized binocular pupillography of the swinging flashlight test detects afferent pupillary defects

To investigate the ability of a portable pupillometer, capable of 20-second binocular recordings of the swinging flashlight test (SFT), to detect relative afferent pupillary defects (rAPDs).

Pupillary response curves were recorded from both eyes in healthy volunteers (n = 22) with and without simulated rAPDs (using neutral density filters (NDFs)) and in abnormal patients (n = 24) with clinically graded rAPDs. The light stimulus (0.2 sec on and 1 sec off, or 2 sec on and 0.4 sec off) alternated between both eyes, simulating the SFT. Constriction amplitude (CA), constriction velocity (CV), and pupillary release were calculated by computer algorithm. In abnormal patients, NDFs were used to neutralize inter-eye differences.

Significant correlation (Spearman's rho 0.71, 0.73) between NDF strength and absolute inter-eye differences was seen for CA and CV in simulated rAPDs. All abnormal patients (15/15) having rAPDs greater than 0.5 log units were distinguished from normals using either the upper bound of the one-sided 95% confidence interval (95% CI) value of CA or CV as determined from 22 healthy volunteers. Inter-eye variability in some normals prevented confident distinction of six abnormal patients with 0.3 log unit rAPDs. Using NDFs, subtle rAPDs were predicted in three patients having questionable rAPDs on clinical examination. CA and CV were more sensitive than pupillary release for all comparisons.

This binocular pupillometer identified all of our patients with > 0.5 log unit rAPDs. Using NDFs, all of our abnormal patients were accurately identified and their rAPDs quantified. Variability in some normals makes them indistinguishable from patients with subtle rAPDs.