A study was conducted to investigate the relative afferent pupillary defect (RAPD) by swinging flashlight as a potentially useful screening test for glaucomatous optic neuropathy. The authors recruited 107 subjects with or without glaucoma from a clinic population. A medical student with no prior ophthalmology experience was trained to test for RAPD using neutral density filters by a neuroophthalmologist. The student performed this masked study on all subjects and those that showed no RAPD then had the swinging light test repeated with 0.3, 0.6 and 0.9 neutral density filters. A result was deemed positive if the neutral density filter in front of the two eyes with subsequent RAPD testing resulted in an asymmetric pupillary response only when the filter was placed in front of one of the two eyes, but not the other. The medical charts were then reviewed to determine the absence or presence of glaucoma. Subgroup analysis was then performed on 67 subjects who had previously undergone cataract surgery. The authors report that RAPD with neutral density filters demonstrated a sensitivity and specificity of 66.7% and 82.9%, respectively, for all subjects and 68.8% and 88.6%, respectively, for those who had not previously undergone cataract surgery when used to screen for glaucomatous disease. A higher negative predictive value was, however, seen in the subgroup that had undergone cataract surgery. The authors recognised a number of limitations with the study, including clinic setting, personnel performing the test and the test was not deemed suitable for mild or advanced disease. However, this test combined with a number of other screening tests could be performed by a non-ophthalmologist making them useful screening tools.