Abstract

A large proportion of pathologies that affect the retina and visual pathways reduce a patient's sensitivity to light in one eye relative to the other. The swinging flashlight test, first described by Levatin (Arch. Ophthal. 62:768,1959) is a clinically useful way to detect such imbalances. The examiner shines a flashlight into one eye for a few seconds, then shifts abruptly to the other for a few seconds, and continues swinging back and forth while watching whichever eye is being illuminated. As reported by Levatin, when this test is performed on a normal visual system the pupils show little or no reaction because signals from each retina drive both pupils and shifting the same light from one retina to the other, then, should cause no change in the drive to either pupil. However, if the test is performed on a patient whose left retina, for example, is less sensitive than the right, then both pupils will constrict each time the right eye is illuminated and both will dilate each time the light shifts to the left eye. Such a result is called a Relative Afferent Pupillary Defect (RAPD). (It is relative because it will only appear if the sensitivities of the two eyes differ; it is afferent because, at least when considering a simplified model of the anatomy, it must result from an imbalance somewhere before the signals from the two eyes converge to drive both pupils.)

© 1991 Optical Society of America