What does a positive result in the swinging flashlight test indicate?

A positive result in the swinging flashlight test indicates a relative afferent pupillary defect (RAPD). This test is designed to assess the function of the afferent pathway of the visual system, specifically the optic nerve and its ability to transmit visual signals from the eye to the brain.

When a light is swung from one eye to the other, a normal response would elicit constriction in both pupils due to consensual reflex action. However, if there is a defect in the afferent pathway of one eye (often due to conditions such as optic neuritis or glaucoma), the affected eye will not constrict as much as the unaffected eye when light is directed into it. As a result, the pupil may either remain the same size or even dilate instead, showing a relative afferent pupillary defect.

This test is crucial for determining the functional integrity of the optic nerve. The presence of an RAPD suggests that there may be a significant compromise to the visual pathway, distinguishing it from other conditions such as decreased visual acuity or ocular muscle weakness, which can have different physical presentations and implications that do not directly relate to the afferent pathway's integrity.