relative afferent pupillary defect
Also written as: RAPD — relative afferent pupillary defect
An asymmetry in pupillary light responses indicating unilateral or asymmetric optic nerve dysfunction, detected by swinging flashlight test.
Full Definition
A relative afferent pupillary defect (RAPD) is a crucial clinical sign indicating asymmetric dysfunction of the afferent pupillary pathway, typically at the level of the optic nerve or retina. When a bright light is alternately presented to each eye (swinging flashlight test), the pupil paradoxically dilates when the light moves from the normal eye to the affected eye, despite continued bright illumination. This occurs because the affected eye sends a weaker neural signal to the bilateral pupillary control centers in the midbrain. The presence of an RAPD indicates significant unilateral optic nerve pathology and is one of the most important signs in neuro-ophthalmology.
Usage
Usage note: Grade from trace to 4+; also known as Marcus Gunn pupil after the neurologist who described it.
In Context
- "A 2+ relative afferent pupillary defect was present in the left eye, consistent with optic neuritis." — Neuro-ophthalmological examination
- "The absence of a relative afferent pupillary defect helped exclude significant optic nerve involvement." — Differential diagnosis note