Relative Afferent Pupillary Defect (RAPD)

Relative Afferent Pupillary Defect (RAPD) is a condition affecting the eye's response to light. It involves a problem with the nerve pathway that carries signals from the eye to the brain, specifically the optic nerve. When one eye has RAPD, it does not react normally to light compared to the other eye. This can cause an abnormal pupil reaction when light is shone alternately in each eye. RAPD is a sign of damage or disease in the optic nerve or severe retinal disease. It affects how the pupils constrict, which is important for controlling the amount of light entering the eye. Detecting RAPD helps doctors understand if there is a serious underlying problem with vision.

Relative Afferent Pupillary Defect (RAPD) is a clinical sign indicating an asymmetry in the afferent visual pathway, typically caused by unilateral or asymmetric optic nerve dysfunction or severe retinal disease. It results from impaired transmission of light signals from the affected eye to the pretectal nuclei in the midbrain, leading to a reduced pupillary constriction response when light is shone in that eye. The most common causes include optic neuritis, ischemic optic neuropathy, severe retinal detachment, or compressive optic neuropathies. RAPD is detected by the swinging flashlight test, which reveals a paradoxical dilation of the pupil when the light is moved from the normal to the affected eye. This defect is significant because it localizes pathology to the anterior visual pathway and helps differentiate optic nerve disease from other causes of vision loss. RAPD is not present in lesions behind the optic chiasm or in purely motor pupillary defects.