pupillary light reflex
Automatic pupillary constriction in response to bright light, mediated by the parasympathetic nervous system through the pretectal nuclei.
Full Definition
The pupillary light reflex is a brainstem-mediated response that causes bilateral pupillary constriction when light is directed into either eye. The afferent pathway involves the optic nerve, chiasm, and tract, with fibers synapsing in the pretectal nuclei. From there, parasympathetic fibers travel via the Edinger-Westphal nuclei and third cranial nerve to constrict both pupils. Testing involves examining both the direct response (constriction of the illuminated pupil) and consensual response (constriction of the contralateral pupil). Abnormalities in this reflex can indicate lesions anywhere along the visual or pupillomotor pathways and are crucial for localizing neurological pathology.
Usage
Usage note: Always test both direct and consensual responses; document any asymmetry or abnormal responses.
In Context
- "The pupillary light reflex was sluggish in the right eye, suggesting an afferent defect." — Neurological examination
- "Both direct and consensual pupillary light reflexes were absent following the third nerve injury." — Clinical assessment