Pupilrefleks

Pupilrefleks, or the pupillary light reflex, is the automatic constriction or dilation of the pupil in response to changes in ambient light. It helps regulate the amount of light reaching the retina and protects photoreceptor cells while aiding visual clarity. The reflex produces a direct response in the illuminated eye and a consensual response in the contralateral eye.

The afferent limb begins with retinal photoreceptors and travels via the optic nerve to the pretectal area of the midbrain. From there, signals project bilaterally to the Edinger–Westphal nuclei. Parasympathetic fibers travel with the oculomotor nerve to the ciliary ganglion and then to the sphincter pupillae, producing pupil constriction.

A separate sympathetic pathway dilates the pupil. It starts in the hypothalamus, descends through the brainstem and spinal cord to the superior cervical ganglion, then travels with the internal carotid plexus to innervate the iris dilator muscles, causing pupil dilation, particularly in darkness or arousal.

In addition to light, the near response—consisting of accommodation, convergence, and pupil constriction—adjusts the pupil when focusing on nearby objects.

Clinical significance: Pupillary reactions are routinely evaluated to assess central nervous system integrity. Tests such as the swinging flashlight test compare direct and consensual responses and can detect afferent or efferent defects. Abnormalities include sluggish or absent constriction, anisocoria with varying daylight dependence, or light-near dissociation seen in certain neurologic conditions (for example Parinaud syndrome) or Adie’s pupil.