pupilsrefleks

Pupilsrefleks, commonly referred to as the pupillary reflex, describes automatic changes in the diameter of the pupil in response to light and focusing distance. The most studied component is the pupillary light reflex, the constriction of the pupil in response to bright light, which helps regulate retinal illumination and protect the retina. Pupils also constrict during the near reflex, a triad of accommodation, convergence, and pupil constriction when focusing on a near object.

Pathways: light reflex. The afferent limb begins with retinal ganglion cells sending signals through 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 sphincter pupillae muscle, causing constriction. Because the input reaches both EW nuclei, both pupils typically constrict, producing a direct reflex (stimulated pupil) and a consensual reflex (other pupil). The near reflex involves higher cortical input for accommodation and convergence, but still output reaches the iris sphincter via the same oculomotor pathway.

Clinical significance. Pupillary testing is a standard part of neurological and ophthalmological examinations. Afferent defects (e.g., optic neuropathy) can produce a relative afferent pupillary defect (RAPD or Marcus Gunn pupil), best detected with a swinging flashlight test. Efferent defects (e.g., oculomotor nerve palsy) cause a dilated, poorly reactive pupil on the affected side. Anisocoria (unequal pupil sizes) has various causes, including Horner syndrome, which may show greater anisocoria in dim light due to impaired dilation, or pharmacologic mydriasis.

Normal size and reactivity vary with light, age, and health, but typical resting pupils are about 2–4 mm in bright light and may enlarge in darkness; brisk constriction to light is expected in healthy individuals.