irisreflekser

Irisreflekser, or iris reflexes, are reflexive responses that regulate pupil size in the iris in response to changes in light and focusing distance. The pupil is controlled by two muscle groups: the sphincter pupillae, which constricts the pupil under parasympathetic control, and the dilator pupillae, which dilates the pupil under sympathetic control. The primary reflexes involve direct and consensual pupillary light responses and the accommodation reflex.

The direct pupillary light reflex occurs when light is shone into one eye, causing constriction of that pupil. The consensual reflex is the simultaneous constriction of the opposite pupil. Both responses rely on a pathway that begins with the retina (afferent input via the optic nerve), projects to the pretectal area in the midbrain, and then proceeds bilaterally to the Edinger–Westphal nucleus. Efferent signals travel via the oculomotor nerve to the ciliary ganglion and short ciliary nerves, constricting the sphincter pupillae.

The accommodation reflex, or near reflex, includes pupil constriction, convergence of the eyes, and lens thickening for near vision. This reflex uses parasympathetic output to the ciliary muscle and sphincter pupillae, coordinated with ocular motor convergence.

Clinical relevance includes assessment of neurological function through pupillary reactions. Tests such as the swinging flashlight test can reveal a relative afferent pupillary defect. Anisocoria (unequal pupils) may indicate various conditions, including Horner’s syndrome or oculomotor nerve pathology. Age, drugs, and light conditions can also affect irisreflekser.