pupilreaktion

Pupil reaction, sometimes written as pupilreaktion in some contexts, describes the changes in pupil size in response to light and focusing tasks. The most studied aspect is the pupillary light reflex, which adjusts the amount of light entering the eye to optimize vision and protect retinal cells. Pupil size also varies with accommodation, arousal, and autonomic tone.

The neural circuit for the pupillary light reflex begins with retinal photoreceptors that send signals via the optic nerve to the pretectal area of the midbrain. From there, bilateral connections route signals to the Edinger–Westphal nuclei. Parasympathetic fibers travel with the oculomotor nerve to the ciliary ganglion and then to the sphincter pupillae, producing constriction in both eyes (direct and consensual reflex). The sympathetic pathway, extending from the hypothalamus to the superior cervical ganglion and onward to the dilator pupillae, mediates dilation, especially in darkness or when aroused.

Clinically, pupillary reactions are assessed by directing a light into one eye and observing the direct constriction in that eye and the consensual constriction in the other. Accommodation testing assesses the near response. Abnormal results help localize lesions: afferent defects reduce or abolish constriction when light is shone in the affected eye; efferent defects produce anisocoria with diminished constriction in the affected pupil.

Pupillary reactivity is a core part of neurological examination and reflects brainstem integrity, cranial nerve function, and autonomic status. Common abnormalities include anisocoria with unequal reflexes, Adie tonic pupil, Argyll Robertson pupil, and Marcus Gunn pupil. Horner syndrome presents with ptosis and miosis due to disruption of the sympathetic pathway. Pharmacological agents, such as mydriatics or cholinergic drugs, can also alter pupillary responses.