Blinkreflekser

Blinkreflekser, or blinking reflexes, are involuntary closures of the eyelids in response to sensory stimuli near the eye. They serve protective purposes for the eye and help maintain tear film and ocular surface health. The most studied example is the corneal reflex, which protects the cornea from irritation and injury.

The reflex arc involves a trigeminal afferent and a facial efferent pathway. Afferent signals travel via the ophthalmic division (V1) of the trigeminal nerve to brainstem nuclei, and efferent signals travel via the facial nerve (CN VII) to the orbicularis oculi muscle. The blink reflex has two components: a short-latency R1 response that is typically ipsilateral and a longer-latency R2 response that is bilateral. R1 is thought to use a more direct brainstem pathway, while R2 involves additional interneurons and can recruit both eyes.

Clinically, the corneal reflex is used to assess brainstem and cranial nerve function. It can be elicited with a mild corneal stimulus such as a sterile cotton wisp or a gentle air puff. The presence, symmetry, and timing of the R1 and R2 responses help localize potential lesions in the trigeminal (V) or facial (VII) nerves or in brainstem circuits. Absence or marked asymmetry may indicate neurologic impairment, and in comatose patients the corneal reflex has prognostic value in some contexts. In infants, blink reflexes are present early and can reflect neurological status, but responsiveness may be altered by sedation or developmental factors. Related reflexes include the photic or dazzle reflex, which are evoked by bright light and involve somewhat different pathways.