The blink reflex protects the eye from potential damage when foreign objects make contact with the cornea or conjunctiva (1). This reflexive blinking is accomplished through a reflex arc between the trigeminal nerve (CN V) and facial nerve (CN VII) (2). When the cornea or conjunctiva are stimulated, sensory information is transmitted via the ophthalmic division of CN V to the trigeminal nucleus in the brainstem (3). Interneurons in the trigeminal nucleus then relay this sensory information to the facial nucleus, which activates the orbicularis oculi muscle via CN VII to produce blinking (4).

There are two stages to the blink reflex. The early, ipsilateral stage results from direct synaptic activation of facial motor neurons by trigeminal afferents. This causes rapid unilateral eyelid closure on the stimulated side (5). The late, bilateral stage involves activation of facial motor neurons on both sides and is mediated by interneurons in the brainstem reticular formation that project bilaterally (6). This bilateral blinking helps further protect the eye. Lesions at different points along the reflex arc produce characteristic deficits in the blink reflex stages (7).