Blinking

Reflex blinking

• Caused by various stimuli:
• Optical 
• Auditory
• Tactile 

• Corneal reflex (touch stimulation) triggers brainstem reflex involving fifth and seventh cranial nerves (cortical function is not needed). 

• Sensory ending in corneal epithelium,
• Afferents: long ciliary nerves, nasociliary then ophthalmic
• Synapse in spinal nucleus of trigeminal
• Synapse in facial nucleus
• Efferents: temporal and zygomatic branches of facial nerve
• Effector muscle is orbicularis (palpebral fibres)
• Palpebral (aka ‘pretarsal’) fibres of orbicularis initiate reflex blinking
• Orbital portion of orbicularis responsible for squeezing eyes tight shut

Spontaneous blinking

• Absent until third month of life

• Does not require retinal stimulation (therefore occurs in blind people)
• 15 per minute lasting 0.3-0.4 seconds each
• Levator relaxes prior to blinking to allow closure by gravity
• Spreads tear film over the cornea and conjunctiva

Other movements

• Bell’s phenomenon
• Upward movement of globe with eye closure
• Absent in 10% of normal people
• Marcus-Gunn phenomenon
• Autosomal dominant
• Rhythmic upward jerking of upper lid associated with jaw movements
• Due to synkinesis (common linkage of levator and pterygoid muscles)
• Fibrillary twitching may be associated with refractive error