Orbicularis oculi: gentle versus tight eyelid closure
Orbicularis oculi is the ring of muscle round the eye socket that closes the eyelids: its palpebral (eyelid) part closes them gently and its orbital (socket) part closes them tightly.
Remember
The palpebral part of orbicularis oculi gives the gentle closure of a blink, the orbital part gives the tight squeeze, and the facial nerve supplies the whole muscle.
Memory aid
palpebral fibres sit in the palpebrae (eyelids) and do the blink, while orbital fibres ring the orbit and do the squeeze
Match each part to its place: the part in the eyelids does the blink and the part ringing the orbit does the squeeze.
The orbicularis oculi is the ring-shaped muscle that surrounds the eye socket (the orbit) and extends into the eyelids. It has three parts.
The palpebral part (palpebral means 'of the eyelid') lies in the eyelids and gently closes them. That is the movement of an ordinary blink, and it also happens in sleep. The orbital part rings the orbit and closes the lids tightly, as when you screw your eyes shut. The lacrimal part (lacrimal refers to tears) is involved in the drainage of tears. You can remember the pattern by matching each word (palpebral, orbital, lacrimal) to its job.
When you blink, tears are spread across the cornea, the clear front surface of the eye, which means a weak blink can leave the eye dry. The lacrimal gland makes the tears, but it supplies only the fluid; the palpebral fibres move the lids.
The facial nerve (cranial nerve VII) supplies the whole muscle. Two other muscles do the opposite job and open the upper eyelid. The levator palpebrae superioris, the lifter of the upper lid, is supplied by the oculomotor nerve (cranial nerve III). The superior tarsal (Müller’s) muscle is a small muscle that helps the levator and is supplied by sympathetic nerves, part of the sympathetic nervous system.
Weak blinking with a forceful squeeze that still works points to the palpebral part, because the orbital part produces the squeeze. Both parts depend on the facial nerve, so a different nerve supply for the orbital part does not explain why the squeeze still works.
Key facts
- Palpebral part
- lies in the eyelids and closes them gently, as in blinking and in sleep.
- Orbital part
- rings the orbit and closes the eyelids tightly, as when screwing the eyes shut.
- Lacrimal part
- is involved in the drainage of tears.
- Nerve supply
- the facial nerve (cranial nerve VII) supplies orbicularis oculi.
- Opening the upper lid
- the levator palpebrae superioris and the superior tarsal muscle open the upper eyelid, the opposite job to closure.
- Weak blink
- a weak blink with a preserved (still working) squeeze points to the palpebral part.
Exam traps
- The orbital part of orbicularis oculi is not the gentle closer: it closes the eyelids tightly, as when screwing the eyes shut, and gentle blinking belongs to the palpebral part.
- Orbicularis oculi is the right muscle for closing the eyelids, but the oculomotor nerve is the wrong nerve for it, because that nerve supplies the muscle that lifts the lid, not the one that closes it, and the facial nerve supplies the closer.
- The lacrimal gland makes the tears and blinking spreads them across the eye, but the gland does not move the eyelids.
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