The inferior tarsal muscle is the lower eyelid homologue of Mueller's superior tarsal muscle, both receiving sympathetic innervation. Its loss contributes to the lower lid elevation in Horner syndrome.
| Origin | Lower border of the inferior rectus muscle sheath |
|---|---|
| Insertion | Inferior tarsal plate of the lower eyelid |
| Nerve Supply | Sympathetic fibres from the superior cervical ganglion |
| Blood Supply | Inferior palpebral artery |
| Actions | Retracts the lower eyelid slightly — widens the palpebral fissure; Acts with Mueller's superior tarsal muscle to maintain the palpebral opening |
|---|
In Horner syndrome, loss of sympathetic innervation to both Mueller's (upper) and the inferior tarsal muscle (lower) produces the classic partial ptosis (upper) and lower lid elevation (apparent enophthalmos). The reverse ptosis (lower lid rising) is the inferior tarsal muscle component of Horner syndrome.
Not directly palpable — assessed by lower lid position in sympathetic testing.
Loss of inferior tarsal muscle sympathetic tone in Horner syndrome producing lower lid elevation (reverse ptosis) contributing to the narrowed palpebral fissure appearance.
