Ptosis can be caused by dysfunction or damage to which of the following muscles?

The correct response highlights the superior tarsal muscle, also known as the muscle of Müller, which plays a critical role in eyelid elevation. This muscle is a smooth muscle located beneath the levator palpebrae superioris and is innervated by the sympathetic nervous system. When there is dysfunction or damage to the sympathetic pathway, it can result in ptosis, as the superior tarsal muscle fails to provide adequate lift to the upper eyelid.

Understanding the role of the superior tarsal muscle is essential, as ptosis typically originates from issues with the muscles responsible for eyelid elevation. While other muscles, like the inferior rectus, are involved in eye movement, they do not directly affect the positioning of the eyelid. Similarly, Riolan's muscle, part of the orbicularis oculi, primarily contributes to eyelid closure and does not have a significant effect on , while the muscle of Horner is not a separate muscle; rather, it is often confused with the components of Horner's syndrome that can also lead to ptosis, but it is not itself a specific muscle. Thus, focusing on the superior tarsal muscle clearly establishes why it is directly linked to the condition of ptosis.