In a patient with ptosis, which of the following is the cause of retraction of the ptotic eye lid on chewing?
**Core Concept**
The retraction of the ptotic eyelid on chewing is a clinical phenomenon related to the innervation of the muscles controlling eyelid movement. It involves the coordination between the sympathetic and parasympathetic nervous systems, specifically the superior tarsal muscle (also known as Müller's muscle) and the levator palpebrae superioris muscle.
**Why the Correct Answer is Right**
The correct answer is related to the activation of the levator palpebrae superioris muscle by the superior cervical ganglion, which is part of the sympathetic nervous system. When the patient chews, the superior cervical ganglion stimulates the levator palpebrae superioris muscle, causing it to contract and lift the ptotic eyelid. This is a compensatory mechanism to counteract the effect of the ptotic eyelid.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not address the specific mechanism of retraction of the ptotic eyelid on chewing.
* **Option B:** This option is incorrect because it refers to the inferior oblique muscle, which is responsible for elevating the eye, not the eyelid.
* **Option D:** This option is incorrect because it refers to the superior rectus muscle, which is responsible for elevating the eye, not the eyelid.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that the retraction of the ptotic eyelid on chewing is a sign of intact sympathetic innervation, which can be useful in diagnosing Horner's syndrome, a condition characterized by the absence of sympathetic innervation to the eye.
**Correct Answer: C. The levator palpebrae superioris muscle is activated by the superior cervical ganglion, causing retraction of the ptotic eyelid on chewing.**