**Core Concept**
The oculomotor nerve (cranial nerve III) is responsible for controlling several extraocular muscles, including the medial rectus, superior rectus, inferior rectus, inferior oblique, and levator palpebrae superioris. It also regulates pupil constriction and accommodation.

**Why the Correct Answer is Right**
Oculomotor nerve palsy typically results in weakness or paralysis of the affected muscles, leading to symptoms such as ptosis (drooping eyelid), diplopia (double vision), and limited eye movement in the affected direction. The patient may also exhibit a dilated pupil due to the loss of parasympathetic innervation, which normally stimulates pupil constriction.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because oculomotor nerve palsy primarily affects the medial rectus, superior rectus, and inferior rectus muscles, resulting in difficulty moving the eye inward, upward, or downward. It does not typically cause nystagmus.
**Option B:** This option is incorrect because oculomotor nerve palsy can indeed cause diplopia, as the affected eye may not move properly in conjunction with the unaffected eye.
**Option C:** This option is incorrect because oculomotor nerve palsy can lead to ptosis, as the levator palpebrae superioris muscle is weakened or paralyzed.

**Clinical Pearl / High-Yield Fact**
A useful mnemonic to remember the extraocular muscles controlled by the oculomotor nerve is "SOO IL": superior oblique, oculomotor, inferior oblique, and inferior rectus. Note that the superior rectus is also controlled by the oculomotor nerve, but this mnemonic helps to remember the other muscles.

**Correct Answer: C. Ptosis is not a characteristic of oculomotor nerve palsy.**