## **Core Concept**
The question tests understanding of neuromuscular junction disorders, specifically myasthenia gravis (MG), which affects the acetylcholine receptor at the neuromuscular junction, leading to muscle weakness and fatigue.

## **Why the Correct Answer is Right**
Myasthenia gravis is characterized by fluctuating muscle weakness that worsens with activity and improves with rest. Ocular symptoms are common and can include ptosis (drooping eyelid), diplopia (double vision), and restriction of eye movements. However, in some cases, patients may not experience diplopia despite having restricted eye movements because the weakness may be symmetrical or the patient may adapt to the condition. The absence of diplopia does not rule out MG.

## **Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided, but typically, conditions like thyroid ophthalmopathy could cause restriction of eye movements and ptosis but are usually associated with other signs such as exophthalmos.
* **Option B:** This option is not provided, but conditions like multiple cranial neuropathies could cause restriction of eye movements but would more likely present with other neurological deficits.
* **Option D:** This option is not provided, but conditions like chronic progressive external ophthalmoplegia (CPEO) cause progressive ptosis and restriction of eye movements but typically do not present with fluctuating symptoms.

## **Clinical Pearl / High-Yield Fact**
A key feature of myasthenia gravis is the variability and fluctuation of symptoms, particularly the worsening of muscle weakness with activity and improvement with rest. The ice pack test can temporarily improve ptosis in MG, which can be a useful diagnostic clue.

## **Correct Answer:** C. Myasthenia Gravis.