**Core Concept**
Chronic progressive external ophthalmoplegia (CPEO) is a rare, degenerative eye muscle disorder characterized by progressive external ophthalmoplegia, often presenting with ptosis and limited eye movements in all directions without diplopia or squint. This condition is associated with mitochondrial dysfunction and typically affects middle-aged adults.

**Why the Correct Answer is Right**
CPEO is caused by mutations in mitochondrial DNA, leading to impaired energy production in muscle cells, including those of the extraocular muscles. This results in progressive weakness and limited eye movements, as seen in the patient. The lack of diplopia or squint is due to the symmetrical involvement of both eyes. The patient's age and the absence of other systemic symptoms are consistent with CPEO.

**Why Each Wrong Option is Incorrect**
**Option A:** Thyroid ophthalmopathy typically presents with exophthalmos, eyelid retraction, and diplopia due to inflammation and fibrosis of the extraocular muscles and surrounding tissues. It is not characterized by progressive external ophthalmoplegia.

**Option C:** Myasthenia gravis is an autoimmune disease causing fluctuating muscle weakness, including extraocular muscles, which can lead to diplopia and ptosis. However, the weakness in myasthenia gravis is typically more pronounced in certain eye movements and does not progress in a symmetrical, chronic fashion.

**Option D:** Multiple cranial nerve palsies would result in a more complex pattern of eye movement abnormalities, including potential diplopia and squint, as well as other cranial nerve deficits.

**Clinical Pearl / High-Yield Fact**
CPEO is often associated with other mitochondrial disorders, such as Kearns-Sayre syndrome, which can present with additional systemic symptoms like heart block, ataxia, and pigmentary retinopathy. Recognizing the link between CPEO and mitochondrial dysfunction is crucial for accurate diagnosis and management.

✓ Correct Answer: B. Chronic progressive external ophthalmoplegia