This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ocular motility and squint, Subject name: Ophthalmology
[{'content': 'A 26 yrs old male with restriction of eye movements in all directions &moderate ptosis but with no diplopia or squint. Diagnosis is - \nSelect and explain. \nA. Thyroid ophthalmopathy, B. Chronic progressive external ophthalmoplegia, C. Myasthenia gravis, D. Multiple cranial nerve palsies', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Chronic progressive externalophthalmoplegia (CPEO), is a type of eye disorder characterized by slowly progressive inability to move the eyes and eyebrows. It is often the only feature of mitochondrial disease, in which case the term CPEO may be given as the diagnosis.', 'role': 'assistant'}]