This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Neuro Ophthalmology, Subject name: Ophthalmology
[{'content': "A 72 year old man complains of drooping of lids for last 2 months. On awakening he is able to open his eyes, but few hours later his ptosis progressively worsens with increasing diplopia most likely diagnosis? \nSelect and explain. \nA. Thyroid ophthalmopahty, B. Horner's syndrome, C. Myasthenia gravis, D. 3rd nerve Palsy", 'role': 'user'}, {'content': 'Answer: C \nExplanation: Myasthenia gravis is a disease characterized by generalized muscular weakness and rapidly developing fatigue of the muscles due to an auto-immune disorder in which damage of the acetylcholine receptors takes place at the post-synaptic membrane. Anti-acetylcholine receptor antibodies are found in approximately 80% of patients with myasthenia, the levels correlating with the severity of the disease. The ptosis is nearly always bilateral and is increased by prolonged fixation or attempts to look upwards; effective compensation by overaction of the frontales is impossible. Ophthalmoplegia externa, paial or complete, occurs in 50% of the cases, but the intrinsic muscles are not affected. Nystagmoid jerks are not uncommon.', 'role': 'assistant'}]