This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Guanethidine is used in the treatment of which of the following condition? 
Select and explain. 
A. Thyrotoxic ophthalmopathy, B. Ptosis, C. Bell's palsy, D. Horner's syndrome
A: Thyrotoxic ophthalmopathy
Answer: A: Thyrotoxic ophthalmopathy 
Explanation: Guanethidine (10%) eye drops is useful in decreasing lid retraction in Thyrotoxic ophthalmopathy. It is an adrenergic neuron blocker which acts by inhibiting the release of noradrenaline in response to nerve stimulation.