This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diseases of Thyroid, Subject name: Medicine
Which one of the following clinical signs is not seen in ophthalmic Grave's disease? 
Select and explain. 
A. Lid retraction, B. Frequent blinking, C. Poor convergence, D. Upper lid "lad" on down gaze
B: Frequent blinking
Answer: B: Frequent blinking 
Explanation: In thyrotoxicosis the increase in sympathetic activity due to increased T3 and T4 leads to contraction of Muller's muscle. Hence these patients would have infrequent blinking and infact some of them might sleep with their eyes open leading to corneal erosions. Lid retraction, causing a staring appearance, can occur in any form of thyrotoxicosis and is the result of sympathetic overactivity. However, Graves' disease is associated with specific eye signs that comprise Graves' ophthalmopathy. The earliest manifestations of ophthalmopathy are usually a sensation of grittiness, eye discomfo, and excess tearing. The most serious manifestation is compression of the optic nerve at the apex of the orbit, leading to papilledema; peripheral field defects; and, if left untreated, permanent loss of vision.