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: Ophthalmology
Unilateral proptosis with bilateral VI
th
 nerve palsy,diagnosis is - 
Select and explain. 
A. Grave's disease, B. Retinoblastoma, C. Pseudotumour of orbit, D. Cavernous sinus thrombosis
D: Cavernous sinus thrombosis
Answer: D: Cavernous sinus thrombosis 
Explanation: Unilateral proptosis and bilateral 6th nerve polsy suggest the diagnosis of CST.
Bilateral 6th nerve palsy suggests the involvement of opposite side cavernous sinus. In more than 50% of the patients of CST opposite side is involved. 6th nerve is earliest to be involvement.