This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Vitreous and retina, Subject name: Ophthalmology
In retinal sealing/retinopexy, what is used? 
Select and explain. 
A. Sulphur hexafluoride, B. Carbon monooxide, C. Nitrous oxide, D. S02
A: Sulphur hexafluoride
Answer: A: Sulphur hexafluoride 
Explanation: The gases commonly employed for tamponading the retina are sulphur hexafluoride (SF6) or perfluoropropane (C3F8). These are injected after sealing the breaks with cryopaxy. The gas bubble remains in contact with the tear for 5-7 days and are absorbed later. Ref: Parson's 22 nd edition page no. 335