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
Sclera, the protective covering of the eye, is thinnest at the following site: 
Select and explain. 
A. Apex, B. Limbus, C. In front of inseion of rectus muscle, D. Behind inseion of rectus muscle
D: Behind inseion of rectus muscle
Answer: D: Behind inseion of rectus muscle 
Explanation: The sclera is the fibrous outer coating of the eye, consisting almost entirely of collagen. It is 1 mm thick posteriorly, 0.66 mm at the inseions of the rectus muscles, 0.33 mm beneath the rectus muscles and is thinnest just behind their inseions. Ref: Parsons' Diseases of the Eye By Ramanjit Sihota & Radhika Tandon, 21st edition, Page 218.