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
Which of the pa of the sclera is thinnest? 
Select and explain. 
A. Limbus, B. Equator, C. Anterior to attachment of superior rectus, D. Posterior to attachment of superior rectus
D: Posterior to attachment of superior rectus
Answer: D: Posterior to attachment of superior rectus 
Explanation: The sclera averages 0.5 mm in thickness, is relatively avascular, and consists of tough, dense connective tissue containing flat type I collagen bundles which intersect in various directions. Sclera is thinner in children than the adults and in females than the males. Sclera is thickest posteriorly (1 mm) and gradually becomes thin when traced anteriorly. It is thinnest at the inseion of extraocular muscles (0.3 mm), especially just posterior to the rectus inseions; elsewhere it is about 0.6 mm thick. Ref: Ophthalmology: Expe Consult edited by Myron. Yanoff, Jay S. Duker, James J. Augsburger, 2009, Page 1301.