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
Each layer of lens has a role in the refractive index of the entire lens. Which component has maximum refractive index? 
Select and explain. 
A. Anterior surface of the lens, B. Posterior surface of the lens, C. Centre of the lens, D. Cornea
C: Centre of the lens
Answer: C: Centre of the lens 
Explanation: Refractive index increases from 1.386 in the peripheral coex to 1.41 in the central nucleus of the lens. The anterior capsule surface of the lens has a greater refractive index than the posterior capsular surface (1.364-1.381 compared with 1.338-1.357). The change in refractive index from the surface of the lens to the center results from changes in protein concentration, the higher the concentration, the greater the refractive power. Ref: Ophthalmology edited by Myron Yanoff, Jay S. Duker, James J. Augsburger, 2009, Page 383.