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
In an aphakic eye posterior focal point from the back of cornea is about: 
Select and explain. 
A. 23 mm, B. 25 mm, C. 31 mm, D. 21 mm
C: 31 mm
Answer: C: 31 mm 
Explanation: Ans. 31 mm