This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cornea, Subject name: Ophthalmology
The critical angle of cornea-air interface is 
Select and explain. 
A. 36 degree, B. 46 degree, C. 56 degree, D. 66 degree
B: 46 degree
Answer: B: 46 degree 
Explanation: Critical angle refers to the angle of incidence in the denser medium, corresponding to which angle of refraction in the rare medium is 90deg. At the tear-air interface, the critical angle is approximately 46deg. Made use of in construction of gonio lenses where this interface is changed and as a result critical angle becomes larger allowing for the reflected light to escape the eye and get reflected on the gonio mirrors which helps the examiner visualize the angle of the eye