This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Optics and refraction, Subject name: Ophthalmology
Shoening of 2 mm of axial length of eye ball causes- 
Select and explain. 
A. 3D myopia, B. 6D myopia, C. 3D hypermetropia, D. 6D hypermetropia
D: 6D hypermetropia
Answer: D: 6D hypermetropia 
Explanation: Axial hypermetropia is by far the commonest form. In this condition the total refractive powerof eye is normal but there is an axial shoening of eyeball. About 1-mm shoening of the anteroposterior diameter of the eye results in 3 dioptres of hypermetropia. So shoening of eyeball about 2mm results in 6D hypermetropia Reference : A K KHURANA OPHTALMOLOGY,Edition 4, page-29