Shoening of 2 mm of axial lengsth of eye ball causes -
1 mm change in axial length leads to ametropia of 3d. For example 1 mm shoenign an axial length causes hypermetropia of 3D. Reference :Khurana 7th edition,page28
3D myopia
6D myopia
3D hypermetropia
6D hypermetropia
Optics and refraction