Shoening of 2 mm of axial length of eye ball causes-
3D myopia
6D myopia
3D hypermetropia
6D hypermetropia
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
Optics and refraction