Most important factor determining convergence of light rays on the retina is
refracting structures with their refractive indices given in parentheses-cornea (1.37), the aqueous humour (1.33), the crystalline lens (1.42), and the vitreous humour (1.33).
The total dioptric power of the eye is about +60 D out of which about +44 D is contributed by the cornea and +16 D by the crystalline lens.
Length of eyeball
Refractive index of cornea
Dioptre power of lens
Physical state of vitreous