Most impoant factor in the convergence of light rays on the retina is

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. The human eye is spherical and its internal pas are transparent so that the maximum amount of light can reach the retina. The cornea surrounds and protects the eye. It is made of transparent gel-like material that helps converge light rays onto the retina. Khurana 4e pg: 26