Which part of human eye has the maximum refractive index?

The refractive indices of the different components of the human eye are approximately as follows:
* Aqueous humour: $1.336$
* Vitreous humour: $1.336$
* Cornea: $1.376$
* Crystalline Lens: Varies from $1.386$ at the outer layers to about $1.406$ at its inner core.

Therefore, the crystalline lens has the highest refractive index in the human eye.