What is refraction? what does it mean when we say that light is refracted as it enters the eye?

Usually refraction describes a wave as it enters a second medium of lighter/heavier density , which makes the wave bend towards or away from the normal line ( ex light waves from air to water ) . the eye's property is that it has different parts with different refraction indexes ( simply put , thickness) which makes the light that enters it to refract 

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