how does change in refractive index affect power of contact lens?

Answer 1

A higher index of refraction (IR) would cause light to bend more as compared to a lower IR. A higher IR would result to either thinner lenses of the same power or lenses of the same thickness with more refractive power (as compared to a lower IR).

Answer 2

Light bends toward the normal (perpendicular) when travelling from a less dense medium to a more dense medium.

Answer 3

it's all in how it bends light which is picked up by the retna, etc. and you see stuff