Refractive index

The refractive index determines how much light is refracted when entering the eye. The value of the contact lens materials should be close to the refractive index of the cornea in order to minimize the number of refractions before entering the eye. The value of the contact lens material is in the range 1.3 to 1.6.
Refraction is the bending of light (it also happens with sound, water and other waves) as it passes from one transparent substance into another.

This bending by refraction makes it possible for us to have lenses, magnifying glasses, prisms and rainbows. Our eyes depend upon this bending of light. Without refraction, we wouldn’t be able to focus light onto our retina.

Isaac Newton performed a famous experiment using a triangular block of glass called a prism. He used sunlight shining in through his window to create a spectrum of colours on the opposite side of his room. This experiment showed that white light is actually made of all the colours of the rainbow.