Scuba Diving Vision

When light travels from one medium to another medium of different density (refractive index), it changes its path. When light strikes the cornea in air, it bends the light with some help from the lens in the eye, to bring it to a focus on the retina.
One pair of glasses can never fullfill all of your visual functions

Eye care needs can more or less be divided into two age groups. Under forty and over forty or, pre-presbyopic and presbyopic. From the age of forty onwards, the focusing mechanism of our eyes starts to deteriorate and what this means, is that we require different strengths of lenses for distance vision and near vision. When we fixate close-up, the lenses in our eyes, at lighting speed, change shape and give us more focusing power to obtain clear vision at near. It is this focusing power that we begin to lose because the lenses start to lose their elasticity. This a normal aging process.