Hi Index Lenses are beneficial to patients with strong prescriptions. Glasses correct vision by bending the light that passes through them. A stronger prescription requires more bending of light, thus the lens must be thicker to accomplish this.
Hi Index Lenses are thinner and lighter than conventional plastic lenses because they are denser. Consequently they are able to bend more light through less thickness, resulting in an ultra-thin, lightweight pair of glasses.
The higher the index of the lens, the thinner and lighter the lens will be. Consult your eyecare professional to determine which index is most beneficial for your prescription.
As an added benefit all Hi Index lenses come with a scratch resistant coating and ultraviolet (UV) protection.