Single vision lenses

Single Vision (SV) Lenses are lenses designed with only one power and are what most people use.

Modern SV lenses are very sophisticated compared with older designs. The majority of lenses today are made of a resin material ("plastic" is too general a term and does not reflect the high quality materials used) and although mineral glass does still have a place, all the areas where it has traditionally been used are being invaded by modern resins.

For the spectacle wearer the most important thing after seeing well is COMFORT. Generally the lighter and thinner a lens is the better.

The thickness of a lens is a combination of many factors.

The size of the lens	a smaller lens can be made thinner
The refractive index of the material	the higher the refractive index (often just called index) the thinner the lens
The steepness of the curvature of the surfaces of the lens	In general the flatter the lens, the thinner it looks
The type of surfaces used	an aspheric surface can make a lens much thinner than a spherical surface.

The standard resin lens material is called CR39 and is only 1/2 the weight of glass.