The thickness of a spectacle lens can be controlled by
the refractive index (density) of the lens material. By increasing the
density of the lens, the curvature of the lens surfaces required to
produce the prescription is less, creating a flatter, thinner lens.
Originally produced in glass, there are now several plastic options
available making thick lenses a thing of the past. Also, as lens
thickness reduces, so does the weight.
lenses are available in most forms including Bifocal and Varifocal and
are supplied with an anti-reflection coating as standard (See coatings).