Read here about the history of glass and what optimisations have emerged over the years for the spectacle lens industry.
Before 1886 the standard crown and flint glasses were the only types known. The development of new materials started after this date.
Initially, the low-index CR 39 remained the only material used for plastic lenses. It was not until the mid-1980s that the development of plastic materials with a higher refractive index began.
Photochromic lenses gradually darken when exposed to an increasing intensity of short-wave light and return to their original state when the light is removed. They adapt automatically to changing light conditions and therefore provide optimum protection against glare in every situation.