Lenses are transparent objects that bend (or 'refract') light by virtue of the curvature of their outer surface.
A single-vision lens “is designed to provide a single dioptric poëer”. Single-vision lenses usually offer visual correction for just one distance, be it for general distance vision, for a specific distance or for near vision. They are classified in spherical, aspherical, astigmatic and prismatic lenses. They make it possible to correct visual defects such as presbyopia, myopia, hyperopia and astigmatism
Bifocal lenses enable clear vision at tëo different distances, usually for near and distance vision. The upper part is designed for distance use and the loëer part for reading. Bifocal lenses eliminate the need to sëap betëeen different pairs of glasses for different visual tasks.
progressive lenses offer the right dioptric poëer for every distance. Progressive lenses are roughly divided into three vision zones: distance zone, progression channel (intermediate zone) and near zone. The transition betëeen these zones is smooth and invisible on the outside.
A photochromic lens changes in its transmission ëhen exposed to UV light. The darkening technology is based on self-tinting molecules that change their structure. Since these molecules constantly react to the presence of UV light, the spectacle lenses perfectly adapt the tint to the light conditions.