Types of Spectacle Lenses?
Single Vision lenses – spherical or with astigmatic correction – in plastic or glass Bifocal Lenses – made of a main lens and an additional segment for near vision – variety of shapes of near addition Trifocal Lenses – composed of a main lens and two reading ssegments; one for near and one for intermediate distances (about arm lengths) Multifocals – composed of main lens and continuously variable addition for various near reading positions Aphakic Lenses – high power plus lenses used for cataract patients. – made with aspheric surfaces to minimise aberrations due to shape of the lens Photochromic lenses – darken when exposed to short wavelength radiation (300nm – 400nm) or ultra-violet light – rate of darkening and final transmission of the lens (saturation transmission) depends on the ambient temperature. – lenses will not become as dark when driving due to UV absorption by the car windscreen. – available in plastic lenses now – Transitions+ and Spectralite are two common lens names.
