Source:http://linkedlifedata.com/resource/umls/id/C0181607
UMD: Lenses designed to be mounted, usually in pairs, in frames that hold them in an appropriate position before the eyes (i.e., eyeglass frames) to assist vision. Lenses are usually made of glass or plastic (e.g., polycarbonate) and graduated to improve teh visual acuity of the wearer, they may be configured as monofocal, bifocal, trifocal, or progressive. Eyeglass lenses are used mainly as a vision aid, but some lenses are designed to protect the eye (e.g., sunglasses) or used for aesthetic purposes.