A form of a lens is define as the way lenses are dispensed or prevented to patient either by glazing it on a spectacle frame or by infusing it directly in the eye. In other to make direct contact with the cornea without a frame. Spectacle lenses are lenses that are glazed to the size and shape of the frame, fit on it and ways in front of the eye for vision correction. Spectacle lens are of various types namely the single vision (plus and minus lens) lens produced from polymethame thycrylate (PMMA) by inlithami.
The bifocal lens was produced by Benjamin Franklin 1954 for the correction of both distance and near vision, while varilux lens was introduced by Bennard M in the year 1952 for correction of presbyopia, a refractive error which affect adult already the age of 40yrs.
According to Inlithami Fernblour, contact lens is defined as a piece of plass or plastic materials use for correction, cosmetic and therapeutic purpose. Contact lens are produced based on the functions, specifically design to increase better vision, for cosmetic purpose making the appearance of the eye look more attractive, they are also produced for treatment management of non-refractive disorder of the eye but are for treatment of dry eyes, cornea edema, karatocloful, corneal ectosis. Contact lens also serves in purpose based on the construction materials. The hard contact lens are impermeable to chemical compounds such as oxygen that is of great value to the eye, the cause irritation which now lead to excessive secretion.
Concave and contact lenses are used for the correction of both short sightedness and long sightedness. Also toric lens is directly used to correct astigmatism (unegue/curvature of the cornea). Bifocal lenses are lenses used to correct presbyopia.
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