Contact Lenses

Lenses worn on the eye to correct vision, their types and history

Overview

Contact lenses are thin lenses placed directly on the surface of the eye to correct refractive errors or for therapeutic or cosmetic purposes. The idea is often traced to sketches by Leonardo da Vinci, and the first practical lenses, made of blown glass and covering the sclera, were produced in the late 1880s, with the German physician Adolf Fick among the pioneers. Rigid lenses made of PMMA plastic followed in the mid twentieth century, and soft hydrogel lenses were developed by the Czech chemist Otto Wichterle around 1960. Silicone hydrogel materials introduced in the late 1990s transmit considerably more oxygen to the cornea. Today soft lenses, including daily disposable and planned replacement types, are the most widely used, alongside rigid gas permeable lenses, which give sharper optics on irregular corneas, scleral lenses, and orthokeratology lenses worn overnight to temporarily reshape the cornea. Toric and multifocal designs correct astigmatism and presbyopia. The most serious complication is microbial keratitis, a corneal infection caused by bacteria such as Pseudomonas or, less commonly, by fungi or the amoeba Acanthamoeba, and overnight wear, exposure to water, and poor lens hygiene are well established risk factors. Other complications include corneal hypoxia, giant papillary conjunctivitis, and contact lens related dry eye.