Bandage contact lens

A contact lens, or simply contact, is a thin lens placed directly on the surface of the eye. Contact lenses are ocular prosthetic devices used by over 150 million people worldwide, and they can be worn to correct vision, for cosmetic, or therapeutic reasons. In 2004, it was estimated that 125 million people worldwide use contact lenses, including 28 to 38 million in the United States. In 2010, the worldwide market for contact lenses was estimated at $6.1 billion, while the US soft lens market was estimated at $2.1 billion. Multiple analysts estimated that the global market for contact lenses would reach $11.7 billion by 2015. As of 2010, the average age of contact lens wearers globally was 31 years old, and two-thirds of wearers were female. People choose to wear contact lenses for many reasons. Aesthetics and cosmetics are the main motivating factors for people who want to avoid wearing glasses or to change the appearance of their eyes. Others wear contact lenses for functional or optical reasons. When compared with spectacles, contact lenses typically provide better peripheral vision, and do not collect moisture (from rain, snow, condensation etc.) or perspiration. This can make them preferable for sports and other outdoor activities. Contact lens wearers can also wear sunglasses, goggles, or other eyewear of their choice without having to fit them with prescription lenses or worry about compatibility with glasses. Additionally, there are conditions such as keratoconus and aniseikonia that are typically corrected better with contact lenses than with glasses. Leonardo da Vinci is frequently credited with introducing the idea of contact lenses in his 1508 Codex of the eye, Manual D, wherein he described a method of directly altering corneal power by either submerging the head in a bowl of water or wearing a water-filled glass hemisphere over the eye. Neither idea was practically implementable in da Vinci's time.:9 He did not suggest his idea be used for correcting vision, as he was more interested in learning about the mechanisms of accommodation of the eye. Descartes proposed another idea in 1636—a glass tube filled with liquid placed in direct contact with the cornea. The protruding end was to be composed of clear glass, shaped to correct vision; however, the idea was impracticable since it made blinking impossible. In 1801, Thomas Young made a pair of basic contact lenses based on Descartes' model. He used wax to affix water-filled lenses to his eyes, which neutralized its refractive power. He then corrected for it with another pair of lenses. However, like da Vinci's, Young's device was not intended to correct refraction errors. Sir John Herschel, in a footnote of the 1845 edition of the Encyclopedia Metropolitana, posed two ideas for the visual correction: the first 'a spherical capsule of glass filled with animal jelly', and 'a mould of the cornea' that could be impressed on 'some sort of transparent medium'. Though Herschel reportedly never tested these ideas, they were both later advanced by several independent inventors such as Hungarian Dallos with István Komáromy (1929), who perfected a method of making molds from living eyes. This enabled the manufacture of lenses that, for the first time, conformed to the actual shape of the eye. In 1888, German ophthalmologist Adolf Gaston Eugen Fick constructed and fitted the first successful contact lens. While working in Zürich, he described fabricating afocal scleral contact shells, which rested on the less sensitive rim of tissue around the cornea, and experimentally fitting them; initially on rabbits, then on himself, and lastly on a small group of volunteers. These lenses were made from heavy blown glass and were 18–21 mm (0.71–0.83 in) in diameter. Fick filled the empty space between cornea and glass with a dextrose solution. He published his work, 'Contactbrille', in the journal Archiv für Augenheilkunde in March 1888. Fick's lens was large and unwieldy, and could be worn only for a couple of hours at a time. August Müller in Kiel, Germany, corrected his own severe myopia with a more convenient blown-glass scleral contact lens of his own manufacture in 1888.