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A contact lens (also known simply as a contact) is a corrective, cosmetic, or therapeutic lens usually placed on the cornea of the eye. Modern soft contact lenses were invented by the Czech chemist Otto Wichterle and his assistant Drahoslav Lím, who also invented the first gel used for their production.
Wichterle thought pHEMA might be a suitable material for contact lenses and gained his first patent for soft contact lenses. In 1954 this material was first used as an orbital implant. In 1957 Wichterle produced around 100 soft lenses from closed polystyrene molds but the edges split and tore as the lenses were removed. In addition, they ...
Legally blind indicates that a person has less than 20/200 vision in the better eye after best correction (contact lenses or glasses), or a field of vision of less than 20 degrees in the better eye. Totally blind students learn via braille or other non-visual media.
A lens may be considered a thin lens if its thickness is much less than the radii of curvature of its surfaces (d ≪ | R 1 | and d ≪ | R 2 |).. In optics, a thin lens is a lens with a thickness (distance along the optical axis between the two surfaces of the lens) that is negligible compared to the radii of curvature of the lens surfaces.
Intraocular lenses that are implanted into eyes after the eye's natural lens has been removed during cataract surgery are known as pseudophakic. Phakic intraocular lenses are indicated for patients with high refractive errors when the usual laser options for surgical correction (LASIK and PRK) are contraindicated.
Children's eyesight is steadily getting worse with one in three now short-sighted or unable to see things in the distance clearly, a global analysis suggests. The researchers say Covid lockdowns ...
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