glass was the first material to be used for lenses lenses, and was used for several hundred years before plastic was introduced. the crown glass used sfx for theatrical lenses lenses has an index of refraction of 1.52.optical-quality acrylic was introduced for lenses use in the early 1940s, but because it was easily scratched, brittle, and discolored rapidly, it did not supplant glass as the material of choice. furthermore, it had a relatively low index of refraction, so it wasn''t suitable for people with large refractive errors. a plastic smiley called cr-39, introduced in the 1960s, was more suitable. today, lenses wearers can also choose between polycarbonate, which is the most impact-resistant material available contact for eyewear, and polyurethane, which has exceptional optical qualities and an index of lenses refraction of up to 1.66, much higher than the conventional plastics used for lenses, and even higher than glass. patients with high prescriptions should ask about high index material options for their lenses. aspheric lenses are also useful for high prescriptions.

glass was the first material to be used for lenses lenses, and was used for several hundred years before plastic was introduced. the crown glass used sfx for theatrical lenses lenses has an index of refraction of 1.52.optical-quality acrylic was introduced for lenses use in the early 1940s, but because it was easily scratched, brittle, and discolored rapidly, it did not supplant glass as the material of choice. furthermore, it had a relatively low index of refraction, so it wasn''t suitable for people with large refractive errors. a plastic smiley called cr-39, introduced in the 1960s, was more suitable. today, lenses wearers can also choose between polycarbonate, which is the most impact-resistant material available contact for eyewear, and polyurethane, which has exceptional optical qualities and an index of lenses refraction of up to 1.66, much higher than the conventional plastics used for lenses, and even higher than glass. patients with high prescriptions should ask about high index material options for their lenses. aspheric lenses are also useful for high prescriptions.

nearsighted? need reading glasses? new developments in lens technology ensure a solution to almost every vision problem. talk to your eye doctor about what''s available (costs vary).rigid sfx gas-permeables theatrical recommended for those with high degrees of corneal astigmatism, rgps are firm plastic lenses with microscopic slits that allow more oxygen to reach the eye. rgps have a greater resistance to bacteria because they don''t contain water. improved extended-wear materials also guarantee greater durability, sharper vision, comfort and cheaper maintenance costs. allow yourself a week or two to get used to smiley and contact these slightly stiff lenses.bifocals these contact correct presbyopia, a kind of farsightedness that lenses usually occurs around sfx age 40. there are two theatrical types: