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 for 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 discountcoloredcontactlens with large refractive errors. A plastic called CR-39, introduced in the 1960s, was more suitable. Today, lenses discountcoloredcontactlens wearers can also choose discountcoloredcontactlens between polycarbonate, which is the most impact-resistant material available for eyewear, and polyurethane, which has exceptional optical qualities and an index of 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 gas-permeables 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, discountcoloredcontactlens comfort and cheaper maintenance discountcoloredcontactlens costs. Allow yourself a week or two to get used to these slightly stiff lenses.Bifocals These contact correct presbyopia, a kind of farsightedness that usually occurs around age 40. There are two types: