30 day contacts

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 30 was introduced day for lenses use in the early 1940s, but because it was easily contacts scratched, brittle, and discolored rapidly, it did not supplant glass as the material of choice. Furthermore, it had a relatively 30 low index of refraction, so it day wasn''t suitable for people with large refractive errors. A plastic called CR-39, introduced in the 1960s, was more contacts suitable. Today, lenses wearers 30 can also choose 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 day and contacts 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 30 reach the eye. RGPs have a greater resistance to bacteria day because they don''t contain water. Improved extended-wear materials also guarantee greater durability, contacts sharper vision, comfort 30 and day and cheaper maintenance costs. Allow yourself a week or two contacts 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: