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 with large refractive errors. A plastic 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 for eyewear, and polyurethane, which has exceptional optical qualities and an index of refraction of up to 1.66, much higher sfxtheatricalgreencat than the conventional plastics used for lenses, and even sfxtheatricalgreencat 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 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 with large refractive errors. A plastic 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 for eyewear, and polyurethane, which has exceptional optical qualities and an index of refraction of up to 1.66, much higher sfxtheatricalgreencat than the conventional plastics used for lenses, and even sfxtheatricalgreencat 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.

The primary drawback to wearing contact, especially for children, is the requirement that they be cleaned and disinfected daily in order to prevent an infection, which could result in permanent damage to the eye. Careful choice of lenses and consistent lens care will minimize the risk of infection. Wearers of best lenses are the least prone to infection but the lenses are much less comfortable, more expensive, and can pop out of the eye more easily than lenses. Daily wear lenses put the wearer at a slightly higher risk of infection because they absorb more external liquids and airborne contaminants.