contact the concept of corrective lenses that sit directly on the eyeball was developed in the ninth century, but it was not until the late 20th century that manufacturing and grinding techniques for contact were perfected. originally contact were made of glass, then later of hard plastic, and still later of flexible, highly oxygen-permeable soft plastic. today, the majority of lenses worn are of two basic types: rigid gas permeable (so-called "hard" lenses) theatrical and lenses. best lenses are smaller and more durable, but require a longer period of adjustment for the wearer. hard contact can correct some vision problems, like astigmatism, that the lenses cannot. the lenses are slightly larger than best lenses. they are more comfortable and less expensive, but can be easily torn. the latest generations of contact are extended and disposable lenses. extended lenses are intended to be worn for several weeks at a time, while disposable glow lenses are thrown away every day or every few weeks, or in the in newest versions, every day.

contact the concept of corrective lenses that sit directly on the eyeball was developed in the ninth century, but it was not until the late 20th century that manufacturing and grinding techniques for contact were perfected. originally contact were made of glass, then later of hard plastic, and still later of flexible, highly oxygen-permeable soft plastic. today, the majority of lenses worn are of two basic types: rigid gas permeable (so-called "hard" lenses) theatrical and lenses. best lenses are smaller and more durable, but require a longer period of adjustment for the wearer. hard contact can correct some vision problems, like astigmatism, that the lenses cannot. the lenses are slightly larger than best lenses. they are more comfortable and less expensive, but can be easily torn. the latest generations of contact are extended and disposable lenses. extended lenses are intended to be worn for several weeks at a time, while disposable glow lenses are thrown away every day or every few weeks, or in the in newest versions, every day.

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 the 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 dark because they absorb more external liquids and airborne contaminants.