Contact lenses, also known simply as contacts, are small, thin curved discs made of glass or plastic and fitted on the eye. Today almost 30 million people in the U.S. wear contacts. They have become the first choice for those needing vision correction.

Contacts are very convenient eye aids compared to traditional glasses. They provide all kinds of vision corrections and more. They do not fall off, do not become steamed up - hampering your vision - and are very convenient for those having very poor natural vision, which requires continuous wearing of glasses or lenses.

However since they cover the eye cornea, depriving it of nourishing oxygen, some corneal complications can arise. Corneal complications among wearers are a major problem. Another problem is that contacts obstruct the smooth flow of tears. This can produce another set of complications because tears serve the very useful function of cleaning the eyes. Current research development of contact lenses is focused on lessening these complications by making the lenses more permeable to oxygen and less of a hindrance to tear flow. However, the problems have not been resolved as yet.

History

Contacts were first introduced in the late 19th century, when they were made of glass. These lenses covered the entire eye and hence were called scleral lenses. In the 1930s, lenses were made from a plastic material called polymethyl methaclyrate. While these were better than glass contacts, due to their low oxygen permeability, their use was not popular. The development of contacts began in a major way in the 1950s when corneal lenses were introduced, which covered only the cornea. Corneal lenses are easier to fit and allow better flow of oxygen and tears. Most lenses today are corneal or semiscleral. Scleral lenses are preferred for those with severe keratoconus, irregular corneas and certain other special eye surface disorders.

Modern lenses are mainly corneal and made from two types of plastics, rigid gas permeable (RGP) and silicon-gel plastic.

Uses

Contacts are used for both refractive disorders like near or far sightedness and astigmatism, and also for non-refractive vision disorders like glaucoma and cataracts. They are also used for therapeutic purposes to protect the eyes after certain eye surgeries. They are furthermore used for cosmetic purpose to change the appearance of the eye or to mask any eye injury.

Types of contact lenses

Contacts, as mentioned earlier, are mostly made from silicon gel material and RPG. These are called soft contacts and hard or rigid gas permeable RGP contacts respectively.

Soft contacts

They are used by about 75% of the contact lens wearers today. They have higher water content, making them flexible, soft and therefore comfortable to wear. Soft contacts are of the following types.

Daily wear contacts: Most people choose to wear daily wear contacts, which have to be inserted and removed every day. Wearing them during sleep is not advised. If cleaned and maintained well, they should last around a year.

Disposable contacts: Depending on their composition, they are used for periods ranging from one day to three months, after which they are thrown away. Their main advantage is that they carry less risk of infection.

Extended wear contacts: They are made from super permeable silicon hydrogel and so have a higher oxygen permeability allowing you to sleep with them still on your eyes. Depending on the type of lens, they are worn continuously for a week to 30 days. Silicon lenses exhibit far fewer eye complications

RGP lenses

RGP lenses are used to correct all types of vision problems including astigmatism. They are made from harder material and therefore feel uncomfortable initially. However, RGP lenses have higher oxygen permeability and carry fewer chances of corneal infections than soft contacts. They are easier to maintain and are more durable, lasting for two to three years.

Lenses for astigmatism

A class of lenses, called toric lenses, is used exclusively to correct types of astigmatism. These are also made from RGP and soft contact material but are given a special surface treatment to correct astigmatism and, with some types of lens, for correcting vision.

Contact lens complications

The fact that lenses are a barrier to normal flow of oxygen to the cornea exposes the wearer to various complications. These complications are unavoidable. At best, with improved material and design we can expect these complications to become easier to treat.

Cleaning regimen

Cleaning non-disposable lenses regularly is vital not only for the lenses but also for your eyes. Many complications are preventable if you strictly follow the cleaning regimen prescribed by the doctor. Indeed, complications due to a faulty cleaning regimen are a common problem.