A contact lens is a piece of transparent material that refracts light to form a clear image on the retina (light-sensitive layer of nerve tissue at the back of the eye). The shape of a lens causes rays of light to converge on or diverge from a single point.

There are many different types of contact lenses, and each offers its own set of advantages. Some are more comfortable than others, while some are better suited for certain vision needs.

Types

There are several different types of contact lens. The most common are soft lenses made of water-absorbing plastic. They cover the iris, cornea and some of the sclera of the eye. These lenses can correct vision problems such as myopia (short-sightedness) and hyperopia (long-sightedness).

Rigid gas permeable (RGP or PMMA) contacts are less flexible, but they provide crisp optics. They can be used to correct myopia, hyperopia and astigmatism.

Hybrid contact lenses combine the above two lens types -- a center of rigid gas permeable plastic is surrounded by a layer of soft lens material. This design provides the sharp optics of a GP lens with the comfort of a soft lens. These lenses can be used to correct myopia, hyperopia, astigmatism and keratoconus.

Materials

There are different types of materials used to make contact lenses. Your optometrist can recommend the right type for you based on your lifestyle, eye health and vision correction needs.

Rigid gas permeable lenses (also known as GP or RGP) are made from a hard plastic called polymethyl methacrylate, or PMMA. They have high oxygen permeability ratings and are ideal for those with specific eye conditions such as keratoconus.

Soft contact lenses made from cellulose acetate butyrate, ethyl methacrylate, and cellulose trioxide are brittle when dry, making them uncomfortable to wear for long periods. They also tend to build up with protein deposits.

In the 1970s, improved rigid contact lens materials that are oxygen permeable were developed. These are known as GPs or Rigid Gas Permeable lenses.

Benefits

Most contact lens wearers agree that wearing contacts makes them feel more confident, attractive and improves their quality of life. These deeper benefits are reported by both men and women, older and younger wearers alike. These benefits are even more pronounced in people who wear their lenses frequently.

Most soft lenses are disposable and can be thrown away after each use, making them more convenient than glasses. They also gather fewer deposits of allergens and germs, which helps protect the eyes.

Multifocal contact lenses correct the same refractive error as bifocals and can help patients with presbyopia. Rigid gas permeable (RGP) lenses vault over the cornea and trap a small reservoir of water on its surface, helping keep it moist and reduce symptoms of dry eye.

Complications

Many contact lens wearers experience a non-ulcerative complication at some time in their life. These may be related to the contact lenses themselves, or to the solutions used to clean, soak and disinfect them. They are usually associated with a preservative or irritant response. The symptoms are generally self limiting, and the patient can be reverted back to safe contact lens wearing once the condition is resolved.

A thorough slit lamp examination without the lenses in place should be performed to assess the health of the ocular surface. Sodium fluorescein can be used to highlight dead epithelial cells in areas of damage or dystrophia.

Non-infectious complications of contact lens wear are grouped into corneal infection (microbial keratitis), metabolic conditions, toxic and hypersensitivity disorders, and mechanical and tear resurfacing disorders.

Cost

The price tag of contact lenses varies depending on the type and brand. Prices also vary based on whether or not you have vision insurance and whether or not you purchase through a private-practice optometrist or an optical center that offers one-stop shopping.

Rigid gas permeable lenses (RGPs) are less expensive than soft lenses, although they do have a higher initial cost. RGPs resist deposit buildup better than soft lenses and provide a clearer, crisper vision.

Wearing daily disposables reduces lens care time and waste, including the hydrogen peroxide that is used to clean and disinfect lenses. It is important to encourage patients to stick to their two-week or monthly replacement schedule. Failure to do so increases the risk of lens deposits and irritation.