What is Contact lens its types and material

 

What is Contact lens

Contact lenses are thin, transparent plastic discs that you wear on your eye to improve your vision or for cosmetic purpose . Contact lenses float on the tear film that covers the cornea.

Types and Materials of Contact Lenses

Soft Contact Lenses

Soft contact lenses are made of plastic, but not the type of plastic used in garbage bags or paper plates. Instead, these flexible lenses are made of hydrophilic plastics - a special type of water-absorbing plastic that remains soft and moist while absorbing a significant amount of water.

If you wear soft contact lenses, you may have already noticed how this plastic works. When the lenses dry out, they become brittle to the point where they can even break. As long as the plastic remains moist either inside the eye or in a case, it stays flexible and soft.

To your eyes, this smooth flexibility translates to comfort! When your eyes are dry, your lenses start to feel uncomfortable because they rely on moisture to stay in place and remain flexible.

Soft contact lenses are categorized by the amount of water they contain. They can be classified as high water content or low water content lenses.

Extended-Wear Soft Contact Lenses

Most extended-wear contact lenses are made of silicone hydrogel - a material that combines the water-absorbing plastic of soft lenses with silicone. The addition of silicone to the hydrogel plastic creates a lens that remains moist and allows more oxygen to pass through the lens to the eye. This keeps the eyes healthier during contact lens wear. The additional benefit of increased moisture and oxygen reaching the eye is why this material was added to extended-wear contact lenses.

Any contact lens wearer who keeps their lenses in both day and night or leaves them in for consecutive days needs a lens that allows their eyes to breathe. The addition of silicone to the lens provides this functionality for optimal contact lens health.

Gas permeable lenses

RGP lenses are also made of plastic. Unlike the plastic that makes up a soft contact lens, gas permeable lenses transmit oxygen without absorbing water. Instead, RGP lenses have microscopic holes that allow oxygen to pass through. For this reason, RGP lenses are classified by their oxygen permeability rather than their water content. Most RGP lenses are now made from three main materials: acrylate, silicone, and fluorine.

RGP lenses are sometimes referred to as "rigid" lenses, but they are not like the "rigid" lenses of decades ago, primarily made of acrylate. These lenses are no longer prescribed because there is not enough oxygen to pass through that type of material. Lens manufacturers added silicone to increase oxygen permeability over the years and eventually added fluorine to help keep the lenses wet while maintaining their shape. This shape-retaining property allows them to be used as a treatment for correcting eye problems such as keratoconus (when the cornea is misshapen).

Some contact lens wearers who desire a better visual experience through their contact lenses also appreciate the resulting visual acuity from using lenses that are firmer and stay in place on the eye.

Hybrid Contact Lenses

Although less common, there are hybrid contact lenses that combine the materials of an RGP lens and a soft contact lens. These lenses have the acrylate-silicone-fluorine combination in the middle of the lens for clear central vision, and water-absorbing hydrogel for soft contact lenses at the edges for increased comfort.

These hybrid lenses are often used for multifocal lenses (bifocal or progressive contact lenses) or for treating irregular astigmatism.