What Are Contacts Made Of?
Did you know that contact lens types vary based on the materials that they're made of? Below are the four main types of contact lenses and the different materials used to manufacture them.
Soft Contact Lenses
Soft contact lenses are made of plastic, but not the type of plastic used in garbage bags or paper plates. Instead, soft lenses are made of hydrophilic plastics - a special type of water-absorbing plastic that stays soft and moist as long as it is absorbing lots of water.
If you wear soft contact lenses, you've likely noticed the way this plastic works. If your lenses get dried out, they become brittle to the point where they could even break. As long as that plastic stays nice and wet either inside your eye or in a case, the plastic stays pliable and soft.
To your eyes, this soft flexibility spells comfort! When your eyes are dry, your lenses will begin to feel uncomfortable because they depend on moisture to keep them in place and pliable.
Soft contact lenses are categorized by the amount of water they contain. They can be classified as either high water or low water.
Soft Contact Lenses for Extended Wear
Most extended wear contact lenses are made out of silicone hydrogel - a material that combines the water-absorbing plastic of soft lenses with silicone. Adding silicone to the hydrogel plastic creates a lens that stays moist and allows more oxygen to transmit through the contact lens into the eye. This keeps the eyes healthier during contact lens use. The added benefit of more moisture and oxygen reaching the eye is why this material was added to extended wear contact lenses.
Any contact lens wearer who keeps their contacts in during the day and at night, or leaves lenses in for days at a time needs a contact that allows their eyes to breathe. The addition of silicone to the lens offers this functionality for optimal contact lens health.
Rigid Gas Permeable Lenses
Rigid gas permeable lenses (RGP lenses) are also made of plastic. Unlike the plastic that makes a soft contact lens, the rigid gas permeable lens transmits oxygen without absorbing water. Instead, RGP lenses have microscopic holes in them that allow the oxygen to filter through. For this reason, RGP lenses are classified by their oxygen permeability instead of their water content. Most RGP lenses are now made of three main materials: acrylate, silicone and fluorine.
RGP lenses are sometimes called "hard" lenses, but they aren't like the "hard" lenses of decades ago that were made mostly of acrylate. Those lenses are no longer prescribed because not enough oxygen could get through this type of material. Lens manufacturers added silicone to increase oxygen permeability over the years and eventually added flourine to help keep the lenses moist while still retaining their shape. This shape-retaining property allows for them to be used as treatment for the correction of eye issues such as keratoconus (when the cornea is misshapen).
Some contact lens wearers who crave a better visual experience through their contact lenses also like the visual acuity that comes from wearing a contact lens that is firmer and stays put on the eye.
Hybrid Contact Lenses
Though more rare, hybrid contact lenses exist that combine the materials of an RGP lens and a soft contact lens. These lenses have the acrylate-silicone-flourine combination in the middle of the lens, for sharpened central vision, and soft contact lens water-absorbing hydrogel around the edges for increased comfort.
These hybrid type lenses are often used for multi-focal lenses (bifocal or progressive contact lenses) or for treating irregular astigmatism.