Contact lenses are plastic-based eyewear worn directly on the cornea. They help correct refractive errors by bending light to focus on the retina, which transmits images to the brain for interpretation.

Before handling a lens, wash and rinse your hands thoroughly. This helps prevent eye infections. Then dry your hands with a lint-free towel.

What is a lens?

Made of slightly flexible plastics that allow oxygen to pass through them to the eye, contact lenses move with your eyes and provide a natural field of vision. They don't have frames that obstruct your view or fog up, so they're great for people who work outdoors or play sports.

The word "lens" is actually derived from the Greek for lentil, and it refers to the shape of the transparent material used to make objects visible. The shape of a lens can cause light rays to converge or diverge, which is why it's important in imaging tools like telescopes, binoculars, and cameras.

Your eye care provider will determine the right kind of contact lenses for your needs, based on the results of your eye exam and other health information. Your prescription will include a power, which is the amount of correction built into the lens.

Convex lenses

Convex lenses are used to magnify objects and bring them into focus. They do this by combining light rays that are coming into the lens from different directions, which creates an image on the other side of the lens. These are real images and can be enlarged or inverted relative to the object. They have positive focal lengths and are often used in cameras to brighten the image of a small object on film or an electronic sensor.

A lens is said to be convex if it converges parallel light rays at a point on its principal plane, also known as the real focal point. A lens with two convex surfaces is called a biconvex lens; if one of the sides is flat, it's a plano-convex lens.

Aspheric lenses

Aspheric lenses have flatter curves, which means they’re thinner and lighter than regular lenses. This makes them more comfortable and allows you to wear a wider variety of frames. They also correct distortion and create a higher-quality image.

Aspherical lenses reduce spherical aberration, which is an inherent lens flaw that causes incident light rays to focus at different points and create a blur. Optical manufacturers use mathematical models and simulations to adjust the surface of the aspheric lens, which results in a sharper and clearer lens.

High precision molded aspheric lenses require a complex design and manufacturing process, which can lead to increased cost. They also have strict alignment and tolerance requirements that can make them fragile.

Rigid gas permeable (RGP) lenses

Rigid gas permeable lenses (RGP) are custom-made of a firm, durable plastic that allows oxygen to pass through to the eye’s cornea. They can be more comfortable to wear than soft contact lenses and are less prone to tearing. They also tend to last longer, lasting one year or more if cared for properly.

They can correct astigmatism, and many patients find that GP bifocals give them both near and distance vision. They can be used for ortho-k, a process in which the GP lens vaults right over the cornea while you sleep to reshape it and improve your vision.

Unlike soft contacts, RGPs do not contain water, so they don’t attract and hold protein or other harmful deposits as easily. This may make them less likely to develop a cloudy appearance, but they can still become blurry due to midday fogging, which is usually caused by tiny debris stuck inside or around the lens.

Soft lenses

Soft contact lenses are made from gel-like water-containing plastics called hydrogels or a combination of these materials. They rest directly on the cornea and offer the advantage of correcting both near sightedness (myopia) and far sightedness (hyperopia), as well as astigmatism.

Rigid gas permeable (RGP) or 'hard' contact lenses are also available. These are much less flexible than soft lenses and maintain their shape better, but they allow more oxygen to reach the cornea. They can be more uncomfortable and may require some time to adjust to.

Newer soft lens materials include silicone-hydrogels that allow for more oxygen to pass through to the eye. They are available in daily, weekly, monthly and extended wear disposables.