Contact lenses are small prescription lenses that float on a thin layer of tears on the surface of your eye. They function much like eyeglasses, bending and focusing light that enters your eyes to focus on the retina (the light-sensitive layer at the back of the eye) to create clear vision.

Corneal

A contact lens is an artificial device worn over the front surface of the eye to correct vision and replace the natural lens. If not taken care of properly, contact lenses can cause a number of corneal and conjunctival complications including hypoxia, chemical toxicity, hypersensitivity reactions, mechanical trauma and infection.

Rigid gas permeable (RGP) contact lenses are made of a rigid material that allows oxygen to pass through it, providing crisper and clearer vision than soft contact lenses. They are also durable and easier to handle. However, they can take some time to get used to wearing and they require a more involved cleaning and disinfection process than soft lenses.

Some eye conditions such as keratoconus can change the shape of your cornea making it difficult for traditional contacts to fit comfortably. In these cases, you may benefit from a larger, more rigid scleral contact lens that offers the advantages of clear vision and can help with your keratoconus treatment.

Scleral

This is a customized contact lens designed for patients with unique corneal conditions such as high astigmatism and keratoconus. The scleral lens vaults over the diseased irregularly shaped cornea, and when worn correctly helps keep the eye hydrated while correcting vision.

The large size and hard material of scleral lenses allow for easier insertion and removal from the eye. They also provide a wet cushion that is safer and more comfortable than conventional soft or small diameter corneal gas permeable lenses. Scleral lenses also reduce the risk of rubbing of the corneal surface, and thus reduce the risk of abrasions.

The scleral lens may be further modified into mini-scleral, semi-scleral (also known as intralimbal), or corneo-scleral types, based on how the edges of the lens rest on the sclera or cornea. Since scleral lenses have complex proprietary designs that cannot be duplicated by a commercial laboratory, they are only available directly from your prescriber. This ensures that you always get exactly the lens that was intended, and it allows your prescriber to offer warranted lens exchanges for free within the prescribing period.

Soft

Soft contact lenses rest right on the surface of the eye, and they provide much clearer near and far vision than glasses. They can correct short sightedness (myopia) and far sightedness (hyperopia). They also provide improved side and peripheral vision compared to glasses.

Most soft contacts are manufactured using a process called injection molding, where a molten lens material is injected into a mold that is held by centripetal forces while it is being formed. Then, the lens is shaped by radial force. The result is a soft, flexible, and stable lens that can be inserted and removed easily with your fingers.

Some types of soft lenses can be worn continuously, including while sleeping (extended wear), but most are disposable and require a case and daily, two-weekly, or monthly replacement. They have a lower risk of infection than rigid gas permeable lenses, but can still develop protein deposits and other bacterial debris that can irritate the eyes.

Rigid

Rigid gas permeable (GP) lenses are hard contact lenses made of oxygen-permeable plastics that can help correct astigmatism. They are able to hold their shape better than soft contact lenses and reduce the likelihood of shifting. This helps the lens provide stability and clarity of vision, while also preventing the progression of the condition keratoconus.

The lenses are designed with a base curve and peripheral curves that are flatter than the corneal periphery. This allows the free flow of precorneal fluid under the lens, which can help reduce tearing and dry eye symptoms. These curves may be two, three or four diopters flatter than the base curve and are typically blended to give a smooth transition between different zones of the lens.

GPs are often easier to get used to than soft lenses and can last longer. However, they can be more expensive than soft contacts, especially in the long run. They can take up to two years to reach the end of their lifespan and must be kept clean to ensure they remain comfortable.