Types of Contact Lenses

PMMA lenses
Rigid or “hard” contacts were the first lenses; they were developed in the 1960’s. They are made of a type of plastic called PMMA (polymethyl methacrylate), which is very durable, but does not allow oxygen in the air to directly reach the cornea. When the eye blinks, the lens moves, which allows the oxygen dissolved in the tears to reach the cornea. Rigid lenses are the least comfortable type of contacts and are not really used anymore. However, some people still prefer them for their durability and lower cost
These lenses are rarely fitted these days because of advances in other contact lens materials

Gas-permeable lenses
These lenses are also known as “RGPs.” They are newer rigid or “hard” lenses made of plastics combined with other materials, such as silicone and fluoropolymers, which allow oxygen in the air to pass directly through the lens. For this reason, they are called “gas permeable.”
Once fitted, they should be replaced roughly every two years.
The main advantages of RGPs are that they can provide very crisp vision even with astigmatism, they are robust and economical and they allow air to reach the eye easily.
Disadvantages would be that they take a while to adapt to, and require more cleaning and maintenance when compare to say a daily disposable

Soft contact lenses
These lenses are made of plastic materials that incorporate water. The water makes them soft and flexible, as well as allowing oxygen to reach the cornea

Silicone Hydrogel lenses are the latest development in soft contact lens materials. They are healthier than conventional soft lenses because they allow up to 6 times more oxygen to pass through them and increased oxygen transmission results in better overall eye health

Soft contact lens options:
Daily disposables – These are one-use throwaway lenses. They are easy to carry around and do not require the use of contact lenses cleaning fluids. They come in blister packs filled with a solution to keep them hydrated.

Monthly disposables – These are soft lenses that when used are cleaned and stored in a container. After a month they are then disposed of. They sometimes can cost less than daily disposables and comes in a broader range of parameters, which are more suitable for some wearers. Along with daily disposables they have become the most commonly fitted type of contact lens

Non-disposable lenses – These are lenses designed to last up to two years. They can be used for specialized custom fit lenses or for regular prescriptions as an economical option

Extended wear – These are lens that can be slept in overnight. They generally are monthly lenses made of silicon hydrogel, which is excellent at allowing oxygen to the eye compared to standard materials

Nearly all the above options come in other variations e.g. toric (to correct astigmatism)
coloured and presbyopic (to correct reading vision)