The contact lenses material is the first consideration when choosing the lens. There are 5 types of lens material and each material makes a great difference in the comfort, style, and looks. There are Silicone hydrogel lenses, soft lenses, gas permeable lenses, hybrid contact lenses, and PMMA lenses.
Silicone Hydrogel lenses:
Silicone hydrogel contact lenses are the popular type used in the USA. In 2014, about 68% of contact lens users were using this type of contact. It is mostly used because of its comfortability as it allows 5 times more air to pass through them to the cornea than the normal hydrogel lens. These lenses are made of plastic which is hard but gets soften like a gel upon absorbing water. Therefore, it is easy to find out whether the lens is suitable for use or not as it will become hard, deformed and easily breakable but it will become soft and useable again when dipped in the contact lens solution.
One of the greatest misconceptions about Silicone Hydrogel lenses is that they are made of Silicon. However, silicone is a complex compound containing silicon, carbon, oxygen along with various other elements. It is an extremely flexible material that is used in multiple medical devices because of its characteristic of oxygen permeability.
Silicone Hydrogel lens prevents hypoxia which can be caused because of a lack of oxygen. Symptoms of hypoxia are corneal swelling, red eyes, eye discomfort, and blurred vision. These symptoms can lead to a number of serious eye infections.
These lenses are crafted from water-containing polymers which give a gel-like texture. That material is called hydrogel. These kinds of lenses are extremely thin and flexible allowing them to perfectly hug the front of the eye.
The lens is actually made of a polymer called hydroxyethyl methacrylate or HEMA. This material was extremely comfortable due to which the term “intermittent contact lens wear” came in. The hydrogel lens had built-in water content which allowed oxygen transmission through it but this oxygen transmission was lesser than the Gas permeable lenses because of their tear exchange and movement.
The wearers of the soft contact lens have to follow a diverse care regime for which various kinds of contact lens solutions were made to rinse, clean, hydrate, and disinfect these lenses. Also, the wearers have to keep these lenses hydrated and not use them for an extended period of time.
Soft lenses were first introduced in the 1970s and they instantly became popular because they provided more comfort than any lens before. There was only one alternative to it at that time i.e. PMMA plastic lenses. Soft lenses are still one of the top-selling lenses in various countries.
Gas Permeable Lenses:
These lenses are developed after noticing the importance of the passage of oxygen through the lens material. Gas permeable lenses are also called RGP or GP lenses. They are hard and rigid lenses that look and feel very much like polymethyl methacrylate but RGP lenses are porous that allow oxygen to pass through to the cornea.
RGP lenses conform closer to the eye because of their permeability than PMMA lenses which makes them more comfortable than them. RGP lenses have largely replaced PMMA lenses which are less porous. Also, gas permeable lenses offer better and sharper vision than silicone and soft hydrogel lenses especially for the people who have astigmatism.
Normally, your eyes take some time to get used to these lenses when you first start using them, but after your eyes adjust to the lenses, they feel as comfortable as hydrogel lenses.
Gas permeable lenses were approved by the FDA in 1978 after the addition of Carbon, Fluorine, and Silicone to the basic material i.e. Cellulose acetate butyrate.
There has been a sharp and constant decline in the wearers of RGP lenses for the last two decades because of changing trends and innovations in lens materials.
Hybrid Contact Lenses:
These lenses provide crystal-clear vision and comfort that parallels with silicone and soft hydrogel lenses. They have a hard permeable optical zone in the center which is surrounded by a “skirt” of silicone or soft hydrogel material.
Hybrid Contact Lenses haven’t become as popular as other kinds of lenses. The reason for them being unpopular is that they don’t easily fit and are more costly to replace then silicone or soft hydrogel lenses.
Hybrid lenses are perfect for patients who have corneal astigmatism. They feature an advanced design that allows maximum flow of oxygen to the eye. The soft portion around the lens keeps the dust particles out and offers comfort all-day.
These lenses are perfect for: patients who complain about soft toric contact lens movement; patients with astigmatism and presbyopia; patients who prefer crisp vision with comfort; and for those who have irregular cornea problems. However, hybrid contact lenses are not good for lenticular astigmatism. It becomes more expensive and takes more time if a patient requires a diagnostic fitting. They require more care, education, and training for correct insertion and removal. The hybrid lens may flatten the cornea over time even if the lens fit perfectly in the beginning.
These lenses are made from a stiff transparent plastic material known as polymethyl methacrylate (PMMA). PMMA material is also used in shatterproof window glass. PMMA lenses are the oldest type of lenses. They offer good vision but do not allow passage of oxygen through them to the cornea which makes them uncomfortable so it is difficult to get used to them. Therefore, they have been replaced by other more comfortable forms of lenses like GP and hydrogel lenses.
PMMA material was first introduced in 1937 which was very much like the scleral lens but had a larger diameter. PMMA lens is cheap and durable but does not mold to the shape of the eye. Those who wear this kind of lenses are at risk of hypoxia which can lead to other serious infections.
If PMMA lenses are still being used today, it is because of their lightness, stability, and clarity of vision. It provides outstanding optical quality for maximum performance and a predictable outcome.