There are two categories in types of contact lenses, Rigid and Soft. Rigid Lenses, more commonly known as “hard lenses”, are placed directly on the pupil. Scientifically termed as Rigid Gas Permeable Lenses (RGP), they were developed in the late 1940’s using a material called Polymethylmethacrylate [POLY-MEH-THAL-MUH-THAK-KRUL-LYTE], or PMMA. It was the standard contact lens until the early 1980’s. RGP lenses have several advantages, especially over soft lenses. Vision is more acute, especially with those whom suffer with corneal astigmatism; and last longer because they are more durable than soft lenses. Although seen as the worst of luck, if lost (fell out of your eye), they can be more easily found than that of the softer lens. Last but not least, they are inexpensive.
Although they were convenient and advantageous, they were met with some disadvantages as well. Being made of plastic material, it became harder to adapt to the comfort once in the eye. “Hard lenses” gave many corneal complications as well, with no oxygen transmissibility or permeability – the cornea would swell or suffer other warpages. With these complications in mind, scientists sought safer and more comfortable contact lenses.
With this came the rise of the Soft Lens. Made with new types of plastics — they were developed, introduced and made available in the 1970’s. Using these new types of plastics and Silicone, more oxygen was permissible to enter the eye; enabling better oxygen flow to reach the cornea. They are more advanced, usually comfortable (more than RGP), may be tinted, and hydrophilic.
With every up comes a down, as with the soft lens. Although oxygen flow is permissible, they may become dehydrated under certain conditions – such as indoors during the heating season and in air-conditioned rooms and especially for those who are partial to blinking and produce an inadequate volume of tears. They are easily damaged by many substances. If handled too frequently the lens may form a tiny crack, eventually splitting it. Rough removal or a sharp fingernail could tear the lens as well.
These two categories in types of lenses could also be simplified into sub-categories, or “Types of the TYPES” – if you will. The Corneal Contact Lens would be a lens smaller than the cornea. The Scleral (Haptic/Bandage) Contact Lens, is helpful in the healing of a scratched or irritated cornea. The Semi-Scleral Lens covers the limbus, cornea, and small part of the sclera adjacent to the limbus. Just a few examples of what I like to call circumstantial lenses.
Dr.Khanna a Los Angeles LASIK surgeon advises regarding contact lenses to patients in Beverly Hills and Los Angeles.