Types of contact lenses
Contact lenses are an excellent choice for nearly anyone who needs vision correction and doesn’t want to wear eyeglasses full time or undergo LASIK surgery. Here are the basics you should know about contact lenses before seeing your eye doctor if you are interested in wearing contacts.
Contact Lens Materials
The first choice when considering contact lenses is which lens material will best satisfy your needs. There are five types of contact lenses.
Soft lenses are made from gel-like, water-containing plastics called hydrogels. These lenses are very thin and pliable and conform to the front surface of the eye. Introduced in the early 1970s, hydrogel lenses made contact lens wear much more popular because they typically are immediately comfortable. The only alternative at the time was hard contact lenses made of PMMA plastic. PMMA lenses typically took weeks to adapt to and many people couldn’t wear them successfully.
Silicone Hydrogel Lenses:
Silicone hydrogel lenses are an advanced type of soft contact lenses that are more porous than regular hydrogel lenses and allow even more oxygen to reach the cornea. Introduced in 2002, silicone hydrogel contact lenses are now the most popular lenses prescribed in the United States.
Gas permeable Lenses:
Gas permeable lenses — also called GP or RGP lenses — are rigid contact lenses that look and feel like PMMA lenses but are porous and allow oxygen to pass through them. Because they are permeable to oxygen, GP lenses can be fit closer to the eye than PMMA lenses, making them more comfortable than conventional hard lenses. Since their introduction in 1978, gas permeable contact lenses have essentially replaced nonporous PMMA contact lenses. GP contacts often provide sharper vision than soft and silicone hydrogel contacts especially if you have astigmatism. It usually takes some time for your eyes to adjust to gas permeable lenses when you first start wearing them, but after this initial adaptation period, most people find GP lenses are as comfortable as hydrogel lenses.
Hybrid contact lenses are designed to provide wearing comfort that rivals soft or silicone hydrogel lenses, combined with the crystal-clear optics of gas permeable lenses. Hybrid lenses have a rigid gas permeable central zone, surrounded by a “skirt” of hydrogel or silicone hydrogel material. Despite these features, only a small percentage of people in the U.S. wear hybrid contact lenses, perhaps because these lenses are more difficult to fit and are more expensive to replace than soft and silicone hydrogel lenses.
PMMA lenses are made from a transparent rigid plastic material called polymethyl methacrylate (PMMA), which also is used as a substitute for glass in shatterproof windows and is sold under the trademarks Lucite, Perspex and Plexiglas. PMMA lenses have excellent optics, but they do not transmit oxygen to the eye and can be difficult to adapt to. These (now old-fashioned) “hard contacts” have virtually been replaced by GP lenses and are rarely prescribed today. In 2017, 64 percent of contact lenses prescribed in the U.S. were silicone hydrogel lenses, followed by soft (hydrogel) lenses (22 percent), gas permeable lenses (11 percent), hybrid lenses (2 percent) and PMMA lenses (1 percent).
Very important: Always make sure you discuss and make decisions about your eye care based upon a formal appointment with your optician.
For more information and to book and eye examination please contact us:
Specs Direct | Professional Affordable Eyewear
20 McIntyre Street, Parow, Cape Town 7500
Tel: 021 939 1020
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