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> Types of Contact Lenses
What are the different types of Contact Lenses?
There are two general categories of contact lenses – soft and rigid gas permeable (RGP). All contact lenses require a valid prescription.
Soft Contact Lenses
Soft contact lenses are made of soft, flexible plastics that allow oxygen to pass through to the cornea. Soft contact lenses may be easier to adjust to and are more comfortable than rigid gas permeable lenses. Newer soft lens materials include silicone-hydrogels to provide more oxygen to your eye while you wear your lenses.
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Rigid Gas Permeable (RGP) Contact Lenses
Rigid gas permeable contact lenses (RGPs) are more durable and resistant to deposit buildup, and generally give a clearer, crisper vision. They tend to be less expensive over the life of the lens since they last longer than soft contact lenses. They are easier to handle and less likely to tear. However, they are not as comfortable initially as soft contacts and it may take a few weeks to get used to wearing RGPs, compared to several days for soft contacts.
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Extended Wear Contact Lenses
Extended wear contact lenses are available for overnight or continuous wear ranging from one to six nights or up to 30 days. Extended wear contact lenses are usually soft contact lenses. They are made of flexible plastics that allow oxygen to pass through to the cornea. There are also a very few rigid gas permeable lenses that are designed and approved for overnight wear. Length of continuous wear depends on lens type and your eye care professional’s evaluation of your tolerance for overnight wear. It’s important for the eyes to have a rest without lenses for at least one night following each scheduled removal.
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Disposable (Replacement Schedule) Contact Lenses
The majority of soft contact lens wearers are prescribed some type of frequent replacement schedule. “Disposable,” as defined by the FDA, means used once and discarded. With a true daily wear disposable schedule, a brand new pair of lenses is used each day.
Some soft contact lenses are referred to as “disposable” by contact lens sellers, but actually, they are for frequent/planned replacement. With extended wear lenses, the lenses may be worn continuously for the prescribed wearing period (for example, 7 days to 30 days) and then thrown away. When you remove your lenses, make sure to clean and disinfect them properly before reinserting.
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Lens Comparison
The American Optometric Association has more detailed information about contact lenses including a lens comparison chart.
Lens Comparison Chart
American Optometric Association
http://www.aoa.org/x5234.xml
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Specialized Uses of Contact lenses
Conventional contact lenses correct vision in the same way that glasses do, only they are in contact with the eye. Two types of lenses that serve a different purpose are orthokeratology lenses and decorative (plano) lenses.
- Orthokeratology (Ortho-K)
Orthokeratology, or Ortho-K, is a lens fitting procedure that uses specially designed rigid gas permeable (RGP) contact lenses to change the curvature of the cornea to temporarily improve the eye’s ability to focus on objects. This procedure is primarily used for the correction of myopia (nearsightedness).
Overnight Ortho-K lenses are the most common type of Ortho-K. There are some Ortho-K lenses that are prescribed only for daytime wear. Overnight Ortho-K lenses are commonly prescribed to be worn while sleeping for at least eight hours each night. They are removed upon awakening and not worn during the day. Some people can go all day without their glasses or contact lenses. Others will find that their vision correction will wear off during the day.
The vision correction effect is temporary. If Ortho-K is discontinued, the corneas will return to their original curvature and the eye to its original amount of nearsightedness. Ortho-K lenses must continue to be worn every night or on some other prescribed maintenance schedule in order to maintain the treatment effect. Your eye care professional will determine the best maintenance schedule for you.
Currently, FDA requires that eye care professionals be trained and certified before using overnight Ortho-K lenses in their practice. You should ask your eye care professional about what lenses he or she is certified to fit if you are considering this procedure. For more in-depth information on Ortho-K, go to:
Keeping an Eye on Contact Lenses
FDA CONSUMER, March-April 1998
http://www.fda.gov/fdac/features/1998/298_lens.html
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- Decorative (Plano) Contact Lenses
Some contact lenses do not correct vision and are intended solely to change the appearance of the eye. These are sometimes called plano, zero-powered or non-corrective lenses. For example, they can temporarily change a brown-eyed person’s eye color to blue, or make a person’s eyes look “weird” by portraying Halloween themes. Even though these decorative lenses don’t correct vision, they’re regulated by the FDA, just like corrective contact lenses. They also carry the same risks to the eye. These risks include:
- conjunctivitis (pink eye)
- corneal ulcers
- corneal abrasion
- vision impairment or blindness
FDA is aware that consumers without valid prescriptions have bought decorative contact lenses from beauty salons, record stores, video stores, flea markets, convenience stores, beach shops and the internet. Buying contact lenses without a prescription is dangerous!
If you’re considering getting decorative contact lenses, you should:
- get an eye exam from a licensed eye care professional
- get a valid prescription that includes the brand and lens dimensions
- buy the lenses from an eye care professional or from a vendor who requires that you provide prescription information for the lenses
- follow directions for cleaning, disinfection, and wearing the lenses, and visit your eye care professional for follow-up eye exams
FDA issued a guidance document, "Guidance for Industry, FDA Staff, Eye Care Professionals, and Consumers - Decorative, Non-corrective Contact Lenses" on November 24, 2006. This guidance document explains the recently enacted legislation which make all contact lenses, including decorative, non-corrective contact lenses medical devices. The document also gives instructions on how to provide comments and suggestions to FDA about this issue.
For more information on decorative contact lenses, see:
FDA Reminds Consumers of Serious Risks of Using Decorative Contact Lenses without Consulting Eye Care Professional
FDA News, October 27, 2006
http://www.fda.gov/bbs/topics/NEWS/2006/NEW01499.html
FDA Warns Consumers of the Dangers of Using Decorative Contact Lenses Without Proper Professional Involvement
FDA News, October 28, 2004
http://www.fda.gov/bbs/topics/news/2004/NEW01127.html
FDA Issues Warning on Decorative Contact Lenses
FDA CONSUMER, January-February 2003
http://www.fda.gov/fdac/features/2003/103_eyes.html
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Updated July 28, 2008 |
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