Soft Contact Lenses
Over 90% of contact lens wearers choose soft lenses. Soft contact lenses are broadly categorized according to how frequently you should replace them (replacement schedule) and how many hours you can wear them before giving your eyes a break (wearing schedule).
Soft Contact Lenses: Replacement Schedule
Soft contact lens replacement schedules can range from a single day ("daily disposable" lenses) to several months ("conventional" lenses). Over the years, research has consistently shown that your risk for eye irritation and infection from wearing soft contacts increases the longer you go before discarding your lenses. Deposits (mucous, protein, oils, bacteria, minerals) accumulate on soft lenses even with the best cleaning techniques. Today, most doctors recommend disposable soft contact lenses and a two-week replacement schedule. If you want the cleanest lenses and the convenience of not having to clean your contacts every day, try 1-day disposable lenses. At the end of the day, you just throw them away!
Soft Contact Lenses: Wearing Schedule
Soft contacts are also categorized according to wearing schedule: daily wear, flexi-wear, or extended wear. Daily wear contacts are FDA-approved for wear only while you are awake. Flexi-wear lenses are FDA-approved for daily wear but also occasional overnight wear or napping. Extended wear lenses are FDA-approved for continuous day-and-night wear. Generally, it appears to be safer to wear soft contact lenses on a daily wear basis. Sleeping while wearing contacts that are not designed for that purpose can increase your risk of serious eye infections and the growth of abnormal blood vessels into the cornea.
If you desire the option to wear your soft contact lenses continually (day-and-night), ask your eye doctor about silicone-hydrogel contact lenses. These are new-generation contacts that transmit up to six times more oxygen to the eye than standard disposable contacts. Many people can safely wear these lenses up to 30 days without removal. You should only sleep in contact lenses under the direction of your eye doctor.
Color Contact Lenses
Soft contacts for changing the color of your eyes are readily available. There are even theatrical contacts which make your eyes look like those of a cat, robot, vampire, etc. These color contacts are especially popular around Halloween. Most of these lenses are limited to daily wear only. And even though color contact lenses are available in non-prescription format, they are still a medical device, and you need a prescription from an eye doctor for them. (The prescription verifies that an optical professional has performed a contact lens fitting and that your eyes can tolerate contact lens wear.)
NEVER share your cosmetic contact lenses with anyone else. Sharing lenses can transfer bacteria that can cause a serious eye infection. Another way to avoid getting an eye infection is to practice proper contact lens handling and hygene. Bacterial infections like acanthamoeba keratitis can lead to developing a corneal ulcer.
For complete information on contact lenses, visit the Consumer Guide to Contact Lenses. Also, the Contact Lens Manufacturers Association provides good information about contact lenses.