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contact lenses can be quite handy as well as necessary. Handy when wearing a helmet driving a motor cycle, necessary if you have myopia and still want to play rugby. Quite uncomfortable if you're drunk and want to go to bed (and have the lenses yo do need to remove before sleeping) or staring to the computer screen for too many hours. Aka, pros and cons. Therefore I wanted to be well-informed before purchasing them.

There are two types of contact lenses: hard and soft ones.
Hard lenses are more durable than soft contact lenses and, when taken good care of, last up to five years (in that case cheaper than soft lenses). They're considered as healthier for your eyes because they are oxygen permeable ("rigid gas-permable lenses") and are more often cleansed, which prevents eye infection. The lenses are made from plastic polymers like cellulose acetate butyrate, polyacrylate-silicone or silicone elastomers. Hard lenses must be carved to fit and will slip if not correctly formed. This is often considered as a (initial?) major drawback of starting to wear hard lenses.
Soft lenses are less durable, depending on the type you buy: sports lenses, one-day, one-month or about two years. They are made from hydrogel polymers; combined with the water of the eyes carrying the required oxygen. However, this system provides less cleansing (especially getting rid of those sticky proteins is important), hence there's a greater chanche of eye infections like Keratitis (inflammation of the cornea by Pseudomonas and Acanthamoeba strains). On the other hand, they easily take the shape of your eyeball, adding up to convenience.

Some statistics: in 1998 there were appoximately 270312000 US citizens (according to my atlas), 34 million people wearing contact lenses and fewer than 15% of the contact lens wearers use hard lenses. One of the myopia write-ups says that about 50% of the population does use either type of eye-correction. 34 million of that equals about 25% of of the total group of "visually impaired" people; or 75% is still wearing glasses, whatever way you want to put it.

For you people who want to know: I've had soft contact lenses for 2 years, but because of the prize difference I went back to wearing glasses, and I'm used to them again. Other advantages are that I've the option to change my look every couple of years and I'm taken more seriously...

Information from the optician and the article "Working Knowledge" from the Scientific American, October 2000.