Different types of contact lenses

 
Contact lens help
Lens fitting and care
Lens insertion and removal
Contact lens disinfection
Contact lens protein removal
Lens solution incompatibility
Contact lens history
Contact lens future
Contact lens glossary
 
Types of contact lens
Soft contact lenses
Hard contact lenses
Disposable contact lenses
Extended wear contact lenses
Bifocal contact lenses
Contact lenses for astigmatism
Therapeutic contact lenses
 
Contact lens problems
Contact lens dry eyes
Damage to lenses
Contact lens infections
Eyelid inflammation
Corneal complications
Contact lens conjunctivitis
Giant papillary conjunctivitis
Peripheral corneal infiltrates
 
Types of Contact Lenses

Hard Contact Lenses

These were the first type of contact lenses available and they were composed of plastics called polymethylmethacrylte, or PMMA, also known as Plexiglass. They are not much in use today though they have several advantages. They can be inserted in the eye with ease and taken out without much problem. Also, since they are made up of hard plastics, they do not get contaminated easily and do not cause eye infections. They are easier to maintain and are less expensive than the more popular soft contact lenses, which are prescribed more often nowadays. Also for some people, eyesight improves with their use.

However, these hard lenses covered the entire cornea and were made of PMMA, they did not permit much oxygen to reach the cornea, which is a clear dome in front of the eyeball and posed risks of a damaged cornea. They were invariably uncomfortable to wear especially during the initial periods of use.

Gas Permeable Contact Lenses

By the end of the 1970’s and throughout the 80’s and 90’s a range of oxygen permeable, but rigid, materials were created to counter the problems faced due to hard lens usage. These gas permeable lenses were known together as RGP lenses. These lenses are known as rigid lenses and are easier to maintain and to care for than soft lenses. Also gas permeable lenses can correct many vision problems.

However, the period for adjustment for these types of lenses is much longer than with soft contacts. And though some newer gas permeable lenses are approved for extended wear, doctors usually advise that it is better to remove contacts during sleep. It is always advisable to consult the eye specialist before using gas permeable lenses for extended wear.

Soft Contact Lenses

Despite continual improvements in hard lenses or RPG’s, these remained uncomfortable for most people to wear. The Czech chemist Otto Wichterle was the inventor of hydrogel lenses, which were made with soft water absorbing plastic known as hydroxethyl methacrylate, first produced in 1951. Contact lenses using these materials were approved by the U.S. FDA by 1971 and marketed by Bausch & Lomb. Unlike RGP’s and hard lenses, soft contacts do not cause any initial discomfort and the adjustment time period is much less. Soft lenses can also correct various eyesight problems. They are an ideal type of lens for sportsmen or for people whose activities would be hampered if hard lenses or gas permeable lenses were used. Moreover, the soft lenses have much less chance of slipping out of the eye accidentally.

However, inserting soft lenses in the eye require a bit of practice initially and they are more difficult to maintain than hard lenses. They have to be very carefully handled, cleaned and sterilized with extreme care. Because they have several advantages over hard or RPG lenses, soft lenses are invariably more expensive though less durable. Also, they need to be replaced more frequently. People using soft contact lenses have to invest in cleaning and storing solutions for soft lenses.

People using soft contacts are prone to more allergies and infections especially if they use soft lenses for an extended period of time. Infections leading to corneal ulcers are considered extremely harmful to the eyes. People having dry eye disease are unable to wear soft contacts.

Disposable Contact Lenses

These are soft contact lenses, which are used for a specific period of time for e.g. a week, a day or a month and then discarded. Never should these disposable contacts be used again after discarding. They have less chance of getting contaminated and infected as they are replaced at short intervals. However, if worn beyond the specified time period they will adversely affect the health of the eyes.

These lenses are extremely convenient as they provide lucidity and comfort that can be experienced with new lenses. They will help people who are allergic to contact lens solution or protein deposits as these are discarded before deposits are allowed to infect the eye. Due to all these advantages and comfort, they cost much more than regular soft lenses.

Bifocal Contact Lenses

These contact lenses are used to correct presbyopia of the eyes. That means they are meant for people who have a distance, as well as a reading, prescription in each eye. These come in two types - soft lenses or gas permeable lenses and they can be either daily wear, nightly removal or extended wear types. However, a period for trial and adjustment is required.

Other Types

Other types of lenses are soft lenses to treat astigmatism, a condition present in about 25% of the population, known as toric lenses. Extended wear lenses, which are used overnight are also used by some people. A number of colored and tinted contact lenses for cosmetic use have also become popular in recent years.