contact lens answers

contact lens answers
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What are contact lenses or contacts?

Contact lenses, or contacts, are small curved glass, plastic or polymer pieces shaped to fit over the cornea of the eye. They float on the tear film in front of the cornea. Contact lenses correct most vision problems in the same way as conventional glasses do. They can also correct some vision problems, like keratoconus, that glasses cannot correct. They are lightweight and virtually invisible.

When are they used?

Contact lenses are used for corrective, therapeutic and cosmetic reasons.

Corrective contact lenses are used to correct vision problems known as refractive disorders. These include short sightedness, long sightedness, and astigmatism. Also, X-chrome contact lenses are used by colorblind people to help distinguish colors.

Therapeutic contact lenses are used to manage non-refractive disorders like cataract removal, corneal damage and dry eyes. They protect the eyes, after the treatment, allowing the wound to heal.

Cosmetic contact lenses are used for changing the appearance of the eye by using tinted lenses. They are also used to mask some eye defects.

Contacts also are used for practical reasons. Contacts a wider field vision in focus compared to glasses. Moreover, they do not fall off, get wet when it rains, or fog up. Sportspeople, as well as others in some work situations, find contacts more convenient than conventional glasses.

What are the types of contact lenses available?

The first contacts were made from glass and a plastic called polymethyl methylcrylate or PMMA, also known as plexiglass. These lenses blocked oxygen supply to the cornea and so are now almost obsolete.

Today the two main types of contact lenses available are rigid gas permeable lenses and soft contact lenses.

Rigid gas permeable or RGP contact lenses are made from improved polymers. They have higher gas permeability and so allow more oxygen to enter the eye, lessening the risk of eye infections. They can replace the natural shape of the cornea by giving it a new refracting surface and are useful in correcting vision in cases of astigmatism. Being rigid their shape cannot be distorted.

Soft contact lenses are a relatively recent development. They are manufactured from plastics called water loving or hydrophillic hydrogels. They also have high oxygen permeability.

Soft lenses have rapidly become popular because their softness makes them more comfortable to wear. Their flexibility makes them easily adapt and adjust to the shape of the cornea. The adjustment time to wearing soft lenses is much less than with hard contact lenses. However, soft contact lens wearers are also more likely to develop corneal infections.

Later, silicone lenses were launched, which had still higher oxygen permeability. However, silicone being water repellant or hydrophobic causes eye dryness. To reduce hydrophobicity, water attracting or hydrophillic hydrogel is now added to the silicone. This material is called silicone hydrogel.

Both gas permeable and soft lenses can be made into bifocals. These can also be tinted for use as sunglasses or for cosmetic purposes.

Where can you get contact lenses?

Contacts can be prescribed only by an authorized eye specialist after examining your eyes. He/she will decide whether contacts suit you and, if they do, will recommend the type of contacts you need.

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contact lens answers