Artificial Tears

Artificial tears are lubricant eye drops used to treat the dryness and irritation associated with deficient tear production in keratoconjunctivigis sicca (dry eyes). They are also used to moisten contact lenses and in eye examinations

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Artificial tears are available over-the-counter. Artificial tears are supplemented with other treatments in moderate to severe forms of dry eyes.

Chemistry
Preparations contain carboxymethyl cellulose, hydroxypropyl methylcellulose (a.k.a. HPMC or hypromellose), hydroxypropyl cellulose and hyaluronic acid (a.k.a. hyaluronan, HA). They contain water, salts and polymers but lack the proteins found in natural tears. Patients who use them more frequently than once every three hours should choose a brand without preservatives or one with special non-irritating preservatives.

Effects
Application of artificial tears every few hours can provide temporary relief from the symptoms of dry eyes. Hydroxypropyl cellulose stabilizes and thickens the precorneal tear film, and prolongs the tear film breakup time.

Usage
Artificial tears usually are the first line of treatment for dry eyes. While mild cases require application of lubricant drops four times a day, severe cases require more aggressive treatment, such as ten to twelve times a day. Thicker artificial tears can be used in severe cases, although these may temporarily blur vision.
Precautions
Drops for red eyes can make the eyes even drier. If wearing contact lenses, rewetting or lubricating drops specifically for contact lenses should be used. Other types of drops may contain ingredients that damage the lens.
　
Adverse Effects
Possible adverse effects of carboxymethyl cellulose and other similar lubricants include eye pain, irritation, continued redness, or vision changes. Use should be discontinued if any of them occur. Those of hydroxypropyl cellulose include hyperaemia, photophobia, stickiness of eyelashes, discomfort, and irritation. Long term use of preservatives present in some artificial tears may harm the eye.

Artificial tears have no reported interactions. A documented contraindication of artificial tears is hypersensitivity.

Veterinary Uses
Artificial tears are a part of the topical therapy for keratoconjunctivitis sicca for animals such as dogs, cats and horses.
　
http://en.wikipedia.org/wiki/Artificial_tears