An eyedrop is a generic term that describes any manner of liquid medication applied directly to the surface of the human eye. Eyedrops, depending on their formulation, may be used to treat a mechanical problem with eye function, such as a chronically dry eye, or as a relief from friction caused by foreign objects, including dirt or the presence of a contact lens. Eyedrops are also administered to treat numerous kinds of illnesses and disease that may affect the permanent health of the eye.

The eye is a complex structure that is exposed to a number of forms of stress in its daily function. Vision is achieved in the human eye when light enters the opening in the center of the colored part of the eye (iris), called the pupil. The cornea and lens, both located near the surface of the eye, focus incoming light onto the retina, located at the rear of the eyeball. The eye continuously adjusts the amount of incoming light to maintain a constant quality of image. These images are transmitted to the brain by way of the optic nerve. The conjunctiva is a membrane immediately adjacent to the upper and lower eye lids that covers the visible portion of the eye; it is kept moist through the action of nearby tear ducts. The eyeball is connected suspensory ligaments that enable it to withstand forces generated by the motion of the body.

Keratoconjunctivitis sicca is the medical condition known as chronic dry eye, which results from the body's inability to produce sufficient tears to keep the surface membrane moist. Tears are important to the overall function of the eye, because they lubricate the eye surface, reducing friction between the eyelid and the eye surface. Tears also act as the vehicle by which both oxygen and essential proteins for nourishment are carried to the eye membrane surface. Under circumstances in which the tear ducts become inflamed, tear production is reduced. Medicated eyedrops including cyclosporine and other anti-inflammatories, both steroidal and nonsteroidal, are often employed to correct this malfunction.

The eye often becomes irritated by allergies, airborne pollens, or through exposure to harsh chemicals such as the chlorine used in public swimming pools. When the body is susceptible to an allergy, it will produce the chemical histamine as a counter to the allergic effect; histamine increases the production of bodily fluids such as mucus and tears. Airborne particles often create redness and irritation on the surface of the eye. There are many nonprescription eyedrop medications commercially available to provide temporary relief from these conditions; the eyedrops clean and lubricate the membrane.

Infections of the conjunctiva are called conjunctivitis, commonly known as pink eye. In forms of this

French tennis star Mary Pierce applies some eye drops before she starts her first round match.
infection that are either caused by bacteria or virus, pink eye is highly contagious; pink eye is especially common in institutional or group settings, such as schools or sports teams, since it is easily transmitted by close personal contact.

Eyedrops containing anti-infective agents are also employed after an eye operation. A common serious eye injury sustained by athletes is a partially or fully detached retina, which can happen when a hard blow, such as a boxing punch or contact with the head in any contact sport, or a severe fall in sports such as cycling, causes the retina to become separated from the back of the eyeball. A partially or fully detached retina results in blindness in the affected eye if not treated. Eyedrops are used to limit the risk of infection after the surgical reattachment procedure is complete.

Eyedrops are also commonly administered to treat infections that occur due to the improper wear or inadequate cleaning of contact lenses. In contact lens wearers, the infection often takes the form of a fungus, which may extend along the entire cornea, causing both discomfort and impairment of vision. The majority of contact lens-related infections are not a serious threat to long-term eye health or vision.

Another common sports injury is a cut or scratch on the cornea, the outer membrane of the eyeball. This can happen when the eyeball is struck by an opposing player's finger or other object. The resulting injury can be extremely painful. Antibiotic eyedrops are often prescribed for these injuries.

SEE ALSO Abrasions, cuts, lacerations; Dose and dosage; Ear drops.