dry eye


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eye

 [i]
the organ of vision; see also Plates. In the embryo the eye develops as a direct extension of the brain, and thus is a very delicate organ. To protect the eye the bones of the skull are shaped so that an orbital cavity protects the dorsal aspect of each eyeball. In addition, the conjunctival sac covers the front of the eyeball and lines the upper and lower eyelids. Tears from the lacrimal duct constantly wash the eye to remove foreign objects, and the lids and eyelashes help protect the front of the eye.
Structure. The eyeball has three coats. The cornea is the clear transparent layer on the front of the eyeball; it is a continuation of the sclera (the white of the eye), the tough outer coat that helps protect the delicate mechanism of the eye. The choroid is the middle layer and contains blood vessels. The third layer, the retina, contains rods and cones, which are specialized cells that are sensitive to light. Behind the cornea and in front of the lens is the iris, the circular pigmented band around the pupil. The iris works much like the diaphragm in a camera, widening or narrowing the pupil to adjust to different light conditions.
Function. (See also vision.) The refraction or bending of light rays so that they focus on the retina and can thus be transmitted to the optic nerve is accomplished by three structures: the aqueous humor, a watery substance between the cornea and lens; the lens, a crystalline structure just behind the iris; and the vitreous humor, a jelly-like substance filling the space between the lens and the retina. Unlike the lens of a camera, the lens of the eye focuses by a process called accommodation. This means that when the eye sees something in the distance, muscles pull the lens, stretching it until it is thin and almost flat, so that the light rays are only slightly bent as they pass through it. When the object is close, the muscles relax and the elastic lens becomes thicker, bending the light rays and focusing them on the retina.ƒ

Because the eye must function under many different circumstances, there are two types of nerve cells in the retina, with different shapes: the cones and the rods. They cover the full range of adaptation to light, the cones being sensitive in bright light, and the rods in dim light. The cones are responsible for color vision. There are three types of cones, each containing a substance that reacts to light of a different color, one set for red, one for green, and one for violet. These are the primary colors in light, which, when mixed together, give white. White light stimulates all three sets of color cells; any other color stimulates one or two.

The optic nerve, which transmits the nerve impulses from the retina to the visual center of the brain, contains nerve fibers from the many nerve cells in the retina. The small spot where it leaves the retina does not have any light-sensitive cells, and is called the blind spot.

The eyes are situated in the front of the head in such a way that human beings have stereoscopic vision, the ability to judge distances. Because the eyes are set apart, each eye sees farther around an object on its own side than does the other. The brain superimposes the two slightly different images and judges distances from the composite image.
Disorders of the Eye. If the eyeball is too short or too long, the lens focuses the image not on the retina but behind or in front of it. The former condition is called hyperopia (or farsightedness) and the latter myopia (or nearsightedness). An irregularity in the curvature of the cornea or lens can cause the impaired vision of astigmatism. strabismus (or squint or crossed eyes) is usually caused by weakness in muscles that control movement of the eyeball. conjunctivitis is an inflammation of the membrane that covers the front of the eyeball and lines the eyelids. When small pieces of the retina become detached from the underlying layers, the result is a retinal detachment; surgery may be necessary to prevent blindness. presbyopia (usually taking the form of hyperopia) occurs in older persons and develops as the lens loses its elasticity with the passing years. Correction is easily made with properly prescribed eyeglasses.ƒ

Foreign bodies in the eyes are common occurrences. Protective eyewear should be worn by individuals at risk. Cinders, grit, or other foreign bodies are best removed by lifting the eyelid by the lashes. The foreign body will usually remain on the surface of the lid, and can easily be removed. Particles embedded in the eyeball must be removed by a qualified health care professional.

Eyestrain is fatigue of the eyes caused by improper use, uncorrected defects in the vision, or an eye disorder. Symptoms may include aching or pains in the eyes, or a hot, scratchy feeling in the eyelids. Headache, blurring or dimness of vision, and sometimes dizziness or nausea may also occur.
Anatomic features of the eye. From Ignatavicius and Workman, 2002.
artificial eye a glass or plastic prosthesis inserted in the eye socket to replace the eyeball; most are designed to be worn day and night. When patients become debilitated and unable to care for such a prosthesis, they must depend on members of the health care team to give proper care according to the chosen preferred routine.ƒ

Cleaning of a prosthetic eye is similar in principle to care of dentures; both are handled with care to avoid damage and are cleansed according to good hygienic principles. The prosthesis is removed while the patient is lying down so that it falls into the hand and is not likely to be dropped and broken. It is removed by depressing the lower eyelid, allowing the prosthesis to slide out and down. Mild soap and water are most often used for cleansing the prosthesis. Alcohol or other chemicals can damage prostheses made of plastic. If it is not replaced in the socket immediately after cleansing, it is stored in water or contact lens soaking solution. Insertion of the prosthesis is done by lifting the upper eyelid with the thumb or forefinger and placing its notched edge toward the nose. It is placed as far as possible under the upper lid and then the lower lid is depressed to allow it to slip into place. The process can be made easier by first moistening the prosthesis with water. If it is necessary to wipe the eye area of a patient wearing a prosthesis, one should gently wipe toward the nose in order not to dislodge the prosthesis.
cross eye esotropia.
pink eye popular term for acute contagious conjunctivitis.
raccoon e's ecchymotic areas surrounding both eyes, suggestive of a basilar skull fracture.
wall eye exotropia.

dry eye

n.
Keratoconjunctivitis characterized by decreased tear flow and thickening and hardening of the cornea and conjunctiva.

dry eye

Insufficient quantity and/or quality of tears caused by aging, the environment, hormonal changes, or disease. This condition produces pain and discomfort in the eyes. Dry eye may occur in any disorder that scars the cornea (such as erythema multiforme), Sjögren syndrome, lagophthalmos, Riley-Day syndrome, absence of one or both of the lacrimal glands, paralysis of the facial or trigeminal nerves, medication with atropine, and deep anesthesia. Suitably prepared water-soluble polymers are effective in treating this condition. Synonym: alacrima. See: Sjögren syndrome
See also: eye

dry

a state of dehydration or relative deficiency of water.

dry bench
1. that part of a radiographic dark room where film and cassettes are handled, i.e. there is no chance of film being contaminated by chemicals.
2. a slang expression for simulated research work, for reported experiments that were not actually done.
dry coat syndrome
dry eye
see keratoconjunctivitis sicca.
dry feeding
the entire ration is made up of dried stored grain or hay.
dry food
the meal or biscuit type dog and cat foods that contain approximately 10% water. Economical, easily transported and stored; in many countries, this is the most commonly used form of mass produced pet food.
dry ice
solidified carbon dioxide; in an icebox, it produces temperatures of about −76°F (−60°C).
dry lot
the livestock, usually cattle, are kept in a small area with a firm floor but no roof or walls. All food and water are brought to them. Refers usually to dairy herds. See also feedlot.
dry mash
a method of feeding poultry. Essentially a mixture of grain and supplements.
dry rales
see rale.
dry sow
pregnant sow.
dry sow house/room
area where sows are housed and fed between mating and farrowing. Called also gestation barn.

eye

the organ of vision. In the embryo the eye develops as a direct extension of the brain, and thus is a very delicate organ. To protect the eye the bones of the skull are shaped so that an orbital cavity protects the dorsal aspect of each eyeball. In addition, the conjunctival sac covers the front of the eyeball and lines the upper and lower eyelids. Tears from the lacrimal duct constantly wash the eye to remove foreign objects, and the lids and eyelashes aid in protecting the front of the eye.
The eyeball has three coats. The cornea is the clear transparent layer on the front of the eyeball. It is a continuation of the sclera (the white of the eye), the tough outer coat that helps protect the delicate mechanism of the eye. The choroid is the middle layer and contains blood vessels. The third layer, the retina, contains rods and cones, which are specialized cells that are sensitive to light. Behind the cornea and in front of the lens is the iris, the circular pigmented band around the pupil. The iris works much like the diaphragm in a camera, widening or narrowing the pupil to adjust to different light conditions.
The optic nerve, which transmits the nerve impulses from the retina to the visual center of the brain, contains nerve fibers from the many nerve cells in the retina. The small spot where it leaves the retina does not have any light-sensitive cells, and is called the blind spot.

eye adnexa
include orbital fascia, ocular muscles, eyelids, tunica conjunctiva, lacrimal apparatus and, in the pig, the orbital ligament.
almond-shaped eye
observed with dehydration in birds, where the eyeball is sunken, particularly in raptors which normally have a prominent, round globe.
blue eye
a common term for corneal edema. See also blue eye.
cancer eye
common lay term for ocular squamous cell carcinoma.
cherry eye
china eye
one with a blue iris.
cross eye
esotropia.
diamond-shaped eye
seen in dogs with sunken eyes and loose skin in the eyelids which drop inwards, such as St. Bernards and Newfoundland. Often contributes to entropion.
eye drop
vestibular nerve lesion will cause the eye on the affected side to deviate downward more than the opposite eye when the head is lifted.
dry eye
fatty eye
permanent protrusion of the lower conjunctival sac; thought to be inherited in some breeds of guinea pigs.
mirror eye
term for congenital cataracts in guinea pigs.
pink eye
pinkeye.
eye preservation reflex
red eye
an eye showing dilation of conjunctival, episcleral or ciliary blood vessels.
eye reflexes
includes eye preservation (menace), pupillary light, consensual light reflexes.
eye specialist
eye teeth
see canine teeth.
wall eye, walleye
the irregular distribution of melanin in a blue iris. Seen commonly in dogs with merle coat color and Siberian huskies. Called also heterochromia iridis. In humans, the term refers to exotropia, or divergent strabismus. See also walleye.
eye wash
various medicated solutions used to flush the eye; called also collyria.
watch eye
one with an iris containing blue and yellow or brown pigment.
eye white percentage
an estimate of the startle response and an indicator of fear in dairy cattle.
white eye syndrome
congenital cataract associated with congenital bluetongue infection in calves.
eye worm

Patient discussion about dry eye

Q. What Causes Dry Eyes? I have been suffering from eye dryness lately, what causes this situation?

A. Dry eyes are often caused when the lacrimal gland does not produce sufficient tears to keep the entire conjunctiva and cornea, that are normally covered by a complete layer of tear film. This usually occurs in people who are otherwise healthy. Increased age is associated with decreased tearing. if it causes you real discomfort talk to a doctor.

Q. what can i do about dry eyes?

A. i suggest treating it symptomatically with visine in the meantime

More discussions about dry eye
References in periodicals archive ?
Dry eye can make it more difiua"cult to perform some activities, such as putting on contact lenses, using a computer or reading for an extended period of time, and it can decrease tolerance to dry environments, such as an aircraft cabin.
It helps us as clinicians to know what dry eye is and what it isn't," he elaborated, adding that it was difficult to calculate global prevalence of dry eye if different countries were using different definitions.
I recommend Mega-3 for patients suffering from dry eye symptoms associated with MGD [Meibomian gland dysfunction] who are looking for relief," said optometrist Milton Horn.
Clinical research demonstrates that a single oral capsule daily relieves dry eye syndrome within 30 days and provides lasting relief--without risky prescription-drug eye-drops' side-effects.
The potential of cyclosporine-A for treating dry eye disease was initially recognized in dogs who developed spontaneous keratoconjunctivitis sicca.
Certain risk factors make you more vulnerable to dry eyes (see What You Should Know).
Although Dry Eye Syndrome is not a frequent cause of blindness, it has emerged as a public health problem.
Common symptoms of dry eye syndrome typically include dryness, foreign body sensation, secretion, burning, redness, fatigue, blurred vision, blinking, and itchiness.
The eligibility criteria for patient entering the study were previous clinical diagnosis of dry eye associated with meibomitis.
The handheld stimulator was investigated for temporarily increasing tear production upon activation in patients with dry eye disease due to decreased tear production.
Dry eye affects not only your eye's appearance and your vision; it is often linked to skin conditions and other eye diseases such as glaucoma.
A I sympathise with your discomfort as I have dry eyes myself.