Dry eye is an eye condition which consists in a reduction in the quantitative and / or qualitative alteration of the tear film, which mainly has a water-retention function of the ocular surface. The disease can be harmful because it can cause injury to the external structures of the eye: the tear film tends to 'break up', resulting in exposure to dehydration of the corneal epithelium and the anterior palpebral conjunctiva. 
Dry eye is more common in their forties , and in those who use contact lenses, for those who use a lot of the display screen or are exposed to the sun and wind.
The most common symptoms are feeling of sand (foreign body) in the eye, redness, pain,  burning,  and photophobia appearance of ulcers (in very severe cases).
External factors can cause major disorders of the eyes. The dislacrimie are all the alterations of the tear film. To understand the pathophysiology of these disorders is well to mention the anatomy and physiology of the lacrimal system. Tears are the thin liquid film in constant change that protects the ocular surface exposed. Produced by the main lacrimal glands, located in the upper outer wall of the orbit, and the lacrimari accessory glands that are located in the conjunctival stroma, are excreted through the nasolacrimal duct into the oropharynx. The tear film is composed of three layers: an intermediate aqueous layer, the more often, whose most important task is to provide atmospheric oxygen corneal epithelium; an outer layer, of lipidic nature, which has the function of delaying the evaporation of the aqueous layer, to lubricate the eyelids during the sliding of the bulb; one deep mucosal layer, which has the ability to transform the corneal epithelium from hydrophobic to hydrophilic. The component has a basal tear secretion and reflected. The innervation of the lacrimal gland is the main parasympathetic nature; the peripheral afferents are mediated by the ophthalmic branch of the trigeminal nerve. The main functions of the tear film interesting this report, the metabolic lubricant and diopter. Why do you have the feeling of well-being must the lacrimal system is in perfect condition: any alteration will cause ocular discomfort of varying degrees. The tear film can be altered by intrinsic or extrinsic factors, and environmental. They act in various ways on the stability of the tear film, causing eye discomfort resulting in symptoms such as heartburn, feeling of a foreign body and tearing. This vicious self-perpetuating inflammatory.
Among the leading causes of dry eye:
Decrease in the aqueous component of the tear film, the most widespread caused by inflammation such as the syndrome of Mikulicz or rheumatoid arthritis
Decreased production of the mucous membrane of the tear film due to alterations of the conjunctiva result from autoimmune diseases such as Stevens-Johnson syndrome, Sjogren's syndrome, or in the case of burns, ocular pemphigoid,  typical in less advanced countries the cases of trachoma.
Overuse and misuse of contact lenses
Alteration of the surface of the cornea, caused by scars or dystrophies
Physiological dysfunctions (glands Meibonio and vitamin A deficiency).
Other minor causes are the so-called syndrome of "ocular discomfort", and has been shown by studies that being diabetic is a risk factor.
One cause of decreased tear production is due to the action of certain drugs such as beta-blockers, antihistamines and antidepressants.
On physical examination will detect changes in the eye conjunctiva, tear film; moreover, you can also perform quantitative and qualitative tests: Schirmer test (which you do by putting small strips of paper towel on the eyelid margin) is used to evaluate the quantity of tears produced in a given period of time; but the tests (analysis of the appearance of cracks on the surface of the tear film colored with fluorescein) allows to obtain a qualitative assessment of the lipid film surface.
The treatment of these abnormalities is based on restoring the tear film and ocular lubricants (artificial tears or moisturizing gel). Crucial also is the correction of underlying conditions (eye or not), the revaluation of systemic drug therapies that can induce dislacrimie, and edit any incorrect lifestyle, especially nutrition - fatty foods affect the secretion lacrimal negatively - and smoke, its irritating action directly and indirectly. Finally, the patient is useful to give guidance on how to reduce the phenomena astenopeici as often blink, look away from objects near and those far away unobstructed, make small breaks regularly, check the lighting, remove dazzling reflections, adjust humidity and ventilation.
Regarding the drugs still are not held with certainty their usefulness, except in the case is also present Sjögren's syndrome (in which case it seems useful administration of pilocarpine hydrochloride)