The lachrymal system comprises the ducts through which the tears flow from the moment they are secreted to bathe the eye until they leave through the four entry points (puncta) to the canaliculi into the lachrymal sac and from there to the lachrymonasal duct and out through the nostrils.

In 20% of babies there is permanent tearing that cannot be corrected with gentle massage on the internal portion of the palpebral fissure. Some cases resolve spontaneously and for that reason a seven-month period is allowed before performing lachrymal probing in order to solve the epiphora.

This procedure is performed in cases of total obstruction of the lower lachrymal system, i.e. the lachrymal sac and lachrymonasal duct.

When there is a definitive upper obstruction (canalicular) a Pyrex tube is implanted in order to drain the tears into the nose. Infections and tumors may be found in this area requiring prompt and adequate treatment.

Also called (dry eye sindrome) occurs when people don’t have either enough tears, or the correct composition of tears, on the surface of their eyes to lubricate the eyes and keep them comfortable.

Tears are much more than just water. They're a complex mixture of water, fatty oils, proteins, electrolytes, bacteria-fighting substances and growth factors that regulate various cell processes. This mixture helps make the surface of your eyes smooth and clear. Without tears, good vision is impossible.

The tear film has three basic layers: The outer, oily layer of the tear film is produced by the meibomian glands in the eyelids and reduces evaporation of the tears. When the oil layer is abnormal, the watery layer evaporates too quickly. Dry eye problems are common in people whose meibomian glands are clogged. Meibomian dysfunction is more common in people with inflammation along the edge of their eyelids (blepharitis), rosacea and other skin disorders.The thick, middle, watery layer makes up about 90 percent of tears, this layer, produced by the lacrimal gland above the upper eyelid, cleanses your eyes and washes away irritants. The inner, mucus layer is secreted by the goblet cells in the conjunctiva of the eyelids; allows tears to spread evenly over the surface of your eyes and helps the tear film stick to the cornea; Dry spots form easily in any part of the cornea that has patchy loss of the mucus layer.

Causes

Dry eye’s prevalence increases with age, so that it is extremely common in older people of both sexes. The condition affects more women than men especially after menopause. This may be due in part to hormonal changes. Damage to the tear glands from inflammation or radiation can hamper tear production. Dry eyes are also associated with medical conditions such as diabetes, rheumatoid arthritis, lupus, scleroderma and Sjogren's syndrome. Although some disorders primarily involve a single layer of the tear film (e.g.,decreased mucus production in vitamin A deficiency, reduced aqueous production in keratoconjuntivitis sicca, or abnormal lipid production in meibomian keratoconjuntivitis).

Through blinking — normally at a rate of about 10-12 blinks each minute — your eyelids spread a continuous thin film of tears across the surface of your eyes. Tasks that require intense visual concentration — such as working at a computer, driving or reading — tend to decrease your blink rate, thereby increasing tear evaporation. In addition problems with your eyelids can impair the complex blinking motion required to spread these tears, resulting in dry eyes. Eyelid problems that may develop as you age include an out-turning of the lids (ectropion) or an in-turning of the lids (entropion).

Dry eyes can be worsened by exposure to many environmental conditions that have a drying effect, such as sun, wind, high altitude, a dry climate, hot blowing air and the dry air that commonly occurs in the cabins of commercial airplanes.

Other Causes:

The types of common medications, that can cause dry eyes include:
• Some drugs commonly used to treat high blood pressure
• Antihistamines and decongestants
• Sleeping pills
• Birth control pills
• Tricyclic antidepressants

In some people, the cause of dry eyes is an allergic reaction to eyedrops or ointments.
Refractive surgery (LASIK,PRK,LASEK)

Symptoms:

The most common complaints are: A stinging, burning or scratchy sensation in your eye, Stringy mucus in or around your eyes, Increased eye irritation from smoke or wind, Eye fatigue after short periods of reading, Sensitivity to light, Difficulty wearing contact lenses, Blurred vision, often worsening at the end of the day.
Although it sounds like a contradiction, you may have dry eyes and still at times find yourself with tears streaming down your cheeks. What's called reflex tearing produces large quantities of tears in response to eye irritation or emotions. Reflex tears contain much more water than do basic tears, and they're low in mucus and oils, because these tears are of poor quality, they don't help the dryness.

Most people with dry eyes don't experience any long-term complications. However, if left untreated, severe dry eyes may lead to eye inflammation, infection and scarring on the surface of your cornea, or even corneal perforation as in Rheumatoid Artritis.

Treatment:

For treatment a step-by-step approach can be followed according to the patients condition:

1-Replacement using tears substitutes, with treatment of associated problems ( blefaritis, avitaminosis, lids malposition, etc)

2-Decrease tear evaporation (glasses with lateral protection)

3-Decrease tear drainage ( punctum plugs or definite surgical clousure of lacrymal punctums)

4-Increase tear production (specific medication)

Many brands are available without a prescription. For mild cases, try several to find the one you like best. In more severe cases follow the prescription of your doctor, who will take care of your individual problem.