Dry eye syndrome is one of the most common conditions that an ophthalmologist can confront. Usually is caused by issues of the tear film that hydrates our eyes.
Tear film is consisted by 3 layers:
• The outer layer creates an oily (lipid) film that covers the tear layer and prevents evaporation.
• The middle aqueous layer, which provides moisture and carries oxygen, as well as nutrients to the cornea. This layer consists of 98% water, minor amounts of sodium chloride (salt), proteins and other components.
• The mucin layer covers the cornea (the outer surface of the eye), creating a low adhesion to him, offering tears stability on the eye.
Tears are created by many eye glands. The 2nd layer (aqueous layer) is produced by the lacrimal gland, which is located in the base of the upper eyelid. Many small glands among the bases of the eyelids are producing lipid and mucin layer.
With each blink, the eyelids spread the tears over the ocular surface. The residual tears flow into the two small pores on the edge of the eye, which are located near the nose. These pores lead to the canaliculi that leads to the nasal cavity.
The communication between the lacrimal pores and nasal cavity explain why when we cry, our nose run!
Apart from eye hydration, the tear production is reflective to external stimuli such as emotion or injury. However, this kind of tears offer little relief to a patient with dry eye syndrome and that’s why a patient with “wet” eyes may still complain of irritations.
The dry eye syndrome has many causes, with the most common one, that of aging. As we become older, our body produces less fat substances-60% less at age of 65 than at the age of 18. This is more evident in women, who tend to have drier skin than men. Lack of oily substance, affects tear film too. Without the essential oily substance, the oily (lipid) layer of the tear film cannot supply all the tear film. Thus, the entire tear layer evaporates more quickly and makes several corneal areas dry.
Other factors such as heat, drought, wind, high altitude, cigarette smoke, usage of certain medication can also cause dry eye. Many people feel their eyes dry when reading or working on the computer. Short, often breaks between work, provide hydration to the eyes and relieve from the dry eye symptoms.
Contact lens wearers can also suffer from dry eye, because contact lenses absorb the tear film, creating long formation of protein deposits on contact lenses. Also, certain drugs, thyroid problems, lack of vitamin A can also cause dryness.
In addition, patients with Parkinson or Sjogren syndrome suffer from dryness. Hormonal changes to women after 50 can cause dry eye too.