Dry eye is a very common condition and occurs when people have either an inadequate amount tears (tear deficient dry eye) or an incorrect composition of tears (evaporative dry eye), both of which keep the eye from being properly lubricated.
Tear deficient dry eye
Glands around the eye produce tears to keep the eye well lubricated. When these glands do not produce enough tears, the condition is referred to as tear deficient dry eye. Two types of tear deficient dry eye exist: Sjogren syndrome and non-Sjogren syndrome.
Patients with Sjogrens syndrome not only have dry eyes but also have dry mouth and in many cases, arthritis. Other coexistent connective tissue diseases (Rheumatoid arthritis, lupus etc) may also be present.
Non-Sjogren dry eyes do not produce enough tears because of a disease of the tear gland. Many diseases can cause the tear gland to decrease tear production such as vitamin A deficiency, trachoma, atopy, sarcoidosis and trauma as well as diabetes, herpetic eye infection (simplex and zoster) as well as chronic contact lens wear.
Evaporative dry eye
The tear film is composed of three layers, the outer oily layer which is contact with the air, the middle aqueous layer (holds all of the water and the mucous layer which is in direct contact with the cornea (the clear outer covering of the eye). If the oily layer, which is produced by the Meibomian glands, is affected because of Meibomian gland disease, the oily layer cannot prevent the underlying aqueous layer from drying-up and therefore the tears are lost due to evaporation.
Symptoms associated with dry eye include intermittent blurring of vision especially while reading, a burning and/or gritty sensation, itching and generalized pain. Mnay times these symptoms worsen during the day. Many patients describe their eye feeling tired all the time. Certain medications show side effects of drying the ocular surface such as antihistamines, decongestants, diuretics, antidepressants, beta-blockers, oral contraceptives, blood pressure medications, and tranquilizers.