What is the cornea?
The cornea is the clear, dome-shaped outer surface that covers the eye in front of the iris. The iris is the colored part of the eye. The cornea helps protect the rest of the eye from germs, dust and other harmful matter. The cornea bend slight entering the eye, and accounts for most of the eye's total focusing power. It also serves as a filter to screen out most of the damaging ultraviolet (UV) wavelengths in sunlight. The cornea is a highly organized, clear structure made up of a group of cells and proteins precisely arranged in layers, but it has no blood vessels to nourish or protect it against infection. Instead, it receives its nourishment from the tears and the watery fluid (aqueous humor)
What are tears, and how do they relate to dry eye?
The lacrimal gland produces tears, which are necessary for overall eye health and clear vision. Tears bathe the surface of the eye, which keeps it moist and washes away dust and debris. They also help protect the eye from bacterial and other types of infections.
Tears are composed of three layers
a) The outer, oily, lipid layer produced by the meibomian glands
b) The middle, watery, lacrimal layer produced by the lacrimal glands
c) The inner, mucous or mucin layer produced by goblet cells locates.
Tears are made of proteins, electrolytes and vitamins that are critical to maintain the health of the eye surface and to prevent infection .Tears are constantly produced to bathe, nourish and protect the eye surface. They are also produced in response to emergencies, such as a particle of dust in the eye, an infection or irritation of the eye or an onset of strong emotions.
When the lacrimal glands fail to produce sufficient tears, dry eye can result. Any disease process that alters the components of tears can make them unhealthy and result in dry eye.