Tears are secreted from the lacrimal glands through ducts to the surface of the eyes between the eyeball and the lid.
The lacrimal gland, one for each eye, is located at the back of the top eyelid. When we blink, tears known as lacrimal fluid, are distributed over the eye surface.
The lower eyelids have minute orifices called puncta on their margins and bottom corner that collect tears and pass them down to the inner nose.
This is the reason that the nose runs if there is an excess of tears caused for example by crying, laughter or peeling onions.
As the flow of tears increase so the eyes flood as the puncta cannot cope and the excess of tears run down the cheeks.
It is important that the eye surface (cornea) is kept continually moist and nourished by tear fluid which at the same time washes away any dust or other small foreign particles that are virtually a constant in our modern world.
Another important function of tear fluid is to fight any bacterial infection that can attack the eyes.
Tears consist of water, mucin, lipids, lysozyme, lactoferrin, lipocalin, immunoglobulins, glucose, urea, sodium and potassium.
Tears form three distinct coatings on the eye surface, each having a specific and important function in normal circumstances. This coating or film is known as the precorneal film.
- The outer layer or lipid layer is responsible for preventing the surface from drying out by forming a hydrophobic barrier to slow down evaporation. At the same time this barrier retains the tears from running onto the cheeks.
- The middle layer, known as the aqueous layer, fights infections and assists in spreading the tear film over the eye surface.
- The inner or mucous layer function as the water-bonding layer that is responsible for even distribution of all three layers over the eye surface. It also contains mucus that helps to protect the cornea.
Healthy tear production is essential for eye health. The older we are the less tears we produce.
Curiously and very misleading is the fact that although the eyes are watering profusely, we can still be suffering from a lack of healthy tear fluid over the entire surface of the eyes.
Should this be occurring without any noticeable cause do go and see your eye consultant to have it checked out. Ignoring the symptoms, which may not appear constant, can lead to sight problems.
Depending on the sufferer’s condition, ophthalmologists can provide either a cure or hold the condition in check. The inner puncta sometimes blocks but can be restored to normal by laser treatment.
Various eye drops such as
are available that encourage sufficient tears to keep the eye surface healthy
Insufficient or thin tear fluid levels have caused problems to contact lens wearers but modern technology has largely overcome this problem as contacts have become more flexible, disposable or oxygen permeable.