If your eyes make insufficient tears the tear film is spread too thinly over the eye's surface.
If your tears are chemically imbalanced they evaporate too quickly before the next blink comes along. Either way dry spots appear causing sore eyes. Tears are made from a mixture of secretions from glands at different locations around the eye. Tears have 3 layers: oil, water and mucous.
The mucous layer connects with the eye's surface and serves to support the whole tear film. It is formed by the secretions of 10 million tiny conjunctival goblet cells living within the white of the eye and inner lid surfaces. Overlying this mucous is a watery layer, produced by one large lacrimal gland which is located just below the eyebrow. During wakening hours, the lacrimal gland pumps watery tears at a background level adjusting for environmental conditions. When there is an irritant, extra "crying" tears are made almost instantly. This is why as odd as it sounds many dry eye sufferers experience watery eyes- the lacrimal gland overcompensates for irritation caused by an abnormal tear film.
During sleep the lacrimal gland is inactive which is why eyes feel sore and dry on wakening. The oil layer sits on top of the watery layer - sealing the tear film by preventing evaporation. This oil is derived from lipids exuded from twenty three meibomian gland openings along the edge of the eyelids. Blocked meibomian glands cause deficiency in tear lipids and dry eye by excessive evaporation. This is called meibomitis or posterior blepharitis and is a chronic recurring condition. Several conditions can masquerade as dry eye syndrome and a detailed examination will rule out co-existing conditions, such as blepharitis. Around 70% of patients have dry eyes due to lack of tear volume (aqueous deficiency) and 30% have evaporative dry eyes. Many patients have both aqueous and evaporative components to their dry eye and successful treatment depends on targeting the root cause of each.
To test for these conditions, at Osborne Harle we use a fluorescent yellow dye which is painlessly introduced into the tears of each eye. Viewed with a slit lamp microscope under blue light, any area on the surface of the eye damaged by dehydration glows brightly. Tear evaporation rate is measured as the number of seconds after a blink before the tear film de-stabilises and tear volume assessed by analysing the "pool" of tears clinging along the edge of the lower eyelids. The dynamic flow of tears following a blink and their exit through your tear ducts are also assessed. At Osborne Harle we can offer you two stages of treatments:
Short term relief
For less severe dry eye cases, artificial tears offer immediate relief. Unfortunately, many widely used eye drops contain preservatives which can cause a worsening of the dryness with long term use. These agents corrupt conjunctival goblet cells which then fail to produce tear mucous. Often low-grade allergies develop. There really is nothing better than human tears.
Longer term relief
In cases of more persistent dry eye symptoms, closure of the tear duct openings, may be the best option. At Osborne Harle we do this using punctum plugs. This conserves precious tears by restricting drainage. Your eyes are bathed with your own natural tears without the bother of constantly supplementing the tear film with artificial drops.
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