Dry eyes associated with contact lenses

 
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Dry Eye Problems

For comfortable and successful contact lens wear experience, it is important that the tear film in the eye is sufficient and of good quality. If there is any disruption in the quantity and quality of the tear film then it will lead to contact lens wear intolerance and damage to the ocular surface.

What is Dry Eye?

Dry eye is a condition in which there are insufficient tears in the eye to keep it optimally comfortable. A more comprehensive explanation would be that this is a problem of inadequate quantity of tear film or a disturbance in the quality or stability of tear film causing damage to the interpalpebral ocular surface. The tear film function is controlled by neurohormonal interactions. The disturbance of tear film is associated with inflammation and structural changes of the eye surface in turn leading to discomfort in using contact lenses.

Factors Responsible for Dry Eye Disease

Dry eyes can occur as a result of mucin deficiency in which the moistness of the eye surface is decreased. It can also be brought about by insufficient lipids or abnormal lipid layers by which the stability of the tear film is affected. The third cause can be attributed to aqueous deficiency whereby there is less than required volume of liquid to the tear film. Also abnormalities in the eyelids and inappropriate blink function could lead to the inability of the distribution of the tear film. Finally, if there is eye surface alteration and abnormality, tear film stability is hampered.

Whichever may be the reason, the conclusion drawn points towards the important role of the tear film as a surface active layer, which when disturbed either by physical, physiochemical or structural causes results in problem of dry eyes.

Classification of Dry Eyes

Dry eyes can be further classified into two types- tear deficient dry eye and evaporative dry eye. Tear deficient dry eye can be further subdivided into Sjogren’s syndrome related and non-Sjorgen’s syndrome tear deficiency. The former is more severe in nature and is associated with systemic abnormalities (keratoconjunctivitis sicca).

Tear Deficient Dry Eye

The structure of the tear film is not only constituted of water but is an integrated layer of lipids, aqua and mucin components whose function is not only as a cleansing and protective liquid but a supportive film for the eye surface as well. Aqueous deficient dry eye is often related to decrease in the production of tears. Proteins present in tears such as lysozome and lactoferrin were found to be much lower in tears of patients with dry eye. Topical applications of different types of liquids and polysaccarides and polymers are commercially available and can be used to replace the volume of tear film. Also a variety of vitamins, electrolytes and minerals have been included to improve lachrymal function but these only soothe but do not solve the underlying problem of dry eye. Despite all attempts, the perfect tear substitute is yet to be created.

The presence of post inflammatory cytokines in the tears and conjunctiva of dry eye patients, point to the fact that inflammation leads to the development of aqueous deficient dry eye. Studies have shown that androgen permits the inflammation when reduced leading to dry eye. This explains why the incidence of dry eye disease most commonly occurs in postmenopausal women and elderly people.

Evaporative Dry Eye

This is caused by lipid insufficiency, blepharitis, eyelid pathogenic conditions, contact lens wear and ocular surface abnormalities. Evaporative dry eye is more often a result of meibomian gland disease.

The tear film is composed of thixotropic layer with the interaction of lipids covering the surface of tears. If there is increased evaporation of tear film, which results in tear film instability, it leads to meibomian gland disease. The presence of estrogen and androgen receptors in the meibomian glands are similar to the lachrymal gland surface and ocular surface and these glands are controlled by hormonal interactions and may be part of the disturbance of androgen metabolism present in aqueous deficient dry eye. More evaporation often aggravates an aqueous deficient dry eye because these two types are concurrent and frequently happen together.

Contact lens wear and dry eye

Tear film is responsible for lubrication and moistening the contact lenses. Movement of tears and hyration behind lenses assures flow of oxygen to the cornea and proteins protect eye surface and decrease contamination of the lenses by bacteria. Contact lenses can aggravate evaporation of tear film and lead to dry eye reducing corneal sensitivity and disrupts balance between tear secretion and ocular surface. So, the least the contact lenses change the corneal sensation and tear physiology, the better the tolerance level of lenses.

Thus, contact lenses are ideal for those having normal lid function and tear film stability.