What is a tear film and why is it so important?

It constantly covers the surface of the eye ball. Its most important role is to moisture and nourish the surface of the eye, which prevents corneal damage. It acts as a lubricant, facilitating free eyelid movements. Chemical substances contained in the tears (sodium chloride, albumins, lysozyme, globulin, ascorbic acid, sugar, urea and electrolytes), have antibacterial, antiviral and antifungal effects, consequently protecting the eyes from infections. It focuses the rays of light on the retina, which is why even minor disturbances in the continuity of the tear film affect visual acuity deterioration.

The tear film consists of three layers:

• The mucin (mucous) layer – located closest to the surface of the eye, the thinnest of the layers. It aids adhesion and maintenance of the tear film on the surface of the cornea. It is secreted by the conjunctival cup cells.
• The watery layer – the thickest, middle part of the tear film, which consists of water, electrolytes, mucin and protein. It is secreted by the lacrimal glands. It oxygenates, lubricates and nourishes the corneal epithelium. It removes all impurities and foreign objects from the surface of the eye. By eliminating minor irregularities in the anterior surface of the cornea, it maintains a smooth optical surface.
• The lipid layer – the outer layer, which retards tear evaporation, stabilizes the tear film, and acts as a lubricator, so that the eyelids can move freely. Additionally, it protects against infections. It is secreted by the meibomian glands.

Consequences of film tear disorders

The tear film must have an adequate composition and be produced in the right amount in order to be able to properly nourish and lubricate the eyes. Any abnormalities in one of the layers lead to a condition known as a dry eye syndrome. Most often, symptomatic treatment is used, but everything depends on which layer the disorder has occurred in.

• The watery layer – the cause of the decrease in the secretion of tears is a damage to the corneal sensation (reflex secretion of tears). This problem may for instance affect people who wear contact lenses. Moisturizing eye drops, also known as artificial tears, are frequently used as a treatment method.
• The mucin layer – disorders may be caused by vitamin A deficiency, or diseases, such as chronic conjunctivitis, erythema multiforme, trachoma and chemical or thermal damage.
• The lipid layer – symptoms may be connected with abnormal functioning of the meibomian glands, which may result from chronic inflammation of the edges of the eyelids or the glands themselves caused by a bacterial infection. What is often used to treat this problem is a liposomal spray.

Moreover, abnormalities in the action of the tear film can occur in the elderly due to age-related atrophy of the lacrimal glands, which in turn results in a decrease in the secretion of tears. This may also be caused by the use of certain medicines, including the ones used to treat hypertension, and arrhythmia, antihistamine ones or topical eye medications. Blinking enables an even tear distribution across the surface of the eyes. This is why too infrequent blinking, e.g. while looking at a computer screen, may also cause tear film impairment.

Tear film disorders may foreshadow a dry eye syndrome (DES). If you often experience dryness, burning, a sensation of a foreign body in the eye, or deterioration of visual acuity, you should contact an ophthalmologist and undergo a specialist examination to check whether you have the dry eye syndrome. Only a properly selected treatment, based on thorough examination, can bring satisfactory results.

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