What causes dry eyes?

The terms "dry eye" and "dry keratoconjunctivitis" are synonyms. There are 2 main forms:

1. hypo-secretory dry eye Sjogren, in particular, Sjogren or non-Sjogren syndrome,
2. impaired evaporation of tears.

But these two states do not exclude each other.

Clinical physiology

The main lacrimal glands produce about 95% of the water component of tears, and additional tear glands Cruse and Wolfring - 5%. Secretions of tears can be both basic (constant) and much more pronounced reflex products. Reflex tear production is developed in response to sensory stimulation of the cornea and conjunctiva, rupture of the tear film, and the formation of dry spots or inflammation. Reflex tear production is reduced under the influence of local anesthetics. Earlier the main tear production was attributed to additional lacrimal glands, and the reflex - to the main lacrimal glands. Now they believe that the whole mass of tear tissue works as a whole. Pre-corneal tear film has 3 layers: lipid, water, mucin.

External lipid layer

The outer lipid layer is secreted by meibomian glands.

Lipid layer functions

• Retards the evaporation of the aqueous layer of the tear film.
• Reduces the surface tension of the tear film, which, in turn, attracts the water component in the tear film and thickens the aqueous layer.
• Lubricates the eyelids, which repeat the relief of the surface of the eye.

Dysfunction of the lipid layer can lead to the syndrome of the "dry" eye due to the increased volatility of the tear.

Medium water layer

The middle water layer is secreted by the lacrimal glands and consists of proteins, electrolytes and water.

Functions of the water layer

• Delivery of atmospheric oxygen to avascularized corneal epithelium.
• Antimicrobial protection due to the presence in the tear of proteins such as IgA, lysozyme and lactoferrin.
• Elimination of foreign bodies from the surface of the cornea.
• Cleaning the wound from products of inflammation.

Deficiency of the water layer leads to a dry secretory "dry" eye.

Internal mucin layer

The inner mucin layer is secreted by the goblet cells of the conjunctiva, Menle crypts and Manz glands.

Functions of the inner mucic layer

• Humidification of the cornea by converting the hydrophobic surface of the corneal epithelium to hydrophilic.
• Lubrication.

Insufficiency of the inner mucic layer can cause both hypoxecretion and a state with increased evaporation of tears.

The lacrimal film spreads over the eye surface mechanically due to reflex blinking movements and after a certain period of time is excreted through the tear ducts. Three factors are necessary for the normal distribution of the tear film: a normal blinking reflex, a complete correspondence between the anterior surface of the eye and the eyelids, and a normal corneal epithelium.

[1], [2], [3], [4], [5], [6], [7]

Hypoecretory dry eye (dry keratoconjunctivitis) Sjogren

Sjogren syndrome is an inflammatory process caused by the reaction of cytokines, which affects the lacrimal glands and ducts that causes tearing of the tear film and can often damage the surface of the eye.

1. The primary syndrome of Sjogren is characterized by dry mouth (xerostomia) and the presence of antibodies that are characteristic of the autoimmune process.
2. Secondary Sjogren syndrome is characterized by the presence of systemic autoimmune connective tissue disorders and manifests itself in the form of the following diseases: rheumatoid arthritis, lupus erythematosus, systemic sclerosis, dermatomyositis and polymyositis, mixed connective tissue pathology, recurrent polychondritis or primary cirrhosis. All these conditions complement the primary syndrome Sjogren.

Hypoecretory dry eye (dry keratoconjunctivitis) non-Sjogren

1. Primary, associated with age - the most common.
2. Destruction of the lacrimal gland tissue caused by a tumor or inflammation (eg, pseudotumor, endocrine ophthalmopathy or sarcoidosis).
3. Absence of a lacrimal gland due to surgical interventions, rarely - congenital.
4. Occlusion of ducts of the lacrimal gland due to cicatrical changes in the conjunctiva (for example, scarring pemphigoid and trachoma).
5. Neurological disorders, such as familial vegetative-vascular dystonia (Rilay-Day syndrome).

Dry eye, which is associated with impaired evaporation of tears

1. Lipid insufficiency is most often due to the dysfunction of meibomian glands.
2. Violation of the integrity of the surface coating of the eye with tear film due to inconsistency of the eyelid edges or disturbance of the flashing process.

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