Causes and Trigger Factors

Causes and trigger factors of dry eye

• The aetiological factors of dry eye may be classified as pathological or non-pathological. In addition, advancing age is often one of the most important underlying factors. Dry eye is thought to affect around 75% of people over the age of 65. As we grow older, fewer tears are produced and evaporation increases due to reduced lipid production. Without as much lipid to seal the aqueous layer, the tear film evaporates much faster, leaving dry areas on the cornea. However, dry eye is often not diagnosed in older people because the effect of dry eye is often balanced by another age-related change: poor tear drainage. The result of this is a balance between not making enough lacrimal fluid and not being able to drain away the resulting tears properly.

• Long-term use of contact lenses can also trigger dry eye as, over time, they reduce corneal sensitivity. The sensitivity of the cornea and the entire ocular surface determines the amount of tears the lacrimal gland will secrete. The less sensitive the cornea, the fewer tears that are produced. In addition, contact lenses absorb the tear film, causing proteins to form on the surface of the lens. They also disturb the lipid layer, resulting in increased evaporation of tears from the ocular surface.

Common causes of dry eye

Pathological causes

• As already discussed, certain diseases or disorders can result in dry eye. One of the most important pathological factors is Sjögren's syndrome, an immune-mediated disease that affects the lacrimal and salivary glands. The condition can occur in isolation or be associated with other autoimmune conditions such as rheumatoid arthritis or systemic lupus erythematosus (SLE). Any disease that reduces the function of the lacrimal or Meibomian glands can cause dry eye, as can blepharitis, Parkinson’s disease, vitamin A deficiency, neurotrophic keratitis, VII nerve palsy and numerous other disorders.

• Systemic drugs such as corticosteroids, antihistamines, antibiotics, anti-diuretics, contraceptives and beta-blockers can trigger dry eye. In addition, certain ophthalmic products can sometimes adversely affect the tear balance, which is why doctors often prescribe lubricant eye drops in conjunction with ophthalmic treatment.

• Fluctuations in hormonal levels, particularly estrogens and androgens, are another common cause of dry eye. Pregnant women, women who use oral contraceptives, menstruating and post-menopausal women frequently report the condition

Non-pathological causes

• Environmental factors such as pollution, wind, hot and dry atmospheres, air conditioning and cigarette smoke all contribute to dry eye. Looking at a computer screen for too long also plays a role because the blinking rate is reduced, leading to a
  decrease in the production of lacrimal fluid and increased tear evaporation.

• Long-term use of contact lenses can also trigger dry eye as, over time, they reduce corneal sensitivity. The sensitivity of the cornea and the entire ocular surface determines the amount of tears the lacrimal gland will secrete. The less sensitive the cornea, the fewer tears will be produced. In addition, contact lenses absorb the tear film, causing proteins to form on the surface of the lens. They also disturb the lipid layer, resulting in increased evaporation of tears from the ocular surface.

• As already discussed, dry eye is often experienced for several weeks following ocular surgical procedures such as LASIK or PRK. Artificial tears are usually recommended to help lubricate the eye.
  
  

  It is important to note that in many patients, the cause of dry eye remains unknown. However, treatment can still be instigated.

Please also view our Dry Eye Video here: http://vismed.trbchemedica.co.uk/patient-information/dry-eye-video

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