- Dry eye develops when a reduction in the quantity or quality of tears occurs, causing the tear film to become unstable and break up earlier than normal, leading to dry spots on the cornea
- Dry eye can be defined as a disorder that is caused by tear deficiency or excessive tear evaporation
- Features common to all forms of dry eye include symptoms, damage to the ocular surface, tear instability and tear hyperosmolarity
- Dry eye can be caused by pathological (e.g. Sjögren's syndrome) and non-pathological factors (e.g. smoke, computer screen use, contact lens wear)
- Dry eye develops as a result of:
- aqueous deficiency (the majority of patients with dry eye present with a decrease in the aqueous component – KCS)
- mucin deficiency (caused by a decrease in the number of goblet cells as a result of, for example, vitamin A deficiency)
- lipid abnormality (tear production is adequate, but lipid–mucin interactions occur, causing dry spots)
- impaired lid function (affects the blinking process)
- epitheliopathy (for example, corneal scars cause the tear film to become unstable, leading to localised areas of drying)
- KCS is often used synonymously with dry eye and is applied equally to disorders involving insufficient tear production or excessive tear evaporation
- KCS can be classified as:
- Tear-deficient dry eye (TDDE), which occurs as a result of defective lacrimal function; classified into Sjögren's and non-Sjögren's syndrome
- Evaporative dry eye (EDE), which occurs when lacrimal function is normal and the volume and composition of the lacrimal fluid are sufficient; the disorder is caused by conditions that lead to increased tear evaporation (e.g. blepharitis, contact lens wear)
- Age is one of the most important underlying causes of dry eye
- Other causes include disease, certain drugs, changes in hormone levels, environmental factors, long-term use of contact lenses, some surgical procedures
- Quite often, the cause of dry eye remains unknown. However, treatment can still be instigated
- Dry eye has several consequences, including damage to the corneal surface, an increase in tear osmolarity, inflammation of the eyelids and conjunctiva, dry spots on the cornea and, in severe cases, vision loss
- Symptoms of dry eye include itching, dryness, burning, redness, irritation, foreign body sensation, grittiness, stringy mucus, blurred vision, photosensitivity, excessive tearing, increased discomfort when wearing contact lenses.
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