Dry eyes are caused by a disruption in the tear film that normally lubricates and protects the surface of the eyes. The tear film consists of three layers: oily (fatty) oils, aqueous fluid (water), and mucus. Problems with any of these layers can lead to dry eyes.

Main causes of dry eyes:

• Decreased tear production: This occurs when the eyes do not produce enough aqueous fluid. Common reasons include aging, certain medical conditions (such as Sjögren's syndrome, rheumatoid arthritis, lupus, thyroid disorders, and vitamin A deficiency), some medications (antihistamines, antidepressants, hormone therapy, blood pressure drugs), nerve damage from contact lens use or eye surgery, and autoimmune diseases that damage tear glands

• Increased tear evaporation: The oily layer, produced by meibomian glands in the eyelids, can become clogged or dysfunctional (meibomian gland dysfunction), causing tears to evaporate too quickly. Factors that increase evaporation include eyelid inflammation (blepharitis), skin conditions like rosacea, reduced blinking (common when concentrating or due to diseases like Parkinson’s), eyelid problems (e.g., lids turning inward or outward), environmental factors (wind, smoke, dry air), eye allergies, and preservatives in eye drops

Additional contributing factors:

• Hormonal changes, especially in women during pregnancy or menopause, can reduce tear production

• Prolonged screen time reduces blinking, increasing tear evaporation

• Environmental conditions such as dry, windy, or smoky climates exacerbate tear evaporation

• Certain systemic diseases (diabetes, Graves' disease, sarcoidosis) and autoimmune disorders increase risk

• Use of contact lenses and some eye surgeries (e.g., LASIK) can temporarily reduce tear production

In summary, dry eyes result from either insufficient tear production or excessive tear evaporation, often influenced by age, medical conditions, medications, environmental factors, and eyelid gland health