There could be many causes of dry eyes - aging, hormonal changes, environmental exposures (medications, smoke, wind, dry climate, vitamin D deficiency, contact lenses), failure to blink regularly and medical conditions such as rheumatoid arthritis, diabetes and thyroid problems.
The innermost layer of mucin (mucus) helps overlying watery layer ( a very dilute saltwater solution) to spread evenly over the eye. A thin layer of lipids (fats or oils) helps to decrease evaporation of the watery layer beneath. Dry eye occurs when the aqueous layer is deformed, the eye does not produce tears properly, or when the tears are not of the correct consistency and evaporate too quickly. Dry eye may be accompanied by a stinging, burning or scratchy sensation, stringy mucus in or around eyes, increased eye irritation from smoke or wind, eye fatigue, sensitivity to light, eye redness, a sensation of having something stack in eyes, and blurred vision especially after trying to focus on something for a prolonged period.
Dry eye syndrome (DES) is also known as dry eye disease (DED), keratoconjunctivitis sicca (KCS), and keratitis sicca. Itis a common form of ocular surface disease (OSD) and may overlap with other causes of OSD, such as ocular allergy and meibomian gland dysfunction (MGD).