Dry eye occurs, often due to the following factors: deficient tears, dry climates, connective tissue diseases, medication (e.g. nasal decongestants, antihistamines, tranquilizers, etc.).
The tears can keep the eye moist, help wounds heal and prevent eye infection. The tear film contains three layers: lipid layer, aqueous layer and mucin layer. The lipid layer can prevent tears from evaporating. The aqueous layer can help nourish the cornea and conjunctiva. The mucin layer can help to spread the aqueous layer, making the eye remain wet.
In order to keep the eye lubricated, the eye needs to generate enough tears. The generated tears must also have good quality, otherwise they can not remain long enough. If the tears are not enough, or their quality is poor, the eye will easily become dry.