Tears provide lubrication to the eyes and serve as a protective layer from irritating particles such as dust. So naturally, the human eyes have tear films. They help keep the eye surface clear and maintain good vision. They also keep the eyes from drying out and losing their moisture. There are three layers consisting of the tear film: the oily layer, which prevents the tears from drying too quickly; the liquid layer (cleans and washes away particles harmful to the eyes); and the mucus layer (keeps the eye surface moist and enables the tears to stick to the eyes.)
Dry eyes occur for three reasons: One, when there are not enough tears to moist the eyes (the tear gland cannot produce adequate tears due to aging and other medical conditions like Sjogren’s Syndrome); two, the tears produced are of poor quality and cannot lubricate the eyes well), three, if the eyes are too exposed to devices (staring at the mobile phone or computer for several hours without taking in enough liquid for hydration) and finally, if the objects around (such as heater) can quickly dry out the tear film thus, drying the eyes. Then, the eyes feel a stinging sensation.