What is a dry eye?

Under normal conditions, our eyes are constantly making tears to keep the surface of the eye moist. Although tears are typically considered as a simple, homogeneous substance, we have a complex tear film that keeps our eyes healthy and comfortable, which consists of three distinct layers. Every time we blink, the tear film coats the surface of the eye, which helps to keep them clean and clear. If insufficient amounts of the tear film or its composition is off, dry eyes can occur.^[1]