The tear film (or simply known as “tears”) are composed of three layers: mucus, water, and oil (see figure 1).
The mucus layer is a thin layer closest to the surface of our eye. It is produced by cells on the eye, and functions to adhere and helps spread tears evenly over the ocular surface.
The next layer is the water layer. This layer is produced by the lacrimal gland located just behind the outer parts of our upper eyelid (see figure 2). These tears are spread across the surface of our eye with each blink, and then drained through ducts located in the inner corners of our eyelids and into the back of our nose (fun fact: this is why our nose gets runny when we cry!) (see figure 2). The water layer functions to lubricate the eye, reduce risk of eye infection, wash away foreign matter in the eye, and help with clarity of vision by keeping the ocular surface smooth and clear.
The outermost layer is the oil layer. This layer is produced from glands in our upper and lower eyelids and serves to seal the tear film, preventing evaporation of our tears.
Altogether, the tear film helps to maintain the health of our eye while assisting with clear, comfortable vision.