Tears keep the ocular surface lubricated. They do so with three key ingredients: oil, water, and mucus. The oil layer is the outermost layer of the tear film. This layer keeps tears from evaporating too quickly. The oil in tears is produced by the meibomian glands. Water makes up the middle layer of the tear film. It is the most substantial layer, responsible for cleansing the eye and washing away particles that do not belong. The water in tears comes from the lacrimal glands that are located in the eyelid. The innermost layer of the tear film is made of mucus, which helps water and oil stick to the ocular surface. This part of the tear film is made in the conjunctiva.
The layers of tears are produced by the appropriate glands in vital proportions to achieve adequate moisture. When we blink, the tear film is spread across the eye and each gland involved in tear production is stimulated.