Tears wet the front of the eye and the surface under the eyelids. This process repeats every 10–30 seconds. Tears perform several functions. They help to keep the cornea smooth and shiny. They also protect the eye from dryness and irritation and help the cornea function properly. Tears also help to protect the eye from environmental irritants (smoke, dirt, other debris). The tear film has 3 layers – lipid layer, water layer and mucin layer.