The cornea is the part of the eye dry eye patients will primarily be concerned with. Specifically, the epithelium (outer layer of the cornea) is the part which is affected by an inadequate or unstable tear film.
The cornea provides about two thirds of the total focusing power of the eye. Any serious disruption to the health of the surface of the cornea, therefore, can affect one's vision noticeably, and uncontrolled chronic conditions can if serious enough cause scarring which could permanently compromise vision. Maximising the health of the ocular surface therefore is very important to the maintenance of one's vision.