The conjunctiva is the membrane that lines the eyelids and covers the white of the eye, and the cornea is the clear layer in front of the iris and pupil. Keratoconjunctivitis sicca is dryness of the conjunctiva and cornea. There are several causes of keratoconjunctivitis sicca. Which of the following is NOT one of the main causes of keratoconjunctivitis sicca?