Dry eye (DE) or keratoconjunctivitis sicca (KCS) is a painful disease in dogs and humans where insufficient tear production can cause pain, corneal ulceration and blindness. KCS in dogs is commonly immune-mediated, where the dog’s immune system attacks the tear glands. However, the mechanism by which this occurs is not well understood. In humans, long term use of ocular medications containing the preservative Benzalkonium Chloride (BAC) may trigger DE. While no studies have been conducted to explore whether a correlation between BAC and DE exists in dogs, long term ocular treatment for dogs with BAC-containing drugs may cause ocular surface inflammation resembling KCS. The treatments available for KCS (immunomodulating and tear replacement drugs, and surgery) are often not completely effective. The investigators will look for and measure proteins in the tears of dogs affected by presumptive immune-mediated KCS, and the tears of dogs on long term ocular medications containing BAC. This work will help improve understanding of the pathogenesis of KCS and allow development of a non-invasive diagnostic test, which can also be used to monitor progression of the disease and response to treatment.