Optimising tear replacement rheology in canine keratoconjunctivitis sicca.

Dry eye is a substantial problem in a large number of human and canine patients. Numerous laboratory models for tear deficiency exist using genetically predisposed rodent models, animals treated with topical anti-muscarinics, or those kept in environments with increased air flow to produce the ocular surface changes seen in human patients. Canine keratoconjunctivitis sicca, seen in many thousands of dogs kept as companion animals, can provide a valuable spontaneous model for testing tear replacement medications that might better model disease in human patients, existing as it does in an outbred population that live in the same environments as their owners. Here the development of a crosslinked hyaluronic acid topical drop is described together with the results of trials on dogs with spontaneous keratoconjunctivitis sicca. Although hyaluronic acid in its native form in tear replacement drops shows a Newtonian rheology, the crosslinked product described here behaves in a non-Newtonian manner, with the same shear thinning shown by the tear film itself. The crosslinked product thus shows itself as a potentially valuable tear replacement medication for the human dry eye population as well as for dogs with the same condition.