New ocular pharmacologic agents or new uses for familiar products are discovered every year. This article discusses a select
few of these newer therapies in veterinary ophthalmology. For convenience, the medications have been grouped by drug category
or ocular disease process.
TEAR SUBSTITUTES (LACRIMOMIMETICS)
While stimulating tear production is the most effective method of treating keratoconjunctivitis sicca (KCS), often an agent
is needed to improve lubrication and provide comfort until sufficient tear production is attained. If you have only used petroleum-based
artificial tear ointments for your patients with KCS or other tear-film deficiencies, try some of the newer lacrimomimetic
tear substitutes. Lacrimomimetic agents are preferred; they have an aqueous base more similar to natural tears than do petroleum-based
agents, allowing for improved corneal health and animal comfort. However, owners must be able to apply these agents multiple
times a day. Also note that if a lacrimomimetic agent is applied more than six times daily, use preservative-free preparations
to avoid corneal epithelial damage. If owners cannot apply medications frequently, the petroleum-based artificial tear ointments
remain the best choice, as they coat the cornea and slow tear evaporation.
Many tear substitutes are available over the counter. These products are typically polyvinyl alcohol, cellulose, dextran,
or viscoelastic-substance (sodium hyaluronate or chondroitin sulfate) based. Because of the large number of choices, try to
recommend specific products to owners. The following three products work well for dogs and cats.
GenTeal (Novartis Ophthalmics) is a cost-effective over-the-counter preparation that contains a small amount of hydrogen
peroxide as a preservative. When placed on the eye, the hydrogen peroxide is converted into oxygen and water. GenTeal is sold
in multidose vials and is available in gel and liquid formulations. The severe and PF formulations of GenTeal are preferred
since they contain the highest concentration of hydroxypropyl methylcellulose (0.3%) and, thus, will remain on the cornea
Lubrithal (Aventix Animal Health), a veterinary product, is a carbomer gel with sodium hydroxide and benzalkonium chloride
as preservatives. The drop is well-tolerated and provides excellent corneal coverage. Lubrithal also comes in a multidose
container and is slightly more viscous than GenTeal.
I-Drop Vet and I-Drop Vet Plus (I-MED Pharma) differ from GenTeal and Lubrithal because they contain sodium hyaluronate (hyaluronic
acid), which has excellent mucinomimetic properties and is an excellent ocular protectant. I-Drop Vet and I-Drop Vet Plus
also contain glycerin to help retain the lubricant and better disperse it after each blink, thus they require less frequent
application—twice-daily application may be sufficient.
TEAR STIMULANTS (LACRIMOSTIMULANTS)
Many practitioners are familiar with using cyclosporine (Optimmune—Schering-Plough Animal Health) in dogs to stimulate tear
production. The benefit of cyclosporine in patients with kcs stems from its selective t-helper lymphocyte suppression1 and direct lacrimostimulatory properties.2 Because of its selective immunosuppressive properties, cyclosporine is often also beneficial in treating pannus and other
immune-mediated corneal disorders.1
If cyclosporine therapy fails in a patient with KCS or the patient is sensitive to cyclosporine or the lipid bases in which
it is formulated by a compounding pharmacy, consider using tacrolimus.
Tacrolimus is available through compounding pharmacies and should be compounded in a 0.02% ointment or solution. Tacrolimus
is similar to cyclosporine in structure and mechanism of action, but few efficacy and safety studies have been performed.
In one study, 0.02% tacrolimus administered topically twice daily was effective in increasing tear production in dogs that
had never received tear stimulation therapy and in some patients that had responded insufficiently to cyclosporine.3 Since only limited information concerning the efficacy and safety of tacrolimus is available, its use should be reserved
for dogs with KCS that are sensitive to or insufficiently respond to cyclosporine.