In this VETgirl online veterinary continuing education blog, Dr. Shelby Reinstein, DVM, DACVO reviews keratoconjunctivitis sicca (KCS or “dry eye”) in dogs. Last week, we talked about the many forms of dry eye or KCS in dogs. In this week’s VETgirl blog, we review how do we treat KCS in dogs!
The majority of dogs with KCS are managed medically with a combination of tear stimulants, tear substitutes, antibiotics, and anti-inflammatories. Treatment regimens require adjustments based upon serial eye exams and STT measurements. Surgical therapy for KCS is reserved for dogs that do not respond to aggressive medical therapy and are persistently painful.
There are two main categories of tear stimulants: cholinergic agents stimulate lacrimal secretion via parasympathetic fibers, and immunomodulators increase tear production by controlling glandular inflammation and dysfunction.
Cholinergic agents are only used in rare cases of KCS when a neurologic component is suspected. Pilocarpine is administered topically as a 0.125% or 0.25% drop, or orally on the food using the commercially available 1% or 2% ophthalmic solution. Topical administration is often quite irritating, resulting in squinting, conjunctival hyperemia, and a miotic pupil. Oral administration can induce systemic side effects including salivation, vomiting, diarrhea, and cardiac arrhythmias and the margin of safety is exceedingly narrow. The dose should be adjusted slowly and owners should be counseled strongly regarding monitoring.
Immunomodulating agents such as Cyclosporine (CsA) and Tacrolimus are the most commonly utilized medications for the treatment of KCS. These drugs exert their action by inhibiting T-cell activation, which results in a decreased lymphocyte function, reduced glandular inflammation, and an improved secretory potential. Both CsA and Tacrolimus have been shown to increased tear production significantly over time. CsA is available commercially in a 0.02% ointment (Optimmune®, Merck & Co.) or may be compounded into 1%-2% oil-based solutions. The oil vehicle allows for an increased contact time with the ocular surface and improved bioavailability of the drug. These medications are used every 8-12 hours and 30-45 days are required for full response. Dogs which respond well to the initial therapy and achieve STT values > 20 mm/min may be reduced to once or twice daily for long term maintenance. Dogs with severe KCS (STT < 5 mm/min) have a 50-80% chance of responding to CsA. Clinically, dogs should have reduced squinting, a resolution of the redness and ocular discharge, and an improvement in the corneal vascularization and / or pigmentation.
A large number of commercially available products exist that provide replacement therapy for tear deficiencies and the choice is often based upon clinician preference, availability, and cost, as well as the specific need of the patient. These medications play a crucial role in the management of KCS and should be used in combination with tear stimulant therapy. Ointments, gels, and viscous drops are available, and some are preservative-free. Frequency of use is dictated with the severity of KCS, however products containing preservatives should be limited to 6 times daily to avoid epithelial toxicity to the cornea.
Secondary bacterial conjunctivitis is common in dogs with KCS due to reduced debris removal, accumulation of debris, and a lack of the natural antimicrobial tear properties (lysozyme, IgA). Broad-spectrum topical antibiotics should be administered in the early stages of treatment, usually at a frequency of 3-4 times daily. As the tear levels improve and ocular surface inflammation subsides, these antibiotics can be reduced and eventually stopped. Bacterial culture and sensitivity testing is reserved for chronic, non-responsive mucopurulent discharge despite an improvement in tear levels.
Topical anti-inflammatories or anti-inflammatory and antibiotic combinations are useful in reducing ocular surface inflammation, improving comfort, and diminishing corneal opacities and vascularization. Due to the propensity for corneal ulceration, caution should be used when prescribing topical steroid medications to patients with KCS. Fluorescein staining should be performed, and owners should be counseled on the clinical signs and appearance of ulcerative disease.
Surgery for qualitative tear deficiencies is reserved for patients who have failed medical tear stimulant therapy and whose comfort level cannot be maintained with tear replacement therapy. A parotid duct transposition (PDT) is a surgical procedure in which the flow of saliva from the parotid duct is re-routed into the conjunctival fornix. Tear and saliva are physiologically similar in their pH and osmolarity, allowing salivary secretions to be a suitable substitute for tears. The mineral content of saliva is greater than tears however, thus post-operative complications with mineral deposition in the cornea and on the eyelids is fairly common. Other complications include excessive salivary flow with resultant moist dermatitis, inadequate salivary flow due to duct occlusion or fibrosis of the conjunctival opening, and corneal ulceration.
Distributional tear deficiencies resulting from lagophthalmos or facial nerve dysfunction may benefit from temporary or permanent tarsorrhaphies. Brachycephalic patients with concurrent KCS also benefit from palpebral fissure reduction, which improves to corneal coverage and conserves the existing tear film.
When in doubt, appropriately treatment of KCS in dogs is warranted to best relieve patient discomfort and to retain vision!