When you’re presented with an erythematous conjunctiva, there’s likely one of three things going on, says Amy Hunkeler, DVM, DACVO, MBA, a specialist with Eye Care for Animals and recent CVC speaker: an infectious cause, a noninfectious cause or mechanical irritation. And an angry “conj,” as she calls it (think “kawn” and add a “j”), will generally present the same way—chemosis, mucus discharge, hyperemia, scleral injection, facial pruritus and periorbital alopecia—no matter the cause. So how do you know what’s bringing on the wrath of the conj?
First, a quick review of the anatomy and function of the conjunctival tissues. The conj facilitates ocular movement and protects the eye. It houses goblet cells that produce mucin for tears and provide immune function by attracting immunoglobulins. Palpebral conj is tightly adhered to the upper and lower lid; otherwise conjunctival tissue is loose to allow for swelling and movement. The conj folds over on itself in three areas known as the fornix.
Feeling out the conj
When it comes to diagnostics, after the physical exam, Dr. Hunkeler is a fan of conjunctival cytology, quantitative and qualitative tear tests, fine-needle aspiration or biopsy of discrete masses, and fluorescein stain.
For a conjunctival smear, Dr. Hunkeler recommends using a human vaginal cytobrush or the back of a scalpel blade. Happy, normal conj will have a single layer of monomorphic epithelial cells and some lymphocytes present.
Dr. Hunkeler likes to assess tear production as a trend, since tear values can fluctuate from visit to visit. Watching the trend over time, especially in a symptomatic patient, is important: Production numbers can vary in response to ocular inflammation, systemic disease, stress or topical proparacaine. Plus, the paper strip may absorb tears unevenly (depending on tear composition), and there’s the potential for evaporative loss—not to mention user error.
When it comes to the numbers, more than 15 mm/min on a Schirmer tear test is considered normal in dogs, and 14 to 17 mm/min is the range for cats. But some cats, when stressed, may have results near zero and still be perfectly normal (as in many things, cats are not following the same playbook as dogs). Be sure to test both eyes. And remember that sedation can drop tear production up to 40%, so if you test an anesthetized animal, be sure to note the sedation.
Qualitative tear assessment is a relatively new test to the veterinary industry. Some dogs will exhibit signs of keratoconjunctivitis sicca (KCS) even with normal Schirmer tear test times of 16 to 18 mm/min because their tear quality is inferior, with abnormally low aqueous portions or abnormal lipid or mucin concentrations. Causes can be genetic, anatomic or secondary to inflammation.
In these patients, Dr. Hunkeler recommends measuring tear quality with a tear film breakup test. For this you’ll need a Wood’s lamp or slit lamp and fluorescein stain. Place a drop of stain on the eye, mechanically blink the eye, and watch to see how long it takes for the layer of stain to break down, which looks like coalescing black spots in the fluorescein dye layer. Normal times for a tear film breakup test are 19 seconds in a dog, 16 seconds in a cat.
Dr. Hunkeler is not a fan of culturing the conj because even a healthy conj likes “to grow things,” she says. In her experience, 50% to 90% of canine conj swabs will grow in culture even if they’re clinically normal. Staphylococcus species is more common in dogs, while gram-negative bacteria, anaerobic bacteria and fungus are rare. If you have a robust, mucopurulent discharge and a rankled conj that’s nonresponsive to antibiotics, by all means culture—otherwise skip it, Dr. Hunkeler advises.
Noninfectious causes: It’s not you, it’s me
KCS is the number-one noninfectious conjunctival inflammatory condition. It’s thought to be an immune-mediated condition, and it frustrates general practitioners and specialists alike, Dr. Hunkeler says. The lacrimal gland is responsible for 60% of tear production, and nictitans provide the other 40%. Meibomian glands secrete meibum, and goblet cells within the conj produce mucin; together these substances help prevent evaporation of the tear film.
In early disease, Schirmer tear tests measure 10 to 12 mm/min. Clinical signs result from increased friction, with the patient displaying a “miffed conj” and mucoid discharge, Dr. Hunkeler says. These patients will often have an opportunistic bacterial overgrowth, and if the condition is left untreated, corneal inflammation and discomfort will result.
In chronic KCS cases, tear evaporation results in a hyperosmolar and hypertonic tear film, further angering the conj and the cornea, Dr. Hunkeler says. Chronic inflammation leads to thick mucoid discharge, corneal neovascularization, corneal thickening, corneal melanosis, pain and vision loss.
Medical treatment consists of lubrication and tear stimulants. Cyclosporine and tacrolimus work equally well in dogs that still have some tear-producing function, Dr. Hunkeler says; however, client education is paramount, she cautions. These drugs have a long onset of action, so it can take several months to see an increase in tear production, and the patient must receive treatment continually. Even taking a weekend off from medication can cause a setback.
If patients are not controlled on 0.2% cyclosporine, Dr. Hunkeler increases the concentration. She’s been able to control refractory KCS patients on 1% cyclosporine oil or aqueous formulation. A new drug, pimecrolimus, may be in clinical trials soon, Dr. Hunkeler says.
Lubrication is equally important in KCS patients. If the client is willing, Dr. Hunkeler recommends topical application of a lubricant four to six times a day. The most important applications are right before the pet is left alone for a length of time (such as the client going to work) and right before bed. Dr. Hunkeler also advises using a lubricant that contains hyaluron, which she says benefits the aqueous component of tears and the goblet cells.
Client compliance and a long-term partnership between client and veterinarian are absolutely required for successful management of KCS, Dr. Hunkeler says. Get inside your client’s head to determine what’s reasonable and most convenient for the client. And keep in mind that nobody wants pets with constantly gooey eyes! While ointments have traditionally been recommended over aqueous preparations, Dr. Hunkeler usually dispenses aqueous solutions because the no-mess factor increases client adherence in the long term.
Microscopic surgery is available for KCS and is fairly successful and beneficial, Dr. Hunkeler says. The procedure involves transposition of the salivary duct opening from the mouth to the conjunctival fornix. Complications include overproduction of tears and mineral deposits.
Other noninfectious causes of an angry conj include atopy, allergic blepharitis, follicular conjunctivitis, lipogranulomatous conjunctivitis, eosinophilic keratoconjunctivitis, nodular granulomatous episcleritis, plasmoma, meibomianitis, staphylococcal blepharitis and pyogranuloma. Successful management will involve treatment of the underlying condition or referral to a specialist as necessary.
Infectious causes: It’s definitely you
Ocular herpes is the leading cause of infectious conjunctivitis in cats, Dr. Hunkeler says. Signs include mucoid discharge, upper respiratory signs, dendrites, symblepharon formation and corneal changes. The condition is common in kittens, and adult recrudescence can occur. Corneal dendrites are diagnostic, but if you don’t have dendrites and the conjunctivitis does not respond to topical antibiotics and grows worse with topical corticosteroids, perform cytology of the conj, Dr. Hunkeler says. With ocular herpes you’ll see a lymphocytic-plasmacytic distribution of cells. (Ocular herpes is rare in dogs, but when it does occur the signs are the same as in cats.)
Ocular herpes is treated topical with antiviral medication and a topical antibiotic if there is a secondary bacterial infection. Dr. Hunkeler recommends idoxuridine 0.1% applied three to four times daily, along with supportive care. Lysine treats can help cats, but if giving the lysine treat stresses the cat out, don’t use them!
Bacterial conjunctivitis is seen in both dogs and cats and is often opportunistic in cats. Oral doxycycline and enrofloxacin can be used, and topical tetracyclines, oxytetracycline, ofloxacin and tobramycin are all effective, Dr. Hunkeler says.
Parasitic conjunctivitis can occur secondary to infestation with Thelazia, Cuterebra or Onchocerca species worms, which can cause granulomas. Treatment includes mechanical removal and systemic spot-on parasiticides. Fungal conjunctivitis is very rare and patients are systemically ill with additional signs. Treatment involves itraconazole and systemic corticosteroids at an anti-inflammatory dosage.
Mechanical irritation: You’re rubbing me the wrong way
Ectopic cilia and chalazion cause waxing and waning conjunctivitis with marked blepharospasm and mucoid discharge. Dr. Hunkeler knows the ectopic cilia can be hard to find—she recommends playing “ring around the ectopic cilia.” In other words, fluorescein stain applied topically to the conj will make a ring around ectopic cilia. Magnification with a head loupe helps visualization. Once the cilia is identified, excision is indicated. Other causes include foreign bodies, dermoids, hemorrhage due to systemic disease or trauma, orbital cellulitis, or prolapsed nictitans glands.