OPHTHALMOLOGY
When dogs get conjunctivitis , it ’ s most frequently allergic and rarely infectious .
It may be a response to an irritant in the environment , such as pollen or dust . I see allergic conjunctivitis more often in allergy-prone breeds such as cocker spaniels and bulldogs . In these cases the pet may also show other signs of allergy , including paw licking , excessive scratching and red areas on the skin .
Dogs with simple allergic conjunctivitis can be treated with a topical antihistamine . In cases that don ’ t respond , I question my diagnosis of simple allergic conjunctivitis and explore other causes further . If I don ’ t find any , I may use a stronger topical anti-inflammatory , specifically a corticosteroid . Topical corticosteroids have been a mainstay of the treatment of conjunctivitis in dogs for decades .
Dogs can also have conjunctivitis due to concurrent corneal or intraocular disease . In these cases the conjunctivitis is not the primary abnormality but a sign of something else wrong with the eye .
Possibilities include :
• An inappropriate tear film in dogs with dry eye
• Corneal ulceration in dogs that have sustained trauma to the cornea
• Glaucoma
• Intraocular inflammation .
If we treat these animals for simple conjunctivitis , we may delay treatment for the true underlying cause , which can result in permanent eye damage or vision loss .
The Feline Window
Figure 4 shows a 2-year-old cat with significant conjunctivitis secondary to Chlamydophila infection . Both eyes were affected . Treatment involved the use of an oral antibiotic , which cleared the infection and led to resolution of the conjunctivitis .
Cats are quite different from dogs when it comes to conjunctivitis . They rarely get allergic conjunctivitis . Instead , most cases are infectious . The most common infectious agent is feline herpesvirus , but several bacteria can also be involved , including Chlamydophila , Bartonella and Mycoplasma species . Sometimes the clinical exam and history can differentiate among these causes , others , we have to perform additional laboratory testing to definitively diagnose the cause .
Herpesvirus is ubiquitous , with nearly all cats exposed at some point in life . Many cases of herpesviral conjunctivitis in cats are self-limiting , lasting just a few days . For cases that persist , antiviral therapy is the treatment of choice . I used to recommend topical treatment exclusively . But while some cats tolerate this
Figure 4 : A 2-year-old cat with significant conjunctivitis secondary to Chlamydophila infection . Both eyes were affected . Treatment involved the use of an oral antibiotic , which cleared the infection and led to resolution of the conjunctivitis .
therapy well , it can be stressful for other patients — as well as their owners — especially when prescribed three to four times daily . Recently a new oral antiviral , famciclovir , has become available that is very effective at controlling herpesvirus and reducing associated clinical signs .
While the infectious organisms that cause conjunctivitis in cats can be transmitted from cat to cat , the development of clinical disease depends on a cat ’ s immune system , the underlying cause and the cat ’ s previous exposure to that pathogen . Fortunately , I don ’ t often see an outbreak in groups of cats in multipet households — it ’ s usually just one animal affected . However , in areas with high cat populations , such as shelters , it ’ s common for numerous cats to be affected , especially those that are young or have a concurrent systemic disease that stresses the immune system .
Figure 5 shows a 4-year-old cat that presented for squinting , discharge and redness of the right eye . Examination revealed significant inflammation of the conjunctiva . In addition , fluorescein stain applied to the cornea revealed a dendritic ( linear , branching ) superficial corneal ulcer . These signs are pathognomonic for feline herpesvirus . Topical and oral antiviral therapy led to resolution of the clinical signs . Because cats don ’ t tend to get allergic conjunctivitis , corticosteroid medications are almost always contraindicated . In fact , using corticosteroids for common conjunctivitis in a cat may make the patient much worse . Instead I usually prescribe antivirals , either topically or systemically , and may recommend topical and oral antibiotics as well depending on the underlying cause . vet360
Issue 06 | DECEMBER 2017 | 10