Conjunctivitis and keratitis are common eye problems in all ages of cats. Conjunctivitis refers to the inﬂammation of the pink membranes surrounding the eye, whereas keratitis refers to the inﬂammation of the cornea. Cats may either develop signs of conjunctivitis alone, or symptoms coupled with keratitis, which is then termed keratoconjunctivitis. A number of infectious agents, namely viruses and bacteria, have been identified as potential underlying causes of these two conditions. These infections may be contracted as a kitten from the queen shortly after birth or from other cats, and are usually contagious from cat to cat.
The most common clinical signs of feline conjunctivitis and keratitis include red and swollen conjunctiva with excessive tearing, ocular discharge, and/or squinting. The discharge ranges from clear mucous to green- yellow in color. Some cats also rub at the eyes, which indicates discomfort. Sneezing and nasal discharge may also accompany the ocular signs, especially in younger cats. Recurrent bouts of conjunctivitis and keratitis are common, especially in viral cases such as feline herpes virus. Severe infections can cause complications such as permanent scarring of the cornea and conjunctiva. Some cases may have poor tear drainage resulting in chronic tearing onto the face. In young kittens, the inﬂammatory response may cause adherence of the conjunctiva to the cornea, and the eyelids may scar and fuse partially closed. The most severe cases can lead to rupture of the globe and vision loss, especially if untreated.
Severe keratitis can lead to abnormal blood vessel growth into the cornea. When severe infections occur, such as simultaneous viral and bacterial infections, corneal ulceration (a scratch or abrasion) may lead to perforation of the eye. With long-standing ulcers that are slow to heal, a dark brown to black discolored area of the cornea (corneal sequestrum) can form. When corneal ulceration and/or sequestrum occur, they are usually associated with varying degrees of ocular discomfort or pain.
In addition to history and clinical signs, several diagnostic tests may be required to confirm the cause and magnitude of conjunctivitis and keratitis. When a cause is identified, specific treatment directed at the underlying cause produces a faster healing response. Some or all of the following tests may be necessary.
Microscopic evaluation of the cells collected from the ocular surface can help determine the health of the cornea and conjunctiva. Furthermore, it will help identify whether primary or secondary infections are involved. For suspected viral infections, samples can be sent for virus isolation, ﬂuorescent antibody (FA), and/or polymerase chain reaction (PCR) testing by a diagnostic laboratory. Although these tests are highly specific, they are not 100 percent sensitive; therefore, repeated samples may need to be submitted to the lab to achieve a positive result for a definitive diagnosis.
Bacterial culture is often warranted to confirm suspected infections. In order to determine if the right antibiotic is used for a bacterial infection, the diagnostic laboratory can perform an antibiotic sensitivity test for the offending bacteria.
Ocular disease can be the result of internal or systemic conditions; if the patient’s immune system is suppressed or not fully functional, infections are more likely to occur. Specific tests to check the health status of the patient may include a complete blood count, serum chemistry profile, tests for feline leukemia virus (FeLV), and feline immunodeficiency virus (FIV). Blood testing is also available for feline herpes virus.
Common causes of conjunctivitis include feline herpesvirus (FHV-1), chlamydial, and other bacterial infections; a less common cause is allergies. Depending on the cause, certain antibiotic and antiviral agents may be used for treatment. Bacterial and chlamydial infections usually respond well to topical and oral medications. On the other hand, patients infected with viral agents may not respond as well to these treatments. Antiviral therapy requires frequent applications, sometimes as often as every 2-3 hours, in order to achieve the maximal effect. Antibiotic therapy is usually given at the same time as antiviral therapy in order to treat any secondary bacterial infection that may be present. Similar to human cold sores, viral infections are associated with stress; therefore, maintaining a low-stress environment may help reduce recurrences.
Superficial corneal ulcers can usually be treated similar conjunctival abnormalities; however, a large or deep corneal ulcer and corneal sequestrum may require surgical intervention. One specific treatment is surgical removal of infected or devitalized tissue (keratectomy). The cornea may require additional support, such as conjunctival grafting, following the keratectomy. Grafting also enhances the long-term health of a devitalized cornea by introducing blood vessels into a normally avascular area. With chronically infected eyes that contain excessive scarring, scar tissue may be surgically reduced to improve vision or tear drainage.
In general, response to therapy is good with bacterial and chlamydial conjunctival infections. Unfortunately, viral infections may be slow to heal and often recurrent. Because complications can have devastating consequences, such as pain and blindness, it is important that the treatment schedule is followed closely. Re-examinations to monitor progress and to adjust therapy will be advised when necessary.