Feline ophthalmology Part 2: clinical presentation and aetiology of common ocular conditions

conjunctivitis This condition is manifested as congestion or oedema (chemosis) of the conjunctiva. It may be accompanied by an ocular discharge. Secondary conjunctivitis may occur with other ocular conditions, such as uveitis and glaucoma. In cats, conjunctivitis is frequently caused by an infectious agent, and multiple agents may be involved. Resident ocular bacterial flora is present; therefore, a bacteriology swab does not always produce a result with a causative organism. Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus spp and Corynebacterium spp are commonly isolated commensal organisms from the normal feline conjunctiva and eyelids (Gerding and Kakoma, 1990). Many upper respiratory tract pathogens cause conjunctivitis. Feline herpesvirus-1 (FHV-1) can infect domestic and wild cats (Maggs et al.,1999a,b). The virus is considered to be responsible for nearly half of all upper respiratory tract infections in these species. Replication occurs in the epithelium of the conjunctiva, the nasal mucosa, tonsils and turbinates. Replication is more limited in the corneal epithelium and produces characteristic dendritic ulcers, which are almost pathognomonic for FHV-1 infection. These are small branching superficial ulcers, most easily seen with fluorescein or rose bengal stains. Ocular signs (Figure 1) include bilateral conjunctival hyperaemia and ulceration and superficial corneal neovascularisation. Other signs include fever, malaise, anorexia, rhinitis, sneezing, ptyalism and keratoconjunctivitis. Eighty per cent of recovered cats remain latently infected, and viral reactivation can cause recrudescent infections in 45% of these animals (Gaskell and Povey, 1977). Stromal involvement may occur as an immune response to the viral antigen. Upper respiratory signs are usually minimal or absent with recrudescent disease. FHV-1 disease syndromes include keratoconjunctivitis sicca (KCS), corneal sequestration, eosinophilic keratitis, ophthalmia neonatorum, symblepharon (Figure 2), uveitis and periocular dermatitis. Symblepharon is an acquired conjunctival adhesion, which is rare in species other than cats. Primary disease caused by FHV-1 is common, but often self-limiting. Recrudescent disease is less common, but very frustrating.