Diagnosis of conjunctivitis

A diagnosis of conjunctivitis will typically be made on the basis of clinical signs of hyperaemia, chemosis, ocular discharge, discomfort / pruritus and follicle formation.

A thorough ocular examination and general clinical examination is essential to try and establish an aetiologic diagnosis and to check that any conjunctival inflammation is not a sign of more serious ocular or systemic disease.

Additional diagnostic tests that may be necessary to establish the cause of the conjunctivitis include:

• Schirmer tear test (to check for keratoconjunctivitis sicca)
• Fluorescein testing (to check for corneal ulceration)
• Conjunctival scrapings for cytology
• Bacterial culture and sensitivity (typically done if a case has not responded to the initial choice of treatment. Use a saline-moistened swab to collect the sample. Swabs should be taken from both eyes)
• Virus isolation / PCR (for feline viral infections e.g. feline herpesvirus (FHV-1) and feline calicivirus (FCV))
• Conjunctival biopsy (useful to establish a diagnosis of immune-mediated conjunctivitis)

Samples for cytology, culture and sensitivity, and virus isolation / PCR should be taken before the application of topical agents such as fluorescein and local anaesthetics. The Schirmer tear test should also be done before the application of any topicals.