Feline Herpesvirus type 1 (FHV - 1) is believed to be the most common cause of ocular disease in cats. (eyespecialistsforanimals.com)
Because of the difficulty in establishing a definitive diagnosis of FHV - 1 as the cause of ocular disease in most cats, presumption of cause is usually based upon clinical signs (particularly recurrent episodes of keratoconjunctivitis and / or the presence of respiratory signs) and response to treatment. (eyespecialistsforanimals.com)
In addition, I am actively involved in numerous investigations utilizing in vivo corneal confocal microscopy for the diagnosis and characterization of ocular surface diseases in a variety of animal species. (www2.vet.cornell.edu)