Diffuse clouding of the cornea ('corneal oedema', 'blue eye') of sudden onset and usually transient duration and with accompanying anterior uveitis, may be attributable to natural infection with canine adenovirus type 1 (CA-1) or to vaccination with live modified virus. It is now recognised that kerato-uveitis is a manifestation of type III hypersensitivity in which immune complex formation resulting from the release of virus, especially from infected corneal endothelial cells, brings about corneal endothelial damage and hence corneal oedema. A proportion of cases fail to resolve. At least one breed, the Afghan hound, appears to be particularly susceptible. The incidence of ocular lesions resulting from vaccination has stimulated the development of new vaccines incorporating canine adenovirus type 2 (CAV-2), a serotype which has been shown not be cause endogenous ocular disease.