Cavalier King Charles Spaniel Ruby puppies
UK researchers opine that corneal ulcers in cavaliers may be due to the breed standard favoring large eyes. In a by a team of researchers (Rowena M. A. Packer, Anke Hendricks, Charlotte C. Burn) from the UK's Royal Veterinary College, they measured eleven conformational features demonstrated to be breed-defining (muzzle length, cranial length, head width, eye width, neck length, neck girth, chest girth, chest width, body length, height at the withers and height at the base of tail) of 700 dogs, 31 dogs of which were affected with corneal ulcers, including three cavalier King Charles spaniels. They specifically criticized the CKCS breed standard for considering "large" eyes as a desirable feature, and also noted that the cavalier's predisposition to dry eye can lead to corneal ulcers. They stated:"Several brachycephalic breeds have been identified as being predisposed to dry eye, including the Bulldog, Lhasa Apso, Shih Tzu, Pug, Pekingese, Boston Terrier and Cavalier King Charles Spaniel. Even moderately lowered tear production associated with dry eye may produce clinical signs in brachycephalic dogs, as a larger portion of the globe is exposed. In a UK based study, a higher proportion of brachycephalic dogs that were affected by dry eye were also affected by ulcers, than were non-brachycephalic dogs with dry eye, e.g. 36% of Shih Tzus and 30% of Cavalier King Charles Spaniels versus 17% of dogs in the overall study population."
They devised morphometric predictors for corneal ulcers, including the "craniofacial ratio" (CFR), "the muzzle length divided by the cranial length, which quantifies the degree of brachycephaly", to differentiate skull morphologies. [Photos at right: "This Cavalier King Charles Spaniel has a craniofacial ratio of 0.27 (muzzle length 28mm / cranial length 102mm), and a relative palpebral fissure width value of 33.3% ((palpebral fissure width 34mm / cranial length 102mm) *100".]