Professor David Maggs reveals how the seven corneal colours in both cats and dogs can help vets reach a diagnosis.
Dr David Maggs, a professor at the University of California Davis, has spent years travelling the world lecturing veterinarians on various topics. But when it comes to identifying and treating ophthalmic problems in cats and dogs, he says the subject seems to be a somewhat forgotten specialty in veterinary medicine. It’s a gap in the field he’s proud to be addressing – and diagnosis, he says, begins with identifying the seven colours of corneal pathology.
“The seven corneal colours is a concept that I was taught during my ophthalmology residency. We start by breaking down the cornea into its seven essential colours. These include grey when we see fibrosis; blue when we see oedema; red which is, of course, blood vessels; black, which is melanin or pigment; a greasy tan colour, which is fibrin and white blood cells; more pure white blood cells, which are greenish yellow like pus anywhere else in the body; and white or sparkly in the classic colour of mineral or lipid,” says David.
“We’re really lucky because when an animal is in good health, the cornea is clear. But in disease it becomes less transparent and those opacities show up as colour, enabling us to make tremendous corneal and ocular diagnoses.”
There’s a broad variety of common ophthalmic issues in dogs and cats, some genetic and others a result of infection. While there are a number of infectious diseases in both species, cats lead the way with feline herpes and uveitis. When it comes to dogs, cataracts and glaucoma are often the result of a genetic-related issue.
“Glaucoma is the most common and the most serious eye disease we see in dogs. And I say it’s serious because it’s both painful and blinding,” explains David. “As an inherited disease we see it passed from generation to generation, leaving us with a very limited chance to prevent it from progressing to blindness.
“Cats, on the other hand, have a higher propensity for getting infectious disease, so that would be at the top of the list for them. Herpetic disease, serious really through its commonality, can also lead to blindness.”
Injury is another common cause to consider, as it’s something animals will often encounter all too easily and can ultimately lead to a variety of traumatic diseases and corneal ulcers.
One step closer
While there’s no treatment aligned with the seven corneal colours specifically, David explains that each colour enables veterinarians to get one step closer to a diagnosis.
“For instance, there’s not so much a treatment for corneal oedema as there is recognition of corneal oedema and recognition that that oedema represents uveitis, for example keratitis. Further testing and treatment can continue from there,” says David.
Carrying out an exacting and thorough eye exam is David’s final piece of advice for vets.
“Really the words, ‘More is missed through not seeing than not knowing’ are absolutely true for veterinary ophthalmology. If you can do a good eye exam with the goal of identifying the tissue involved and then determine what the pathology in that tissue is, then you will be a fantastic ophthalmologist.”
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