New Bolton's "First Tuesday" lecture series started off its season with a fascinating talk on equine vision by Dr. Catherine Nunnery, who is a large-animal ophthalmologist at the veterinary school. She discussed the physiology of the horse's eye and how it affects how the horse sees: for instance, the tapetum lucidum layer of the eye acts as a sort of mirror, allowing the horse to see better at night than humans do, and the oval pupil broadens the horse's field of view, allowing it to see prey from almost every angle. However, at the very edges of the field of view, the horse's vision is fuzzy and it recognizes only light and motion -- which is why a horse may spook at any movement, no matter how innocuous (e.g., a flapping plastic trash bag).
Dr. Nunnery used a panoramic photo of the entrance off Route 926 to New Bolton to illustrate the wide field of view. But horses have a narrow blind spot right in front of their heads, like a unicorn horn. She showed an amusing photo of a young rider trying to bond with her horse by getting up close -- but unfortunately, her face was precisely in the horse's blind spot.
Dr. Nunnery said most horses have perfect to near-perfect vision, so the answer to everyone's question -- "Does my horse need glasses?" -- is almost always no. She showed a slide of a standard human eye chart and said she wished testing equine vision were that easy. She said they often use what is called the "Menace test," in which the vet moves a hand toward the horse's head and assesses the animal's reaction.
The talk was followed by numerous questions from the audience about UV fly masks, cataracts, what difference eye colors make, treating corneal ulcers, and much more. I love how articulate and enthusiastic the presenters are, and they make wonderful use of graphics.
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