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We apologize for canceling the ophthalmology seminar that was scheduled for April 13th but we’d like to pass on a little bit about the equine “window to the soul”.  The anatomical structure and function of the equine eye is a fascinating subject.

Structure & function;  Horses have the largest eyes of any land mammal except the moose.  Like many prey animals the location of the eyes significantly impacts their function. The wide eye placement gives them a nearly 360 degree field of view but limits binocular vision and therefore visual acuity and depth perception.  The horse mostly sees two separate fields of view sending totally different images to the brain at the same time.  Sounds confusing doesn’t it?  Perhaps this is why horses instinctively back away from strange objects in order to see and evaluate them better.  The horse doesn’t focus its eyes as we do either.  Instead, they lift, lower, or wave their head in order to bring objects into focus. This explains why a horse may raise and lower its head while staring at an object. It is adjusting the focal length between its eyes and the object, as well as adjusting the angle of view, until the image falls into focus on the retina.  There is a very limited area within the horse’s field of view where it can benefit from binocular vision so it is really rather incredible that they trust us enough to do many of the things we ask of them.  Jumping immediately comes to mind when you realize that they rarely ever get a good look at the obstacles they are leaping over.  The bottom line here is that horses do not see the same as we do because of profound differences in structure and function of their eyes. It seems a bit foolish to expect them to respond to objects in their environment the same as we do.  The “spooky” horse is very likely the one who would survive longest out in the wild, an important consideration whenever we handle them!

The eye in general and horse eyes in particular are both tough and incredibly delicate at the same time.  Eye injury and disease are often true emergency situations where rapid attention is vital to maintain vision.  We’ve covered some aspects of one rather common eye condition called “recurrent uveitis” or “moon blindness” here.  A significant correlation has recently been identified between infection with leptospira organisms and the incidence of uveitis and a new vaccine is now available.  We are hopeful that this vaccine will prove helpful for minimizing this debilitating and all too common eye problem in our horses.  If you have questions about it’s applicability for your animals please discuss it with your RBE veterinarian.

Here's a great link on the topic of equine eyes that might interest you;
http://www.thehorse.com/articles/10774/the-equine-eye