This is a 2002 veterinarian-oriented site, with stuff about diopters and all that I only vaguely recall anything about; the quotes below are from below the advert about a vet tonometer (to measure pressure in the eye - like checking for glaucoma in humans). Visual fields and blind spots, as well as binocular vision, are quantified. Effect of vertical (as in cats) vs. horizontal (as in horses & goats) pupils mentioned, as is tendency of near- or far-sightedness, and how Siamese cross-eyed-ness might be compensatory for other defects in that breed's visual system.
http://www.animaleyecare.com/for.htm 1. Small monocular visual fields of peripheral vision in dogs and cats (~80�) as compared to the horse (146�). The horse has a total field of vision of near 350�. [So my guess of ~300o was too small!] 2. Large frontal binocular visual field of 85� in dogs and cats, and 65� in horses. The posterior blind spot of dogs and cats is ~80-120� while the blind spot of the horse is ~3�... ...All evidence suggests that the dog is dichromat with vision similar to a human who is red-green color blind.. Cats are weak trichromats...They live in a world of fuzzy pastels....If normal human vision is 20/20, then that of the dog is 20/50, the horse 20/33, and that of the cat is 20/100....the dog should have good motion detection and high temporal contrast capabilities. Acuity is less than humans and horses, but greater than the cat....The lens of dogs and cats has weak accommodative ability and therefore they have limited near focus capability.... 13. Equine Vision: Very good motion detection but poor acuity in the peripheral retina. The nasal extension of the retina, the laterality of the eyes, and the horizontal pupil facilitate tremendous peripheral vision for the horse standing with its head up. The horse utilizes both eyes until an object approaches within 3-4 feet when it is forced to turn its head continue to observe with one eye. Horses need accommodate < 2D to maintain a focused image on the retina... [D = diopter, which I think is a measure of accomodation, which involves changing the shape of the lens and focal length to retina in order to focus on objects be they near or far; in humans this ability decreases as one ages, so that by the mid-forties, many people begin to have to hold objects further away in order to focus correctly. Technically this is called presbyopia; practically it means 'the age of reading glasses!' ;) ] There are interesting links at the bottom dealing with species- & breed-specific eye problems; frex 'pop-eyed' dogs (such as pugs) are very susceptible to having an eye literally pop out of its socket from trauma such as a hard fall or being struck on the head [this from a dog-showing friend, not sure if this is mentioned in any of the links. This is of course necessitates an emergency visit to an vet specialized in ophthalmology, if there is to be any hope of saving the eye.]. This site is more for the pet owner, and has some very nice color graphics (including the spectrum of visible light with wavelengths identified), with a neat one of how a horse eye is asymmetric, allowing distant objects to be focused on one part of the retina, while nearby ones are focused on a different part. [I wonder if this might be the source of the "magnifying lens" comment Robert's friend made? Note that there is some controversy with this "ramped retina" theory, as discussed in the next site about equine vision.] I would trust the vet-oriented site for accurate field-of-vision figures - note that the "typical herbivore" clearly is not a horse, as a horse's eyes are more set on the side than this diagram. For the equine enthusiast (and these figures agree well with the above vet site): http://www.completerider.com/horsemanfeb2003.html Debbi No Wonder Cats Act Like The World Is Their Oyster...They See With Pastel-Tinted Glasses! Maru __________________________________ Do you Yahoo!? Yahoo! Mail - 50x more storage than other providers! http://promotions.yahoo.com/new_mail _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
