According to recent scientific study, it seems as if the choice between a collar and a harness should no longer be arbitrary. Studies have found that the use of collars in dogs with ocular conditions such as glaucoma or weak corneas can create intraocular pressure (IOP), a condition which can lead to severe eye damage and vision loss.
Published in the Journal of the American Animal Hospital Association, the study found that the pressure created by the use of neck collars significantly increases IOP in certain dogs. Some breeds such as American Cocker Spaniel, Basset hound, Boston Terrier, Chow Chow and Miniature Poodle are predisposed towards eye problems such as glaucoma where the pressure in the eye is elevated due to an obstruction that prevents fluids in the eye from flowing out. If not treated immediately, acute glaucoma can and will lead to irreversible blindness.
Dogs predisposed towards eye problems or with mild glaucoma should wear harnesses, not collars, as the application of neck pressure using a leash attached to a harness results in a significantly less increase in IOP than the use of a leash attached to a collar.
However, a study was conducted on healthy breeds of both sexes including the Alaskan malamute, Siberian husky, Staffordshire terrier, American Cocker Spaniel and the Chinook. While the Alaskan malamute and the Siberian husky generated the greatest tension when pulling against their collar, these two breeds experienced the least increase in IOP than did the other three breeds. Perhaps dogs bred to pull objects may be somewhat resistant to increased IOP.
Since we still have a lot to learn about IOP and its long term implications, any pet with weak eyes or that tends to pull while being walked on a leash may be better off with a harness than with a collar.