Blinders, or blinkers and winkers, as they are otherwise known, are a part of the tack kit used on many horses. Blinders are small squares of firm leather that attach to the bridle at the side of the horse's head. They keep the horse's eye focused on what is ahead, rather than what is at the side or behind.
Blinders in Racing
Carriage racing or harness racing are common equestrian sports where horses are pulling carts, carriages or wagons while racing. The horse's legs are hampered by harnesses, which prevent them from galloping. Instead, the race is won by the horse that can trot the fastest. For many horses, blinders are commonly used in order to prevent the horse from becoming distracted. Horses have their eyes at the sides of their heads, which indicates that they are the hunted -- similar to rabbits, for example -- as opposed to the hunters such as cats. Horses, therefore, have peripheral vision, which means they can end up running off course unless they are made to remain focused.
Farming horses can also be predisposed to distractions and if they are pulling a plow or a wagon they might need blinders to stop them from losing concentration on the direction they are supposed to be headed. The blinders cover the rear vision of the horse, forcing it to look only in a forward direction and keeping it on track. Shire horses are usually given blinders as a matter of practice. Blinders have become part of the "uniform" and are widely recognized as intrinsic to the shire horse tack when they pull the barrel wagons. Blinders are also useful to reduce the chances of the horse being spooked and making a run for it while still attached to the wagon.
Horses without Wagons
Race horses are often given blinders for the purpose of keeping them focused when racing round a racecourse. The jockey has a limited amount of control over the horse. If a horse decides to take a different route, it will simply take the reluctant jockey with it. As this can pose problems, troublesome race horses are fitted with blinders for their own safety and the jockey's safety.
According to the website Grand National, blinders were allegedly invented when a preacher had a wager with one of his friends. The preacher bet that he could make his horse walk up the stairs in his home, which the horse did without any problems. However, when he tried to coax the horse down again, it refused to move. The preacher then decided to cover the horses head and lead him down. This worked and he realized that covering all or part of the horse's vision could encourage it to take chances it would not normally take.