Blinders, also known as blinkers or winkers, are a piece of horse tack that restrict the horse's vision to the rear and, in some cases, to the side. They usually are made of leather or plastic cups that are placed on either side of the eyes, either attached to a bridle or to an independent hood. Many racehorse trainers believe this keeps the horse focused on what is in front of him, encouraging him to pay attention to the race rather than other distractions, such as crowds. Additionally, blinkers (then usually known as winkers) are commonly seen on driving horses, to keep them from being distracted or spooked, especially on crowded city streets. A “set of winkers” can refer to the whole bridle, particularly the heavy bridle used on draft horses.
In racing, blinkers are usually seen attached to a synthetic hood placed under the bridle. In driving, they are attached to the bridle's cheekpieces. A variation, called "side winkers" are seen in Australian horse racing. These are fleece rolls that are placed around the bridle cheek straps. They do not restrict the horse's view as much as blinkers do. Also used in Australian racing are "pacifiers," which are a blinker style hood with mesh eye-covers, thought by some to calm horses. They are banned from use on wet days as they may clog up with mud.
A blinder is also a bag or cloth blindfold put over the head of a difficult horse while it is being handled, loaded into starting gates or mounted. The term is also used metaphorically to refer to people with an overly narrow focus or inability to see the larger picture.