Blinders and blinkers are used on the racetrack and for carriage horses. I think it's helpful to know what they do as you are trying to understand how horses see. For carriage horses it prevents the horse from thinking the carriage is a predator, because part of the carriage is in their blindspot. Since the carriage is following them and every move they make, like a predator would, some horses instincts may overwhelm them to run from the carriage even though other horses are fine without the blinders. It also can help them to focus on what's in front of them since without the blinders they can see all around. 

At the racetrack the blinkers sometimes help a horse and sometimes hinder a horse. The trainers use them to see if it will help the horse focus and run faster but in some horses it works and others, it makes things worse and gives them more anxiety. 

In riding horses we do not use blinders or blinkers but we can do things that get the horses attention focused. The thing is, just like the blinkers, some horses are calmer when they look at things and some horses are not. The trick is, you have to figure that out and know if your horse is getting more amped up looking at something, then you need to do something with him to get his attention back. If your horse is calmly looking and staying relaxed then it is most likely fine to let him look. Every horse is different just like people are different but the good riders will figure out what their horse needs and help them to stay calm and relaxed when they are worried.

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