the White of Their Eyes
Horses can't speak to humans so we must rely on their body language to determine if they are happy, sad, scared or in pain.
Horses can show eye white for a variety of different reasons. If the horse's eye is normally solid colored, white showing can be a sign of fear.
The Horse Is Afraid
If your horse normally has some white showing when he is relaxed, you might have to be observant to see the white area of his eye increase when he is afraid.
The Horse Is Excited
When horses are excited they can also show the whites of their eyes. You would notice this most frequently when horses play together.
The Horse Has Blue Eyes
Horses with blue eyes sometimes look like there is a lot of white. This is especially true if they have light blue eyes.