One of the main differences between human and sheep eyes is the ability to focus. Sheep lack a fovea in the retina and are unable to focus as clearly as humans do.
The location of the eyes is also different in humans and sheep. Sheep have eyes that are located more toward each side of their head. This gives the sheep an advantage in terms of peripheral vision. Humans have eyes that are binocular, meaning they're in the front of the skull. This location gives humans an increased depth-perception, but decreases the peripheral field of vision. The placement of a sheep's eyes is also higher up and farther back on the skull, which gives sheep the benefit of greater visual range when lowering its head to graze. Human eyes are designed for focus and hunting, while sheep are equipped with vision to help them avoid predators.
Other differences are found in tissue structure. Sheep have a unique layer of tissue known as the tapectum lucidum. This keeps excess light out of the eye by reflecting it away, a benefit for an animal unable to focus as clearly as humans. Humans have a greater range of eye movement provided by six muscles. Sheep have only four. This gives humans an increased ability to utilize their eyes to focus on specific objects.