Loss of half the usual area of vision. The affected person may see everything clearly to the left or to the right, the field of vision stopping abruptly at the mid line; they may see things only when straight ahead of them; or they may see objects far out on both sides, although there is a wide area straight in front for which they are quite blind. The position of the blind area is important in localising the position in the brain of the disease responsible for the condition.