Adults with vision greater than or equal to 1.0 or greater than or equal to 5.0 in one eye are considered to have normal vision. If the vision is not normal, there may be an eye disease that causes vision loss, or there is a systemic disease, or it may be caused by a cranio-cerebral lesion, so eye and systemic related examinations are needed to clarify the cause of vision loss. The causes of vision loss are different for different age groups, for example, myopia, hyperopia and astigmatism for teenagers, cataract, glaucoma, fundus hemorrhage and retinopathy for middle-aged and elderly people.