BLINDNESS

is caused by injury or disease of the eye, or of the optic nerve which puts the eye in communication with the brain, or of that part of the brain concerned in vision. The chief cause amongst diseases of the eye is cataract, whilst the chief amongst disorder or disease of the brain are migraine, bysteria and cerebral tumour. Of these blindne due to migraine or hysteria are only temporary. Colour-blindne is duc to a defect of the nervous structures of the eye, which causes inability to distinguish certain colours. The commonest form is that in which red and green are confused. {Refor to Cataract.) [s. 337]