BLINDNESS, a general term to denote partial or complete loss of vision. It is never a disease of itself, but results from a number of extremely diverse diseases, either of the eye itself, or of the nervous pathways which convey light stimuli. It may be a congenital condition also, and here the defect may be due to a great variety of causes. It is comparatively rare; ac cording to the statistics of 1900 there were about 65,000 blind in the United States, i.e., about 1 in 1,000 of the population. In a few cases blindness has an hereditary character,. the %ast majority of the blindnesses result from accident or disease. Bullet wounds in war are the most frequent accidental causes. Disease of the cornea — inflammation (chiefly gonor rhceal)— is responsible for about one-fifth of the blindness in the community. This usually occurs at birth and is largely preventable. Various other disorders of the eyestructures other than the purely nervous ones—cause blindness in a small number of cases. Actual injuries to the eyes in various occupations ac count for a small number.
Disease of the nervous pathways, i.e., the
retina, optic tract, corpora quadrigemina, optic thalamus and occipital cortex result in various types of partial or complete blindness according to the localization of the disorder. Blindness from retinitis, i. e., inflammation or injury of the retina, may result from various poisons, alcohol, lead or certain infectious diseases, such as scarlet fever, typhoid, etc. Pressure within the brain from tumors may cause blindness. Injury to the optic nerves from tumor, from fracture of the skull, from the pressure of glaucoma, from bullet wounds, cause partial or complete blindness. Disease of the optic chiasm, chiefly hypophyseal tumors, causes a partial blindness — hemianopsia, as does injury to the receiving sta tions of the sight pathways in the corpora quadrigemina and the occipital lobes of the brain.
A special type of night blindness is a rare hereditary condition. These patients see well in the daytime but lose their power to see in the dusk or at night. Color blindness is another special type of blindness to certain colors. See