Optic Nerve
in anatomy, the nerve of sight, proceeding from the optic lobes or corpora quadrigemina to the eye, terminating in an expansion called the retina. The inner portion of the fibers of the two optic nerves decussates at the commissure, passing to the opposite eye, while the outer portion continues its course to the eye of the same side, which has been supposed to assist in the production of single vision, although it is more probable that the latter is the result of a mental act. The closest relations exist between the optic nerve, its disk, the retina, and the choroid, as regards the cerebral and intraocular circulation, particularly seen in the course of cerebro-spinal disease. OPTIC NEURITIS. Condition of the optic nerve brought about by inflammation showing two distinct phases, namely, retrobulbar neuritis in which the nerve fibers behind the eye are affected, and papillitis, where the seat of inflammation is in the optic disk. The condition is often the result of brain disease, acute fevers, and syphilis, affecting the vision OPTOMETRY of light and of vision as performed by the human eye. The modern division of the science is into: 1. Sources of light; 2. Transmission, velocity, and intensity of light; 3. Reflection of light-mirrors; 4. Single refraction-lenses; 5. Dispersion and achromatism; 6. Optical instrument; 7. The eye considered as an optical instrument; 8. Phosphorescence and fluorescence; and 9. Double refraction, interference, and polarization.