Optic Neuritis. Inflammation of the optic nerve is a condition readily detected by the use of the ophthalmoscope, which reveals the altered appearances manifested by the optic disc. In the normal condition the margin of the disc is clearly defined and not raised above the surface of the surrounding retina; in neuritis it becomes swollen and woolly-looking; the vessels coursing over it are tortuous, and in places obscured by effused material. Optic neuritis occurs in many forms of disease within the skull, and sometimes the detection of the altered appearance of the optic disc is of great importance in confirming the diagnosis of cerebral tumour or abscess, meningitis, etc. Optic neuritis also occurs in Bright's disease, syphilis, and as the result of the extension of inflammation from neighbouring parts of the eye.