Inflammatory affections of the optic chiasm are probably more frequent than existing records show. According to Duke-Elder, 1 they are seldom recognized. Chiasmal optic neuritis is merely a variant of the well-known condition retrobulbar neuritis. The age and sex incidence of the former corresponds to that of the ordinary case of retrobulbar neuritis, as do its onset and course. The onset is sudden and is sometimes accompanied by headache and sickness and occasionally by visual hallucinations. The visual field findings are bilateral, but these are frequently more pronounced in one eye than in the other. The inflammatory foci in the optic tract may appear and subside. A retrobulbar lesion may often complicate the picture, and cases have been recorded in which the inflammatory process has extended to the optic nerve head, thereby producing a typical papillitis. The pathology of this condition is similar to that of acute retrobulbar neuritis. Traquair