2. Hughlings-Jackson and Gowers181 (1875) relate a case of left homonymous hemianopia with hemianæsthesia and hemiplegia of the same side. The autopsy showed softening of the posterior part of the right thalamus opticus without other lesion.
181 R. L. O. H. Rep., vol. viii. p. 330.
3. Curschmann182 (1879) gives the case of a patient who drank sulphuric acid, which corroded the oesophagus and affected the aorta, causing embolus of the right brachial artery. On the day following there was complete left hemianopia. The autopsy showed a large area of cerebral softening in the right occipital lobe without other lesions. In the discussion of this case at the session of the Berlin Society of Psychiatry and Nerve Diseases, Westphal183 related a case of unilateral convulsions without loss of consciousness where there was homonymous hemianopia, and in which the autopsy showed a large area of softening in the white substance of the occipital lobe in the side opposite to the defect in the field of vision.
182 Centralblatt f. Augenheilkunde, 1879, p. 256.
183 Loc. cit., p. 181.
These cases might be multiplied, but the writer has selected them because they were made by careful and competent observers, and the lesions were so marked and limited in character as not to allow of any other interpretation than that given. If we admit the validity of the evidence, we have proved conclusively that, from a clinical and a pathological standpoint, binocular homonymous lateral hemianopia may be produced by lesions of the optic tract, of the posterior part of the thalamus opticus, and of the occipital lobe of the brain of the side opposite to the defect in the field of vision; and that, therefore, there must be a partial, and not a total, crossing of the fibres of the optic tracts at the chiasm. Moreover, as Foerster has most pertinently remarked, such a state of affairs does not violate the physiological law of the total crossing of other nerves, because in the binocular field of vision the partial crossing causes all objects to the right of the point of fixation to be seen by the left hemisphere, while those to the left of it are seen with the right hemisphere. While this problem appears sufficiently plain, and the view above advocated is adopted by the majority of writers of the present day, it is by no means equally satisfactory when looked at from a purely anatomical or physiological standpoint. Newton184 in 1704 had already appreciated the importance and difficulty of the subject, and in the hope that others might further investigate it asked the question whether the fibres from the right sides of both retinæ do not so unite at the chiasm as to go together to the right side of the brain, those from the left side of each retina pursuing a similar course to the left hemisphere. He further remarks that "if he is correctly informed that the optic nerves of such animals as have a binocular field of vision join at the chiasm, while those of the animals who have no binocular vision, such as the chameleon and some fishes, do not so join."185 Since his day the majority of authors have adhered to this view, until Biesiadecki,186 by careful anatomical studies and lectures, attempted to prove that in both men and lower animals there is a total crossing of the fibres at the chiasm. Twelve years later Mandelstamm,187 by clinical observations of nasal hemiopia and dissections of the chiasm, maintained the same view. In the same year Michel188 supported the same doctrine, and since then Schwalbe189 and Scheel190 have each advanced the same view. However, Von Gudden,191 also basing his opinions upon dissections, takes the opposite ground, and has since endeavored by a series of experiments, in which he enucleated one eye of young rabbits and dogs, to prove192 that if the animals were allowed to live until central atrophy set in there is a partial atrophy of both optic tracts, more marked on the side opposite to that of the enucleated eye, because the crossed bundle is by far larger than the direct.
184 Optiks, London, 1704, p. 136.
185 Loc. cit.
186 "Chiasma Nervorum Opticorum der Menschen und der Thiere," Sitzungsberichte der Wiener Akadamie.
187 A. f. O., xix., 2, pp. 39-58.