The principles and practice of medicine : designed for the use of practitioners and students of medicine / by William Osler.

  • Osler, William, Sir, 1849-1919.
Date:
1907, ©1905
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Licence: Public Domain Mark

Credit: The principles and practice of medicine : designed for the use of practitioners and students of medicine / by William Osler. Source: Wellcome Collection.

Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.

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    how the inflammation may extend down the nerve sheath. In the case of tumor, however, it is probable that mechanical conditions, especially the venous stasis, are alone responsible for the cedematous swelling. It often sub- sides very rapidly after a palliative craniectomy has been performed. (&) Optic Atrophy.—This may be: (1) A primary affection. There is an hereditary form, in which the disease has developed in all the males of a family shortly after puberty. A large number of the cases'of primary atrophy are associated with spinal disease, particularly locomotor ataxia. Other causes which have been assigned for the primary atrophy are cold, sexual excesses, diabetes, the specific fevers, alcohol, and lead. (2) Secondary atrophy results from cerebral diseases, pressure on the chiasma or on the nerves, or, most commonly of all, as a sequence of papillitis. The ophthalmoscopic appearances are different in the cases of primary and secondary atrophy. In the former, the disk has a gray tint, the edges are well defined, and the arteries look almost normal; whereas in the con- secutive atrophy the disk has a staring opaque-white aspect, with irregular outlines, and the arteries are very small. The symptom of optic atrophy is loss of sight, proportionate to the dam- age in the nerve. The change is in three directions: (1) Diminished acuity of vision; (2) alteration in the field of vision; and (3) altered perception of color (Gowers). The outlook in primary atrophy is bad. (3) Affections of the Chiasma and Tract. At the chiasma the optic nerves undergo partial decussation. Each optic tract, as it leaves the chiasma, contains nerve fibres which originate in the retinas of both eyes. Thus, of the fibres of the right tract, part have come through the chiasma without decussating from the temporal half of the right retina, the other and larger portion of the fibres of the tract have decussated in the chiasma, coming as they do from the left optic nerve and the nasal half of the retina on the left side. The fibres which cross are in the middle por- tion of the chiasma, while the direct fibres are on each side. The following are the most important changes which ensue in lesions of the tract and of the chiasma: (a) Unilateral Affection of Tract.—If on the right side, this produces loss of function in the temporal half of the retina on the right side, and in the nasal half of the retina on the left side, so that there is only half vision, and the patient is blind to objects on the left side. This is termed homony- mous hemianopia or lateral hemianopia. The fibres passing to the right half of each retina being involved, the patient is blind to objects in the left half of each visual field. The hemianopia may be partial and only a portion of the half field may be lost. The unaffected visual fields may have the normal extent, but in some instances there is considerable reduction. When the left half of one field and the right half of the other, or vice versa, are blind, the condition is known as heteronymous hemianopia. (b) Disease of the Chiasma.— (1) A lesion involves, as a rule, chiefly the central portion, in which the decussating fibres pass which supply the inner or nasal halves of the retinas, producing in consequence loss of vision in the outer half of each field, or what is known as temporal hemianopia. 65