File:The principles and practice of medicine, designed for the use of practitioners and students of medicine (1892) (14781721865).jpg

Identifier: principlespract00osle (find matches)
Title: The principles and practice of medicine, designed for the use of practitioners and students of medicine
Year: 1892 (1890s)
Authors: Osler, William, Sir, 1849-1919
Subjects: Medicine
Publisher: Edinburgh London : Young J. Putland, c1892
Contributing Library: Dentistry - University of Toronto
Digitizing Sponsor: University of Toronto

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, producing in consequence loss of visionin the outer half of each field, or what is known as temporal hemianopia(Fig. 1 //). (2) If the lesion is more extensive it may involve not only the centralportion, but also the direct fibres on one side of tlie commissure, in whichcase there would be total blindness in one eye and temporal hemianopia inthe other. (3) Still more extensive disease is not infrequent from pressure of tu-mors in this region, the whole chiasma is involved, and total blindnessresults. The different stages in the process may often be traced in asingle case from temporal hemianopia, then complete blindness in oneeye with temporal hemianopia in the other, and finally complete blind-ness. (4) A limited lesion of the outer part of each chiasma involves only thedirect fibres passing to the temporal halves of the retinas and inducing 60 788 DISEASES OF THE NERVOUS SYSTEM. blindness in the nasal field, or, as it is called, nasal hemianopia. This, ofcourse, is extremely rare.
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Fio. 1.—The optic and visual tracts (Starr). iV, Lesion causing nasal hemianopia.J\ Lesions causing temporal hemianopia. //, Lesion causing bilateral heterony-mous hemianopia. B^ Lesion of tract causing homonymous hemianopia. (4) Affections of the Tract and Centres. The optic tract crosses the crus to the hinder part of the optic thala-mus and divides into two portions, one of which goes to the thalamus andexternal geniculate bodies and to the anterior quadrigeminal bodies. From DISEASES OF THE CRANIAL NERVE&. 789 these parts fibres pass into the posterior part of the internal capsule andenter the occipital lobe, forming the fibres of the optic radiation (Fig. 1),which terminate in and about the cuneus, the region of the visual percep-tive centre. The fibres of the other division of the tract pass to the in-ternal geniculate bodies and to the posterior quadrigeminal body. It isstill held by some physiologists that the cortical visual centre is not con-fined to the occipital lobe

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