The cyclopaedia of practical medicine: comprising treatises on the nature and treatment of diseases, materia medica and therapeutics, medical jurisprudence, etc., etc (Volume 1).
- Date:
- 1849-59
Licence: Public Domain Mark
Credit: The cyclopaedia of practical medicine: comprising treatises on the nature and treatment of diseases, materia medica and therapeutics, medical jurisprudence, etc., etc (Volume 1). Source: Wellcome Collection.
Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)
76/822
![[For alteratives, a term—as often used—con- veying no distinct moaning, Dr. DunglisoD has substituted euirophics, promoters of healthy nutrition. See Euthophics.] j Conolly. AMAUROSIS, from aftavo6oi, to obscure. This is the name applied to one of the diseases of the eye, in which defective vision depends on impair- ed sensibility of the retina. The term gut/a terena has also been applied to this disease, from an erroneous notion that the dark enlarged pupil, which sometimes accompanies it, is a drop of black fluid which interrupts the passage of light. In practice, when a patient without opaque cornea, closed pupil, or cataract, complains of lost or defective vision, he is considered to suffer from this disease. Viewing the exquisitely delicate organization of the retina, and the origin, course, and compli- cated connexions of the optic nerve, it is not sur- prising that impaired vision should so frequently be produced by disease in some part of the nervous apparatus. The ultimate fibres of the optic nerve, expanded into a membrane of extreme tenuity, supported and disposed upon a membrane of nearly equal delicacy, from whence it derives its vascularity, and covered and separated from the neighbouring choroid by a tunic of still greater delicacy, present altogether a piece of anatomical organization most likely to have its functions im- paired by slight deviations from the natural or sound condition. Disorganization of the hya- loid membrane, upon which this delicate struc- ture rests, or of the choroid, with which it is ex- ternally in contact, may also materially affect its condition. The optic nerve, with its vascular and membranous accompaniments, enclosed in a sheath of fibrous membrane in its course through the orbit, pierced by the central artery, and close- ly connected with other arteries and nerves, is exposed to many injurious deviations from the natural structure. The same optic nerve within the head, from the vicinity of large vessels, and its complicated nervous connexions at the place of decussation, the tuber cinereum, the crura cerebri, the thalami, and the tubercula quadrige- mina, is liable to suffer from disorganization of its own structure, as well as of any of those parts with which it is connected. A review of the structure of the nerve of vision, from its origin at the tubercula quadrigemina to its anterior termi- nation at the ciliary processes, is the best pre- liminary exern.je for one about to study the dis- ease of amaurosis. Injury or disease of the brain, as ruptured vessels, serous effusion, softening, tumor, or ab- scess, frequently impair the functions of the optic nerve, although such injury or disease should exist in a situation remote from the origin or course of the nerve. Amaurosis may, therefore, be a consequence of cerebral disease, although the optic nerve should be sound from its origin to its termination. [Lawrence on Diseases of Hie Eye, Amer. edit. p. 478 : Philad., 1843.] Injury or disease of a nerve, or morbid con- dition or irritation of particular organs, affect in- juriously the brain and nervous system, and thus impair the functions of the retina : hence amau- losis from gastric, hepatic, or uterine disturbance. AMAUROSIS. The experiments of Magendie, inconclusive as they are, and often proving too much for the hypothesis they are intended to strengthen, at least show that the fifth pair of nerves exerts some very important influence on the function of vision ; pathological observations on this subject, although few in number as yet, lead to the same conclusion, and the effects of injury of the frontal nerve in producing amaurosis, long since observed, establishes the fact. Ptosis, depending on disease of the third pair of nerves, is always accompanied by defective vision. ' Arterial and venous vascularity is an essential part of the organization of the retina, as it is of the whole nervous system; the existence of large vessels carrying red blood in a structure of such delicacy and transparency is even a remarkable circumstance, when contrasted with the apparently bloodless condition of many other white or trans- parent structures. Increased arterial action, or obstructed venous circulation, may, therefore, ma- terially affect the condition of the retina, and im- pair its sensibility. There is great variety in the perfection of vision in different individuals ; which may be attributed partly to a difference in sensibility of the retina, but in a still greater degree to a difference in pow- er of adaptation of the eye to distance. It ap- pears a great mistake to suppose that this differ- ence in perfection of vision depends altogether on the power of adaptation. A difference in perfec- tion of vision is often observed in persons who appear to enjoy an equally perfect power of adap- tation. A single lens remedies, in a great desree, the defect arising from want of power of adapta- tion ; but no single lens will confer on a landsman the distant vision of a sailor, nor on a long-sight- ed person the power of distinguishing minute ob- jects enjoyed by some near-sighted persons. It is scarcely reasonable to suppose that any altera- tion in curvature or relative positions of the cor- nea, or lens, in birds, can take place sufficient to account for the great superiority in vision which these animals enjoy. The sight of nocturnal ani- mals, and of persons who can see perfectly in obscurity, can only be attributed to a superior sen- sibility of the retina, as it is altogether independ- ent of any superior power of adaptation. The sensibility of the retina is increased by two totally different causes,—permanent exposure to a strong glare of reflected light, or a long-contin- ued residence in a darkened apartment. The inhabitants of snowy countries are obliged to adopt the precaution of protecting the eyes by means of a goggle, with a slit opposite the pupil, and the inhabitants of towns in which the build- ings are white are said to suffer from inflammatory affections of the eyes. Persons immured in dun- geons are said to acquire a power of distinguish- ing even small objects in their obscure abodes, in which, at first, they could not delect even a glim- mering of light. The morbid sensibility of the eye to light, in what is called scrofulous ophthal- mia, is in a great degree to be attributed to the injudicious exclusion of light from the eye by the use of shades, or confinement in a darkened room. The effect of light and shade upon the sensibility of the sound retina is beautifully exemplified by the simple experiment of directing the eve to](https://iiif.wellcomecollection.org/image/b21116805_0076.jp2/full/800%2C/0/default.jpg)
