Manual of instructions for the guidance of army surgeons in testing the range and quality of vision of recruits and in distinguishing the causes of defective vision in soldiers / by T. Longmore.
- Date:
- 1875
Licence: Public Domain Mark
Credit: Manual of instructions for the guidance of army surgeons in testing the range and quality of vision of recruits and in distinguishing the causes of defective vision in soldiers / by T. Longmore. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![the fibres of tlie optic nerves decussate at tlie optic commissure explains how any cause, pressure or other, Impairing the conduc- tibility of either optic tract, before it reaches the commissure, may destroy visual power in the right or left halves of the two eyes, while the remaining portions of both retince retain their normal power of perception. The diagnosis can only be made out by noting carefully the field of vision of each eye. The limits of the field of vision sufficiently show the existence of the hemiopia. If the left half of the field of vision of each eye is wanting, loss of power of the right half of each retina will be indicated and vice versa. {d.) Scotoma.—Deficiency or loss of vision in an isolated por- tion or portions of the retina. It is occasionally central, and affects both eyes simultaneously. The defect may be a sequela of retinitis or optic neuritis, or be of cerebral origin. A dark spot, or spots, appear in ordinary vision, corresponding with the portions of the retina that have lost their sensibility to light. The spots move in concert with the movements of the eyes. Besides the amblyopia central scotoma is iisually accompanied with locahsed disturbance of the power of disting-uishing colours, the retina around retaining colour perception in integrity. In some cases a part of the retina may be infiltrated with choroidal pigment, or there may be localised exudative deposits, or a clot remaining fi-om blood eff'usion. In many cases, however, no visible evidence of lesion can be detected. Careful examination of the field of vision is the best guide to diagnosis in these instances. There will be a certain constant space or spaces in the field where impairment or complete loss of vision is marked. [Some other special conditions of defective vision, such as can particularly be distinguished by ophthalmoscopic observation, will be noticed in Part II.] II. Asthenopia. Definition.—Feebleness of vision from deficient or irregular muscular action, altogether irrespective of amblyopia, which may or may not be present. Causes.—Over-fatigue, atony, or paralysis of the ciliary muscle. Weakness of the internal recti muscles, which are chiefly employed for converging the eyes for near objects, as in reading.](https://iiif.wellcomecollection.org/image/b21932463_0068.jp2/full/800%2C/0/default.jpg)
