Illustrations of some of the principal diseases of the eye : with a brief account of their symptoms, pathology, and treatment / by Henry Power.
- Henry Power
- Date:
- 1868
Licence: Public Domain Mark
Credit: Illustrations of some of the principal diseases of the eye : with a brief account of their symptoms, pathology, and treatment / by Henry Power. 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.
671/700 (page 609)
![occurs as the result of simple debility, as during convalescence from fever. In those cases which are associated with hypermetropia, the asthenopia, being dependent upon an abnormal form of the globe, which is frequently an hereditary defect, is itself often observed to be transmitted from parent to child. In this form of the disease, the internal recti preserve their natural power; and if any small object, as a pencil held vertically in the middle line, be slowly approximated to the eye, the gradual convergence of the optic axes can be pro- perly performed and maintained without any tendency to the production of strabismus. In muscular asthenopia, on the other hand, winch accom- panies myopia, the insufficiency of the internal recti conse- quent on over-exertion can be readily made apparent by the above experiment. As the pencil is gradually brought closer to the face, one or the other eye begins to lag behind, then stops in its convergent movement, and finally is drawn out- wards, in consequence of the action of the external rectus preponderating over that of the internal. A still better method of exhibiting the insufficiency of the internal recti muscles consists in directing the patient to fix both eyes on an object at the distance of from eight to ten inches, and then excluding one eye by passing a screen upwards before it. If the internal rectus has been abnor- mally tense, the eye under the screen will pass outwards, and again inwards when the screen is removed. The degree of divergence measures the excess of tension. The insufficient power of the muscle may be also rendered evident by placing a prismatic glass before the eye, with its angle either directly upwards or downwards. This necessarily occasions two images of any small object, which in the normal eye would be ]'laced one above the other; but in the asthenopic con- dition of lli«' eyes we are now considering, the muscles being set free, as it were, to take up their own position, and being 2o](https://iiif.wellcomecollection.org/image/b21072929_0671.jp2/full/800%2C/0/default.jpg)
