Atlas and epitome of operative ophthalmology / by O. Haab ; edited by G. E. de Schweinitz.
- Otto Haab
- Date:
- 1905
Licence: In copyright
Credit: Atlas and epitome of operative ophthalmology / by O. Haab ; edited by G. E. de Schweinitz. Source: Wellcome Collection.
Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)
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![what has already been said it would evidently be wrong to judge of the operability of a cataract solely by the con- dition of the eyesight and to wait until the affected eye becomes totally blind. 2. Function.—Among the conditions affecting the suc- cess of the operation must be mentioned, in addition to ripeness of the cataract, the functional condition of the affected eye—that is to say, the health of the eye—espe- cially as regards the deeper portions which escape inspec- tion in advanced stages of cataract, and are, therefore, judged only by investigating the function. A case of cataract can not be regarded as operable unless the eye still possesses a certain degree of vision, at least for move- ments of the hands at 0.25 to 0.05 m.; it is impossible to give accurate numbers. Whether the retina still retains some central vision may be roughly determined by noting whether the patient is still able to perceive movements of the hands or the flame of a candle in the dark at a distance of 6 m. The latter test, however, in the case of cataract includes much more than the center of the retina, because an opaque lens acts much like a piece of ground glass held before the eye, which diffuses the light from the candle over the entire retina, so that the flame can be perceived even when a central scotoma is present. [The function of the center of the retina should be tested by means of two small flames, which under normal conditions should be readily recognized as such by the patient.—Ed.] However, the candle-test also reveals the light sense of the retina and is useful on that account. The degree of peripheral vision is determined by means of the so-called projection-test, a kind of measuring of the visual field by means of a coarse stimulus capable of affecting the cornea through the cataract. The patient is taken into a dark room, the other eye is bandaged, and his ability to localize with the cataractous eye a candle flame in various portions of the visual field is tested, the examiner covering the patient's eye with his hand while](https://iiif.wellcomecollection.org/image/b21286826_0099.jp2/full/800%2C/0/default.jpg)
