Atlas and epitome of ophthalmoscopy and ophthalmoscopic diagnosis / by O. Haab.

  • Haab, O. (Otto), 1850-1931.
Date:
1910
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Licence: In copyright

Credit: Atlas and epitome of ophthalmoscopy and ophthalmoscopic diagnosis / by O. Haab. Source: Wellcome Collection.

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    area of the fundus ean be examined at one time; 3. Cor- recting lenses on the ophthalmoseope ean be dispensed with; 4. The examination is possible even when the pupil is contracted. On the other liand, with the indi- rect method one sees the eye-ground under a lower magnifying power, and this is the principal ditference between tbe two methods. Enlargement of the Image in the Direct and in the Indirect Method. The size of the image obtained by the direct method depends on several conditions: 1. The refraction of both patient and surgeon ; 2. The distance between the eyes of patient and surgeon ; 3. The distance between the cor- recting glass and the eye under examination. v. Helm- holtz1 and, later, Manthner2 ealeulated the magnitication for emmetropic eyes and found it to be one of 144 diam- eters. L. Weiss3 obtained approximately the same re- sult—15.6—by directly measuring a dcad eye that had been carefully examined in this respect dnring life. In hypermetropia the size of the image is smaller, in myopia 1 arger, tlian in emmetropia, provided that the correeting lens is placed ata distance of 3 cm. front the eye under examination. If the hypermetropia is due to abnormallv weak refractive power, as, for instanee, to aphakia, the image. is smaller tlian in hypermetropia due to shortening of the axis, just as it is smaller in myopia due to the lengthening of the axis tlian in myopia due to abnormallv strong refractive power of the refracting Sys- tem (Manthner, loc. eit., p. 185). In hypermetropia the size of the image is smaller when the correeting lens is at a greater distance from the exam- ined eye, and, conversely, the image is larger in myopia 1 v. Helmholtz, Handbuch der Physiologischen Optik, sccond edition, p. ei7. ‘ Manthner, Lehrbuch dar Ophthalmoskopie, ]>. 177. 3 Ij. Weiss, Arch. f. Ophthalmoloyie, v<d. xxiii.