A manual and atlas of medical ophthalmoscopy / by W. R. Gowers.

  • Gowers, W. R. (William Richard), 1845-1915.
Date:
1879
Catalogue details

Licence: Public Domain Mark

Credit: A manual and atlas of medical ophthalmoscopy / by W. R. Gowers. 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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    tion, and especially by so moving the mirror as to render the illumination slight and oblique. Sometimes, as will be described immediately, the outer coat of the vessel is so thick as to be very conspicuous. The paler line which runs down the centre of each vessel is generally regarded as a reflection from the middle of the anterior surface of the column of blood. It is certainly due to a reflection from the convexity of either the contained blood or the containing wall.* It is distinct only when the vessel lies in a plane at right angles to the line of observation. If the vessel, in consequence of an antero-posterior curve, ceases to be a plane at right angles to the line of observation, this central reflection is no longer visible, and the whole width of the vessel is the same dark colour as the edge. In the case of veins this change is very striking, and the greater amount of colour makes these portions appear even darker than the rest. Many examples of this will be found in the appended plates, as in I. 4, II. 1, III. 2, 4, Y. 5, 6, &c. Size.—In estimating variations in size of the retinal vessels allowance must be made for the refraction, i.e., mag- nifying power of the eyeball, remembering that by the indirect method of examination, in myopic eyes the details appear small, while in hypermetropic eyes the objects appear large. In the direct method there is less variation, because, for distinct vision, the abnormal refraction requires correction by a lens. The apparent size of the disc may be taken as the guide to the amount of magnification. There is no very exact method of estimating the absolute size of the vessels, f Sometimes, however, the alteration is such as to be at once * A case lately under my observation, in which the ordinary central reflection from the veins is, in many vessels, replaced by an irregular, patchy and granular reflection, which changes as the vein pulsates, and can be removed by pressure, seems to reopen the question of the nature of the normal reflection. In another case lately seen, in which there was much tissue about the vessels at their emergence (probably congenital), portions of veins near presented a central reflection of the exact tint of that of the adjacent arteries, the reflection elsewhere being normal. These cases suggest that the wall of the vessel has an important influence on the character of the reflection. t See appendix—Ophthalmoscopic Measurement.