The fundus oculi, with an ophthalmoscopic atlas illustrating its physiological and pathological conditions.

  • Frost, W. Adams.
Date:
1896
Catalogue details

Licence: Public Domain Mark

Credit: The fundus oculi, with an ophthalmoscopic atlas illustrating its physiological and pathological conditions. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

    69/446 (page 45)
    SHAPE OF THE DISC. If the figures be examined it will be seen that, while there is great variety in the distribution of this marginal pigment, it is exceptional for it to be absent altogether. The outline of the disc is usually nearly circular, although minor irregularities, such as a slight flattening of some part of its circumference, are very frequent. Oval discs are, however, by no means uncommon, and then the vertical meridian is always the longer (Plate IT., Fig. 5). Fig. 12 represents rather an extreme example of this, the ratio of the vertical to the horizontal meridian being as five to three. Fig. 12.—Oval disc. The presence of astigmatism, however, may cause a disc to appear oval when it is not so in reality, owing to its being more magnified in one direction than in the other. In direct ophthal- moscopic examination the enlargement is greatest in the meridian of gTeatest refraction, but the actual ettect i^roduced (as is well shown in Fig. 11, p. 44) depends less upon the difference in the apparent length of the meridians of the disc than upon the contrast