Bauhaus-Universität Weimar

Helmholtz's treatise on physiological optics. Volume 1. Edited by James P. C. Southall. Translated from the 3rd German edition
Helmholtz, Hermann von
Anatomical Description of the Eye 
[24, 25. 
the layer of ganglion cells and even into the external molecular layer, 
in both of which they form a large-meshed capillary net. The position 
and form of this vascular arborization is important for certain optical 
phenomena (see §15), and therefore a drawing is inserted here (Fig. 17), 
which was made by Donders from an injection preparation. The 
arteries are shown in outline, the veins in solid black. In the yellow 
spot there are no larger vessels and in the fovea even capillaries are 
absent. The fovea is surrounded by a wreath of terminal capillary 
At the anterior edge (ora serrata) the retina passes over into a layer 
of cells (pars ciliaris retinae) which together with the membrana limi- 
tans (interna) covers over the ciliary processes and the posterior surface 
of the iris. Here it appears to become changed into pigment cells, 
and is closely attached to the underlying structures. 
Inasmuch as the dimensions of the retina and its elements are of much 
importance in connection with many optical phenomena, attached herewith is 
a résumé of certain measurements, as made by various observers, the results 
being all expressed in mm. These data derived from the works of C. Krause, 
E. H. Weber, Brücke, Kölliker and Vintschgau are indicated below by 
the abbreviations Kr., W., B., Ko. and V., respectively. 
Diameter of the optic nerve at its point of entrance: Kr., 2.7 and 2.14; 
W., 2.09 and 1.71. 
Diameter of the vessels contained in it: W., 0.704 and 0.63. 
Distance of the centre of the optic nerve from the centre of the yellow spot : 
W., 3.8. Kr., 3.28 and 3.6. Distance between the centre of the optic nerve 
and the inner edge of the yellow spot: Ko., 2.25 to 2.7. 
Horizontal diameter of the yellow spot: Kr., 2.25; W., 0.76; Ko., 3.24. 
Vertical diameter of the yellow spot: Ko., 0.81. 
Diameter of the fovea centralis^ Ko., 0.18 to 0.225. 
Distance between the ora serrata and the edge of the iris on nasal side: 
B., 6; on temporal side, 7. 
Thickness of the retina near the optic nerve: Ko., 0.22. 
Thickness of the retina at the back of the eye: Kr., 0.164, Ko., 0.135. 
Thickness of the retina at the equator: Kr., 0.084. 
Thickness of the retina at its anterior margin: Ko., 0.09. 
Thickness of the layers in the yellow spot: Ko., ganglionic layer, 0.101 to 
0.117; inner molecular layer, 0.045; inner nuclear layer, 0.058; outer molec¬ 
ular layer, 0.086; outer nuclear layer, 0.058; layer of rods and cones, 0.067. 
Diameter of the ganglion cells: B., 0.01 to 0.02; Ko., 0.009 to 0.036, 
usually between 0.013 and 0.022. 
Diameter of the nuclei: B., 0.006 to 0.008; Ko., 0.004 to 0.009. Of the 
cone-cells: V., 0.0068. 
Diameter of the rods: B. and Ko., 0.0018; V., 0.0010. 
Length of the rods: B., 0.027 to 0.030; Ko., 0.063 to 0.081. 
Diameter of the cones: Ko., 0.0045 to 0.0067; V., 0.0034 to 0.0068. In the 
yellow spot: Ko., 0.0045 to 0.0054. 
Length of the cones: V., 0.015 to 0.020. 
The newer (1845-1854) works on the structure of the retina are: 
1845. F. Pacini in Nuovi Annali delle scienze nat. di Bologna. 1845. 
1851. H. Müller in Siebold und Köllikers Zeitschrift für mss. Zoologie. 1851. S. 234. 
—Verhandl. der Würzburger med. Ges. 1852. S. 216. Ibid. III. 336 and IV. 96.


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