On the Structure of the Retina

ABSTRACT The retina is the sentient part of the eye, for which all the other textures are formed, and to which they may be said to be subservient. It is coextensive with the choroid proper ; it covers the whole of the convex portion of the vitreous humour, and is covered by the choroid. It terminates in a serrated line, ora serrata, which is readily seen with an inch lens, just where the ciliary processes are continuous with the choroid. There is, according to some anatomists, a circular blood-vessel running near to this edge, if so, it is probably a vein, but it rather appears as a series of capillary loops of the central artery. Some of the older anatomists and opticians described the retina as being continuous over the anterior surface of the crystalline lens, an opinion which has been adopted to a great extent by Arnold, who describes and figures the retina as being continuous with the ciliary body and processes to the edge of the lens *,—pars ciliaris retinœ and processus ciliaris retinœ. This, however, is, without doubt, an error ; though the retina does not terminate wholly and absolutely at the ora serrata, as is commonly described. The nervous structure here ends, but there is, continuous with the suspensory ligament of the lens, a cellular layer, as far as the edge of the lens : this is best seen after the eye has been kept for some time in spirit or Goadby’s solution, by which the layer is rendered opaque and white. Its continuity with the retina may then be readily traced, and, indeed, in some eyes it looks so like a continuation of the whole retina as to render the microscope essential to prove that the nerve-structure is not so prolonged. † The retina has, until very recently, been described as the terminal expansion of the fibres of the optic nerve into a membrane. It is, however, much more than this ; it is one of the most complex, perhaps the most complex, structure to be found in the body, and instead of being thought of as simply a terminal nervous expansion, it should be regarded as in itself a nervous centre ; having the fibres of the nerve expanded it is true in it, and by which it is connected with the brain, but possessed itself of structures and properties peculiar to it, and altogether different from those of the optic fibres, which are expanded in and make part of it. These fibres are for the purpose of conveying to the sensorium the impressions excited in the retina, but are not for receiving the impression, while the other complex structures of the retina receive and appreciate the impressions of external objects.