Investigations in the relation between convergence and accommodation of the eyes / by Ernest E. Maddox.

  • Ernest Edmund Maddox
Date:
[1886]
Catalogue details

Licence: Public Domain Mark

Credit: Investigations in the relation between convergence and accommodation of the eyes / by Ernest E. Maddox. 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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    curious way, by ascribing to each fibre of the optic nerve a different degree of tension, like the stiings of a violin or piano, each vibrating in unison with its own retinal area,— a tension, argued Porterfield, impossible in the soft and pulpy structure of the nerve fibres. From the fact that in animals which look the same way with both eyes, the optic nerves meet before they enter the brain, while this union does not occur in those which do not, such as fishes ami the^ chameleon, Sir Isaac Newton suggested an arrangement of the optic fibres at the commissure, which exactly tallies with that now generally received— the fibres on the right side of both (optick) nerves uniting there at the commissure, and, after union, going thence into the brain in the nerve which is on the right side of the head, and the fibres on the left side of both nerves uniting in the same place, and, after union, going into the brain in the nerve which is on the left side of the head. I quote from the 13th Query at the end of his Treatise on Opticks (1718), the more remarkable because it was the belief of anatomists, like Vesalius, that no decussation occurred at the commissure, and that it consisted of fibrous tissue. Dr William Porterfield of Edinburgh is believed to have first enunciated the correct, though still very partial theory of binocular vision. In his Treatise on the Eye (1759)1 he showed that when the eyes are accommodated for anj' object their two visual axes are also exactly converged upon the same point, and since each eye possesses the power, either intuitively or by acquisition, of localising points in space, the object must appear single, it being impossible for us to conceive two objects existing in the same place at the same time. Single binocular vision therefore requires a perfect concert between the efforts of accommodation and convergence. The former secures distinct vision; the latter single vision. Accommodation affects the nature of the images thrown on the retina?; convergence affects their position on the retina?, so that they still fall on the same portions whether the object looked at is near or distant. If distant, both accommodation and convergence are nil. With every approach or recession of the object, they increase or decrease simultaneously. The two efforts are not only associated in their daily exercise, but the nervous centres which govern them are linked in the brain by strong nervous ties, so that the slightest action of one affects the other. This is shown by Donders' experiments, for, though they demonstrate that the desire for single vision has power to overcome the nervous ties within limits, when lenses or prisms are used, yet they show also that the slightest alteration in 1 To which I am indebted for most of what precedes.)
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