The light reflex on the retinal vessels / by John B. Story.

  • Story, John B.
Date:
1892
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Licence: Public Domain Mark

Credit: The light reflex on the retinal vessels / by John B. Story. 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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    by the assumption of a change in the form of the surface of the vessel, making its surface no longer perpendicular to the line of sight. The absence of the light streak in detachment of the retina is better explained by the slanting course of the vessels than by the change of background, while it is not improbable that the real agent may be something quite different from either theory, and the streak is not always absent. I have frequently observed it in typical cases of retinal detachment. Loring's experiment is the most unsatisfactory proof of all. With a mirror placed beneath his glass tube, one sees the tube twice over—viz., the real tube and its image in the mirror. If these two objects are made to coincide the tube seen appears nearly double as bright as it would otherwise appear, but nothing at all resembling the light streak on the retinal vessels can be made out on it which cannot be seen on glass tubes over a dark background. A light streak can be made out easily enough on a glass tube with a less luminous background. In any case Loring's experiment should not be made in air, but in some medium with an index of refraction pretty nearly equal to that of the glass tube and its contained fluid. If this be done (as in the tubes exhibited sunk in glycerine jelly) anyone can convince himself that the only reflex at all resembling that on the retinal vessels is that on the anterior surface of the tube. Again, Schneller's observation that the light reflex moves with the rotation of the mirror is perfectly correct, and disproves Loring's theory completely, as does also the even more incontro- vertible fact that the light streak is not red, but white. The absolutely unchanged character of the reflex, no matter what be the background—white, as in optic disc; black, as over pigment spots ; or red, as over subjacent blood vessels—is also in my own experience an easily observed fact, and one vouched for by the acutest of all ophthalmoscopic observers—the late Ed. V. Jaeger, and it is completely destructive to Loring's theory. When we come to a choice between Jaeger's second theory and his first—which is the one advocated by Schneller—the decision is not quite so easy; but 1 have myself no hesitation in electing to stand by the latter—viz., that the light streak is a reflex from the wall of the vessel. Jaeger's experiment with the glass tubes is perfectly correct, so far it goes, but docs not disprove the theory that the light streak comes