Text-book of ophthalmology / by Ernst Fuchs ; authorized translation from the eleventh revised and greatly enlarged German edition with numerous additions by Alexander Duane.

  • Ernst Fuchs
Date:
[1908]
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Licence: In copyright

Credit: Text-book of ophthalmology / by Ernst Fuchs ; authorized translation from the eleventh revised and greatly enlarged German edition with numerous additions by Alexander Duane. 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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    in the left eye. By examining in this way, we can tell whether the two reactions are equal in amount, as they should be. In examining the pupillary reactions we must remember that the primary contraction, which takes place when the eye is suddenly exposed to the light, is often succeeded by a secondary dilation, and that this latter may occur so quickly that unless we watch closely, the primary contraction may escape us. In cases in which it Is difficult to tell whether the light reaction is present at all or not, Uhthoff's method may be used with advantage. He places the patient in a dark room, blindfolds one eye, and makes him gaze fixedly with the other at a bright light. This light the ob- server focuses sharply on the patient's cornea, with a strong convex lens. Under these conditions, if any light reaction is present, the pupil will be contracted as much as light can contract it. At the same time, there will be no reaction for accomodation or convergence, for the patient will have before his eyes simply a bright blaze of light which by no possibility can form a clear image upon his retina, so that he will make no attempt either to focus or fix it. If now, the lens is suddenly removed, the pupil should dilate. If it does not, the light reaction is absent.—D.] Of the lens we see under ordi- nary circumstances only the small section of the anterior surface, which lies free in the pupil. If we wish to examine the lens more extensively,we dilate the pupil with homat- ropine [or cocaine] and use lateral illumination. As long as the lens is still transparent, the ophthalmoscope gives us the best conclusions in regard to its constitution. Whether the lens is present in the eye at all or not can be determined by investigating the Purkinje-Sanson reflex images. If a candle is placed before the eye and somewhat to one side of it, two brilliant reflections are observed. One of these at once attracts our attention by its size and brilliancy; it is the corneal reflex— that is, the erect image of the flame reflected from the anterior surface of the cornea (Fig. 4, a). It is this reflex which even from a distance is visible in every eye, and gives to the latter its fire and luster. The second reflex is quite as bright, but so small that we have to search for it in order to find it. It represents the very small inverted image of the flame which is reflected from the posterior surface of the lens (posterior lenticular reflex, Fig. 4, c). It is distinguished by moving in the contrary sense to the source of light when the position of the latter is shifted; if the Fig. 4.—Purkinje-Sanson's Reflex Images. The black circle represents the dilated pupil of the eye that is being tested. The candle flame is supposed to be to the right, the observer's eye to the left of the pupil, a, image formed by the anterior surface of the cornea. 6, image formed by the anterior surface of the lens, c, image formed by the posterior surface of the lens.
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