The anatomy of the muscles, ligaments, and fasciae of the orbit, including an account of the capsule of tenon, the check ligaments of the recti, and of the suspensory ligament of the eye / by C. B. Lockwood.

Lockwood, C. B.

Date:: [1885]

Credit: The anatomy of the muscles, ligaments, and fasciae of the orbit, including an account of the capsule of tenon, the check ligaments of the recti, and of the suspensory ligament of the eye / by C. B. Lockwood. 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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$to a clock pendulum beating half-seconds. At one end of a beat pull the stop instantaneously to the right, and at the other end of the beat let it fly back to the left; in so doing it exposes a transitory double image of the central aperture, or at least a perceptible widening. This shows that divergence has commenced in less than half a second. In how much less still remains to be noted, which may be done by short- ening the pendulum; but great quickness of observation would be needed to attain any degree of accuracy. Exp. 22.—Let the central aperture be alone used, and push the stop, alternately from left to right and right to left, at definite intervals. If the intervals are not too short relative divergence sets in, as shown by the apparent displacement of the image to rig]it or left at every move- ment of the stop. The vision of the central aperture is alternately monocular and binocular, the proportion between the two being deter- mined by the rapidity of each movement and the length of the interval between them. At certain rates the relative divergence gradually in- creases, as shown by the greater and greater apparent displacement with each excursion, which proves that a certain proportion of bin- ocular vision to monocular is required to overcome the natural tendency to divergence. The desire for single vision is, as it were, <lilutr<l by interruptions. There appears to be a certain rate at which the relative divergence neither increases nor diminishes, and a quicker one still at which, if divergence is present to begin with, it slowly diminishes, and yet a further rate at which it docs not appear at all; but a mechanical apparatus would have to be used to obtain really reliable results. The widtli of the stop, of course, greatly affects the proportion of binocular vision, as also does the length of its slit. If the stop were just wide enough to cut off in the middle of its course the view of the central aperture by both eyes, vision would be wholly monocular; with each diminution of size there would be a larger pro- portion of binocular vision. It may be that this method would furnish a comparative means of estimating the efficiency of the fusion centre, by noting the amount and nature of the dilution required to make the desire for fusion in- capable of preventing either the occurrence of relative divergence or its continuous increase. Two points would have to be considered— the frequency of the interruptions, and the length of each; the former would depend on the number of side to side movements per minute, the latter on the rate and length of each movement, t\i% pause at the end of each, and the widtli of the stop. It is possible that a certain duration of the two pictures in the brain is necessary to elicit the desire to fuse them at all. If a wide stop were used, and an up and down movement given to it in the slit, binocular vision would be diluted, not by monocular, but by intervals of no vision at all. Whether the result would be the same I do not know. Exp. 23.—If, after looking at the central aperture for a little time with the stop to the right, the latter then be pushed quickly to the middle, the central aperture appears duplicated for a moment by the$