Observations on the ophthalmoscopic appearances of the eyes of the order of primates / by G. Lindsay Johnson.

  • George Lindsay Johnson
Date:
[1897]
Catalogue details

Licence: Public Domain Mark

Credit: Observations on the ophthalmoscopic appearances of the eyes of the order of primates / by G. Lindsay Johnson. 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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    quite reconciled and contented. I found that extreme gentleness, together with petting the animals, overcame their fears, so that no force was needed; nor, indeed, would 1 have suffered it to be employed under any circumstances. A few of the Monkeys and Jjemurs M'ere observed in the Belle Vue (Jardeus, Manchester, some in Mr. Jamrach's and Mr. Hamlin's collections, and in various travelling menageries, since they were not to be found in the ►Society's Gardens. In all examples of 38 distinct species of Monkeys and Lemurs were examined, including forms of every genus which could be found in the Society's and other menageries. All the observations were made by w hat is termed the direct method with the ophthalmoscope, the instrument being used within an inch of the animal's eye without an interposed mag- nifying lens, thus presenting to the observer an upright picture of 10 diameters' magnification. This method is preferable to the indirect in which a lens is used, as the image then obtained is invei'ted, and only of 3 to 4 diameters' magnification, which is also less distinct than the larger upright image. In most cases cocaine and homatropine were dropped iuto the eye to obtain a larger pupil and consequently more light. The fundus of the fair European human eye appears, when viewed with the ophthalmoscope, of an orange-red colour, pretty uniformly distributed over the entire fundus ; only when we get towards the confines of the visible field does the background become more intermixed with streaks of pigment. A little to the inner or nasal side of the centre of the field we observe the disc of the optic nerve, of a pinkish colour and slightly oval shape, with the major axis vertical. From the centre of this disc the scarlet arteries and lake-red veins of the retina proceed, passing in every direction, dividing iuto numerous branches. In the dark-coloured races the appearances are similar, save that the orange-red background is replaced by a reddish brown, owing to the great increase of dark pigment (see Plate II.). Only one part of the fundus is wholly free from vessels, and that is at and around the macula lutea or yellow spot. The macula is a small pit or depression situated in the axis of vision, about 2g disc breadths from the disc to the outer or temporal side. It appears different in colour in the eyes of different individuals. Generally it appears as a dark-reddish circular patch, with a bright spot in the centre, and in some cases surrounded by a circular glistening halo or ring, well defined on its internal margin, but fading away into the general background towards its external border (marked cZ, Plate II,). Occasionally a second or even a tliird ring may be seen inside this large one, all having the fovea as a common centre. The macida being in ourselves the seat-of most acute vision, considerable attention has been given to this highly differentiated area, which has an actual diameter of about 1*5 mm. It is only in this region, the size of a pin's head, that we see perfectly, our acuteness of vision decreasing rapidly outside this region. In [2J
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