Eyes and spectacles / by M. von Rohr ; rendered into English by A. Harold Levy.

  • Rohr, M. von (Moritz), 1868-1940.
Date:
[1912?]
Catalogue details

Licence: In copyright

Credit: Eyes and spectacles / by M. von Rohr ; rendered into English by A. Harold Levy. 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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    EYES AND SPECTACLES. I. THE EYE AND ITS USE IN VISION. The eye is undoubtedly the most important of optical instruments. In the following pages we shall deal not only with the optical arrangements of the eye, but also with certain incidences of the act of vision ; more especially with the quick and easy movement of each eye in its orbit, and with the yoked actions of the two eyes. In the discus- sion of these various points it will be seen how an instrument which, from the point of view of technical optics, is fairly imperfect, becomes capable of such extensive and accurate performances. The Eye as a Fixed Optical System. Light rays entering the eve first fall upon the cornea. This forms the anterior, more highly curved portion of the first coat which surrounds the whole eyeball. The cornea forms the front bound- ary of the anterior chamber which is filled with the aqueous humour. The iris is the back boundary of the anterior chamber. Immediately behind the iris is the crystalline lens, the surfaces of which in the normal eye, as will be mentioned later, can be altered in curvature.* Behind the lens lies the vitreous, a jelly-like mass which fills the greater * We must, however, remark that the crystalline of children and young people under twenty consists of extremely thin layers, the indices of which increase gradually towards the centre of the crystalline. C. Hess, the Wurzburg1 ophthalmologist, has shown that for people over twenty this gradual increase no longer holds good, but that two surfaces exist where the index shows an abrupt increase. These two surfaces include between themselves a biconvex nuclear lens ; whereas the two including lenses have the form of thin dispersive menisci. As the function of such a