. A treatise on the diseases of the eye. catch the rays emanating from the eye of thelatter. By shifting the cone of light from one portion of the cornea or lensto another, we may rapidly, yet thoroughly, examine its whole expanse anddetect the slightest opacity. In order to gain a larger image, we may em-ploy a second lens as a magnifying glass [which should be held directly infront of the patients eye. (Fig. 4.)—H.]. Opacities of the cornea or lenswill appear by the oblique illumination (reflected light) of a light gray orwhitish color, whereas with the ophthalmoscope (transmitted light) the
. A treatise on the diseases of the eye. catch the rays emanating from the eye of thelatter. By shifting the cone of light from one portion of the cornea or lensto another, we may rapidly, yet thoroughly, examine its whole expanse anddetect the slightest opacity. In order to gain a larger image, we may em-ploy a second lens as a magnifying glass [which should be held directly infront of the patients eye. (Fig. 4.)—H.]. Opacities of the cornea or lenswill appear by the oblique illumination (reflected light) of a light gray orwhitish color, whereas with the ophthalmoscope (transmitted light) they willappear as dark spots upon a bright red background. The method of examining the eye Avith the ophthalmoscope will be founddescribed, at length, in the section upon the ophthalmoscope. INTRODUCTION. 35 The mode of ascertaining the degree of intra-ocidar tension is as follows:The patient being directed to look slightly downwards, and gently to closethe eyelids, the surgeon applies both his forefingers to the upper part of [Fig. 4.]. the eyeball behind the region of the cornea [that is, to the sclera; for ifthe pressure be applied directly to the cornea, the tension seems to be in-creased.—B.]. The one forefinger is then pressed slightly against the eye soas to steady it, whilst the other presses gently against the eye, and estimatesthe amount of tension, ascertaining whether the globe can be readily dimpled,or whether it is perhaps of a stony hardness, yielding not in the slightest de-gree even to the firm pressure of the finger. The beginner will do well tomake himself thoroughly conversant with the normal degree of tension, bythe examination of a number of healthy eyes, and then, if he should be atall in doubt as to the degree of tension in any individual case, he should testthe tension of the patients other eye (if healthy), or that of some normaleye, so as to be able to draw a comparison between them. If there is muchoedema of the lids, or conjunctival chemosis, or i
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