Recent advances in ophthalmic science : The Boylston prize essay for 1865 . HTHALMIC SCIENCE. from the invention of certain instruments, by whichwe are enabled to explore the interior of the eje w^ithalmost as much ease as we can its external surface,and determine its condition with nearly equal cer-tainty. An account of the recent advances in oph-thalmic surgery would therefore be scarcely completewithout a description of the means which have facili-tated them. THE OPHTHALMOSCOPE. Notwithstanding some isolated observations ofreflection from the back part of the eye, it was tilllately generall
Recent advances in ophthalmic science : The Boylston prize essay for 1865 . HTHALMIC SCIENCE. from the invention of certain instruments, by whichwe are enabled to explore the interior of the eje w^ithalmost as much ease as we can its external surface,and determine its condition with nearly equal cer-tainty. An account of the recent advances in oph-thalmic surgery would therefore be scarcely completewithout a description of the means which have facili-tated them. THE OPHTHALMOSCOPE. Notwithstanding some isolated observations ofreflection from the back part of the eye, it was tilllately generally believed that rays of light reaching theposterior portion of a healthy eye were absorbed by thepigment layer of the choroid, and that none werereturned to convey an image of its interior to anothereye. This error was due to the fact, that in the ordi-nary inspection of the eye its fundus is but feebly illu-minated, owing to the necessary interposition of theobservers head between it and any available source oflight. Fig. 1. Illumination of the retina by a Figure 1 represents an eye having a portion of Its fundus illu-minated by rays from the flame of a candle. If now, as is shownin the figure, the eye is accommodated for distinct vision at thedistance of the candle, a minute but clearly defined invertedimage of the flame will be formed at the posterior pole, in theregion of the macula lutea, while the general surface of the ret- 4 RECENT ADVANCES IN OPHTHALMIC SCIENCE. ina is left in comparative darkness. In order to obtain a viewof this illuminated region it is necessary that some rays of lightfrom it shall enter the eye of the observer; but these emergentrays can leave the observed eye only in the inverse direction tothat in which the illuminating rays enter it, that is, in the exactdirection of the candle. It is evident, however, that if the ob-servers head be interposed between the candle and the observedeye it will cut off the illuminating rays from all th
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Keywords: ., bookcentury1800, bookdecade1860, bookpu, booksubjectophthalmology
