Barrett—On Entoptic Vision. 71 
opacity was detected by the ophthalmoscope, that led me to 
devise the Entoptiscope ; and I will now give a recent tracing I 
have made of these obscurities. Fig. 1, Plate 1V., is a reproduc- 
tion of the shadows seen by means of the Entoptiscope, respectively, 
in my right and my left eye. That these obscurities are due to 
cataract—that is to say, to partial opacity of the crystalline lens 
or its capsule—there is no doubt, as will be evident from the careful 
drawing of the appearance presented in the ophthalmoscope (fig. 8, 
Plate IV.), which was kindly made for me by the eminent oculist 
Dr. C. Fitzgerald, of Dublin. As already explained in Part I., 
§ 5, entoptic observation inverts both laterally and vertically the 
shadows on the retina, whereas the opacity is seen without inversion 
in the ophthalmoscope. A comparison of the two sets of drawings 
must therefore be made after the complete inversion of one or the 
other. This has been done in fig. 2, Plate IV. Dr. Httles, of 
London, was good enough to spend some time in making as minute 
a drawing as was possible of the cataract in my right eye; and 
a copy of his drawing is given in fig. 4, Plate 1V.1 | The much 
greater detail shown by entoptic observation is obvious; but the 
entoptic drawing in fig. 1, Plate LV., gives no idea of the wonder- 
ful structural detail which the observer sees. The minutest 
change in the opacity is clearly visible; and, as I have said, 
the effect of any therapeutic treatment of cataract, if such should 
ever be found worthy of trial, could be rigorously tested. It 
is, of course, desirable that the Entoptiscope should be kept in the 
hands of the profession ; otherwise nervous people would be apt 
to alarm themselves needlessly by its use. In my own case, if a 
personal reference will be pardoned, I have found the periodic 
examination of my own eyes a matter of considerable, if not very 
exhilarating, interest, inasmuch as the slow progress of the cataract, 
and the curious way in which it spreads, can be watched up to 
the inevitable end. The only inconvenience so far felt has been 
due to the increasing astigmatism, which, as I believe is usual, 
augments with the development of cataract. 
1 I met Dr. Ettles at the Royal Society Conversazione last year, where he was 
exhibiting that fine instrument the Ettles-Curties Ophthalmometer, and was struck with 
his scientific enthusiasm and all too rare knowledge of entoptic phenomeng. 
