Dadoae 
WARE 
ON ENTOPTIC VISION ; 
OR, 
THE SELF-EXAMINATION OF OBJECTS WITHIN THE EYE. 
By PROFESSOR W. F. BARRETT, F-.R.S. 
[Part I.] 
[Read June 20; Received for Publication Junz 23, 1905; Published Marcu 9, 1906. ]} 
dle 
Most people have observed, and many have been needlessly 
alarmed at, the semi-transparent objects like notes of interroga- 
tion, or pearly strings, which occasionally are to be seen moving 
across the retina of the eye. These are the so-called musce voli- 
tantes, and are due to shadows thrown on the retina by the minute 
débris of cells and of smaller vessels which are floating in the 
vitreous humour of the eye, and perceived when they pass close to 
the retina. They come and go, often with the state of health, 
and, as arule, need cause no anxiety.” If instead of a general illu- 
mination of the eye a divergent pencil of rays from a point of light 
near the eye be allowed to enter, the shadows become sharper, owing 
to the absence of penumbra, and under such conditions these and 
other small opacities, in the line of vision, at any part of the eyeball, 
can be seen from their shadows on the retina. A point of light 
can be readily obtained from any luminous source, by using a 
1 This paper has been unavoidably delayed in publication. 
2 These shadows are called musce volitantes (‘flies flitting’) because the shadow 
flits away as the gaze is directed to it. From remote times these musce have been the 
subject of frequent observation and discussion. The learned Jesuit Deschales wrote 
an essay on the subject in the sixteenth century. When the eyeball is kept motionless, 
the musee@ appear to be slowly descending ; owing to the fact that the shadow when 
projected from the retina is inverted, the musc@ are therefore ascending, and hence are 
somewhat lighter than the vitreous humour in which they are floating. 
SCIENT. PROC. R.D.S., VOL, XI., NO. VII. I 
