1864.| Nunnexey on the History and Uses of the Ophthalmoscope. 425 
admission into the observer’s eye, and thus the experiment is inter- 
fered with in two ways. With the mirror, is frequently used a double 
convex lens of about two inches focus, which is held between the mirror 
and the eye to be observed, for the purpose of concentrating the rays 
of light before they fall upon the observed cornea. This lens is 
necessary when the observed eye is flat, or presbyopic ; but when the 
cornea is convex, or myopic, the rays of light will fall upon the 
retina with sufficient accuracy, without other “concentration than the 
eye itself is capable of affording. 
For making the observation, the eye to be operated upon should 
have had the pupil well dilated by the introduction of atropine ; for 
unless this is done, sufficient light will not enter the eye to be reflected 
from the fundus and render the illumination clear, nor will the field 
of vision be sufficient to enable an examination to be made of the whole 
interior, and disease may likely enough exist, which lying behind the 
undilated iris must necessarily escape observation. The patient 
should then be placed in a darkened room, and directed to hold the 
head as steady as possible with the eyelids widely open, and the 
eyes looking directly forward fixed as immovably as possible. If a 
strong illumination is not required, a wax-candle, or if it be necessary, 
an argand gas-burner, or a camphine lamp, must be placed a little behind, 
and at the same side of the head as is the eye to be examined, and on 
the same level as the eyes. The observer then places himself directly 
before the patient, bringing his’ eye with the mirror held before it, as 
nearly as he can in the same plane with the patient’s eye, when the rays 
of light, falling upon the mirror, will be reflected as a diffuse circle of 
light; this, by adjusting the position of the mirror, may easily be so 
focrssed as to fall directly upon the dilated pupil, when a brilliant 
illumination of the fundus of the eye will be obtained, and of course 
any abnormal condition of its various parts may be at once observed. 
A more interesting and striking picture can scarcely be imagined than 
a brilliant view of the blood-vessels of the retina and choroid coat of a 
healthy living eye. Neither do we know of a more beautiful and simple 
application of optical science, nor of one which is more rich in the ad- 
vantages which it is likely to conferupon mankind, To those familiar 
with the more simple of optical laws, the mode in which this image 
is obtained, will be at once so obvious as to require no explanation ; 
while it would hardly be possible, without the aid of diagrams and a 
larger space than we can spare, to render it intelligible to those who 
do not understand them. 
We must, however, guard our readers against at once jumping to the 
conclusion, that because it is now easy for any competent observer to 
see clearly into the very bottom of the living eye, it is therefore easy 
to make the observation useful. None but a skilful anatomist and 
physiologist can do this; inasmuch as he must first not only know of 
what the marvellously minute tissues of the interior structures of the 
eye consist, but he must also, by patient and repeated observation, 
have rendered himself familiar with the appearances which this 
healthy condition presents under examination with the ophthalmoscope, 
before he can venture upon the attempt at discriminating between 
