en. LVL] 



THE OPHTHALMOSCOPE 



793 



mounted on a handle, and is perforated in the centre by a small hole 

 through which the observer can look. 



The methods of examining the eye with this instrument are the direct and the 

 indirect : both methods of investigation should be employed. A drop of a solution 

 of atropine (two grains to the ounce^ or of homa- 

 tropine hydrobromate, should be instilled about 

 twenty minutes before the examination is com- 

 menced ; the ciliary muscle is thereby paralysed, 

 the power of accommodation is abolished, and 

 the pupil is dilated. This will materially facili- 

 tate the examination ; but it is quite possible to 

 observe all the details to be presently described 

 without the use of such drugs. The room being 

 now darkened, the observer seats himself in 

 front of the person whose eye he is about to 

 examine, placing himself upon a somewhat 

 higher level. Let us suppose that the right eye 

 of the patient is being examined. A brilliant 

 and steady light is placed close to the left ear 

 of the patient. Taking the mirror in his right 

 hand, and looking through the central hole, the 

 operator directs a beam of light into the eye of 

 the patient. A red glare, known as the reflex, 

 is seen; it is due to the illumination of the 

 retina. The patient is then told to look at the 

 little finger of the observer's right hand as he 

 holds the mirror ; to effect this the eye is rotated 

 somewhat inwards, and at the same time the 

 reflex changes from red to a lighter colour, 

 owing to the reflection from the optic disc. The 

 observer now approximates the mirror, with his 

 eye to the eye of the patient, taking care to 

 keep the light fixed upon the pupil, so as not to 

 lose the reflex. At a certain point, which varies 

 with different eyes, but is usually reached when 

 there is an interval of about two or three inches 

 between the observed and the observing eye, the 

 vessels of the retina become visible. Examine 

 carefully the fundus of the eye, i.e., the red 

 surface until the optic disc is seen; trace its 

 circular outline, and observe the small central white spot, the porus opticus, or physi- 

 ological pit : near the centre is the central artery of the retina breaking up upon 

 the disc into branches ; veins also are present, and correspond roughly to the 

 course of the arteries. Trace the vessels over the disc on to the retina. Somewhat 

 to the outer side, and only visible after some practice, is the yellow spot, with 

 the smaller lighter-coloured fovea centralis in its centre. This constitutes the direct 

 method of examination ; by it the various details of the fundus are seen as they 

 really exist, and it is this method which should be adopted for ordinary use. 



FIG. 588. The Ophthalmoscope. The 

 small upper mirror is for direct, the 

 larger for indirect, illumination. 



If the observer is myopic or hypermetropic, he will be unable to employ the 

 direct method of examination until he has remedi 

 proper glasses. 



remedied his defective vision by the use of 



In the indirect method the patient is placed as before, and the operator holds the 

 mirror in his right hand at a distance of twelve to eighteen inches from the patient's 

 right eye. At the same time he rests his left little finger lightly upon the patient's right 

 temple, and holding a convex lens between his thumb and forefinger, two or three 

 inches in front of the patient's eye, directs the light through the lens into the eye. 

 The red reflex, and subsequently the white one, having been gained, the operator 

 slowly moves his mirror, and with it his eye, towards or away from the face of the 



