THE OPTHALMOSCOPE 



743 



and the pupil is dilated. This will materially facilitate the examination; 

 but it is quite possible to observe all the details to be presently described with- 

 out the use of this drug. 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. A subdued but steady light is placed close to 

 the left ear of the patient in the examination of the right eye. Guiding 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, called in practice the reflex, due to the 

 illumination of the retina, is seen. 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 inward, and at the same 

 time the reflex changes from red to a lighter color, 

 owing to the reflection from the optic disc. The 

 observer now approximates the mirror, and with it 

 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 distance, which varies with 

 the refractive power in different eyes, but is usually 

 an interval of about two or three inches between 

 the observed and the observing eye, the vessels of 

 the retina will become visible as lines running in 

 different directions. The smaller and brighter red 

 arteries can be distinguished from the larger and 

 darker colored veins. An examination of the 

 fundus of the eye reveals the optic disc and the 

 entrance of the blood vessels, the macula lutea, 

 and the fovea centralis. No blood vessels are seen 

 in the fovea. This constitutes the direct method 

 of examination, figure 468; 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. 



If the observer is ametropic, i.e., is myopic or 

 hypermetropic, he will be unable to employ the 



direct method of examination until he has remedied his defective vision by 

 the use of proper glasses. 



In the indirect method, figure 469, the patient is placed as before, and the 

 operator holds the mirror in his right hand at a distance of 30 to 40 cm. 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 the 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, 

 toward or away from the face of the patient, until the outline of one of the 

 retinal vessels becomes visible, when very slight movements on the part of the 

 operator will suffice to bring into view the details of the fundus above described, 

 but the image will be much smaller and inverted. The lens should be kept 

 at a fixed distance of two or three inches, the mirror being alone moved until 

 the disc becomes visible: should the image of the mirror obscure the disc, 

 the lens may be slightly tilted. 



FIG. 470. The Ophthal- 

 moscope. The small upper 

 mirror is for direct, the 

 larger for indirect, illumi- 

 nation. 



