326 



PHYSIOLOGY 



CHAP. 



its means the rays reflected from the fundus (no matter what the 

 refraction of the observed eye) become convergent, and form an 

 inverted image between the lens and the mirror. If the observer 



M 



i/ 



FIG 150. Diagram of Elite's ophthalmoscope. 



is short-sighted, he is able to see the image without other aid ; if 

 normal or long-sighted, he is obliged, if his accommodation is not 



sufficiently powerful, to 

 place a second slightly 

 convex lens behind the 

 mirror. 



The first object in an 

 ophthalmological observa- 

 tion is to see the papilla of 

 the optic nerve distinctly. 

 In order that it may come 

 into the visual field of the 

 observer, the observed eye 

 must be turned a little in- 

 wards and its pupil dilated 

 as much as possible. 



The ophthalmoscopic 

 image of the fundus of the 

 normal eye exhibits all the 

 . details shown in colour 



FIG. 151. Ophthalmoscopic appearance of the fundus of -\K-\\ 



the normal eye in a young person, with scanty pig- (.Tig. 101 ). 

 mentation the fovea centralis is plainly visible. T-L.^ ^-^fio -nni-iilln 



(Ut.hoff.) . ine optic papuia 



appears as a roundish or 



oval disc of pale pearly grey, which stands out sharply from the 

 red colour of the rest of the fundus. From its centre issue the 

 central artery and vein, which form a delicate arborisation over 





