326 



PHYSIOLOGY 



CHAP. 



its means the rays reflected from the t'undus (no matter what the 

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



It" the observer 



inverted image between the lens and tlie mirror. 



1 D of Bute's ophthalmoscope. 



is short-sighted, be is able to see the ima-e without other aid; if 

 normal or lonu-si^lited, lie 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- 

 |n 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 

 v# 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 



Kic. 151. Ophthalmoscopic :iii>i-aranc.-f of the fundus of 



tip- iininial eyr in a yminx [M-ISOM, with scanty pij;- (Jcig. 151). 



mentation the fovea centralis is plainly visible. m, - ln 



(Uthoff.) J-he optic papilla 



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 



