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A TEXTBOOK OF PHYSIOLOGY 



liis eye will accommodate for the source of light or its image forme t 

 by the mirror. An inverted image of the illuminated area of the 

 retina will be formed at a certain distance behind the mirror. The 

 rays issuing from the eye are intercepted by a rather strong convex 

 lens held close to the cornea, so that the observer, looking through 

 the aperture of the mirror, obtains a clear view of a considerable 

 portion of the illuminated retina. 



Ophthalmoscopes are generally supplied with a revolving disc of 

 lenses of different strengths. These are used to correct any error of 

 refraction in the subject's or observer's eyes. 



It is frequently a matter of difficulty to obtain a clear view 

 of the back of the eye, or fundus, unless atropine has been 

 applied previously which causes dilation of the pupil. For practice in 

 Jthe use of the ophthalmoscope, the eye of an albino rabbit which has 

 been treated with atropine can be advantageously substituted for the 

 human subject. 



