940 



nervi optici. The whole field is remarkably flat, and sharp up to 

 the edges. The magnifieation is generally about 14 diameters, or 

 about the same as when tiie eye is examined with the direct method, 

 but with an angle of view many times greater. By using stronger 



eyepieces the image, which is in the upright position, can be magnified 

 up to about 50 times, the angle of view of course being somewhat 

 reduced. As the illuminating filament can be regulated to any 

 desired degree of brightness we can even with this high magnifi- 

 cation get a profusion of liglit, and exceedingly clear and sharply 

 defined images of the fundus. 



When in use the distance from the patient's eye to the instru- 

 ment is about 90 millimeters. The only change necessary when 

 examining different patients, is the focussing. In cases of strongly 

 myopic, hypermetropic or astigmatic eyes, examination is still possible 

 with the patient wearing his own glasses. 



The ophthalmoscope lens in this instrument is one of the well- 

 known aspheric aplanatic single lenses of 43 mm. clear aperture, 

 made by Zeiss. One might use any other aplanatic combination of 

 lenses, provided the focal distance and aperture were satisfactory. 

 The multiple reflexes from a combination of lenses would be obscured 

 as effectually as those from a single lens. 



