Physiology. — "A new ophthalmoscope" . By Prof. J. K. A. Wehtheim 

 Salomonson. 



(Communicated in the meeting of December 28, 1918). 



In a former comninnication made at the meeting on Apiil 27''' 

 1917 I showed a collection of photographs of the living human 

 retina. 1 described and exhibited two different photographic ophthal- 

 moscopes, the second of which Jias been in regular use and gives 

 satisfactory results. x\s a matter of fact we can also use it for 

 simply showing a retina to any person not familiar with ophthal- 

 moscopy, as the instrument can be easily adjusted in exactly the 

 right position before the eye to be examined, the observer only 

 having to focus the image. But if an instrument of this kind has 

 to be used solely for demonstrating purposes a thorough reconstruc- 

 tion including many modifications might prove judicious. In that 

 case we ought to provide for the possibility of using several diffe- 

 rent magnifications, which in the case of the photographic instru- 

 ment, giving a real image of 40 millimetres in diameter would 

 have been irksome. With the photographic instrument the ocular 

 magnification amounted to 3.5 times, corresponding to an absolute 

 enlargement of the fundus of about 15 diameters. 



In the second place we should have to discard the arclamp the 

 light of which for our purpose can only practically be dimmed by 

 absorbing light-filters. 



We might have substituted for the small screens used for inter- 

 cepting the light reflected by the ophthalmoscope lens some more 

 appropriate means, at least if photography were not intended. 



Lastly it should be possible to materially reduce the dimensions 

 of the whole apparatus, rendering it more easy to handle. 



Starting from these considerations, I have built an entirely new 

 instrument, to be used solely for viewing the retina and showing 

 it to students as yet unskilled in the art of ophthalmoscopy. 



The principle of indirect ophthalmoscopy has been applied as was 

 also the case with the photographic instrument. For illumination a 

 small 25-candle power gas-filled lamp with a straight tungsten 

 filament-spiral was used, nofmally burning on a 4-cell accumulator 

 or on a small alternating current transformer for 8 Volts secondary. 



