328 



b}' slight niovements of (he üphthalmoscope lens can always be 

 removed from anj part of the real image of the fundus. 



But their presence is an absolute hindrance to photography. They 

 cause the appearance on the negative of one or two large spots, 

 covering its central part and having a diameter of nearly ^/j of the 

 whole negative. The brightness of these reflexes is several hundred 

 times larger than that of the image of the fundus. I have tried in 

 many different ways to eliminate these reflexes and have found that 

 they could be reduced so as to be almost invisible by means of two 

 small screens. 



In accordance with this principle I constructed a new photographic 

 ophthalmoscope. The diameter of the negative is 40 mm. The retina 

 is photographed with aT magnification of 4.7 times, over an angle 

 of 33 degrees, giving an image with a diameter of about 57, times 

 as large as the normal optic disc. The small arclamp of 4 to 5 

 Amperes with which the instrument is lifted allows of exposures of 

 7i4 of a second, though this may be reduced to ^',0 of a second in 

 some cases. However as the reflex time for the orbicular muscle 

 reflex is much longer there is no advantage in further reduction of 

 the time of exposure. The exposures are short enough to give sharp 

 negatives even in a case of nystagmus. 



The quality of the negatives is generally sufficient. They are 

 sharply defined. Generally the middle part is more strongly impressed 

 than the marginal parts, as was to be expected. Yet direct enlarge- 

 ments or prints can nearly always be made without any retouching. 



The whole apparatus, which will be fully described elsewhere can 

 be used for both eyes without any alteration except the ordinary 

 focussing. The dimensions are only slightly larger than those of the 

 Gullstrand-Zeiss demonstration-instrument. Its use is not much more 

 difficult than the making of an ordinary photograph with a studio- 

 camera. 



