Volltext: Photography of the fundus of the human eye (20)

might possibly be rendered suitable for such. After a few prelimi¬ 
nary trials I had an instrument made for me, differing in many 
respects from the original one. 
The Nernstlamp was discarded and was replaced by a lamp of 
greater intrinsic brilliancy. The arrangement of the illumination-tube 
was slightly changed so as to allow a relatively greater part of the 
light reaching the eye. 
In the Zeiss instrument the image of the Nernst filament is pro¬ 
jected upon a slit and by means of a second condensor into the 
pupil of the eye. The light, after leaving the second condensor is 
deflected by a glass plate, making an angle of 45° with the axis of 
the tube. The optical system for viewing the fundus looks through 
this glass plate. With this construction about 8.5 °/0 of the light 
leaving the second condensor is projected into the eye and 91.5°/0 
of the light leaving the eye reaches the objective of the viewing- 
tube. I placed the glass-plate so as to make an angle of 65° with 
both tubes, which allowed about 21 % °f the light to enter the 
eye and 79 % to reach the observing eye. In this way the amount 
of light falling on the photographic plate was about doubled. 
The Nernstlamp has an intrinsic luminosity which I measured as 
of 3.1 Hefnercandles per square millimeter. By the use of a special¬ 
ly constructed halfwattlamp of low voltage I got an intrinsic bril¬ 
liancy of nearly 29 units per square millimeter. A suitable small 
camera having been adapted to the instrument I got, after a few 
failures, usable negatives of a diameter of 26 to 30 millimeters, 
showing about 27 degrees of the fundus and covering an area of 
4Vs times the diameter of a normal optic disc. 
The negatives were sometimes good, though very often blurred, 
owing to the long exposure of 0.4 to 0.5 of a second. I have tried 
to get- better results with a small arclamp of about 5 amperes but 
without much success. Though the intrinsic intensity was 3 times 
greater, the arqa was notably smaller. With an entirely modified 
construction and with an arclamp of 25—30 amperes better results 
might be expected as the exposure might have been reduced to 
*/8 of a second. As the angle of view was also rather small and 
could only be enlarged by a complete reconstruction of the appa¬ 
ratus, I have kep^ the instrument as it was, and have tried to get 
more satisfactory negatives in quite another way. 
With the indirect ophthalmoscopy we can entirely eliminate the 
reflexes on the cornea and the lens by following Gullstrand’s method. 
But we always retain two reflexes on the ophthalmoscope lens. 
These do not hinder visual observation as they are rather small and


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