This communication presents a method for making measurements on the fundus of the eye with a degree of accuracy never before obtained. The heliometer eyepiece for the Gullstrand ophthalmoscope, constructed by Lobeck in 1935, introduced a technical refinement that has made such accuracy feasible. However, with the original method of use as described by Lobeck the possible error of any individual measurement was as great as with many previous methods that have been discarded. With the application of the method introduced in this paper, measurements with the Lobeck eyepiece may be corrected to an accuracy of 0.01 mm.
The development of the ophthalmoscope in the middle of the last century opened a new avenue for the study of the living human body. The advantage of such a direct method of examination for the investigation of local conditions in the eye is obvious, but it was recognized early that this procedure