44 MICROSCOPY OF THE LIVING EYE 



this photograph) bearing Koeppe's colour-filters, e.g., a red-free 

 filter for use in examining blood vessels, and other colours for use 

 in examining the iris and other parts, but this filter is of no 

 practical use with the filament slit-lamp ; its use necessitates a 

 more powerful light-source such as an arc-lamp. The chin and 

 head-rest for the patient under observation are shown in H, Fig. 9. 

 The binocular stereoscopic microscope (Fig. 9, M, and Fig. 12) 

 is supported by a footpiece which stands on a glass-topped table ; 

 this simple arrangement, in which coarse adjustment of the posi- 

 tion of the microscope is made with great ease and simplicity, 

 is far more suitable than having the microscope mounted on a 



'*..._ / 



> H 



I 



4 



PRerocAL FOCAL PasrncAL 



> 70 



:0:; 



PREFOCAL FOCAL PoSTf^'i 



Fig. 11. — Influence respectively of the 100 cm. and the 70 cm. 

 focusing lenses on the configuration of the focused slit-beam. 



mechanical stage with crossed rack adjustment. The microscope 

 is supplied with binocular eye-pieces, usually of two alternative 

 powers, and with three binocular objectives, giving magnifications 

 ranging from x 9 to X 45 ; for routine clinical work one magnifica- 

 tion, X 9, and a second, X 24, is the most satisfactory combination 

 to have. The mistake is commonly made of using too high a 

 magnification for work on the living eye ; the lowest, X 9, seldom 

 used, is one of the best because its field just covers the diameter of 

 the cornea. One eye-piece can be fitted with a micrometer-scale 

 for recording measurements. There are other makes of slit-lamp 

 on the market, some good, some with the general fault of being 

 too elaborately constructed in respect of means for their mechanical 

 adjustment, the maker losing sight of the fact that the clinical 

 observer wants simple and easy means of adjustment in relation 



