70 



MICROSCOPY OF THE LIVING EYE 



V 



borders on zero. Neither the relucency nor the specularly reflect- 

 ing property of a tissue is to be taken clinically as a measure of 

 its capacity to obstruct the passage of light ; the term opacity 

 should be concerned only with retroillumination and not with 

 direct illumination. 



It has seemed aj^propriate, for this book, to confine the account 



of Microscopy of the Living 

 Eye mainly to technique, 

 partly because the princi- 

 ples are quite probably 

 applicable in other useful 

 fields, e.g., zoological work ; 

 and also because in the 

 space available a com- 

 prehensive account of 

 common normal and patho- 

 logical clinical features 

 could not well be given. 

 For this, reference should 

 be made to other publica- 

 tions {e.g., 1, 2, 3, 4, 5). 

 However, it may be appro- 

 priate to conclude with 

 some remarks bearing on 

 the clinical application of 



Fig. 41.— Retroillumination : dissimilarity the subject, illustrated by 

 of binocular images when under high a few examples of clinical 

 magnification. i . , . 



conditions. 



In 1911, at the Heidelberg Ophthalmological Congress, Gull- 

 strand showed his slit-lamp which was combined later for use with 

 the Czapski binocular microscope. The slit-lamp then had two 

 outstanding defects by comparison with the models which were 

 evolved later : the focusing-lens was not achromatic, and the 

 optical system furnished a focal beam of relatively insufficient 

 intensity. Vogt, of Basle (later of Zurich), in co-operation with 

 the late Dr. Henker, director of the Medical Optical Department 

 of Carl Zeiss, modified the apparatus, taking advantage of the 



