60 



MICROSCOPY OF THE LIVING EYE 



Fig. 36. — Vacuoles in the anterior 

 lens-cortex by retroillumination. 



in I, Fig. 41, Thus Fig. 38 diagrammatically represents intra- 

 epithelial vacuoles of the cornea seen against a small circular beam- 

 patch sharply focused on 

 the iris. Fig. 39, A, 

 represents correct, and B 

 incorrect focusing for the 

 R.I. patch on the iris. It 

 will be noted that while 

 the microscope is focused 

 on the cornea the illumina- 

 tion is focused on the iris, 

 and the latter must be 

 sharply focused if to give 

 the required sharp margin to the retroillumination ; the observer 

 must accustom himself always to be adjusting the illumination 

 focus, knowing that the patch 

 of light itself is in focus when 

 it is at its smallest. It often 

 happens that pathological 

 features in the cornea are 

 readily visible by R.I. to a 

 quite casual observer viewing 

 the cornea opposite the illu- 

 minated pupil-edge, even 

 though he does not trouble to 

 use a small beam or to focus 

 it correctly ; this is because 

 the pupil-edge (Fig. 40) 

 itself affords the necessary 

 sharp demarcation between 

 light and dark visual back- 

 ground. Fig. 40 shows a 

 disease of the cornea in 

 which the deep face reveals 



Sectufn, 



J^oo 



Pcrs^ 



ecdti/e 



Fig. 87. — Intraepithelial corneal vacuoles 

 seen with retroillumination by a small, 

 sharp cylindrical beam traversing the 

 substance of the cornea. 



permanent intrinsic changes of the nature of irregular and nodular 

 thickenings. In an advanced stage of the affection the patient 

 may proffer that he feels as if looking through corrugated or 



