ON THE ESSENTIAL ORGANS OF SIGHT. 



761 



ize the eye. It operates by grasping the conjunctiva on the inner 

 angle of the organ, and keeping it motionless by a shght pres- 

 sure. The lids are kept widely separated by means of the specu- 

 lum ocuH already mentioned. There are three principal modes of 

 operation besides these, which are used in human surgery, which 

 result in the union of these priucipal methods. 



1st. Method. Dislocation of the Lens. — It is intended to 

 displace the cataract en masse from the pupHar focus, and to fix 

 it in a dependent part of the chamber, behind the iris, where it 

 will no longer intercept the light. 



It is generally performed in two ways — through a puncture of 

 the sclerotic (Scleroticonyxis), or by puncture through the cornea 

 (Keratonyxis). The instrument used is called Scarpa's needle 

 (Fig. 543). This is either straight or curved. The eye being fixed, 



Fig. 543.— Scarpa's Needles. 



and the pupil dilated, the needle is introduced through the scle- 

 rotic, on the outside, and lower part of the globe, a short distance 

 back of the cornea (Fig. 544), pushing it in a direction first sHghtly 

 obliquely upward, and then horizontally. The needle has thus 



Fig. 544.— Operation of Cataract by Displacpment of the Lens 



