752 OPEEATIONS UPON THE EYE AND EAR. 



penetrated between the ciliary processes and the border of the 

 lens, and presently becomes visible to the operator, passing be- 

 yond the internal border of the pupil. By a slight motion up- 

 ward and downward, the capsule is then opened and the lens 

 depressed, first backward, then vertically, and pushed downward 

 into the lower part of the vitreous humor. A gentle rotation of 

 the instrument then releases it from the substance of the lens, and 

 it is returned to its horizontal position. The instrument is not 

 withdravm until it is ascertained that the lens is established in its 

 new position. 



When the puncture is made through the cornea the entrance 

 into the eye takes place near the center of this membrane, and 

 the access to the lens takes place through the opening of the 

 pupil. 



In either case the wound of the globe is insignificant. 



2d. Method. Extraction. — There are two principal modes of 

 operation, one by extraction through a flap of the cornea upward, 

 and another by a linear incision on the side of the globe. 



In the operation by the fiap upward, the knife of Richter, 

 modified by Beer (Fig. 545), is introduced horizontally through 



FlO. 545.- Knife of Beers. 



the cornea, near the sclerotic border, a little above the horizontal 

 diameter of the globe, with the edge turned upward, and as soon 

 as the point of the instrument has entered the anterior chamber 

 of the eye, it is pushed in a straight, horizontal direction, passing 

 into the anterior chamber (Pig. 546), and when its point reaches 

 the opposite side of the cornea, it is pushed through it in such 

 a manner that its exit and its entrance occur at equal distances 

 from the sclerotic border. 



The flap is completed by pushing the instrument directly out, 

 when the aqueous humor escapes, and the cornea collapses. 



The anterior wall of the crystalline cover is then divided with 

 the kystitome (Fig. 547). The hook of which turns backward, 

 and is made to tear the envelope by moving it from above down- 

 ward and from within outward. The upper lid being raised with 

 forceps, and a gentle pressure made with the finger at the lower 



