Fig. 5.—Double edged lance-knife (Beer).
Fig. 12.—Iris-knife (Walton, after Beer).
The Various Knife-Needles and Iris-Knives Mentioned in the Text.
(Grouped together for study and comparison.)
8. The knife-needle, which I invariably use, is a modified pattern of that devised by Hays. The form of this instrument lies midway between the falciform knife and the bistoury, and possesses the advantages of both. It has a very delicate point which punctures easily, and an excellent cutting edge of sufficient length (7 mm.). If the shank is properly rounded it can be used with a sawing motion, sliding backward and forward through the corneal puncture without injuring the cornea, and without allowing the aqueous to escape. To accomplish this the more easily, the shank has been made 4 mm. longer than the original model. This instrument, therefore, seems to meet all the requirements of a perfect iris-knife, viz., a falciform point which makes the best puncture, a straight edged blade which makes the best incision, and a cutting edge 7 mm. long, which is the best length for properly executing the sawing movement. My model[32] of knife-needle (Fig. [37]) resembles Cheselden’s knife, as shown by Sharpe (Fig. [4]), even more closely than the original pattern of Hays does.
Fig. 37.—Ziegler’s model of knife-needle.
ESSENTIALS OF SUCCESS IN IRIDOTOMY BY THE KNIFE-NEEDLE METHOD.
1. A good knife-needle must be carefully selected. We have already concluded that the modified Hays knife-needle is the best model for this purpose. The knife-needle must, of course, have a well sharpened point and edge.