History of Iridotomy / Knife-Needle vs. Scissors—Description of Author's V-Shaped Method

by S. Lewis Ziegler

THE CHOICE OF A KNIFE-NEEDLE.

1. Cheselden’s knife-needle (Figs. [3] and [4]) was a splendidly designed instrument, but a poorly executed one. The blade was too large (11 mm.) and the shank improperly rounded, so that both aqueous and vitreous were liable to escape through the scleral puncture. This leakage may explain many failures, although the single iris incision was undoubtedly the most serious fault of the method.

2. The iris-scalpel of Adams (Fig. [7]) was poorly designed but splendidly executed, the long blade completely filling the wound and thus preventing the escape of any fluid. The cutting edge, however, was too long (15 to 20 mm.), and especially so for the execution of the sawing movement advised by Adams.

3. The double-edged lance-knife (Figs. [5], [12] and [33]) employed by Heuermann, Beer and von Graefe, was useful for the long sweeping incision in the iris-membrane which they advocated, but is not adapted for the method which will be described later. The same shaped knife (Fig. [33]) with a smaller blade and a longer shank is also used for this purpose, but is likewise too broad, too oval pointed and too much bellied to cut well, while the upper edge is liable to scarify Descemet’s membrane at the same time that the lower edge is executing the incision in the iris tissue.

4. The sickle-shaped knife (Fig. [16]) which von Graefe recommends and Galezowski employs, is excellent for making the puncture, but for the go-and-come movement, which Galezowski advises, is not nearly so good as the straight blade with a slight falciform point. It closely resembles the older falciform knife of Scarpa.

5. The knife-needle of Knapp (Fig. [34]), which is so generally used for capsulotomy, is unfortunately not well adapted for iridotomy. The point is too oval, the cutting edge is too much bellied, and the blade is too short (5 mm.). It will not easily puncture a dense iris-membrane, and the long sawing incision can not be well executed, because the short blade either persists in slipping out of the iris incision or else allows the membrane to ride up on the shank, in either case interfering with the completion of the operation.

6. Sichel’s iridotome (Fig. [35]) closely resembles Knapp’s knife-needle, and although specially designed for this purpose, has the same faults, an oval point and a bellied edge. On the other hand, the blade is too long (11 mm.) to be easily manipulated in the anterior chamber.

7. The Hays knife-needle (Fig. [36]), as suggested in the early part of this paper, has the same general shape as Cheselden’s instrument, although much smaller. It was devised by Dr. Isaac Hays, an early surgeon of the Wills Hospital, and, although not well known to the profession at large, has been in constant use by the staff of that hospital for more than half a century. I may be pardoned for briefly quoting the original description of the instrument as published by Hays[31] in 1855:

“This instrument from the point to the head, near the handle (a to b, Fig. [36]), is six-tenths of an inch, its cutting edge (a to c) is nearly four-tenths of an inch. The back is straight to near the point, where it is truncated so as to make the point stronger, but at the same time leaving it very acute, and the edge of this truncated portion of the back is made to cut. The remainder of the back is simply rounded off. The cutting edge is perfectly straight and is made to cut up to the part where the instrument becomes round, c. This portion requires to be carefully constructed, so that as the instrument enters the eye it shall fill up the incision, and thus prevent the escape of the aqueous humor.”

Fig. 4.—Cheselden’s knife-needle (after Sharpe).

Fig. 37.—Ziegler’s model of knife-needle.

Fig. 36.—Hays’ knife-needle, exact size and enlarged (Hays).

Fig. 16.—Sickle-shaped knife, Aiguille-à-serpette (Galezowski).

Fig. 35.—Sichel’s iridotome (after Meyer).

Fig. 34.—Knapp’s knife-needle.

Fig. 7.—Adams’ iris-scalpel; large and small size.

Fig. 33.—Double edged lance-knife (modern model).

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.