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:
[31] Amer. Jour. of the Med. Sciences, July, 1855, p. 82.
“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.”
[Illustration: Fig. 4.--Cheselden’s knife-needle (after Sharpe).]
[Illustration: Fig. 37.--Ziegler’s model of knife-needle.]
[Illustration: Fig. 36.--Hays’ knife-needle, exact size and enlarged
(Hays).]
[Illustration: Fig. 16.--Sickle-shaped knife, Aiguille-à-serpette
(Galezowski).]
[Illustration: Fig. 35.--Sichel’s iridotome (after Meyer).]
[Illustration: Fig. 34.--Knapp’s knife-needle.]
[Illustration: Fig. 7.--Adams’ iris-scalpel; large and small size.]
[Illustration: Fig. 33.--Double edged lance-knife (modern model).]
[Illustration: Fig. 5.--Double edged lance-knife (Beer).]
[Illustration: Fig. 12.--Iris-knife (Walton, after Beer).]
[Illustration: The Various Knife-Needles and Iris-Knives Mentioned in
the Text. (Grouped together for study and comparison.)]
[Illustration: Fig. 37.--Ziegler’s model of knife-needle.]
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.
[32] This knife-needle has been carefully made for me by Luer, Paris,
and by Ferguson, Philadelphia.