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13 Instruments, Tools, and Their Use |
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With a memory material, it is important for the surgeon to retract the tool back into the shaft before the tool is withdrawn (see Sect. 21.7).
13.2.3 Non-squeezable Hand Instruments
As mentioned above, there are instruments that do not require complex extraocular maneuvers; the surgeon’ fingers are used for a single maneuver: moving the entire tool around.
13.2.3.1 Bent (Hooked, Barbed) Needle
Epiretinal membranes can be picked up (see Chap. 32) with forceps, a membrane scraper, (vertical) scissors, or a needle31 with a small hook at its tip (see Fig. 13.8 and Table 13.1.). The barbed needle is a very versatile tool, among others for the following purposes.
•Creating a PVD by carefully scratching the retinal surface (see Sect. 27.5.1).
•Slicing open, even lifting, an elastic preretinal membrane (see Fig. 13.9).
•Separating scar tissue from the retina, whether in the macula or elsewhere and irrespective of how thick (thin) the membrane is. The technical difficulty presents when working over detached retina (see Sect. 53.2).
•Identifying and then lifting invisible membranes off the retinal surface.
•Incising the ILM reduces the potential risk of direct forceps grabbing (see Sect. 32.1.2.2).32
Fig. 13.8 The barbed (hooked) needle. (a) If 23 g surgery is performed and the needle is 25 g, it is better to create the hook outward: this improves the visibility of the tip during the delicate maneuvers of picking up tissue without damaging what lies underneath. (b) If 23 g surgery is performed and the needle is 23 g, the hook must face inward; otherwise, it may not slide through the cannula – or even if it can be forced in, it will likely remove the cannula upon withdrawal (see Sect. 21.7). (c) Preparation of the hook: the needle is gently pressed against a smooth, flat metal surface and only for a split of a second. It is very easy to “overdo” this, and create a hook that is too large or at too much of an angle. (d) The ideal appearance of the barb. It is visible, even at this high magnification, mostly because of the different light reflex (which is in turn due to the angle). (e) A proliferative membrane, which has caused a large tractional retinal break, has been hooked with the needle and is being separated from the retina. The hook is turned toward the retina. (f) In this case, the hook faces away from the retina; this is recommended only after the membrane has been identified and partially separated from the retina (i.e., there is now space between them). The needle can then act as a spatula, but in case the membrane is lost or the surgeon seemingly reached the end of the membrane, the barb can again be turned toward the retina and continue the search for separation elsewhere. If the needle’s hook is covered by tissue, the surgeon need not remove the tool but “twang” it intravitreally (see Sect. 32.1.3) and then continue with the membrane work
31In lieu of a bent-tip MVR blade, this is my favorite tool to start lifting fine, often even thick, epiretinal membranes and identifying invisible ones in proliferative diseases such as PVR or PDR.
32Other potential uses outside the vitreous cavity (e.g., see Fig. 13.3) are not listed here.
13.2 Hand Instruments |
107 |
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a b
108 |
13 Instruments, Tools, and Their Use |
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c |
e |
d |
f |
Fig. 13.8 (continued)
Table 13.1 The bent (hooked) needle for the removal of epiretinal membranes*
Variable |
Comment. |
General |
Being a tool that requires no squeezing, it provides maximal control for the |
advantages of |
surgeon |
the bent needle |
The hook is small and is unlikely to cause significant retinal damage even if |
|
pressed too deep |
|
The hook can be turned downward to find and lift the membrane then upward |
|
to continue with the lifting and extend the separation sideways (acting as a |
|
spatula) |
|
Having decently sharp edges, the needle can cut adhesions of the membrane to |
|
the retina, provided the adhesion is weak |
Advantages |
The ILM on which the epiretinal membrane rests has no edge; gently scraping |
over forceps |
on its surface will not break the ILM; therefore, it is easier with the needle |
use |
than with forceps to identify the correct depth (i.e., identify the true |
|
thickness of the EMP) so that the separation does not create a |
|
“membranoschisis”a but occurs between the EMP and the ILM |
Advantages |
Because of the angle of the blade, it may be difficult or even dangerous to start |
over scissors |
the separation of the membrane. As described above, it is easier and safer |
use |
to the find the correct cleavage plane with the hook on the needle |
Advantages |
The vector of the scraper in use is partially downward, unavoidably putting |
over scraper |
pressure on the retina, which in turn is pressed against the hard sclera |
use |
underneath. The downward pressure decreases the surgeon’s control over the |
|
maneuver. This is not a contraindication to scraper use, but the pressure on the |
|
retina (and choroid) represents a potential risk that the surgeon must appreciate, |
|
even if the tool’s advocates rarely mention it. Again: the needle is indeed a |
|
sharp tool but gives the surgeon much more control over what happens |
*The epiretinal membrane is quite often multilayered (see Sect. 32.2.2.3).
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109 |
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a
M
R
VRA |
VRA |
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|
VRA |
b
c
Fig. 13.9 Schematic representation of using the barbed needle to open an elastic preretinal membrane. (a) The membrane (M) may be an anomalous PVD or a newly formed one in diabetes, and it may or may not have attachments (VRA) to the retina (R); the space between it and the retinal surface may be extremely tight (as on this image) or virtually nonexistent. The surgical goal is to open and then to remove the membrane without damaging the retina. (b) If the surgeon tries to incise the membrane with a sharp (not barbed) needle or blade, he has to sink the tool into the membrane; in other words, he pushes the sharp tip toward the retina, more or less perpendicular to it (arrow). The membrane, however, is elastic: instead of opening up, it gets forced against the retina. The risk of direct retinal injury is considerable since the surgeon is not absolutely certain how deep his tool is (how much he must push toward the retina as opposed to moving the needle sideways). (c) Conversely, if a barbed tool is used, the vector of the tip’s movement is a combination of a retina-perpendicular and retina-parallel one (arrows); eventually the membrane opens, without undue risk to the retina, and can safely be lifted with the barbed needle or a forceps