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13.2.1.3 Forceps
The surgeon should have a large variety of forceps available for different tasks since their design greatly influences their functionality.15
a
M
b
X
M
Fig. 13.6 Schematic representation of the serration on the forceps jaws. (a) Current designs have the serration perpendicular to the axis of the forceps (the lower jaw is shown from above). The area of contact with the membrane (M) is small. (b) From a side view, it is even more obvious that only a single tooth is grabbing the membrane (M). If the membrane could be grabbed along the membrane’s long axis (X), the contact area increased greatly. Since this is rarely possible in real life, the serration in this case should be turned by 90°. The ideal serration angle would be at 45°, allowing decent grabbing in all membrane positions
•Pointed tips can pick up finer membranes but increase the risk of tissue damage, and they are more prone to tear the grasped membrane since they have a small contact area.
•Serration on the jaw surfaces increases the firmness of the grab.
•“End-gripping”16 forceps (see Fig. 13.7) come in a wide variety (see also Sect. 32.1.1).
–In general, the finer their tip, the better visibility the surgeon has of what exactly the jaws are coming into contact with.
15Unfortunately the so-called “crocodile” (serrated) forceps has the serration edged perpendicularly to its axis; this limits the surface of contact to be small in most cases and may allow the subretinal membranes that are directly underneath the retinotomy or in close proximity to it to slip from the forceps jaws (see Fig. 13.6).
16End-gripping means that the jaws close only at their very tip.
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13 Instruments, Tools, and Their Use |
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Fig. 13.7 Schematic representation of standard vs end-gripping forceps designs. Crosssectional view, forceps in the open position. (a) When the standard type of forceps is closed, the entire surface of the jaws will come into contact: a relatively large area. (b) In the closed position of an end-gripping forceps, only the tips will touch each other; an open space is left behind them, which may increase the visibility of the tip when it is in action
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–The larger the tip, the easier it is to grab the membrane and the smaller risk of tearing it – but it is more difficult to have decent visual feedback of what exactly is being grabbed.
Q&A
Q Why does a forceps lose its ability to grab fine membranes?
AApart from the obvious (damage sustained during sterilization), the nurse may damage the tip intraoperatively as she tries to clean the jaws (remember, she does it in relative darkness and without the use of the microscope; see Chap. 6); the actuating mechanism may get stuck (silicone oil helps), or a piece of the membrane may remain caught between the jaws (see Sect. 32.1.3). The surgeon can also be responsible: serially grabbing thick membranes will destroy the fine-grasp capability of any forceps, not allowing it to grab delicate tissues anymore.
13.2.1.4 Scissors
•Scissors with long blades allow the surgeon to see the tip of the blade emerge from under the membrane on its far side. This enhances safety – otherwise, the surgeon can never be absolutely sure that he is not cutting retina underneath the membrane.
–Another advantage of the long blade (of a vertical scissors; see below) is that if the surgeon keeps the forceps in the closed position, the blades can be used as a blunt spatula.17
–A further disadvantage of the short blades is the membrane’s tendency to be pushed away (distally) as the forceps is actuated; with long blades the risk of the membrane slipping out of the blades is much smaller.
•The blade angle has 3 basic variations: vertical, straight, and curved.18 Each has some advantages, but by far the vertical is the most versatile one. It is also the least risky (causing iatrogenic retinal damage) as its sharp tip does not directly point toward the retina.19
–In the open position, the vertical scissors can act as a bent needle (see below, Sect. 13.2.3.1). In most cases, with careful maneuvering, even the lower blade with a sharp superior edge can act on the already lifted membrane as a spatula would.20
Pearl
In an experienced surgeon’s hands, a sharp but non-squeezable tool is more precisely controllable and thus less risky than a blunt instrument that requires squeezing.
17The disadvantage is that the surgeon has to pay attention to keeping the handle squeezed – which also interferes to some extent with how delicate his finger movements can be.
18The blade is perpendicular to the axis, is a linear continuation of it, or is in-between. The first two have straight blades. The vertical may also be asymmetrical: the lower blade is longer than the proximal one.
19Although occasionally the tip of the vertical blades must be turned toward the retina to pick up a membrane, which is then dragged toward the surgeon. Keep in mind that this is a risky maneuver.
20In other words, the blade will not cut the membrane while it is manipulating it.