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32 Working with Membranes |
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depth to which the tiny hook is sunk into the retina first and then moving the tool “in plane”10 and even that over a little distance only.
Q&A
Q Is it not a contradiction to say that a sharp tool is safer than a blunt one?
ANo – as long as the surgeon is able to control the depth to which he pushes the barb into the retina. With forceps, there are additional variables to control (see below). The third option, the scraper, is even more dangerous, precisely because the surgeon gives up control (see below).
32.1.2.2 Blunt Opening: No Incision
Blunt opening of the ILM is possible in two very different ways: via a primarily vertical movement (forceps) and a primarily horizontal one (scraper).
The ILM Forceps11
The advantage of this technique is that the same tool is used to tear and then peel the ILM. The disadvantages include the difficulty controlling the depth (so as to avoid tearing the nerve fibers, which run just beneath the 2 μ thick membrane) and the complexity of the maneuver.
•Place your forceps over ILM (see above the site-selection criteria).
–All current forceps designs are such that the tip of the jaws is perpendicular to the axis of the jaws – none is slanted. Since the jaws face a concave surface, the initial contact point of the forceps should be rather posterior so that the tip is parallel with the retinal surface (see the concept under Sect. 24.1). Moving it too peripherally means that only the corner-edge of the tip of the jaws, a very tiny area, will be able to grab the ILM (see Fig. 32.3).
•Gently press down with the forceps. The depth should be just enough to create a depression so that when the jaws will be closed, a loop of ILM is caught but no nerve fibers (see Fig. 32.4).
•Close the jaws.
Pearl
The most common error the inexperienced surgeon commits is to combine all movements into a single motion, instead of separating it into its basic elements.
(1) Have your wrist firmly supported and keep your little finger on the patient’s forehead. (2) Position the forceps over the ILM in the selected area. (3) Close the forceps ~80% so that the ILM will easily fit into the jaws yet the distance your fingers will have to travel to close the jaws is shortened. (4) Push down with the forceps so that the ILM bulges as a loop in-between the jaws. (5) Close the jaws. (6) Lift the forceps. (7) Repeat all steps if there is no purchase.
10That is, parallel with the surface.
11See also Sect. 20.2.
32.1 ILM |
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F2
F1
R
Fig. 32.3 Schematic representation of the point of attack with the ILM forceps. If the forceps is used rather centrally within the vascular arcade, the tip of the forceps is parallel with the retina (R), allowing the surgeon to grab the ILM with the entire width of the forceps (F1). If he tries to grab it further away from the central area, only the edge of the tip will make contact (F2), increasing the likelihood that the ILM will tear or that he pushes the forceps too deep
•Lift the ILM gently and hold it for a few seconds. The ILM is rigid and will rip.
•Start peeling it in a certain, predetermined direction and angle.12 Even if the ILM tears subsequently – and it will – from now on, you will have an edge to grab, which is much easier (see below).
The Scraper
The diamond-coated instrument is repeatedly dragged over the ILM until the membrane breaks: the main vector component of the movement is parallel with the retina.
•However, the silicone flap of the scraper must also be pressed downward to allow engagement of the ILM. The surgeon has no visual control over how much downward pressure is exerted.
•Once the ILM has been opened, accidentally dragging the diamond crystals over the now-denuded nerve fibers instantly becomes possible, and tearing of the nerve fibers is almost inevitable. This is especially dangerous if the surgeon is not using an effective dye so that he knows exactly over which surface not to use the scraper.
Q&A
Q Should the scraper be used to open the ILM?
A No. A surgeon who uses the scraper for opening the ILM gives up control in favor of apparent ease. The risk of such a maneuver far exceeds its benefits.
12 Characteristics such as direction and vectors are determined by the pathology (see various chapters in Section 5).