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The tip must be small33 and have an angle of ~30°. The needle can be used with the hook turned toward or away from the retina (see Fig. 13.8).
13.2.3.2 Membrane Scraper
Whether retractable34 or not, the small flap (the working part) of these tools has two sides.
•They bend easily in one direction (perpendicular to their flat surface). This side should be used over attached retina, especially near the fovea. The surgeon must make sure that he keeps the (unavoidable) downward pressure to the minimum.
–When the flat surface is held parallel to the retina and moved tangentially, the thin edge of the silicone flap can be used to break the VR adhesions.
•The scraper has a much higher resistance perpendicular to its thin edges. This side can be used over detached retina when the retina cannot easily be pressed against the sclera.
•The scraper is the ideal tool to move the retina (typically done under PFCL) in an eye that just underwent a large retinectomy. Massaging the retina in this fashion, however, does have some caveats.
–Understand that the typical goal of using the scraper is to lift a membrane off a surface that is (and should remain) stationary: EMP off the retina (ILM); both the EMP and the retina are rather soft. Damaging the EMP to be lifted is not a concern, but damaging the underlying surface is.
–However, when the scraper is used for massaging, a “membrane” (retina) is to be relocated, dragged over a hard and immobile surface (sclera; the choroid in this respect is irrelevant). Both the mobile (retina) and the stationary (in this respect the choroid) tissues require atraumatic handling.
–Never turn the thin edge toward the retina (see above).
–Use the scraper only on the side of the entry (e.g., over the temporal retina if the superotemporal cannula is used). For the opposite half of the retina, you must switch hands; otherwise, the main vector of the scraper’s movement will be perpendicular to the retina, not parallel with it. Attempts to cross over and caress the retina on the side opposite of the entry risk tearing the retina or damaging the choroid.
Pearl
The surgeon must also remember that the scraper is dusted with diamond crystals; dragging them over retina denuded of the ILM means inevitable tearing of nerve fibers. I do not recommend using it for ILM peeling, even if technically this is possible (see Sect. 32.1.2.2).
33Barely visible; this is why the barb is never prepared by hitting (bumping) a metal surface with it.
34Which is the preferred option, to avoid the difficulty of pushing the tool past the cannula’s valve.
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13.2.3.3 Spatula/Pic
These blunt instruments can be used to pick up and dissect epiretinal membranes. The tool must have a bent profile: this allows the surgeon to hold it at two different angles relative to the retina. The membrane needs to be rather mature for such a blunt instrument to be effective.
•If the retina is attached, the initial movement of the spatula is a careful, slow forward thrust (away from you; the main direction of the tool is along its main axis). Hold the tool fairly parallel with the retinal surface. As much as this is possible, try to do all this in the middle section of the membrane.
–The initial separation affects only a small area. Avoid “going deep” and inadvertently pushing, the tip of the tool into the retina.
–Separate the membrane from the retina, keeping the membrane “hooked” by the spatula the entire time. While holding the spatula parallel with the retinal surface, move alternatively toward both endpoints (periphery) of the membrane. If you go “all the way” in one direction, you lost the grip: further separation with the spatula becomes impossible,35 and forceps must be used to complete the procedure (see Fig. 13.10).
•If the retina is detached, a forward motion is usually ineffective: the tool is initially pulled backward, as if it were a rake.36 The tool is held at an angle to the retinal surface.
–The force of the tool’s action is spread over a larger area, and thus there is less of a risk of going too deep with it (i.e., through the retina).
•Once the membrane is hooked, the instrument is moved along two vectors: lifting the membrane somewhat (perpendicular to the surface) and separating it from the retina by moving the spatula sideways (parallel with the surface, perpendicular to the tool’s main axis).
13.2.3.4 Intraocular Magnet
By introducing the magnetic pole into the eye, this instrument virtually eliminates the risk of inadvertent/uncontrolled IOFB movement inside the eye. Unlike with an extraocular electromagnet where the IOFB travels (rockets) toward the magnet’s pole and the surgeon has very little, if any, control over its flight path, with the permanent intraocular magnet the surgeon has absolute control over what happens since he moves the magnetic pole toward the IOFB.37
35As discussed under Sect. 32.2.2.5., the “centrifugal” peeling of an EMP appears similar, but, due to the different characteristics of the tools used (forceps vs spatula), the effect is also different. The forceps, if used to grab the membrane in its central part, causes traction over large area; the spatula has a much more local effect. By moving it sideways and in both directions, the surgeon separates the membrane from the retina in a controlled fashion.
36Similar to what was described above with the vertical scissors (see Sect. 13.2.1.4).
37The surgeon must always make sure that the IOFB is completely freed of all its VR connections before being approached with the intraocular magnet.
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a
b
c
Fig. 13.10 Use of a spatula to separate epiretinal membranes from the retina. (a) The spatula (dark oval shape) must be placed between the membrane (dark line) and the retina (red line), then moved in both directions (black arrows), starting from the membrane’s central area. Roughly equal distances must be covered toward both endpoints of the membrane and only gradually approaching the membrane’s periphery. The breaking of the connections (short black lines) between membrane and retina is in a somewhat symmetrical or mirrored pattern. (b) If the surgeon follows this rule, the membrane is gradually separated from the retina in each direction. (c) However, if the surgeon went all the way in one direction, it becomes impossible to complete the separation in the other direction (gray arrow): there is nothing holding down, and giving resistance to, the membrane from the other direction
13.3Viscoelastics as an Intravitreal Instrument38
Viscoelastic material can be used in the vitreous cavity in different ways.
13.3.1Membrane Dissection (“Viscosurgery”): Viscoelastics as a Spatula
Delamination is possible with viscoelastic use if the cannula is pushed far enough between membrane and retina before injection; however, there are several caveats that the surgeon must keep in mind.
•A cohesive type of visco should be used; it is easier to remove after use.
•Once the viscoelastics started flowing, the “push effect” is of equal strength in a 3-dimensional shape in front of the cannula’s tip.
38 Keep in mind that viscoelastics, unlike watery fluids, have a high internal resistance. The stronger the surgeon’s initial push of the plunger of the syringe, the more resistant the material becomes against the push.
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•Avoid pushing “too hard” to avoid a viscoelastic flow that would be at high pressure.
–Even at low pressure on the plunger, once the viscoelastic material leaves the cannula, the surgeon loses control over its effect (see Sect. 3.2) until he stops pushing the plunger.39
–The effect at any given flow rate (injection force) is determined by the strength of adhesion between retina and membrane and the cohesion of each membrane. If the adhesion between membrane and retina is weak, you get gradual separation, exactly as hoped. If the adhesion is strong, the viscoelastic may initially flow around it and separate the membrane from the retina in the vicinity – but eventually tear the retina at the adhesion site.
–If the cohesion of the retina is weak, the retina will tear.
–If the cohesion of the membrane is weak, the visco will break through.
•The visco is easy to remove with the probe; the flute needle with its passive flow will not work.
13.3.2 Opening a Closed Funnel
Contrary to common belief, PFCL is not the proper tool to help the surgeon open a retina that is completely detached, and its anterior “entrance” is closed. See Sect. 32.3.1.5 on how viscoelastics can be used to open a closed funnel.
39 In fact, because the material is not only viscous but also elastic, the flow does not stop immediately.