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It is a strange paradox that VR surgeons, whose goal is to restore vision, are often forced to work with tissues1 that are very difficult or impossible to visualize. The use of dyes – or markers2 – makes numerous tasks easier for the surgeon and safer for the patient (see also Sect. 27.3.3).
34.1Posterior Vitreous Cortex
Autologous blood3 and ICG are able to faintly stain the vitreous, but the former is not an easy material to prepare and use for this purpose, while the latter does not result in a consistent marking (see Fig. 34.1).
The material of choice is TA. Either use a preservative-free version4 or filter it if you want to leave it behind; if used for diagnostic purposes only, there is no need for filtration.
•Following the creation of a small vitreous-free pocket in front of the posterior pole (see Sect. 27.4), inject a miniscule amount of TA over the posterior pole.
– Aspirate all excess (free-floating, non-sticking) crystals.
Pearl
If the crystals adhere to the surface, this is evidence that there is PVD. If there is no crystal sticking, it is still possible that PVD has not occurred; the inner surface of the vitreous is simply too smooth for the crystal to adhere to it (false-negative result; see Sect. 27.4).
1Healthy vitreous, ILM, fine epiretinal membranes.
2TA does not stain the vitreous (or the ILM; see below); it only marks the tissue.
3Whether via spontaneous bleeding or surgeon-injected blood.
4Triesence (Alcon, Fort Worth, TX, USA).
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DOI 10.1007/978-3-319-19479-0_34
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Fig. 34.1 ICG-staining of the posterior cortical vitreous. The green dye created a faint marking of the vitreous that is still present on the posterior retina. In eyes with poor contrast and lack of the normal pigmentation in the posterior pole this may be the only option to show the presence of the posterior cortical vitreous (see Sect. 56.2)
•If there is TA on the surface, detach the cortical vitreous (see Sect. 27.5.1 and
Fig. 34.2).
Fig. 34.2 TA marking the nondetached posterior hyaloid. The crystals clearly signal the presence of vitreous on the posterior retina. The PVD is created by aspiration using the (20 g) probe. A tiny hole in the middle shows that the posterior cortical vitreous was absent over the fovea
TA is also extremely useful in marking the vitreous that has prolapsed into the AC (see Sect. 63.6) as well as demonstrating the presence of vitreous adherent to the anterior retina. Even though it is not a “chromo-” weapon, air also makes vitreous in the periphery visible (see Sect. 14.1).
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34.2EMP
The membrane can be stained directly (using trypan blue5) or highlighted via “negative staining” against a stained background (see Fig. 32.9b). Trypan blue stains both the EMP6 and the ILM, but the ILM stains much more weakly. A dye combination7 is able to stain both membranes well.
Staining can be done under air or BSS; in the latter case, the surgeon can try to use a cold dye or a solution with a drop of 50% dextrose in it so that the dye readily sinks to the bottom of the eye. For more details about staining, see below.
34.3ILM
Staining this otherwise invisible membrane makes its removal much easier and less traumatic. The best result is achieved using ICG, followed by brilliant blue.8 The latter’s heavier-than-water version is easier to use and has a staining capacity that is almost as good.
TA is also being used to mark the ILM. It settles as a dust on the surface and is thus able to delineate the border between retinal areas with and without ILM cover. The problem with TA use is that while it does show the extent of the ILM-peeled area (“horizontal signaling”), it can interfere with the surgeon’s visual feedback about how deep his instrument is (“vertical signaling”).
A well-stained ILM9 may give a uniform greenish color, show nonstained islands (negative staining; see above), or enhance the visibility of ILM wrinkling: more dye accumulates in the “valleys” than on the ridges (see Fig. 34.3).
34.3.1 False-Positive Staining with ICG
If ICG is injected onto the retina after the ILM has been peeled, the nerve fibers will show a faint and not uniform staining – but staining nevertheless. Since the surgeon may be unaware that the ILM has been peeled,10 it requires extra caution not to start “peeling.”
5MembraneBlue (DORC, Zuidland, The Netherlands), which can also be used subretinally to identify retinal breaks.
6And other proliferative membranes on the retinal surface (see below, Sect. 34.4).
7MembraneBlue-Dual (brilliant blue G + trypan blue; DORC, Zuidland, The Netherlands).
8Brilliant Peel (Geuder GmbH, Heidelberg, Germany), ILM-Blue (DORC, Zuidland, The Netherlands).
9The use of ICG is described here.
10For example, the previous surgery was done elsewhere and the ILM peeling was not noted in the discharge summary. This, unfortunately, is not that rare.
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Fig. 34.3 ICG-staining of a wrinkled ILM. The microfolds in the ILM are not really conspicuous on external examination or even intraoperatively, but staining enhances them because of the increased contrast (see the text for more details)
34.3.2 Injection Technique for Staining the ILM
•Use a tuberculin syringe and a flute needle; make sure that there is no obstruction to the dye’s flow.
•Introduce it into the vitreous cavity and close the infusion.
•Inject the dye over the posterior retina to cover the entire area where you intend to peel (see Fig. 34.4).
–Rather than pushing the plunger with your finger, use your palm to do it (see
Fig. 34.5).
–Use minimal force; if there is no flow, do not push harder on the syringe but withdraw it and flush the needle while having it outside the eye.
–Never aim the jet stream at the fovea.
Fig. 34.4 ICG-pooling on the posterior retina. Simply closing the infusion before the actual injection allows the dye to settle on the macular area. This limits the amount of ICG needed and will not allow the dye to disperse throughout the vitreous cavity
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Fig. 34.5 Injecting dye by minimizing the risk from the jet stream. (a) Upon entry, the syringe is secured with three of the surgeon’s fingers. This kind of support is necessary to guide the tip of the flute needle through the cannula. (b) Just before injection, the way the syringe is held should be changed. The goal is to give the surgeon maximum control over the power of the jet stream. (Occasionally the plunger has increased resistance against the push, which in turn forces the surgeon to increase the force used for injection. The index finger would need to be extended were it to be employed for the push, which reduces control. It is possible that as the resistance of the plunger is overcome, the jet stream is strong enough to create a retinal break and inject the dye subretinally.) The surgeon changes the way he holds the syringe and does the actual pushing of the plunger with the palm of the hand. He must carefully monitor through the microscope the position of the flute needle’s tip while the hand’s position is changed: the risk is pushing the needle into the retina as the surgeon’s fingers “crawl up” the syringe
•Open the infusion after ~10 s and aspirate the dye with the probe.
Pearl
In eyes with a macular hole, several materials have been recommended to protect the RPE by blocking dye-access to it: TA, PFCL, visco, and autologous blood. None is efficient or easy to install and keep over the hole. The TA crystals may also be damaging to the RPE; the PFCL is either too small a bubble and rolls away or too large and then leaves a large area unstained; the visco tends to drift away as the needle is withdrawn; and the autologous blood is cumbersome to produce.