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Q&A
QWhat are the benefits of removing the silicone oil first during a reoperation, rather than “operate under oil”?
AFirst, the true anatomical situation is much more obvious to see, such as the location and strength of traction forces or retinal shortening. Second, TA and stains can be used to search for vitreous remnants and proliferative membranes. Third, if there is subretinal oil, its removal becomes possible. Fourth, if the oil must be reimplanted, its longevity is now increased (the “emulsification clock” starts anew).
35.4.5.2 Emulsification
It may occur a few weeks or several years after installation and has many undesirable consequences. The cause can be “natural aging” of the oil, poor quality (i.e., low purity), or a less than 100% fill (probably due to the oil being shaken during eye/head movements).
•Emulsified oil does not fulfill its intended function – that requires a large, single bubble.
•Visibility is reduced, both for the patient and ophthalmologist.
Pearl
Even if no emulsified oil is seen in the AC (see Fig. 35.6), bubbles may be present but hidden from view at the slit lamp. If the patient has decent vision, ask him whether his vision is worse when he is lying on his back and looks up at the ceiling – the oil bubbles collect in the visual axis in this position. For the same reason, a few previously undetected droplets always become evident as they gather behind the corneal apex when the patient is on the operating table.
•The IOP may rise to such levels that conservative treatment is not able to control it.44
The oil droplets can stick to any surface such as epiretinal membranes, the ciliary processes, or the back of the iris, but especially to vitreous that was left behind (see Fig. 35.7).
35.4.6 Removal
With a few exceptions regarding etiology45 the patient must be told that there is a risk of retinal (re)detachment after oil removal.
44Since the oil removal is never complete (see below), the glaucoma may persist for many months.
45Such as macular hole or VH.
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Fig. 35.6 Emulsified silicone oil in the AC. Some 40% of the AC is filled with emulsified silicone oil. Such a large amount is easy to recognize, but if only a small amount of bubbles is present, this may remain hidden at the slit lamp (see the text for more details)
Fig. 35.7 Emulsified silicone oil stuck to the retinal surface. In this eye there are emulsified oil bubbles within the stillpresent large silicone oil bubble. Upon removal, the surgeon should at least try to remove the small bubbles that are adherent to the retina, but first he must check whether the previous surgeon performed an incomplete PVD. Vitreous remnants have a high affinity for “capturing” emulsified oil bubbles
Q&A
QWhy is RD after silicone oil removal common with some surgeons but rare with others?
AOne of the possible answers is the completeness of the vitrectomy. Silicone oil is not supposed to be implanted in an eye with less than total PPV. Contraction of the residual vitreous or true reproliferation is common after the oil is no longer in the eye. The surgeon should never rely on silicone oil as a substitute for proper vitrectomy, but consider the oil as an additional weapon. If the surgeon says: “well, I will struggle
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removing the peripheral vitreous but, just in case, I’ll use oil anyway,” he may end up not doing a complete job. This happens subconsciously, akin to asking a person to meticulously clean the room. If he is told that another person will also be asked to clean the room after him, he is much less likely to do a meticulous job.
35.4.6.1 Timing
As a general rule, it depends on the etiology, the condition of the eye, and whether emulsification has occurred.46 My personal guiding principles are the following:
•If the silicone oil is used in macular hole surgery, removal is at ~1 month.
•In eyes with RD as the original indication, the removal is at ~4 months if the PVR risk is average and at ~6 months if the PVR risk is high, such as in severe trauma (see Sect. 63.12).
•In eyes with recurrent VH as the original indication, the patient has to decide.
35.4.6.2 Surgical Technique
•If there is little or no oil in the AC, start the oil removal posteriorly (see below). If the posterior maneuvers cannot be visualized because so much emulsified oil is in the AC, clear the AC first.
–Make a paracentesis larger than the diameter of the cannula you want to use.
–Use BSS to flush the droplets out; unlike a large bubble, these droplets will readily exit the eye. There may be a constant resupply of droplets from the vitreous cavity and posterior chamber so that the irrigation may have to be repeated several times before the oil removal can be completed posteriorly.
–Irrigate the AC one more time after the posterior oil has been extracted.
Removal of the silicone oil from the vitreous cavity requires several steps:
Pearl
Place all 3 cannulas before connecting the infusion line to prevent the oil entering the silicone tubing as you insert the superior cannulas. Even with the improved IOP regulation of today’s vitrectomy machines it takes some time to push the oil from the tubing back into the eye.
•BSS entering the eye through the infusion cannula will replace the oil.
–Make sure that the position of the infusion cannula is such that the BSS is directed behind the oil bubble, not anterior to it.
46 And on the individual surgeon’s philosophy. I err on the side of keeping the oil longer.
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•Use active aspiration to speed up the process.47 Some companies supply a short metal cannula that is pushed through the cannula,48 others a silicone tube that is placed over the cannula. In the latter case a non-valved cannula must be used.
–A flute needle with active aspiration (or the probe) can also be used for oil removal. To avoid the clogging of the small-gauge probe by the silicone oil, occasionally operate the cutting function of the probe. Conversely, avoid cutting if the probe has to be pushed into the subretinal space.
•The removal of the oil is through the superotemporal sclerotomy.
•Regardless of the instrumentation or surgical technique, no oil removal will be truly complete as the bubbles adhere to all intraocular structures (see above and 25.2.5).
•Occasionally the oil bubble disconnects from the cannula during extraction. Try to aspirate the large bubble with the probe (see Fig. 35.8) or grab the cannula, rotate the eye so that this is uppermost point of the globe, and let the oil escape (see Fig. 35.9).
Fig. 35.8 Aspiration with the probe of a large residual silicone oil bubble. A large bubble of silicone oil has escaped during removal and is now free-floating in the vitreous cavity. One option to remove such a bubble is to aspirate it with the probe. As the bubble decreases in size, the eye must be rotated so that the tip of the probe is at the highest point of the vitreous cavity; otherwise, the oil can escape again. During aspiration it may be impossible to have visual feedback that the bubble is getting smaller; the surgeon may have to turn the probe sideways and close to the bubble’s edge to be sure that the oil is flowing. The change in the shape of the bubble is a telling sign: a small funnel forms if there is oil drainage (another example showing the need to insert the tool from the temporal side if the manipulations are to be performed in the anterior part of the vitreous cavity.)
47Passive removal is also an option. With a gaped 20 g sclerotomy (the conjunctiva must obviously be opened first), the oil will readily exit the eye, but the surgical field will be messy. Copious irrigation of the ocular surface is needed to avoid trapping silicone oil subconjunctivally.
48This reduces the diameter of the channel through which the oil must flow.
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Fig. 35.9 Passive silicone oil outflow through a non-valved cannula. (a) The cannula is grabbed with a special forceps, and the eye is rotated so that the cannula’s (invisible) tip is at the highest point of the vitreous cavity. If this is successful, silicone oil droplets are seen exiting through the (obviously non-valved) cannula. (b) Once all the silicone oil has drained, the image instantly changes: the BSS is more akin to a jet stream
a
b
•In MIVS a smaller oil bubble will also be trapped around each of the superior cannulas; these bubbles become visible only when you push instruments through the cannulas (see Fig. 35.10).
–You can readily aspirate with the probe the bubble that is stuck to the light pipe. The oil bubble that is adherent to the probe must first be transferred to the light pipe and then removed. The maneuver is similar to how you sharpen a knife, just keep the safe distance from the retina.
–Droplets that are stuck to the retina49 are difficult to remove. You can try to passively aspirate them with the flute needle,50 but do not expect to be able to do a complete job.
49Again, make sure that vitreous is not left on the retinal surface.
50Which will often need to be flushed.
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Fig. 35.10 Silicone oil droplet on the probe. The thick arrow points at the small oil droplet that is stuck to the probe; the thin arrow shows the shadow it casts on the retinal surface. The oil will be removed by first transferring it to the light pipe and then aspirated with the probe. This maneuver may have to be repeated several times in MIVS; in cannula-free 20 g surgery such an issue does not exist
Pearl
If heavy oil has been used, you will likely be forced to use the flute needle and collect droplets from the retinal surface. Because this oil is not viscous, it usually exits the eye without active aspiration (which would be potentially risky since the port faces the retina). However, the droplets may also be so adherent that their removal is extremely difficult.
–Subretinally trapped oil is best removed with active suction via the probe. As the bubble gets smaller, the remnant will eventually “break through” and then be aspirated from the vitreous cavity.
•Gently shake the eye and, if possible, the iris separately to release at least some of the oil bubbles that are stuck to it. Gently aspirate over the posterior capsule and the IOL surface as well.
•Once all of the visible oil bubbles have been removed, perform a F-A-X. Use the probe (not the flute needle)51 to aspirate the fluid.
–Keep the probe on top of the BSS surface and do not use full aspiration. You will see the oil floating on the surface of the water, just as in an industrial oil spill; skim the surface. Keep the port facing the center (i.e., visual axis) so that you can see the floating oil gushing into the port.
–When the meniscus is very close to the disc, replace the probe with the flute needle and collect any remaining BSS/oil. You will see tiny oil droplets rushing toward the needle port. Since you basically have to touch the surface, make sure you adjust the BIOM front lens first.
51 It speeds up the process and prevents blockage.