Cryopexy |
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The endocryo probe used to be standard equipment in 20 g surgery; it was helpful in removing IOFBs or dislocated lens material/IOL. Unfortunately, this tool is not available in MIVS.
Q&A
Q Is it permissible to use “blind” cryopexy?
AAlthough some surgeons still use it over the wound in open globe injuries to “treat invisible or potential future retinal tears,” blind cryopexy is contraindicated. It increases the inflammation, a precursor of PVR; the precise location of the treatment is pure guesswork, and the surgeon knows neither whether his treatment has any effect nor whether he is overtreating.
Transscleral cryopexy today is employed as an adhesion-inducing force in RD surgery as well as a destructive agent in pathologies such as Coats’ disease, vascular tumors and telangiectasias of the retina, and intractable secondary glaucoma.1
29.1Indication in RD
By causing an inflammatory reaction and the breakdown of the blood-ocular barrier with consequent scarring, cryopexy causes chorioretinal scarring around a retinal break. The confluent spots create a “wall,” which seals the lesion. The scar involves all retinal layers,2 a beneficial effect if destruction is the goal (see below, Sect. 29.3). The scar takes up to a week to develop.
1Most of what is discussed here relates to RD surgery.
2Unlike with laser, which typically involves only the external retinal layers (see Chap. 30).
© Springer International Publishing Switzerland 2016 |
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F. Kuhn, Vitreoretinal Surgery: Strategies and Tactics,
DOI 10.1007/978-3-319-19479-0_29
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29 Cryopexy |
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29.2Surgical Technique
The freezing may be applied over the conjunctiva or directly over the sclera. Ideally, the surface is dried first.
•If you have a choice, select a cryoprobe that has a narrow and curved shaft.3
•Test the machine: observe whether an iceball forms over the tip of the probe and how many seconds it takes.
•Open the speculum to the widest possible and try to avoid touching the lids while freezing.4
•Have the nurse activate the machine by stepping on its pedal; you just give clear verbal instructions: “start” and “stop.”
–It is preferable that you concentrate on placing the cryoprobe and the freezing effect.
•Always have visual control over the intraocular effect.
–It is best to perform the cryopexy under the microscope; otherwise, use the IBO.
Pearl
Never count on the time of cryoapplication to determine its efficacy, only on your visual feedback (see Table 29.1).
Table 29.1 The visual feedback options in cryopexy for a retinal break
Color in |
Interpretation |
the area |
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of treatment |
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White |
The retina turns white as it freezes over |
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The application of cryopexy must be stopped as soon as the whitish |
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discoloration starts to appear: the thick iceball seen over a large area is not a |
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sign of “sufficiently strong” treatment but a precursor to PVR |
Dark grey |
It is not only retina that is being treated but the entire area of the retinal break |
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(e.g., retina plus the naked RPE). The retina adjacent to the break turns white |
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but the naked RPE shows a contrasting dark color |
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The only acceptable scenario for this color to appear is a break that is very small |
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(i.e., the size of the break is at most a little larger than the area of contact with |
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the cryoprobe)a |
Pink |
The color is that of an RPE that is being treated, but it is not naked |
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The retina is detached over the area of treatment but the detachment is too highb |
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for the freezing effect to involve it. The ultimate danger in this scenario is that |
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the surgeon either waits until all the subretinal fluid freezes over so that the |
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iceball finally reaches the retinac or that the retinal break upon retinal |
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reattachment will settle over an area that has not been treated. This is the |
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reason why in eyes with a very high RD it is advisable to drain the subretinal |
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fluid prior to cryoapplication |
a“Bull’s eye” sign: a dark area is surrounded by a white ring, which represents the retinal effect. bThat is, bullous.
cAnd the white color appears; see above.
3Some older models have a freezing effect along the shaft, not only at their tip (see the comment about the scleral depressor under Sect. 28.6): the area affected by the freezing is larger than intended.
4Significant and potentially painful lid swelling develops postoperatively if the lid has been caught.
29.2 Surgical Technique |
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•Do not treat the retinal break itself; treat the retina around it (see Fig. 29.1).
•Avoid overfreezing; stop the application as soon as the retina starts to turn white.
•Even if the surface was dried prior to placing the cryoprobe, an iceball forms on the ocular surface. This iceball takes a few seconds to melt after the cryoapplication is stopped. Do not try to lift the cryoprobe off the surface, especially the conjunctiva, before the melting is complete – you may tear the tissue.
a
B
R
b
C
Fig. 29.1 Cryopexy for a retinal break. (a) The retinal break is illustrated by the thick black line. If the cryopexy is done incorrectly (“place the tip over the break”), the entire area freezes over, liberating RPE cells and further increasing the risk of PVR. The “single-spot” treatment is especially dangerous if the break is relatively large: to freeze the entire area takes a long time, and the effect will be greater in the center, where there is no “cover” over the RPE cells. Such a singlespot option is acceptable only if the retinal break is very small. (b) Done properly, the freezing involves only the area adjacent to the break, surrounding it with contiguous, light applications. R retina, B break, C cryo spot
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29 Cryopexy |
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It must be emphasized again that while cryopexy is an effective weapon in creating chorioretinal adhesion in eyes with RD, it has a higher complication rate5 than laser. As much as possible, laser should be selected to treat around a retinal break (see Sect. 54.4.2.2).
29.3Cryopexy as a Destructive Force
Although the technique’s popularity is waning, the cryoprobe can be employed to destroy the ciliary body in eyes with intractable glaucoma and the peripheral retina in diabetic eyes with severe neovascularization or large areas of nonperfusion. In these indications “blind” cryopexy may be permissible: once the effect has been titrated in one location, the same duration of treatment can be applied in the rest of the area.6
•Ciliary body: continuous spots 1.5 mm from the limbus, ~30–50 s each. 180° (no more than 270°) treatment is recommended as the initial step.
– Cryodestruction of the ciliary body risks leading to phthisis.
•Peripheral retina: continuous spots just posterior to the ora serrata (see Sect. 26.2), no more than ~30 s each. The entire area may be treated in one session.
Pearl
Even if the risk of postoperative PVR is higher with cryothan with laser therapy, properly administered cryoapplication remains a useful weapon in the VR surgeon’s armamentarium for diseases such as Coats’, Eales’, familial exudative vitreoretinopathy, and vascular tumors. The effect of cryoapplication must be monitored in these conditions as well (i.e., no blind cryopexy).
The inflammatory response may be severe after the destructive intervention, requiring judicious steroid treatment.
5That is, PVR risk.
6The duration indicated below is therefore only a rough estimate.