Abstract
The original, conjunctiva-opening (20 g) version of vitrectomy is fast giving way to the transconjunctival variety (MIVS), a switch that has many advantages but also a few drawbacks. The placement of the cannulas during the transconjunctival approach, however, is not entirely intuitive. If, as one example, the actual location (in terms of clock hours) of the working sclerotomies is not based on a conscious decision and they are thus placed too superiorly, access to the inferior periphery in the phakic eye becomes impossible. The selection of the sclerotomy location is also influenced by other factors such as the condition of the sclera in the intended area. There are rules regarding the sequence of cannula placement as well as the opening of the infusion. Surgeons must realize that they can actually kill their patient if the cannula is misplaced and the infused air is able to enter the bloodstream. Finally, the removal of the cannulas also needs decisions to be consciously made to avoid postoperative hypotony.
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Notes
- 1.
A few words are included at the end of this chapter on 20 g PPV since it is not completely out yet. It must also be mentioned that transconjunctival surgery is possible with 20 g instrumentation.
- 2.
The 20 g incision is 53% larger than a 23 g one, but it is a difference of only 0.35 mm. I therefore dislike the term “small-gauge surgery” to characterize the 23-25-27 g options. Since sutures are occasionally needed in MIVS as well, I do not prefer the term “sutureless surgery” either. I accept the term MIVS, but interpret it as “transconjunctival vitrectomy.”
- 3.
Especially in the phakic eye.
- 4.
Just look at the videotapes being shown at scientific meetings.
- 5.
The most common reason for the erroneous site selection is simply that the surgeon does not consciously plan it (see 2.1.1).
- 6.
Between 5 and 7 o’clock.
- 7.
Not impossible, though.
- 8.
This is very important to avoid damaging the long ciliary nerves and arteries.
- 9.
In the left eye; in the right eye this is obviously mirrored.
- 10.
It is exceptional that PPV can be performed with a “single in” and “single out.”
- 11.
Except if there is extensive scarring on the inside of the sclera.
- 12.
Supposedly if the conjunctival opening is not right on top of the scleral opening, the risk of endophthalmitis is reduced.
- 13.
The fibers crisscross each other, but run fairly perpendicular to the limbus in its vicinity.
- 14.
Typically, I place the infusion cannula first but do not connect the line and then the superotemporal one because I do not have to exchange the hand holding the pressure plate; finally comes the superonasal cannula (see below, Sect. <InternalRef RefID="Sec9" >21.5</Internal Ref>, the exception to this order).
- 15.
Significant hyphema, white cataract, severe vitreous hemorrhage etc.
- 16.
This is also important when silicone oil is implanted under air: you do not want the oil to coat the posterior lens capsule, but to drip straight down toward the posterior retina.
- 17.
May be compounded by the reduction of the orbital fat so that the eye is deep-seated; this is rather common in elderly patients.
- 18.
Later you will have to “fish it out.”
- 19.
Or appear to be so, due to tissue stretching.
- 20.
It may not since the choroid is elastic, and the opening may immediately close.
- 21.
Bleeding is extremely rare from this. Do not use diathermy because it may shrink the tissue.
- 22.
Which would increase the leakage potential once the cannulas have been removed.
- 23.
There are other causes of inadvertently pulling out the cannula. Thin sclera; material stuck to the external surface of the instrument or the internal surface of the cannula (see below); a curved-tipped memory tool (such as laser probe) was not withdrawn into the shaft prior to tool removal; an outward bent hooked needle of the same gauge (see Sect. 13.2.3.1).
- 24.
The normal sclera does contain some elastic tissue to assist in its capacity to self-close.
- 25.
This would assume a negative IOP, sucking material into the vitreous cavity.
- 26.
Too high an IOP is just as problematic as a too low one (see Sect. <InternalRef RefID="Sec16" >21.8.1</Internal Ref>).
- 27.
Based on my personal preferences.
- 28.
I had used to do extensive diathermy but then stopped unless a well-identifiable vessel caused a major bleeding or the patient had an increased tendency to bleed (see Sect. 40.1). The small hemorrhages soon stop spontaneously.
- 29.
6-0 or 7-0 vicryl.
- 30.
e.g., to remove a larger IOFB.
- 31.
The original one is plugged until the fourth sclerotomy is sutured.
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Kuhn, F. (2016). Sclerotomies and the Cannulas. In: Vitreoretinal Surgery: Strategies and Tactics. Springer, Cham. https://doi.org/10.1007/978-3-319-19479-0_21
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