39.1Paracentesis

An often-utilized procedure, paracentesis is not complicated or difficult, but keeping a few fundamental rules in mind makes the surgeon’s job easier and more effective.

•Choose the location carefully.

–For intracameral manipulations, an entry point in the superotemporal quadrant is the most convenient. The infusion (AC maintainer) is best placed at an inferotemporal location (see below).

•Use a sharp blade to create the incision.1

–The MVR blade is preferred to the “15° blade”; the size of the incision is precisely known with the former. With the latter it depends on how deep it is pushed into the AC (see Fig. 39.1).

1 Not a needle, with the exception of using the paracentesis for an iris retractor or the removal of a PFCL droplet from the AC (see Sect. 35.6).

F. Kuhn, Vitreoretinal Surgery: Strategies and Tactics,

DOI 10.1007/978-3-319-19479-0_39

374 39 AC Basics

L

W

B

c

Fig. 39.1 The effect of the blade’s shape on the creation of a paracentesis. (a) The MVR blade with its known dimensions is used to create the paracentesis. The internal opening of the tunnel has the same width as the external one, matching the largest diameter of the blade. (b) Using the 15° blade, the external opening of the tunnel is wider than the internal one (this is never needed in clinical practice; the opposite, however, rather often is), and neither is precisely known – it depends on how deep the surgeon penetrates into the AC with the blade. (c) If manipulations that take place far from the site and on both sides of the paracentesis, the surgeon can turn the MVR blade in the frontal plane in both directions, and widen the internal opening of the tunnel. This way the manipulations are easily performed without distorting the cornea, without the need to widen the external tunnel opening. I an imaginary line extended as if it were circle, along the path of the internal course of the tunnel ending; L limbus, the entry point for the tunnel; W the wound created by the blade (b)

Pearl

Do not grab the conjunctiva with forceps as you try to fix the eye to make the paracentesis. The conjunctiva is mobile; the grab will not result in a secure fixation; the tissue can also tear or bleed. Support the nasal side of the eye with your index finger (see Fig. 39.2), or use a pressure plate or corneal fixation ring.

Fig. 39.2 Use of the surgeon’s finger as a surgical tool. The globe can be secured against movement by the surgeon’s finger during the creation of a paracentesis. The wound is made on the temporal side with an MVR blade held rather flat; the tool itself is supported by the surgeon’s thumb, index and middle fingers. The ring and little fingers are pressed against the middle finger but also rest on the patient’s forehead. The surgeon’s other index finger secures the globe’s position; the rest of his fingers of this hand are also pressed against the patient’s forehead to prevent even the slightest movement of eye or tool

•The angle of blade entry2 should be such that the wound will be self-sealing (this favors an almost frontal plane) yet allowing the surgeon to maneuver around in the AC with various instruments without distorting the cornea (this favors a more downward-pointing angle).

•If you plan to use a round tool,3 take into consideration the cross-sectional area of the tool and make the paracentesis slightly wider than the diameter of the tool.

•The paracentesis for the AC maintainer should be prepared in the inferotemporal quadrant.

–This site is chosen because the cannula should not be in the visual axis.

–The direction of the intracorneal channel should be so that the cannula will be located over the iris; it should not be too close to the angle where the AC is shallow.

–The cannula is ideally a threaded one, to prevent dislodging during rotation of the eyeball.

2Measured relative to the plane of the iris. The surgeon should remember the parallaxis phenomenon (see Sect. 25.2.2.3).

3Such as a cannula.

•To pull the iris back into the AC, create a separate paracentesis at a convenient location.6

–Insert a long, blunt spatula and carefully pull the iris back into the AC.

–With this technique you will not only reposition the iris in the least traumatic way but also prevent reopening of the wound; this assures maintaining the depth of the AC and eliminating the need for visco7 (even if some aqueous has been lost, it will be rapidly replenished).

a

C

I P

b

V

Fig. 39.4 Schematic representation showing the disadvantage of visco use in corneal wound suturing. (a) Almost all wounds close spontaneously, and the AC recovers at least some depth. Without visco use, the contour of the cornea is close to normal. Only minimal tension on the sutures is required to achieve sufficient compression, and this effect is mainly in the frontal plane (gray arrows; the wound, which always closes spontaneously, is shown here as wide open for demonstration purposes.). (b) With a large amount of visco injected (which is an often-seen error in clinical practice), the cornea bulges, and extra tension is needed on the sutures (overtightening) to achieve sufficient compression. The sutures must not only bring the wound edges together in the frontal plane but also work against the effect of the visco in the sagittal plane, resulting in permanent corneal distortion with consequent astigmia. C cornea, I iris, P pupil, V visco

690°–180° away from the site of the prolapse. Being too close reduces maneuverability.

7Visco use should be avoided so that the corneal contour is not distorted (see Fig. 39.4).