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BOOK
EXCERPT CHAPTER
13 The topic of hydrodissection receives relatively little attention compared to phacoemulsification and intraocular lens (IOL) insertion techniques. It may therefore be the most underrated step of modern cataract surgery. A properly developed hydrodissection fluid wave should hug the internal capsular surface as it travels behind the nucleus.1,2 (Figures 13-1A through C). The subsequent hydrodelineation wave propagates along a more internal plane that cleaves the epinucleus apart from the endonucleus2,3 (Figure 13-1D). There are three important objectives for hydrodissection. First, because the phaco tip is confined to one location, nuclear rotation is integral to every phaco technique. Effective hydrodissection allows the nucleus to rotate without placing undue stress on the zonules. As a second benefit, the hydrodissection wave should loosen and facilitate removal of the epinuclear shell. Even following hydrodelineation, a loosened epinucleus will initially rotate together with the endonucleus. Once the latter is removed, the epinucleus can be more readily mobilized, spun, and flipped if its capsular attachments have been cleaved (Figure 13-2). Finally, the hydrodissection wave should shear the cortical-capsular attachments making cortical aspiration safer, faster, and more complete.1,2,4-6 There are several pearls that can help surgeons to consistently achieve these three important goals. Pearl #1: Decompress the Anterior Chamber Before StartingA common mistake is to initiate hydrodissection while the anterior chamber is over-inflated with viscoelastic. Hydrodissection is easier if the eye is somewhat soft and if the anterior chamber has been partially emptied. Of course, this condition is at odds with the preceding capsulorrhexis step during which an abundant amount of viscoelastic is desirable. Using viscoelastic to deepen the chamber and flatten the anterior capsular convexity makes it easier to control the capsulorrhexis tear. As discussed in Chapter 12, if the chamber shallows, the risk of a peripheral radial tear increases. However, by exerting downward pressure against the nucleus, overfilling the anterior chamber with viscoelastic also increases the resistance that a posteriorly directed hydrodissection wave must overcome. By limiting the escape of injected fluid through the incision, this situation can also lead to excessive deepening of the anterior chamber during the hydrodissection injection. It is therefore advisable to “burp” out some viscoelastic immediately prior to initiating hydrodissection. This can be accomplished by gently pressing the shaft of the hydrodissection cannula against the incision floor prior to the injection. Partially emptying the anterior chamber in this way will permit the nucleus to more readily separate and elevate away from the posterior capsule. Pearl #2: Use Adequate Injection ForceFor the wave to propagate posteriorly and shear the natural epinuclear-capsular adhesions, a sufficient hydrostatic force must be generated. However, fear of “blowing out” the capsule causes many novice surgeons to be overly timid with the injection pressure. Because the volume of fluid that can be injected into the anterior chamber is limited, the most effective fluid jet is one that is brief, sufficiently forceful, and radially directed. The resulting hydrostatic force is proportional to the rate of flow and the cannula resistance. Either a 30- or 27-gauge cannula (see Figure 13-1A) provides enough resistance to generate the necessary force with a small volume of fluid. Since tuberculin syringes hold insufficient volume, the preferred syringe size is 3.0-milliliters (mL). In contrast to larger syringes, this size is small enough to provide good tactile feedback as the plunger is advanced regarding the rate of flow.
Pearl #3: Avoid Capsular-Lenticular BlockAlthough it is possible to rupture the posterior capsule with hydrodissection, nuclear-capsular block is usually a prerequisite.7-11 As a dense nucleus elevates, it may completely seal off the capsulorrhexis opening from below. If fluid cannot escape the capsular bag, continued infusion can over-inflate the bag enough to rupture the posterior capsule.11 The surgeon may not be aware of this complication until the phaco tip is inserted. At this point, the hydrostatic pressure will expand the capsular rent, and the nucleus will drop before or during the initial sculpting strokes. To avoid this complication, one should terminate the injection as soon as a brunescent nucleus “pops up.” The surgeon must resist the temptation to continue injecting until the hydrodissection wave has completely crossed behind the nucleus. Instead, one should stop and reposit the nucleus posteriorly—thus breaking the nuclear-capsular block—before continuing with further hydrodissection or hydrodelineation.
Pearl #4: Achieve Cortical Cleaving HydrodissectionHoward Fine has described the concept of cortical cleaving hydrodissection whereby the cortex is loosened by the fluid wave.1 This is facilitated by tenting the anterior capsule slightly upward with the cannula tip in order to direct the fluid stream along the inside contour of the capsular bag (see Figure 13-1A). A wave that hugs the inner capsular surface will produce a slow advancing fluid front with scalloped edges (see Figures 13-1B and C and Figures 13-3 A and B). These characteristics indicate the resistance that is encountered as the wave shears through the cortical-capsular adhesions, and confirm that all three hydrodissection goals have been achieved. Some surgeons advise leaving one’s thumb off the plunger until the cannula tip is positioned properly. Otherwise, if even a tiny amount of fluid is trickling out, it may prevent the tip from properly tenting up the anterior capsule just prior to the definitive injection.
If the wave propagated so quickly that the surgeon could not observe an advancing edge, it probably traveled along too internal an anatomic plane. A rapid, instantaneous wave without any resistance usually signifies hydrodelineation instead of hydrodissection (see Figure 13-1D). This error occurs more frequently in softer lenses where the epinucleus is proportionately larger. Without hydrodissection, hydrodelineation alone will permit the endonucleus to rotate within a stationery epinuclear shell, but will not loosen the epinucleus and cortex. The adherent epinucleus will subsequently be difficult to aspirate, mobilize, or flip as a unit. Because either hydrodissection or hydrodelineation alone will permit rotation of a moderately dense endonucleus, proper hydrodissection cannot be confirmed until the epinucleus and cortex are removed. In order to flip the epinuclear shell, it is much safer to aspirate the anterior shelf rather than the posterior portion lying in contact with the posterior capsule. If the anterior shelf breaks off as it is being aspirated, the surgeon can rotate the loosened epinucleus counterclockwise with the microfinger to bring a fresh anterior shelf to the contraincisional quadrant. In contrast, an adherent epinucleus neither rotates nor flips, and the distally aspirated anterior shelf eventually breaks off. This leaves a proximal adherent remnant with nothing to grab onto, and increases the risk of aspirating or tearing the posterior capsule with the phaco tip.
Fine described using cortical cleaving hydrodissection to permit cortical aspiration with the phaco tip1 (Figure 13-4). However, even if this maneuver is not attempted, loosening the capsular attachments benefits conventional automated cortical cleanup. For example, a mailing label easily separates in one piece from its waxed paper backing. However, once applied to a cardboard box, it becomes difficult to remove as a single piece. After one strip prematurely shreds and breaks off, one must again struggle to regrasp a new area. The difference in these situations is in the strength of the adhesion. The tendency for hydrodissected cortex to separate easily in sheets, as opposed to small adherent strips, is particularly advantageous in the subincisional area4,5 (see Figure 7-8). Again, the more adherent the cortex, the greater the risk of aspirating or rupturing the posterior capsule becomes. Pearl #5: Initiate the Wave ProximallyThe hydrodissection wave frequently fails to travel completely across the posterior capsule. When a conventional straight cannula is used, a partially completed wave that started from the contraincisional fornix may not adequately loosen the subincisional cortex. The importance of preferentially loosening subincisional cortex means that the hydrodissection wave should ideally commence from the subincisional anterior capsular rim. For this reason, this author advocates using a right angle hydrodissection cannula tip. Like a right-angle I/A tip, this configuration can access the proximal 180 degrees of anterior capsular rim (see Figures 13-3A and B). On the other hand, a straight cannula can only access the distal 135 degrees of capsular rim, and a J-shaped cannula is limited to the subincisional 90 degrees of capsular rim. Pearl #6: Rotate the Nucleus With the CannulaAnother helpful hint is to sever the last remaining endonuclear and epinuclearcapsular attachments by using the cannula tip to rotate the nucleus within the bag prior to phaco. The previously mentioned right angle tip works well at engaging the peripheral anterior nuclear surface and rotating it with circular raking motions (see Figures 13-1E through G). By not having to remove the tip, the surgeon can readily repeat the hydrodissection step if necessary. Technique Using a Right Angle Hydrodissection CannulaThe Chang hydrodissection cannula (Katena; Mastel Precision, Rapid City, SD; and Rhein Medical, Tampa, Fla.) (Figure 13-5) is a reusable, 27-gauge cannula with a short, 1.0-mm right- angled tip. The very end has been flattened to create a slightly fan-shaped fluid stream, and to more snugly nestle beneath the proximal anterior capsular rim. A disposable version is manufactured by Oasis Medical Inc (Glendora, Calif). Hydrodissection success is determined more by technique than by instrumentation. Nevertheless, the small right angle design of this cannula provides several ergonomic advantages.
By angling the shaft within the tunneled incision, one can position the 1.0-mm cannula tip just underneath the proximal capsulorrhexis edge—either slightly left or right of the incision (see Figure 13-1A). This preferentially loosens the subincisional cortex. A right-angled I/A tip configuration provides better access for subincisional cortex for the same reason. The 1.0-mm long tip is small enough to flip around while still inside the anterior chamber. This allows one to sequentially hydrodissect or hydrodelineate both lateral quadrants without having to re-insert the instrument. Because of the tip’s 90-degree bend, rotating it along the axis of the shaft can angle the tip so that it points either slightly above or below the plane of the capsulorrhexis. By initially angling it slightly upward, the undersurface of the anterior capsule is tented. This forces the ensuing hydrodissection wave to hug the inside contour of the capsule. By next angling it slightly downward, the tip rotates into a more internally directed cleavage plane for hydrodelineation (Figures 13-6A through C).
Used like a hook or a pick, the short right-angled tip can spin the nucleus by engaging its anterior surface peripherally and exerting a rotational motion (see Figures 13-1E through G). This repetitive raking motion manually shears the remaining capsular adhesions and confirms successful nuclear rotation. The Chang cannula has a dull point at the tip to further facilitate this maneuver. If the nucleus won’t rotate, the cannula is repositioned for additional hydrodissection attempts. The right angle design keeps the shaft out of the way as fluid is injected behind the nucleus. This can facilitate efforts to prolapse one pole of the endonucleus through the capsulorrhexis and out of the capsular bag. This maneuver can be used in supracapsular flip techniques or for manual small incision ECCE.12 ConclusionBecause surgeons are limited to a single incision in phacoemulsification, cortical cleaving hydrodissection greatly facilitates removal of the nucleus, epinucleus, and cortex. Absent rotation, one cannot as safely remove subincisional nucleus and epinucleus. Overly adherent subincisional cortex increases the risk of a posterior capsule tear during cortical cleanup. Successful hydrodissection improves surgical efficiency, reduces the risk of posterior capsular rupture, and in the case of cortical cleavage by cleaving the cortical attachments, reduces the rate of posterior capsule opacification.5 Optimizing hydrodissection technique and instrumentation allows surgeons to reliably achieve these benefits on a consistent basis. References
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