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Up Front | Sep 2002

Six Tips on Hydrodissection Technique

Use the right tip!

Because the topic of hydrodissection receives relatively little attention compared to phacoemulsification and IOL insertion techniques, I believe it is the most underrated step of cataract surgery. A properly developed hydrodissection fluid wave must travel behind the nucleus along the internal posterior capsular surface. In addition to permitting endonuclear rotation, such a wave also facilitates epinuclear and cortical cleanup by loosening their adhesion to the capsule. There are several tips that will help surgeons attain these three important goals.

TIP No. 1
One of the most common mistakes cataract surgeons make is to initiate hydrodissection while the anterior chamber is overinflated 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 capsulorhexis step in which a generous amount of viscoelastic is desirable.

Using viscoelastic to deepen the chamber and flatten the anterior capsular convexity makes controlling the developing capsulorhexis tear much easier. However, by exerting downward pressure against the nucleus, overfilling the AC with viscoelastic increases the resistance that the posteriorly directed hydrodissection wave must overcome. By limiting the escape of injected fluid through the incision, it can also lead to excessive deepening of the AC during the hydrodissection maneuver. It is therefore advisable to burp out some viscoelastic immediately prior to initiating hydrodissection. This can be accomplished by pressing the shaft of the hydrodissection cannula against the incision floor just prior to the injection. Partially emptying the AC will permit the nucleus to rise anteriorly away from the posterior capsule upon separation.

TIP No. 2
Fear of “blowing out” the capsule causes many residents to be overly timid with the injection pressure. Because the volume of fluid that can be injected into the anterior chamber is limited, it must be injected rather quickly and decisively in order to generate sufficient hydrostatic force. The force is proportional to the rate of flow and the cannula resistance. Either a 30- or 27-gauge cannula (Figure 1A through C) provides sufficient resistance to generate the necessary force. A 3-mL syringe is small enough to provide good tactile feedback regarding the rate of flow. Increasingly larger syringes provide less and less tactile feedback.

TIP No. 3
Although it is possible to rupture the posterior capsule with hydrodissection, nuclear/capsular block is a prerequisite. As a dense nucleus elevates, it may totally seal off the capsulorhexis from below. This prevents any fluid from escaping the capsular bag, and continued infusion can inflate the bag enough to cause posterior capsule rupture.1 The surgeon may not be aware of this complication until he inserts the phaco tip. At this point, the high infusion pressure will expand the rent, and the nucleus will drop before or during the initial sculpting stroke. To avoid this complication, terminate the injection once the nucleus “pops up.” Resist the temptation to continue injecting until the hydrodissection wave has completely crossed behind the nucleus. Instead, stop and reposit the nucleus posteriorly—thus breaking the nuclear/capsular block—before continuing with a second injection wave.

TIP No. 4
I. Howard Fine, MD, of Eugene, Oregon, has taught us to orient the fluid stream along the inner capsular surface by tenting the anterior capsule slightly upward with the cannula tip.1 A wave that hugs the inner capsular surface will produce a slower advancing fluid front with scalloped edges (Figure 1B and C). These characteristics indicate the resistance that is encountered as the wave shears through the cortical capsular adhesions. If the wave moves so quickly that the surgeon cannot track the advancing edge, this may indicate that he achieved hydrodelineation instead of hydrodissection (Figure 2A). Hydrodelineation will permit endonuclear rotation, but the epinucleus and cortex will remain adherent to the capsular bag. Some surgeons have advised leaving your 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 actually tenting up the capsule just prior to the definitive injection.

Because both hydrodissection and hydrodelineation will permit the surgeon to rotate a moderately dense endonucleus, he can confirm proper hydrodissection only once the epinucleus and cortex are removed. A loosened epinucleus will flip when aspirated. If the anterior shelf continues to break off, the surgeon can rotate the epinucleus to bring a fresh anterior shelf to the contraincisional quadrant. In contrast, an adherent epinucleus does not rotate or flip, and the distally aspirated sections eventually break off. This leaves a proximal adherent remnant with nothing to grab onto, and increases the risk of aspirating/tearing the posterior capsule with the phaco tip.

Dr. Fine describes the principle of cortical cleaving hydrodissection whereby the loosened cortex can be entirely aspirated with the phaco tip.1 However, even if the surgeon chooses not to attempt this maneuver, the degree to which the cortex has been loosened is evident during conventional automated I/A. 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, we must again struggle to regrasp a new area. The difference is in the strength of the adhesion. The tendency of loosened cortex to come out easily in sheets, as opposed to small adherent strips, is particularly advantageous in the subincisional area. Again, the risk of aspirating or rupturing the posterior capsule is greater if the cortex remains strongly adherent.

TIP No. 5
A hydrodissection wave frequently fails to travel completely across the posterior capsule. Given the importance of preferentially loosening the subincisional cortex, it is therefore logical to initiate the hydrodissection wave from the subincisional anterior capsular rim. A partially incomplete wave that started from the contraincisional fornix will leave the subincisional cortex maximally adherent.

I advocate a right-angle hydrodissection cannula tip, because, like a right-angle I/A tip, this configuration can access the proximal 180&Mac251; of capsular rim (Figure 1A). A straight cannula can access the distal 135&Mac251; of capsular rim, and a J-shaped cannula is limited to the subincisional 90&Mac251; of capsular rim.

TIP No. 6
I prefer to sever the last remaining capsular attachments by using the cannula tip to rotate the nucleus within the bag prior to phaco. The previously mentioned short, right-angle tip works well at engaging the peripheral anterior nuclear surface and rotating it with circular raking motions (Figure 2B, C, and D). The surgeon can readily perform additional hydrodissection if necessary. The Chang hydrodissection cannula (Katena Products, Inc., Denville, NJ, and Mastel Precision, Rapid City, SD) has a dull point at the tip to further facilitate this maneuver. This reusable, 27-gauge cannula has a short, right-angled tip that is flattened to create a slightly fan-shaped fluid stream, and to more snugly nestle beneath the proximal anterior capsular rim (Figure 1A). A disposable version is available through Oasis Medical, Inc. (Glendora, CA).

Because we are limited to a single incision in phacoemulsification, cortical cleaving hydrodissection greatly facilitates removing the nucleus, epinucleus, and cortex. Without rotation, we cannot otherwise safely access subincisional nucleus and epinucleus. Overly adherent subincisional cortex carries increased risk. Therefore, successful hydrodissection improves our efficiency, reduces the risk of posterior capsular rupture, and by cleaving the cortical attachments, reduces the rate of posterior capsule opacification.2,3 By optimizing our technique and instrumentation, we can reliably achieve these benefits on a consistent basis.

David F. Chang, MD, is a clinical professor of ophthalmology at the University of California, San Francisco, and in private practice in Los Altos, California. He has no financial interest in any product mentioned herein. Dr. Chang may be reached at (650) 948-9123; dceye@earthlink.net.
1. Miyake K et al. New classification of capsular block syndrome. J Cataract Refract Surg. 1998;24(9):1230-1234.
2. Fine IH. Cortical cleaving hydrodissection. J Cataract Refract Surg. 1992;18:508-512.
3. Peng Q, Apple DJ, Visessook N, Werner L, et al. Surgical prevention of posterior capsule opacification. Part II. Enhancement of cortical clean up by focusing on hydrodissection. J Cataract Refract Surg. 2000;26:188-197.
4. Vasavada AR, Singh R, Apple DJ, et al. Efficacy of hydrodissection step in the phacoemulsification for age related senile cataract. J Cataract Refract Surg. 2002 (in press).
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