HYDRODISSECTION

Phacoemulsification is performed more easily and safely when the nucleus is free to rotate within the capsular bag. Firm cortical capsular adhesions restrict this rotation and can cause stress on the zonules or on the bag itself when rotation is attempted. Avoidance of zonulysis and capsule rupture is facilitated by reliable means of nucleus capsule dissection. Fluid hydrodissection is the first and most reliable way to loosen the nucleus. There are many cannulas that permit hydrodissection by injecting a stream of fluid across the posterior capsule. In most patients, these fluid waves are reliable and provide thorough hydrodissection. In some instances however, dissection does not occur under the incision. What appeared to be a strong fluid wave did not achieve total dissection so that nucleus is reluctant to rotate.

One solution to this problem is to enter the anterior capsule (AC) from the side port and irrigate more fluid directly under the incision.

Another solution to avoid this situation is to begin hydrodissection directly under the incision. This could be performed with a J-shaped cannula, but the cannula may be difficult to remove. Its tip has a tendency to get caught on the lip of the incision. A better option is the cannula designed by Leif Corydon for viscoexpression of the nucleus. This cannula can be used for hydrodissection, viscodissection, and manual dissection between the nucleus and the posterior capsule, and even to hook into the nucleus and pull it from the eye.

The Corydon cannula can also be used for hydrodissection of a nucleus within the bag. Its tip is angled back about 150 degrees so it is easy to pass under the subincisional capsule. It is also easily removed from the AC without getting caught on the lip of the incision. To perform subincisional hydrodissection, the cannula is first directed under the subincisional capsule. It can be lifted slightly to tent the capsule off the nucleus. With firm but gentle injection, a fluid wave can be generated. The wave will pass around the equator of the nucleus and tends to be prominent and vigorous, creating superb separation.

After passage of the fluid wave, the cannula can be placed on the top of the nucleus and pressed down against it. This pushes the nucleus posteriorally, against the posterior capsule, squeezing the excess fluid around the equator, thus facilitating cortical cleavage.

The cannula can then be rotated so its tip is buried in the nucleus, just inside the capsulorrhexis. The embedded tip, used like a fulcrum, can then rotate the nucleus. This effectively completes total separation of the nucleus from the bag. The disruptions of the nucleus/cortical/capsular adhesions make aspiration of

cortex during irrigation and aspiration (I&A) easier. The rotation of the nucleus within the capsular bag is a visual check that the hydrodissection is complete.

MANEUVERS TO ELEVATE THE NUCLEUS

OUT OF THE BAG

At times it is necessary to elevate the nucleus out of the capsular bag. An example is significant zonulysis with poor bag integrity. The Corydon cannula is excellent for lifting the nucleus into the anterior chamber without turning it over. This technique requires a capsulorrhexis that is at least 5 mm in size for soft cataracts; slightly larger is better. If the cataract is very dense, the largest capsulotomy possible is suggested. The Corydon cannula is placed under the subincisional capsule and a fluid wave is generated as described above (Fig. 11–1A). Irrigation is continued slowly until the superior pole of the nucleus lifts out of the bag. Once this occurs, the Corydon cannula is rotated so that the curve is horizontal and parallel to the posterior capsule. Irrigation is continued while the smooth curve of the cannula is gently pushed between the posterior capsule and the nucleus. This will manually hydrodissect the nucleus from the capsule. Throughout this maneuver the cannula is slightly lifted to prevent it from catching on the capsule (Fig. 11–1B). When the cannula reaches a position more than halfway across the posterior aspect of the nucleus, it is rotated once again so that the tip of the cannula is now lifted up and impaled into the underside of the nucleus. The cannula is gently lifted and tugged toward the incision. The nucleus, now hooked by the cannula, will lift out of the capsular bag (Fig. 11–1C). The cannula tip is then freed with the application of a little irrigation. Disengaged, it is slipped out from under the nucleus and removed from the eye.

This one-step maneuver for hydrodissection and for lifting the nucleus into the anterior chamber is safe when used with an adequate capsulotomy. The constant irrigation pushes the posterior capsule rearward, separating it from the nucleus, creating sufficient room for the cannula to fit between them. The smooth, rounded curve of the cannula advancing under the nucleus tends to move freely without catching either the nucleus or the bag.

MANUAL DISSECTION

There are situations when hydrodissection is inadequate or should not be performed. One such example is a posterior polar cataract with capsular involvement. In these conditions, manual dissection is an alternative method for nucleus loosening. The Minami M-hook is an ingenious device for this. This

A

B

C

FIGURE 11–1 Lifting the nucleus out of the bag. A surgeon may want to get the nucleus out of the bag electively or because the integrity of the bag support is compromised. One way to do this without placing much stress on the bag is a modified hydroexpression technique. (A) Subincisional hydrodissection is performed with a Corydon cannula until the superior pole of the nucleus lifts. (B) The cannula is rotated so that its flat surface is against the posterior capsule. Irrigation keeps the capsule away from the cannula as it is advanced under the nucleus. (C) The cannula is lifted, either in the flat orientation or “hooked” in the bottom of the nucleus, and the nucleus is brought out of the bag.

instrument has a rounded distal tip designed to rub against the posterior capsule without breaking it. The various curves of the tip are designed so that the surgeon can, by moving fingers or wrist, direct the hook in almost any orientation within the eye. It can be placed around the lens equator and rotated 270 degrees, giving effective manual dissection of the nucleus from cortex and capsule. The M-hook can also be simultaneously lifted to enhance nucleus separation. This hook is also shaped for dividing the nucleus and for holding the capsular fornix stable in the axis of a zonulysis. I use the M-hook as an ad-

CHAPTER 11 STOP AND CHOP PHACO • 87

junct to hydrodissection. Minami uses it instead of hydrodissection (Fig. 11–2).

STOP AND CHOP IN THE

DENSE NUCLEUS

The traditional stop and chop phacoemulsification technique works best for medium-density cataracts. Very dense cataracts are a challenge. The ability to break and separate a dense nucleus is reduced as it becomes more leathery.

Therefore, for a very dense cataract, the concept remains the same but the technique changes. First, a crater is sculpted; this will remove the hard, central core of the cataract. Left behind is the softer peripheral cataract. The sculpting transforms the cataract from a very hard one to a dense but softer one. Next, two relaxing nucleotomies are created. This is done by first sculpting a piece of the nuclear rim about two tip widths wide opposite the incision. Then the nucleus is rotated and a second one is sculpted 180 degrees away. The posterior plate between these two nucleotomies is sculpted for a few more passes to make a thin fault line along which the posterior plate can now be split.

There are now two very dense, very firm, cres- cent-shaped nuclear segments. At this point it is tempting to begin to remove the segments in the usual way, beginning one-third of the way from right to left. Unfortunately, this technique does not work well for very dense cataracts because hard cataracts do not chop easily unless the nucleus is balanced on the phaco tip. If the chop is attempted when there is asymmetry of the nucleus on the tip, the segment will rotate using the tip as a fulcrum.

FIGURE 11–2 Manual dissection. The M-hook (Minami) is designed to slip between the capsular fornix and the nucleus. Sweeping the hook through several clock hours separates adhesions and loosens the nucleus.

Without a balance of forces, the segment will twist, tilting toward the side with more of the nuclear segment. This can then create pressure on other pieces of nucleus, pressing it into the capsular fornix, leading to rupture of the capsule or zonules.

The technique must therefore be modified into what can be termed “repeated bisection.” The phaco tip is placed exactly in the middle of the heminucleus and the chop is performed. This time the forces are balanced on the tip. The chop is efficient. Each of the segment halves can then be bisected into quarters, etc., until the nucleus is chopped into appropriately small sizes. Very dense nuclear fragments tend to chatter. The phaco power needed to emulsify them is greater than the aspiration used to hold the nucleus to the tip. It is helpful, in these cases, to use the chopper to pull the pieces of nucleus to the phaco tip and to gently hold them there, improving the efficiency of the emulsification.

STOP AND CHOP IN THE PRESENCE OF

A SMALL PUPIL

The easiest way to deal with a small pupil is to enlarge it as discussed in Chapter 6. However, if desired, the technique can be modified for phaco of the cataract behind a small pupil. In this situation there are significant hazards. The first is emulsifying the inferior pupil, which can cause problems that range from frayed iris, with strands that will constantly be attracted to the phaco tip. The second is increased miosis, further limiting visibility. Finally excessive iris manipulation will cause release of prostaglandins, with subsequent postoperative inflammation.

A technical difficulty that may occur when working through a small pupil, is the oversculpting and removal of easily visualized nucleus. This results in an intact posterior plate surrounded by hidden nucleus rim. The intact plate prevents the nucleus rim from being pulled into the pupillary space where it can be easily visualized and removed. The procedure is inadvertently made more difficult.

Assuming that the surgery is being performed from the 12 o’clock position, the phaco tip should be kept above an imaginary line between the 3 o’clock and 9 o’clock positions. Therefore, it never is in a position where it could accidentally aspirate and damage the inferior pupil. The phaco tip is used to sculpt a fan-shaped zone, with the narrow portion of the fan just below the incision and the wider portion extending across the nucleus from the 3 o’clock to 9 o’clock positions. Sculpting is continued downward, making this zone as deep as possible and bringing the phaco tip as close to the posterior plate as is feasible.

These steps are performed with the machine at “low flow,” a nebulous term that varies from machine to ma-

chine. The purpose of the low flow is to prevent the iris from being caught in a fluid stream that would propel it toward the phaco tip where it could be aspirated.

Once the sculpted area in the nucleus is considered deep enough, the next step is to create a trench toward the 6 o’clock position. However, if the phaco tip is placed on the surface of the nucleus, as is normally done, the inferior iris will quickly be damaged. Therefore, the strategy is to dig a tunnel deep in the body of the cataract. The tunnel is like a trench, except that, initially at least, some tissue is maintained between the phaco tip and the anterior capsule. To accomplish this, the phaco tip is placed deep in the sculpted area and worked out toward the 6 o’clock position deep within the body of the nucleus. Once the tunnel is partially prepared, it can be unroofed, creating the trench. By applying emulsification power under a roof of protective tissue, sufficient material is removed while minimizing the chance of aspirating iris.

Once the trench has been created, the nucleus should be rotated 180 degrees. This will ensure that the lens will rotate easily prior to attempting removal of the peripheral nucleus. If the nucleus does not rotate, further hydrodissection should be performed, until rotation is obtained.

Once the nucleus has been rotated 180 degrees, the two sides of the trench should be separated, just as in the traditional stop and chop technique. This will break apart the posterior plate. Once the posterior plate is broken, there is no chance of the nucleus being trapped in the peripheral fornix. The nucleus can now be rotated another 90 degrees and the nuclear halves removed by the traditional chop technique.

STOP AND CHOP WHEN THE CHOPPER

SPLITS THE ANTERIOR CAPSULE

When the chopper is placed in the nucleus, it should be placed just inside the capsulorrhexis. Sometimes, if visualization is poor and the capsulorrhexis is not easily seen, a decision about chopper placement becomes mandatory. One choice, the conservative one, is to place it well within the place where the capsulotomy ought to be. Another choice is to place the chopper on top of the nucleus, and then push it out toward the periphery, retracting the capsule in the process. Employing the first choice, if the chopper is placed on and through the AC and pulled toward the phaco tip, will rip the capsule. Fortunately, due to the shape of the chopper, the distal end of the tear is usually slightly rounded. It is therefore unusual for this tear to extend. The surgery can still be performed routinely with pieces of the nucleus being brought to the center of the capsular bag for chopping and removal. This is the appropriate tactic if the

remaining nucleus is small. If, on the other hand, the remaining nucleus is large, and there is danger that the tear in the AC could extend, an alternative technique is to bring the remainder of the nucleus into the anterior chamber. If the nucleus is intact, it can be raised with gentle hydrodissection or viscodissection. If the nucleus has already been broken into two separate pieces and the posterior plate has been separated, only half a nucleus at a time has to be brought into the anterior chamber. The chopper can be slipped under the AC and brought around to the nucleus equator. It can be used to gently tug the equator away from the fornix while lifting gently. At least one portion of the nucleus will come up above the AC where the chopper, combined with the aspiration of the phaco tip, assisted as necessary with viscoelastic, can bring the piece the rest of the way out of the bag. Once in the anterior chamber, the nucleus can be sandwiched in viscoelastic and emulsified directly. The same steps should be repeated for the remaining half of the nucleus.

REMOVING THICK EPINUCLEUS

The removal of thick epinucleus may be a challenge as aspiration instruments have certain limitations, chief among them the small aspiration port. The wide diameter of the phaco tip, although efficient, makes it tricky to control the aspiration level. In addition, while using the phaco tip in phaco mode, the ability to control vacuum is restricted. Therefore, there is usually too little vacuum to easily remove the epinucleus, or so much that it breaks off in fragments.

CHAPTER 11 STOP AND CHOP PHACO • 89

The I&A tip has far more control. This is not only due to the small port diameter, but also because it is used with linear-control of vacuum. Unfortunately, though, the epinucleus is often too thick to be easily aspirated through the standard 0.3-mm orifice. A superb compromise is to continue using the phacoemulsification tip, but to switch the machine to the I&A mode. This allows the phaco tip to be used as an oversized I&A handpiece, with linear control of aspiration.

The phaco tip can be used to remove not only epinucleus in the I&A mode, but thick cortex as well. However, thin cortex is better removed with the small port of the I&A tip. If all the cortex is removed with the phaco tip, the phaco handpiece can be set aside and used later to remove the viscoelastic after lens implantation. The wide bore facilitates the aspiration and evacuation of the viscoelastic from the anterior chamber with remarkable efficiency and thoroughness. It also saves the scrub nurse the necessity of switching the tubing prior to viscoelastic removal.

CONCLUSION

This chapter discussed the most common situations encountered during stop and chop surgery. Naturally, this technique is associated with all the complications that can occur with cataract surgery in general, but if the situations described here are mastered, there will be few occasions when the surgeon will be struck with a surprise situation.