PHACO CHOP

On the afternoon of November 23, 1992, the phaco chop technique was performed for the first time during the phaco of a morgagnian cataract. Prior to this, I had been performing surgery utilizing the technique of divide and conquer. But after this eventful surgery, I had learned the true nature of the nucleus, and my technique gradually changed from divide and conquer to the phaco chop. As the mechanism of this technique resembles wood chopping, I named my new procedure “phaco chop.”

One of the benefits of the phaco chop technique is the dramatic reduction of ultrasonic energy delivered to the anterior segment. When I introduced the technique to cataract surgeons, I thought it would be easy and safe for them to chop the nucleus. However, after its introduction I discovered that, because surgeons did not understand the principles of the procedure, many complications occurred. I realized that some of these complications were serious as I reviewed reports of anterior capsule tears, zonular dialysis, posterior capsule rupture, loss of the nucleus into the vitreous cavity, and endothelial cell damage.

MECHANISM OF THE PHACO

CHOP TECHNIQUE

Phaco chop applies the basic principle of wood chopping. Using an ax, a wood log placed on a chopping block is cracked simply by striking it in the direction of the wood fibers. The block provides counterpressure to the movement of the ax. Phaco chop applies this principle. The crystalline lens fibers run from one equator to the opposite equator through

the center of the nucleus (excluding the complex structure at the Y suture). I discovered that it could be cracked in the direction of lens fibers. Therefore, in the phaco chop technique, the phaco chopper is the ax and the phaco tip is the chopping block. When chopping wood, if the log is not held correctly on the chopping block, it will fall from the chopping block. It might even jump into the air and upon impacting something in the surrounding environment cause an injury. In a similar manner, if the two instruments necessary for the phaco chop procedure are not used properly, such that one stabilizes the nucleus and the other chops, the nucleus is uncontrolled and complications ensue.

KARATE CHOP—AN ALTERNATIVE

TECHNIQUE

In an effort to perform phaco chop in cases of a hard nucleus and/or small pupil, I have modified the procedure. This procedure is named “karate chop.” In the phaco chop technique, the chopper is placed at the hydrodelineation line and the direction of cracking of the nucleus is from the equator toward the center. In the karate phaco chop technique the direction advances from the anterior pole to the posterior. Therefore, in karate phaco chop, it is not necessary to place the phaco chopper under the iris or anterior capsule. Thus, in cases of a small pupil or a large nucleus, or small CCC, the chopper can be placed where it can be seen, making the procedure safer. The karate phaco chop is effective for the hard nucleus, grade 3 or higher. When the ultrasound (US) tip is driven into the nucleus, white smoke, or emul-

sate production, is the sign that the karate phaco chop is effective.

To perform this technique it is important to drive the US tip deeper into the nucleus than required in the usual phaco chop technique. Additionally, more holding power is necessary. The vacuum must be increased to accomplish this. The chopper is stabbed into the nucleus from above and very close to the US tip. It is driven to the same depth of the phaco tip while the two instruments are separated, side to side, to cleave the nucleus. Upon completion of the first chop, the nucleus is rotated and divided into small pieces with repetition of the same procedure.

MAJOR COMPLICATIONS OF

PHACO CHOP

Similar to other techniques of phaco, there are two major categories of complications: (1) those that are visible, such as damage to the anterior capsule, including tears and dialysis, and damage to the posterior capsule, including tears, vitreous loss, and lost nuclear and cortical fragments and nucleus (Table 13–1); and

(2) damage that cannot be immediately visualized, such as endothelial cell damage and iris trauma with resultant damage to the blood–aqueous barrier.

MANAGEMENT OF COMPLICATIONS

Anterior Capsule

During the procedure the phaco chopper can tear the anterior capsule. This is most common in the early phases of the procedure, as the surgeon may have to pass the chopper under the anterior capsular edge to

CHAPTER 13 PHACO CHOP • 95

TABLE 13–1 TYPES OF DAMAGE CAUSED BY THE PHACO CHOPPER AND TIP

Damage caused by the phaco chopper

Tears of the anterior capsule

Dialysis of zonules

Tears of the posterior capsule

Damage caused by the phaco tip

Tears of the equatorial bag

Dialysis of the equatorial bag

Tears of the posterior capsule

engage the nucleus. If the surgeon loses the view of the anterior capsular edge, the chopper may inadvertently be placed over, rather than under, the anterior capsule. The downward pressure of the chopper can tear the edge of the anterior capsule or create a zonular dialysis (Fig. 13–1). One way to avoid this problem is to create a large CCC, usually more than 5 mm. It is important to pay close attention to the edge of the CCC. A careful hydrodelineation will create a cleavage space between the epiand endonucleus, which is proximal to the capsular equator. This is the site of chopper placement to create the initial chop. The hydrodelineation line is more central than the hydrodissection line. This allows placement of the chopper more centrally, protecting the capsular equator from the chopper. In addition, using the aspiration of the phaco tip to pull the endonucleus toward the incision moves the cleavage line more proximally. Both these techniques move the cleavage plane away from the equator and capsular edge so that the edge is more easily visualized and the chopper does not need to be placed as far into the periphery. Finally, when the chopper is placed at

the equator, its tip can be inclined and slid, in direct contact with, and over, the nuclear material, so that it must slip below the anterior capsular edge without tearing or otherwise engaging it (Fig. 13–2). A modified phaco chopper, such as the one designed by R. Olson, may also be useful. It has a raised top section, which is utilized to push the edge of the CCC up so that the instrument slides below the capsular edge without difficulty.

Zonular Dialysis

Zonular dialysis occurs when the anterior capsule, rather than being torn, is engaged and pulled by the chopper. The ensuing dialysis appears opposite to

FIGURE 13–2 The chopper is properly positioned below the anterior capsule in the space created by the hydrodelineation. The need to place the chopper under the iris where it cannot be visualized is therefore avoided.

the incision. In addition it can occur when the nucleus is pushed ahead of the chopper, creating a subincisional dialysis (Fig. 13–3). Finally it can occur during rotational maneuvers in the presence of a poor hydrodissection so that the nucleus pulls on the capsule and tears the zonules (Fig. 13–4). This will create a dialysis 90 degrees away from the incision. Once the zonules are broken, the irrigating solution may pass through the zonular rent into the vitreous cavity. The resultant hydration of the vitreous can cause it to move anteriorally through the zonular defect into the anterior chamber. Alternatively, it can be a cause of progressive shallowing of the anterior chamber during the procedure (see Chapter 8).

This complication can be recognized and prevented as noted immediately above. If the US tip is driven into the center of a hard nucleus with low ultrasonic power and low vacuum, the nucleus is pushed ahead of the phaco tip away from the incision. This may lead to a zonular dialysis in the subincisional area. To avoid this predicament we must use appropriate machine settings of US power, vacuum, and flow. In addition, it is exceedingly important to watch the movement of the nucleus while driving the US tip into it. If the US tip is significantly pushing the nucleus ahead of it toward the equator, then more power and more vacuum should be used, and, if necessary, preplacing the chopper into the hydrodelineation plane for countertraction should be

FIGURE 13–4 Zonular dialysis during rotation of the nucleus when hydrodissection is inadequate.

performed. Whenever the emulsification is occurring near the capsular equator, the chance of inadvertent aspiration of the capsular equatorial bag and subsequent zonular dialysis is increased (Fig. 13–5). Therefore, when chasing nuclear fragments near the equator, vacuum and flow should be adjusted to prevent this problem.

To prevent rotational dialysis due to poor hydrodissection, careful complete hydrodissection must be accomplished. This may require the cannula to be placed below the capsulorrhexis in multiple quadrants to assure unimpeded rotation of the nucleus.

In the presence of a small pupil, or pseudoexfoliation, it may be difficult to make a large CCC, increasing the chance of misplacement of the chopper on

top of the anterior capsule, an anterior capsule tear, or zonular dialysis. In such cases the pupil should be enlarged as noted in Chapter 6.

Emulsification in the Presence of an Anterior

Capsular Tear or Zonular Dialysis

The management of these problems has been discussed in detail previously. The nucleus must be raised into the anterior chamber and emulsified within the protection of dispersive viscoelastic above and below it (see Chapter 5).

Posterior Capsule Rupture

The posterior capsule can rupture at any time during the phaco chop technique. In the case of the soft cataract, the US tip can be passed too deeply into the nucleus. When phaco energy is applied the thicker epinucleus is quickly aspirated. It is just thick enough to raise vacuum so that the thinner cortex follows and is instantaneously aspirated. Not uncommonly, the posterior capsule is the next anatomic structure to enter the phaco tip aperture. If there is any aspiration force present and ultrasonic power is applied, the posterior capsule will be immediately torn and the vitreous face disrupted. This process is more likely to occur with tips that have enhanced occlusive properties such as the 0-degree tip and when beveled tips are used bevel down (see Chapter 15, Fig. 15–3).

Therefore, when emulsifying the soft nucleus, it is best to hydrodissect the entire nucleus into the anterior chamber. There it can be emulsified away from the posterior capsule. Because the material is soft, it can be removed with mostly aspiration forces. Little phaco power is necessary. This will prevent endothelial damage despite the anterior location of the emulsification.

In the case of the moderate nucleus, because the emulsification is carried out at the plane of the iris, it is unusual to tear the posterior capsule.

In the hard nucleus (black, brown, or amber), the risk of a tear of the posterior capsule again increases. This heightened risk is due to the increased force necessary to drive the US tip into the hard nucleus. In addition, due to the increased thickness of the hard nucleus, it may be difficult to get the phaco deep enough into the substance of the nucleus to hold it well enough to create a chop. To avert this problem a crater that is one to two phaco tip diameters deep is created. This provides space to drive the US tip into the center of the nucleus. Additionally, as the diameter of the nucleus is large and cortex is minimal, the enhanced holding power of the deeply placed phaco tip, as well as the use of elevated vacuum, improves holding power. This makes it easier to draw the nucleus toward the incision to make room at the equator for placement of the chopper.

Despite adequate placement of both the phaco tip and chopper the chop is sometimes incomplete. The tip should then be replaced more deeply in the nucleus and the chop repeated and completed. Sometimes it is helpful to rotate the nucleus 180 degrees, replace the phaco tip deeply, and complete the crack from the opposite side.

In cases where the nucleus is particularly leathery it may be impossible to crack through the posterior aspect of the nucleus. An alternative technique may be employed at this juncture. The capsulorrhexis is enlarged to 6 mm as described by Gimbel and Anderson Penno in Chapter 5. The nucleus is hydrodissected again and the pole opposite the incision is prolapsed into the anterior chamber. Cohesive viscoelastic is placed above and below the nucleus

and it is flipped in a supracapsular method. The crack is then completed and the sections emulsified (Fig. 13–6).

Corneal Endothelial/Iris Damage

When I began phaco chop I recognized that some patients seemed to have more postoperative corneal edema represented by folds in Descemet’s membrane and epithelial edema, than when I performed divide and conquer. I postulated that this was due to the preponderance of the procedure being performed at the iris plane rather than within the confines of the capsular bag.

In an effort to minimize edema I use a 0-degree tip, which, due to a smaller surface area, occludes more easily. In addition I use high vacuum (200 to 400 mm Hg) with moderate flow (18 to 20 cc/min). I also use slow pulse or burst phaco for the entire pro-

CHAPTER 13 PHACO CHOP • 99

cedure to decrease the total power delivered to the anterior segment. A dispersive viscoelastic will remain in place during the procedure and protect the endothelium from the ultrasound. In addition, if the nucleus is divided into smaller pieces, the phaco will proceed more rapidly. Once there is room the actual emulsification can be carried out deep to the iris. These same precautions decrease the random power, which causes damage to the blood–aqueous barrier of the iris vasculature.

CONCLUSION

Phaco chop, when performed carefully is a relatively safe phaco technique. Complications should be avoided by attention to nuclear type and phaco machine parameters.

Phacoemulsification has evolved to become the most efficient method to remove cataracts. Many recent improvements have been made in the computerization of the procedure. This has resulted in improvement in power delivery and the fluidics of the procedure. With modern fluidics occlusion of the phaco tip allows for the achievement of the most efficiency. Several methods that have evolved to attain occlusion of the tip include disassembly techniques such as divide and conquer, stop and chop, phaco chop and its variations, and phaco flip. The phaco flip technique is well suited to total occlusion of the phaco tip with the least amount of manipulation in the eye. In addition, the phaco flip procedure and its variants are performed in the center of the pupillary space and in the deepest part of the anterior chamber. By elevating the nucleus to the plane of the iris, phaco is performed far from the lens equator and posterior capsule, thus greatly minimizing the risk of the posterior capsule tearing during the procedure.

PHACO FLIP TECHNIQUE1

This procedure is performed predominantly in the deep anterior chamber at the level of the iris plane. This technique requires movement of the nucleus nearer the cornea than emulsification, which is performed more posteriorly. Endothelial contact and damage is possible especially in certain situations enumerated below. Viscoelastic selection is therefore important. A surgeon with experience in this technique will find any viscoelastic suitable. The choice may be altered due to variations in ocular anatomy

or access. For a surgeon transitioning to this technique, the flipping and phaco maneuvers may initially seem unusual. Therefore, a retentive dispersive viscoelastic such as Viscoat, a soft shell technique, or a visco-adaptive viscoelastic such as Healon5 should be selected.

The phaco flip procedure is performed through a clear corneal incision. A paracentesis incision (or “functional incision”) is executed followed by a phaco incision of 2.5 to 2.8 mm made with a diamond keratome. A capsulorrhexis is performed under viscoelastic with a bent 23-gauge needle or forceps. The size of the capsulorrhexis is between 5.5 and 6.0 mm. The rhexis must be large enough to flip the nucleus but not so large that the insertion of the anterior zonules is encountered. In addition there must be adequate anterior capsular rim to ensure postoperative intraoperative lens (IOL) centration. All capsulorrhexis techniques require the surgeon to regrasp the torn edge of the capsule frequently to prevent inadvertent loss of control of the rhexis. With a large rhexis, regrasping is more important as the tear does not have as far to go to tear into the equator.

Hydrodissection is next performed with an olivetipped cannula (Storz E4414WS or equivalent) placed under the edge of the capsulorrhexis. The cannula tip is lifted to create slight upward tenting of the anterior capsule. This will ensure that the tip is not in the cortex. BSS is slowly injected and directed posteriorly while watching for the classic fluid wave over the red reflex. It is important to hydrodissect deliberately and slowly with the BSS so as to adequately lyse cor- tical-bag connections. Hydrodelineation is not necessary given that with the phaco flip technique keeping

the nucleus and epinucleus intact as a single unit makes the emulsification more efficient.

Next, it is imperative to ensure that the nucleus is completely free to rotate. To do this, the olive-tipped cannula is positioned on top of the nucleus and the nucleus is slowly rocked in the plane of the capsular bag two to three clock hours in each direction. If incomplete lysis of cortical attachments is noted, further hydrodissection is essential.

Once the nucleus is unquestionably established to be completely free, the olive-tipped cannula is positioned toward the equator of the lens. The lens is simultaneously pressed inferiorly while rotating three to four clock hours (Fig. 14–1). With a gentle push, the lens will now flip on its edge with the depressed (subincisional) edge going deep into the capsular bag toward the opposite equator. The olive tip is then used to gently elevate the new distal pole of the nucleus, to complete the flip (Fig. 14–2). The former distal pole of the nucleus must simultaneously flip up, through the rhexis, into the anterior chamber. The entire lens nucleus will now be located vertical, on its side, or on its “back.” It is readily accessible to the phaco tip. At the completion of flipping the nucleus should rest about 45 degrees from the horizontal plane with the “new” uppermost pole toward the incision (Figs. 14–3 and 14–4). It will be resting above the plane of the anterior capsule, but below the plane of the iris. Having the presenting pole of the nucleus tilted toward the incision enhances occlusion with the angled phaco tip. It is neither necessary nor desirable to prolapse the entire nucleus into the anterior chamber. If difficulty is encountered flipping the nucleus with a clockwise rotation, attempting a counterclockwise rotation will usually be effective. The likelihood of tearing the posterior capsule during the flip maneuver is low because, although the

nuclear bulk is substantial, it is smooth and will glide over the capsule.

For emulsification, the nucleus is manipulated with a Bechert nucleus rotator through the side port incision. The Bechert rotator is employed to both rotate and support the nucleus for emulsification above the iris plane. Typically a 30-degree tip is used to engage the nucleus. With the superior pole exposed, this angled tip will be totally occluded by the nuclear material (Fig. 14–5). At the start of phaco a short burst of phaco power removes a portion of the periphery of the epiand endonucleus. With phaco power off, the nucleus is pushed away from the tip with the rotator and rotated so that new material is presented to the phaco tip. Another short burst of power is applied to remove another segment of nucleus. Successive rotation and phaco of the nucleus results in paring down the nucleus. Eventually only a small amount of central nucleus remains. This fragment is easily removed.

Thus, the nucleus is emulsified from the periphery to the center with very little movement of the phaco tip. The phaco tip is energized at the plane of the anterior capsule as close to the mid-pupil as is possible. Thus, ultrasonic damage to the endothelium is minimized.

With appropriate hydrodissection and no hydrodelineation, the epinucleus is often adherent to the nucleus, and there is seldom a need for separate epinucleus removal. Cortical aspiration is accomplished in the usual fashion.

TILT AND TUMBLE TECHNIQUE2

A variation of phaco flip is the tilt and tumble technique described by Richard Lindstrom. This technique utilizes the same iris plane and subincisional rotational phaco of the nucleus and endonucleus, but does not require a true flip of the lens nucleus.