LENS CONSISTENCY

The consistency of the lens nucleus will dictate which emulsification techniques can be most successfully employed. The four-quadrant divide and conquer technique fortunately has a very broad application. The surgeon may encounter difficulty only with lenses that are very soft or very hard.

Soft Lens

If the lens consistency is very soft, the surgeon will initially note little resistance to sculpting during the creation of the first trough. If the lens material seems to “jump” toward the aspiration port more than would be expected, the lens is soft, that is, more cortical in nature. The surgeon, therefore, may encounter difficulty when cracking is attempted. The instruments used may seem to cut through the walls of the trough and the lens material like a wire cheese cutter through cheese, rather than spreading the walls of the trough, thus creating a crack in the posterior lens plate. If the lens is recognized to be softer than expected during the sculpting of the initial trough, shifting to an alternative technique, such as dividing the lens into two heminuclei and subluxing them into the anterior chamber utilizing hydrodissection and then removal using aspiration and lowpower phaco, should be considered.

In some cases the softness of the lens will not have been appreciated during the sculpting maneuver, but when cracking is attempted the walls of the trough crumble rather than spread apart, preventing a crack from taking place. This friable type of lens will still permit the divide-and-conquer technique

provided the trough is deep enough, thus minimizing the amount of posterior plate that must be cracked. Cessation of the cracking maneuver to redeepen the trough before trying to complete the cracking is appropriate.

Hard Lens

Lenses that are very hard may present a challenge not only during the sculpting of the troughs but also during the cracking of the posterior plate. Hard lenses require an increase in ultrasonic power and a decrease in the depth of each emulsification pass across the lens so that the lens does not appear to be pushed away from the ultrasound tip during the sculpting process. They also require sculpting farther out into the periphery. If the ultrasound tip appears to be pushing the lens during the sculpting pass, the phaco power should be increased. An alternative tip that maximizes cavitation power, such as an angled Kelman tip, may be employed. Converting to an extracapsular technique may be indicated. Often, after increasing the ultrasonic power sufficiently to make progress with emulsification, an increase in cavitation bubbles collecting in the anterior chamber will occur. These bubbles will obstruct the view, and should prompt consideration of whether or not it is prudent to continue with this technique in view of the increased time and power that will be required to complete lens removal. Harder lenses will be more difficult to split unless the trough sculpted in the lenses is deep, leaving a very thin nuclear/cortical plate. Deep sculpting in a hard lens is a time-in- tensive effort. Low vacuum settings (dependent on phaco machine capability) help prevent high-power

encounters with the iris, as well as aspiration of the equatorial bag, during sculpting.

If the hard lens is recognized preoperatively, a large capsulotomy should be made to retain the ability to change to an alternative lens management technique and avoid becoming “imprisoned” in the capsular bag by too small a capsulotomy opening.

To split the nucleus, especially if it is hard (nuclear mature), the splitting instruments must be placed at the base of the trough. This will place the vectors for splitting the nucleus in the proper orientation to create a split (Fig. 10–2A). If the instruments are too high in the trough, the posterior plate will be bent but not split (Fig. 10–2B).

Once deep troughs have been sculpted in a hard lens, it is not uncommon to find that the cortical lens fibers that compose the residual posterior plate resist cracking or splitting, much as a piece of leather resists ripping. In this situation, despite the difficulty in creating the sequential cracks in the nuclear plate, it is mandatory to pay close attention and to be sure that the split separating each quadrant is complete. If it is not, great difficulty will be encountered when trying to manipulate each single quadrant during the quadrant management phase of the procedure. Additional sculpting to thin the residual posterior plate and its split-resistant fibers may be necessary. Caution should be used as the posterior capsule is approached with the ultrasound tip. The normal trough color change (see below) may not be present as a visual clue in this situation.

A nuclear cracker (Katena K5-7240 Ernest cracker, or K5-7244 Dodick cracker) may be exceedingly helpful to crack a dense, leathery posterior plate. This is used after the troughs are created to an adequate depth and the posterior plate is seen not to crack. The troughs are sculpted slightly more deeply and the phaco tip is withdrawn. The anterior chamber is then filled with viscoelastic. The cracker is placed into the depth of the trough and separated until a crack occurs. This procedure is repeated until all four cracks are created (Fig. 10–2C).

TECHNIQUE PROBLEMS

Pupil Size/Capsulotomy Size

A small pupil and an ensuing small capsulotomy present difficulties in visualization of and access to the nucleus. If the pupil size is considered inadequate, it should be enlarged (see Chapter 6).

The divide-and-conquer technique can be successfully employed in small pupils. However, some limitations are likely to be encountered with smallpupil cases. A small pupil will limit peripheral visualization during the trough sculpting maneuver,

thus leading to the creation of troughs that are shorter in length than usual. One trick is to expose 1.0 to 1.5 mm of ultrasound tip beyond the irrigation sleeve. Then the relationship of the ultrasound tip to the posterior capsule, while sculpting beneath the iris, can be mentally visualized. It may be more prudent in this situation to use a second instrument to gently retract the pupil margin above the trough being sculpted so that the sculpting can be extended peripherally under direct visualization.

The edge of a small capsulotomy opening is more likely to be contacted by the emulsification tip and/ or irrigation sleeve than a large one. Being aware of this potential contact and the possibility of tearing the anterior capsulorrhexis rim during the sculpting of the troughs should prompt the use of extra care to avoid the anterior capsule and contact during this stage of the procedure.

More commonly, a small capsulotomy opening will be the cause of difficulties during the quadrant removal phase of the procedure. This is due to the confined space that limits quadrant manipulation. Some of the quadrant management techniques1,6 require more space for quadrant manipulation than others,7 so alternative techniques for quadrant management should be available. These are explained below in the quadrant mobilization section.

Sculpting

Machine Settings

Ultrasound Power The ultrasonic power used must be balanced to manage the lens consistency. If the power setting is too low, the ultrasound tip will appear to push the lens ahead during the sculpting process. In this situation, either the ultrasonic power is increased or the depth and forward speed of each sculpting pass is reduced. Use of excessive power delivers more energy than necessary and could lead to either sculpting through the lens and posterior capsule unexpectedly or increased postoperative inflammation due to damage to the blood–aqueous barrier.

Ultrasound Tip Design The divide-and-conquer technique can be successfully performed with a variety of ultrasound tip configurations. Some tip designs may require a slight modification of tip positioning or technique to minimize complications. For example, the angled Kelman tip, which makes trough sculpting easier, should be rotated 90 degrees during the quadrant emulsification phase to minimize the tip proximity to the posterior capsule.

Vacuum Level At present, because ultrasound tip cooling depends on fluid flow through the ultrasound tip as well as leakage through the incision, a

minimal amount of vacuum should be maintained during the trough sculpting maneuver. The use of no vacuum in this situation may lead to incision burns. A vacuum setting that is too high may cause unintentional aspiration of peripheral cortex and capsule, or iris, at the peripheral end of the sculpted trough. The vacuum setting during the sculpting stage should be just high enough to clear the emulsified nuclear particles without attracting other ocular structures.

Trough Dimensions

Length The length of the trough is determined by the amount of lens visible. In eyes with widely dilated pupils, the peripheral end of the trough will approach the lens equatorial cortex and the capsule. In smaller pupils the trough will usually be shorter, being limited by visualization. Because it is the trough depth rather than the trough length that seems to be most critical for the cracking or splitting of the posterior plate, shorter troughs in smaller pupils do not preclude successful nucleus splitting. As mentioned above, surgeons can use a second instrument to gently retract the pupil margin during trough sculpting, thus allowing them to create a longer trough than they would otherwise have been able to see when the pupil is small.

The longer the trough that is created, the more space becomes available for quadrant manipulation during the next phase of the procedure. Short troughs, although not inhibiting the cracking or splitting of the lens, will reduce the ability of the surgeon to manipulate the quadrants, particularly when accompanied by a small capsulorrhexis opening.

Depth The depth of the trough will determine the ease with which the residual posterior plate can be cracked or split. A deeper trough leaves a thinner posterior plate. This is easier to split. In addition, a deeper trough will have more wall area against which the instruments used for cracking can be placed. If the lens material at the proximal end of the trough has physically prevented the ultrasound tip from reaching adequate depth initially it may be necessary to redeepen the initial troughs before splitting is attempted. The trough depth can be judged best by the color and apparent texture of the bed. As the depth of the trough increases, and more lens material is removed, the bottom of the trough changes color from gray to orange-red. A simple rhyme may help: “If it’s gray, you’re OK; if it’s red, danger ahead.” In addition, as the depth of the trough increases, the cortical lamellae change orientation from convex anteriorly to concave posteriorly. This gives a change to the appearance of the trough bed from

smooth to coarse, just as wood has a different appearance when cut with the grain as opposed to across the grain.

Width The width of the sculpted trough can be varied in proportion to lens consistency. Soft lenses, prone to instrument “cheese-wiring” as previously mentioned, should have troughs sculpted that are narrow (one phaco tip wide), thus retaining as much of the wall in the central portion of the lens as possible. This preserves the hardest element of the lens so that the splitting instruments may be maximally effective. Harder lenses may have wider troughs (two-plus phaco tips wide) and still be successfully split. However, the extra time expended for trough sculpting, a relatively inefficient method of lens material removal, should be balanced against the time utilized during quadrant emulsification, which allows the ultrasound tip to remove large portions of the lens efficiently.

SPLITTING POSTERIOR

PLATE/SEPARATING QUADRANTS

There are a great variety of approaches (parallel or cross-action) and instruments (spatula, forceps, etc.) that can be used for the splitting or cracking of the posterior plate to create the quadrants. All approaches depend on the appropriate placement of the instruments within the depth of the trough, rather than at its surface. Then the gentle separation of the instruments will move the trough walls peripherally, creating the crack (Fig. 10–2A). If the instruments are not deep in the trough, on attempted cracking the posterior plate will bend, but not separate (Fig. 10–2B). As the crack forms in the posterior plate, the posterior capsule should be observed. The accompanying distortion of the capsule should be minimized. Placement of the instruments used for cracking will determine whether the crack begins peripherally and extends centrally or vice versa. If placed peripherally, the crack begins peripherally. The firmer the lens, the more peripherally the instruments can be placed.

Incomplete splitting of the posterior plate will make manipulation and removal of the quadrants more difficult. If the posterior plate is too thick, the shallow walls of the trough will tend to crumble as the instruments are separated. Once recognized, this problem is rectified by continued deepening of each of the troughs, then reattempting cracking. If the crack in the posterior plate is not observed to extend centrally enough, so that it connects with previously made cracks, the cracking instruments should be relocated more centrally and separated to extend the crack centrally.