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Today's Practice | Oct 2010

Fundamentals of Nucleus Removal

An overview of basic techniques for dividing the nucleus.

In the 1970s and 1980s, surgeons treated the nucleus as a monolith. Phacoemulsification involved gradually eating away the nucleus from the outside. This was enabled by the crude anterior capsular openings employed at the time. The nucleus was easily prolapsed into the anterior chamber to be attacked. When the capsulorrhexis was developed by Thomas Neuhann, MD, and Howard V. Gimbel, MD (independently but at the same time), in the late 1980s,1 surgeons began to realize that the intact curvilinear opening in the anterior capsule was strong and elastic; therefore, the chances of radial extension of tears to or beyond the equator were significantly reduced. Additionally, surgeons were able for the first time to consistently place IOLs in the capsular bag.

The capsulorrhexis caused the surgeon problems accessing and attacking the monolithic nucleus in the conventional way. This led to the development of techniques to break the nucleus into smaller pieces so that they could be moved into the capsular opening or into the anterior chamber to be consumed. Divide and conquer was the first of such techniques to be widely adopted, but others rapidly followed. The same principle applies to all of the techniques: divide the large nucleus into smaller, manageable chunks to be consumed.

One fundamental aspect of nucleus removal is complete hydrodissection with or without hydrodelineation. This allows the nucleus to be rotated within the capsule during the dividing process. If performed well, hydrodissection also makes cortex removal easier and safer (for more information, see The Key to Successful Hydrodissection by Khiun Tjia, MD, in the January 2010 issue of CRST Europe). Another fundamental aspect is that whichever nucleofractis technique is used, the most important point is that the nucleus must be completely divided from top to bottom, including the posterior plate.

DIVIDE & CONQUER

Background. The divide-and-conquer technique was widely used in the early 1990s and is still popular among many surgeons today. The name—divide and conquer— refers to previous methods that regarded the nucleus as a monolithic enemy or target to abolish. The name alludes to the military strategy probably developed or adopted by Julius Caesar, but popularized by Niccolò di Bernardo dei Machiavelli. Divide and conquer is ideal for beginners because it allows them to learn how to manage chunks of nucleus. This technique can be applied to all grades of cataract, although, as with other techniques, very soft cataracts present challenges.

Technique. Two deep trenches at right angles are sculpted. The silicone sleeve around the tip (in coaxial surgery) is wider than the actual tip, and therefore from time to time some material must be shaved away from the sides of the trench to allow unimpeded access of the sleeved tip to the deepest part. However, the trenches should not be made too wide, as cracking then becomes more difficult. In order to deeply sculpt the center of the lens—the thickest part—the forward stroke should commence proximal to the center. The aim is to sculpt deeply enough to see return of red reflex in the bottom of the trench before attempting to divide the segments (Figure 1).

To split or crack the segments, place the phaco needle and the second instrument deeply into the trench and gently initiate a split through the remaining nucleus and epinucleus. If the instruments are too superficial, the action of trying to split the segments will force them together (Figure 2). If the split does not occur or does not cross the center of the lens, stop and sculpt further. Most lenses are more than 4 mm thick, and phaco probes are approximately 1 mm in diameter. Use this knowledge to help assess whether you have sculpted deeply enough. It will be easier to rotate the nucleus if the quadrants are left in place until they have all been divided.

For sculpting, one should use low flow and low vacuum with higher power. Once the nucleus has been divided into pieces, different settings are used for quadrant removal. Use less power and higher flow to attract the material to the tip and higher vacuum to hold the piece on the tip and help to mold it into the lumen for consumption.

STOP AND CHOP

Background. Kunihiro Nagahara, MD, of Japan, first described chopping the nucleus—without the time-consuming and power-hungry process of sculpting deep trenches—at the American Society of Cataract and Refractive Surgery (ASCRS) annual meeting in 1993.2 The main drawback to this technique was the difficulty of disentangling the pieces of the nucleus (ie, the jigsaw effect). At the following ASCRS meeting, a compromise technique—stop and chop—was described by Paul Koch, MD.3

Technique. The stop-and-chop technique begins like the standard divide-and-conquer technique. After the first trench is cut, the nucleus is split in half and then chopped. The advantage of this approach is that space is created into which the first fragments can be pulled, keeping them away from the capsule periphery and creating space to disentangle chopped pieces. For surgeons ready to transition from divide and conquer to chopping, this is an ideal intermediate technique.

CHOPPING TECHNIQUES

Background. Chopping techniques are more efficient and quicker than sculpting one or more grooves. Sculpting a single groove, as in stop and chop, can use up to 30% to 50% of total phaco energy for nucleus removal. Many variations of the chop technique have been described and named, but the two basic types are horizontal chopping and vertical chopping. There are advantages and disadvantages to each.

Horizontal technique. The phaco tip is partially buried into the center of the nucleus, and the chopper is passed under the rhexis margin toward the equator of the lens. The chopper is then slowly dragged through the nucleus toward the phaco tip, and, once in the center, the two instruments are separated in the horizontal plane.

Vertical technique. The phaco tip must be fully embedded into the nucleus, and then the chopper (usually with a sharp point) is driven vertically into the nucleus adjacent to the tip. The two instruments are separated vertically. The phaco tip is pulled upward against the downward movement produced by the chopper, and, simultaneously, the instruments are parted slightly in the horizontal plane.

Foot pedal. With any chop technique, good foot control is important for switching between pedal positions 2 and 3. The needle must have sufficient bare metal at the tip to allow penetration into the nucleus. First, starting proximal to center, the nucleus is impaled deeply using power. Foot position 2 is used to allow vacuum to build up and be maintained. Chop and look for the split developing in the nucleus before separating the instruments. Some surgeons are concerned that, with horizontal chopping, the chop instrument has to be placed around the lens equator while its tip is out of sight. The risk that the chopper is placed outside the capsule (therefore injuring the zonules and the capsule with an attempted chop) can be reduced or removed by first clearing away the anterior cortex within the capsulorrhexis. The chopper can then be placed on the surface of the nucleus and passed under and through the cortex toward the equator, thus guaranteeing that it is within the bag (Figure 3).

PRECHOP

Background. Phaco prechop is a nuclear fracture technique that is performed under an ophthalmic viscosurgical device (OVD) prior to phacoemulsification. Using this simple procedure, the surgeon can divide the nucleus without grooving or sculpting, which significantly facilitates phacoemulsification.

Technique. The nucleus is chopped into quadrants (or more pieces) with a prechop instrument before phacoemulsification is performed. It is particularly useful for soft and medium cataracts, although Takayuki Akahoshi, MD, who originally described the technique, claims that with modification it is also appropriate for very hard cataracts.4

After making a complete continuous curvilinear capsulorrhexis, sufficiently hydrodissect the nucleus. Fill the anterior chamber with an OVD so that the anterior cortex is removed the nuclear surface is exposed. Place the sharpangled edge of the prechopper blade at the center of the nucleus. Insert the closed prechopper directly into the nucleus by pushing downward. Open the prechopper blades slowly while pushing the nucleus downward. With proper force, the nucleus is cracked completely with a single action. Always insert the blade along the direction of the lens fibers. If one is unable to achieve bisection, I suggest placing the closed blades at the deepest portion of the nuclear crack and then reopening.

Divide each bisected nuclear fragment in the same way. If any OVD leaks during the procedure, inject more to maintain the anterior chamber depth. Finally, divide the nucleus completely into four pieces for removal with phacoemulsification.

CONCLUSION

All modern phaco techniques involve breaking the nucleus into small, manageable pieces for consumption (although very soft nuclei may be removed en-bloc). It is important to ensure that all pieces are completely separated. Divide and conquer is widely used and is safe, but it is relatively power-hungry. The other chopping techniques described use less power, but they may be more difficult with hard nuclei.

David Allen, BSc, FRCS, FRCOphth, is a Consultant Ophthalmologist specializing in cataract surgery at Sunderland Eye Infirmary, United Kingdom. Mr. Allen states that he has received travel and accommodation and adhoc honoraria from Alcon Surgical. He may be reached at e-mail: allen401@btinternet.com.

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