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Chopping techniques beneficial for nucleus removal
This preferred method for cataract surgery requires technical skills but is safer and more efficient than a divide-and-conquer approach.
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The most efficient technique of nucleus disassembly is a purely mechanical one in which the nucleus can be chopped into segments within a few seconds. These smaller segments can then be easily removed with relatively little phaco energy. Compare this with the divide-and-conquer technique in which a tremendous amount of ultrasonic energy is required to create the grooves that are used to create the quadrants. A simple analogy is splitting firewood: A grooving technique is similar to using a saw to cut through the piece of wood, whereas a chop technique is like using an axe to chop and split the firewood along the grain.
 Uday Devgan |
The basic concept of chopping is holding the nucleus with the phaco probe while the chopping instrument splits it into pieces. The most common difficulty that beginning surgeons have in chopping techniques is failure in adequately fixating the nucleus so that it can be chopped. If you are going to use a fork and knife to cut a piece of meat, you must first hold and immobilize the meat with the fork so that the knife can do the cutting. Similarly, the phaco probe must achieve a high enough vacuum level to firmly fixate the nucleus so that the chopper can do the mechanical splitting of the cataract.
A high vacuum level is required to achieve the holding power that we desire for chopping. Depending on the phaco needle size that you are using, the vacuum level should be between 250 mm Hg and 400 mm Hg, and if you are using a peristaltic fluid pump, remember that total occlusion of the phaco tip is required to achieve the maximum preset vacuum level. With the vacuum setting high, bury the phaco tip into the nucleus using phaco power (foot pedal position 3), then once you have full occlusion of the tip, back off the pedal into position 2 so that the nucleus is being held by the high vacuum level. Now the cataract is well-fixated and we are ready to employ a chop technique.
Horizontal chopping
The original technique of chopping described by Nagahara is a horizontal chop (Figures 1a, 1b and 1c). The phaco probe is embedded into the nucleus and the chopper is passed under the capsulorrhexis and toward the lens equator. Once at the lens equator, the chopper is brought toward the phaco tip. It is this action of moving the chopper and the phaco tip together that does the chopping. When this is accomplished, the pieces need to be separated by pulling the two instruments apart. For most surgeons, this means bringing the chopper toward the left, while the phaco probe is pushed toward the right. A complete separation of the two pieces is required for complete mobilization of the halves and for further chopping into segments.
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| Stop and chop technique (Figures 1a-1c). The phaco probe is embedded into the nucleus and the chopper is passed under the capsulorrhexis and toward the lens equator. Once at the lens equator, the chopper is brought toward the phaco tip. It is this action of moving the chopper and the phaco tip together that does the chopping. Images: Devgan U |
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Vertical chopping
In a nucleus with more density, vertical chopping is an effective and safe technique (Figure 2). The phaco tip is embedded into the nucleus and a high vacuum level is used to fixate it. The chopper is then placed vertically, into the center of the nucleus, well within the confines of the capsulorrhexis. Once the chopper and phaco tip are fully buried in the center of the nucleus, the two instruments are pulled apart: the chopper to the left and the phaco probe to the right, thereby separating the two nuclear halves. These nuclear halves can then be further chopped into smaller segments and emulsified.
Tilt and chop
To minimize the stress on the capsular bag, which is particularly helpful in cases of pseudoexfoliation or trauma in which there is zonular weakness, the nucleus can be tilted out of the capsular bag (Figure 3). A relatively large capsulorrhexis of 5 mm or more, combined with hydrodissection or viscodissection, will aid in partially prolapsing the nucleus out of the capsular bag. With the nucleus tilted out of the capsular bag, it is easy to place the chopper around the lens equator or even behind the nucleus. The chopper is brought toward the phaco tip and the two instruments are pulled apart to create the two nuclear halves. The tilt-and-chop technique is my preferred technique for dense cataracts in which a significant amount of force is required to propagate the chop through the nucleus. By placing the chopper behind the nucleus, with the phaco probe in front of it, I am able to exert a high degree of chopping force while being gentle to the zonules and other intraocular structures.
Chopping techniques are quickly becoming the preferred method for cataract surgery because of the efficiency and safety that they provide. Although the technical skill required for chopping is higher, the great majority of ophthalmologists can master it with practice.
For more information:
- Uday Devgan, MD, FACS, is in private practice at Devgan Eye Surgery in Los Angeles, Beverly Hills, and Newport Beach, California. Dr. Devgan is Chief of Ophthalmology at Olive View UCLA Medical Center and an Associate Clinical Professor at the Jules Stein Eye Institute at the UCLA School of Medicine. Dr. Devgan can be reached at 11600 Wilshire Blvd., Suite 200, Los Angeles, CA 90025; 800-337-1969; fax: 310-388-3028; e-mail: devgan@gmail.com; Web site: www.DevganEye.com. Dr.Devgan is a consultant to Abbott Medical Optics and Bausch & Lomb, and is a stockholder in Alcon Laboratories and formerly in Advanced Medical Optics.