Lanjutan (selesai), PHACOEMULSIFICATION: NONCHOPPING TECHNIQUES

  • 04/10/2021
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IV. GROOVING TECHNIQUE

In creating the initial lens sulcus, the depth of the groove is of the utmost importance because this will allow the surgeon to ideally position the phaco tip and second instrument to crack the base of the lens. In general, the groove does not need to extend into the periphery, maintaining the peripheral rim keeps the bag distended and the posterior capsule on stretch. A useful guide is to use the extent of the capsulorrhexis to gauge the length of the groove.

The sweeping arcuate movement of grooving should simulate the posterior curvature of the nucleus. Familiarity with the dimensions of the lens will provide the surgeon with a level of confidence that the posterior capsule is not at risk during this phase of the case. The average lens has a diameter of 9 mm and a thickness of 4.5 mm centrally. The rationale for limiting the length of the initial groove is that the lens thickness and the proximity of the posterior capsule decrease in the periphery. How do these dimensions compare to the length of the phaco tip? A useful guideline is to create a groove that is 1.5 phaco tips wide and 3 deep. The standard phaco tip is 1.2 mm in diameter, thus yielding a groove that is 1.8 mm × 3.6 mm centrally. In making smooth passes, there should be no ridges or step-offs in the groove. Widening the groove to 1.5 times the width of the thinner portion of the phaco tip will create adequate space to accommodate the phaco tip and second instrument for cracking. The goal of grooving should be to achieve 90% depth centrally with a length of approximately 6 mm (Figure 13-1). The power should be adjusted so that the nucleus is being sculpted and not rocked. There can be significant nuclear movement during the grooving step.

In soft lenses, the Y sign can be used to indicate that the groove is of adequate depth and that the nucleus is ready to be cracked. The Y sign has been described by Kurian et al and is used to describe the posterior embryonal Y suture that can be visualized at the center of the trench and can be used as an endpoint for grooving.

V. CRACKING TECHNIQUE

Achieving a consistent, even crack of the posterior cataract is an important piece in mastering the divide-and-conquer technique. A complete posterior crack reflects that the entire nuclear component of the lens has been thoroughly bisected. Extension of the crack into the far periphery is not nearly as vital because the peripheral cortex and epinucleus can be easily divided with a second instrument during quadrant removal. The second instrument is inserted through a paracentesis site that is positioned 2 to 3 clock hours from the main wound site.

The position of the phaco tip and the second instrument in the deepest central portion of the groove is critical. It is often easiest to position the phaco tip first and then place the second instrument immediately adjacent to it (Figure 13-2). It is critical to place the instruments deep in the groove prior to cracking the lens. The second instrument is manipulated with a spinning motion between the thumb and index finger, which will result in a paddle- like movement of the second instrument within the eye, with no movement or distortion of the paracentesis (Figure 13-3). The movement is one of spinning, not pulling. Pulling causes distortion of the cornea and also displaces the eye, significantly diminishing the surgeon’s view. Pushing and pulling at the paracentesis or the wound can also create an increase in vitreous pressure, causing collapse of the anterior chamber and potential rupture of the posterior capsule.

The initial crack in the technique described here is performed after formation of the initial groove. An alternative is to create a “maltese-cross” configuration by creating grooves at 90 degrees from the initial sulcus (Figure 13-4A). However, this technique can prove more difficult because the lateral walls have less surface area for opposition of the instruments when attempting to crack. Another alternative to the separation movement of the instruments as described here is to use a criss-cross action in separating the halves (Figure 13-4B). This technique is effective but can be more difficult to master because the phaco tip can obstruct the movement of the second instrument.

Once the posterior crack is visualized, it can be carefully extended subincisionally by moving the phaco tip and second instrument toward the subincisional portion of the groove and again performing the separation to ensure that the posterior crack is complete. As Koch stated, “The densely packed dry nucleus cracks easily. The looser, more hydrated cataract resists cracking.”If the posterior plate does not crack, the best approach is to carefully shave the plate to make it thinner and to attempt cracking once more.

VI. BISECTION OF THE TWO HALVES

The final step in cracking requires bisection of the 2 halves. The required motion is one of posterior to anterior grooving of the halves followed by the orientation of the phaco tip and second instrument deep in the sulcus to separate the 2 quadrants (Figure 13-5). This step can be quite challenging because the grooves are shorter and shallower than the initial groove. In addition, the 2 instruments must fit into a tighter space and the separation movement must be oriented posteriorly to achieve cracking of the posterior portion of the cataract.

Ideally, 4 equal quadrants are produced. However, this is not always possible and, not infrequently, the surgeon is faced with 3 unequal pieces. This scenario does not preclude advancing to quadrant removal, which can still be performed safely and efficiently with less-than-perfect segmentation of the nucleus (discussed further next). In this circumstance, however, chopping techniques become desirable because these pieces are very amenable to manipulation with the phaco tip and chopper.

VII. QUADRANT REMOVAL

The preferred method of quadrant removal is to present the posterior edge of the fragment to the phaco tip by gently lifting the fragment with the second instrument and engaging the piece with higher vacuum and higher flow rates and drawing it into the pupillary center (Figure 13-6). The phaco tip is used to impale the fragment, the vacuum is then allowed to increase, and the piece is drawn into the papillary plane. The second instrument remains under the segments being emulsified in order to protect the posterior capsule. By using the second instrument to coax the fragments toward the anterior chamber, the phaco tip is kept at a safe distance from the posterior capsule. “Fishing” for these pieces with the phaco tip is a risky maneuver that is certain to result in capsular rupture.

If the surgeon is faced with unequal segments, the more prudent approach is to remove the smaller pieces first. The smaller pieces are much easier to engage, and once they have been removed, a greater “working space” exists for removal of the larger portions. Often the remaining fragment is a full half that was unable to divide further. It is not unusual for experienced surgeons to prolapse a large fragment into the anterior chamber and carefully perform removal, often with the assistance of a chopper. The result will be favorable as long as care is taken to complete the bulk of the work in the pupillary space and avoid contact with the endothelium. Judicious use of a viscodispersive agent can help protect the endothelium in the latter maneuver.

Quadrant removal for beginning surgeons is often made difficult by the inability to establish sufficient vacuum to draw the pieces into the pupillary center. The dexterity to approach the lens fragment, to deliver a single millisecond pulse of phaco power to firmly engage the piece, and then to return to foot position 2 and allow vacuum to build takes many months to master. One method of avoiding frustration during this period is to use viscoelastic to float the pieces into the pupillary plane and safely perform removal. However, these types of tricks should be seen as temporizing measures that should be used until the appropriate technique has been mastered.

VIII. ALTERNATE APPROACHES TO NONCHOPPING

There are many variations to the nonchopping technique, including chip and flip, down slope sculpting, and phaco sweep. Familiarity with many different techniques enables the surgeon to select the most efficient method of extraction for each individual lens. Fine introduced the “chip and flip” technique for lens removal. Central sculpting of the nucleus is performed after hydrodelineation and hydrodissection until only a thin nuclear plate remains. A second instrument is then introduced through the side-port incision to move the inferior lens edge toward the center of the capsular bag. The pieces of the rim are then removed at the 5:00 to 6:00 positions. The nucleus is rotated, and the rim continues to be removed at the 6:00 position. Once the entire rim is removed, the second instrument is used to elevate the remaining nuclear plate anteriorly. The plate can then be emulsified safely. The epinucleus is then engaged and removed with aspiration alone.

Gimbel’s down slope sculpting technique involved sculpting the upper central aspect of the nucleus. This is a useful technique for patients with small pupils. Sculpting is done after gently moving the lens inferiorly with a second instrument. Sculpting can then be performed parallel to the posterior capsule. This method of sculpting minimizes the chance of rupturing the posterior capsule. Once the groove is sufficiently deep, the instruments are placed deep within the lens and a fracture is made. The remaining nucleus can then be removed with the divide-and-conquer technique previously described.4

The phaco sweep is a modification that Gimbel made to the down slope technique. A central groove is formed in this approach, followed by sculpting lateral to the initial groove. The result is a horizontal shelf that can be easily cracked. This is accomplished by stabilizing the upper portion of the lens with the phaco tip and using the second instrument to push against the inferior wall. The remainder of the lens can then be removed as described previously.

IX. CONCLUSION

Nonchopping phacoemulsification techniques allow efficient removal of cataracts. The divide-and-conquer technique described is an organized and systematic approach to lens removal. It involves groove formation and cracking followed by quadrant removal. This technique, when mastered, can be nucleofractis successfully to remove most types of cataracts.

*Dikutip dari Buku Essentials Of Cataract Surgery 2nd Ed, halaman 127-133

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