FIGURE 25–7 (Top) Correct approach. The phaco tip is held at the appropriate angle to match the tip angle to the fragment. This will enhance occlusion and holding power. (Bottom) Incorrect approach. The phaco tip at the wrong angle will not occlude well, thus diminishing holding power or creating the need for excessive phaco energy to bury the tip.

FIGURE 25–8 (Top) Incorrect approach. The bevel-up 45-degree phaco tip is not completely embedded in the nucleus. There is no occlusion and therefore no holding power. (Top inset) Incorrect approach. The 0-degree phaco tip is not adequately occluded. Holding power is poor. (Bottom) Correct approach. Performed correctly, the 45-de- gree bevel-down phaco tip is easily occluded with nuclear material. Holding power is excellent.

performed, it is undesirable to have occlusion near the equator. Therefore, low or zero vacuum should be programmed. This will prevent an inopportune occlusion. It is therefore vital to first optimize surgical technique to facilitate the most efficient utilization of the phaco machine so as to avoid setting unnecessarily high parameters that compromise intraoperative safety.

When a high vacuum level is required for a given case, the surgeon can, in certain phaco machines, augment the safety margin by setting a longer rise time on the phaco machine, rise time being defined as the time that is required for vacuum to build just inside the phaco tip up to the vacuum limit preset (on a flow pump) or to the commanded vacuum at the pump (on a vacuum pump). A longer rise time gives the surgeon more time to react in the event of inadvertent incarceration of unwanted material such as iris or capsule; the foot pedal can be raised out of position 2 to engage venting before too much vacuum produces irreversible damage. On a flow pump, the rise time can be extended by decreasing the flow rate. This in turn slows the rotational speed of the pump head. Another way to modulate rise time is via the speed with which the foot pedal’s linear range in position 2 is traversed, when it is controlling the vacuum limit preset in a flow pump or the commanded vacuum in a vacuum pump. This latter method of rise time modulation is especially important with vacuum pumps, which otherwise on occlusion, have typically rapid rise times as vacuum transfers quickly from the pump to the aspiration port.

ULTRASONIC COMPLICATIONS

In addition to the fluidic modulation discussed above, ultrasound must also be modulated correctly so as to avoid complications. Ultrasonic complications typically fall into three categories. First, failure to utilize adequate ultrasound power can produce zonular and capsular stress and even rupture during sculpting. Ultrasound should be titrated along with the linear speed of the sculpting pass as well as the amount of the tip engaged so as to allow effective carving through the nucleus without pushing it. Second, the use of too high a power setting when inadvertent material such as iris is incarcerated can generally be avoided by the effective use of mechanical force (cracking and especially chopping) to segment the nucleus to minimize the need for sculpting, which typically involves the highest power settings and closest proximity of the tip and capsule or iris. The surgeon then uses effective titration of fluidic parameters (flow and vacuum) so as to attract and

aspirate these segments, minimizing the need to move the phaco tip toward the periphery of the anterior chamber to chase after the segments. Furthermore, ultrasonic aspiration of fragments is more efficient than sculpting because the full tip occlusion allows vacuum to augment ultrasonic action; therefore, lower power levels are used with correspondingly lower risk of damage to inadvertently incarcerated tissue. During carouseling emulsification of fragments, flow and vacuum are titrated to the level of applied ultrasound, which is itself titrated to the nuclear density. Preferably, fluidics and ultrasound are titrated simultaneously in a linear fashion for the most effective and efficient control; however, this type of control is currently available only in the latest generation of phaco machines. Third is the potential for thermal injury at the incision because of frictional energy from the rapidly vibrating phaco needle. Surgical technique is particularly relevant in avoiding corneal wound burns. For example, one should avoid maintaining high ultrasound power for long, continuous intervals. Furthermore, avoiding handpiece positions that result in lifting or extreme angulations at this location can prevent unnecessary wound pressure.

CONTROL OF HEAT GENERATION

Fluidic parameters can influence heat production by affecting flow rate; less heat is produced to the extent that more anterior chamber fluid exchange and more fluid flow around the needle shaft provides cooling. Recall that aspiration line fluid becomes more viscous as viscoelastic and dense nuclear emulsate are aspirated, and that flow is consequently diminished, especially with vacuum pumps; machine parameters should be adjusted accordingly, especially when sculpting. One should especially avoid maintaining high ultrasound power while the aspiration port is occluded and thereby prohibits any cooling flow; however, this caveat does not preclude the use of occlusion phaco methods. For example, some chopping maneuvers require the aspiration port to be fully occluded to effectively build vacuum and gripping power, but this can be accomplished by a brief application of moderate ultrasound to embed the tip followed quickly by a return to pedal position 2 to titrate vacuum appropriately without any further ultrasound until the chop is completed. Furthermore, occlusion methods of carouseling do not necessarily produce excessive heat even though ultrasound power is applied from short to moderate periods. The reason is twofold: first, only moderate levels of ultrasound are required because of the greater efficiency of occlusion methods; second, full occlusion

is rapidly and intermittently interspersed with moments of flow that facilitate cooling as well as removal of emulsified material.

Different needle designs have been developed to decrease the likelihood of wound burns as the silicone sleeve is pressed against the vibrating needle by the surgical incision. Graham Barrett designed the MicroFlow needle to incorporate longitudinal grooves along the outer shaft, which continue to channel cooling irrigation fluid even when the silicone sleeve is compressed against the outer needle surface. The Surgical Design’s silicone sleeve applies this principle in reverse, with the sleeve itself having the grooves that maintain irrigation flow even with compression against the needle. Richard Mackool developed the MicroSeal needle (as well as the similarly designed Mackool System needle), which maintains flow via a rigid Polyimide (plastic) sleeve between the needle and the compressed sleeve; the Polyimide additionally provides heat insulation via its own material properties.

With regard to avoiding wound burns, surgical technique is important not only relative to handpiece manipulation as mentioned previously, but also with regard to correct handling of nuclear segments when attempting ultrasonic aspiration. For example, the phaco tip in Figure 25–9A has impaled a nuclear fragment, boring almost completely through it. Maintaining pedal position 3 in this case invites disaster because of the aspiration flow (arrow) tending to draw unwanted material like iris or capsule into the port. Furthermore, without complete occlusion of the aspiration port, vacuum cannot aid in aspirating the fragment; similarly, the flow does not help to aspirate the fragment because fluid is drawn into the tip prior to affecting the fragment. Recall that because of the axial orientation of ultrasound needle vibration, continuation of position 3 will not accomplish any further emulsification of the fragment; the needle will simply vibrate back and forth along the axis of the hole it has bored. In another illustration (Fig. 25–9B), the phaco needle cannot progress any further through the fragment because of the physical obstruction from the silicone irrigation sleeve. The corrective action in this case is to back off to foot pedal position 1 to maintain the anterior chamber; then use a second instrument through the side-port incision to push the fragment off of the phaco tip and then reengage to emulsify in a carousel fashion, manipulating and feeding the fragment to the tip with the second instrument as necessary (Fig. 25–9C). Note how the segment’s sharp tip was ultrasonically removed prior to carouseling to prevent it from spinning into the capsule or cornea.

Engaging fragments in a tangential fashion for carouseling enables efficient emulsification as both flow and vacuum continue to feed new material into

the phaco tip as the previously engaged portion is emulsified and aspirated in an efficient occlusion mode of operation. Note the nontangential fragment engagement shown in Figure 25–10A,B in which the phaco needle has bored into part of the fragment; maintaining position 3 with a dense nuclear sclerotic fragment would not produce any further emulsification because the silicone sleeve will prevent vacuum from drawing the fragment any further into the needle. Furthermore, because the aspiration port is completely occluded, maintaining position 3 will cause potentially dangerous heat buildup from incisional friction caused by the vibrating ultrasonic needle in the absence of a cooling flow current. Fragments engaged in this fashion should be removed by reflux-

ing or with a second instrument so that they can be reengaged for emulsification in a carousel fashion as in Figure 25–10C,D. Larger fragments generally require more manipulation by a second instrument to maintain optimum tangential positioning for carouseling; therefore, chopping methods, because smaller nuclear fragments are generated, are typically more efficient than quadranting techniques.

CONCLUSION

Modern phaco machines offer unprecedented levels of control and safety. To fully exploit these values, a thorough understanding of the principles by which

More difficult to occlude tip, requiring deeper plunge into nucleus

FIGURE 25–10 (A,B) The fragment is not aligned with the phaco tip. Occlusion is difficult. If emulsification is successful, the tip will eventually be stuck within the fragment with the sleeve precluding further efficient emulsification. (C,D) The fragment has been maneuvered such that the fragment angle matches the tip angle. This facilitates occlusion and promotes efficient emulsification of the fragment.

the machines operate is essential. By studying these fundamental phacodynamic principles, the surgeon can determine the proper machine parameters for each moment of an operation, thus maximizing both safety and effectiveness. In particular, the surgeon must appropriately adjust flow rate, vacuum, ultrasound power, and bottle height as necessary for a given patient and for a given surgical stage based on visual intraoperative feedback. Complications can arise not only when a parameter is set excessively, but also when it is employed insufficiently, thereby requiring the surgeon to compensate for the machine’s inefficiency. This vigilance and attention, coupled with meticulous technique designed to optimize the machine’s performance, will result in the safest, most efficient phacoemulsification surgery.

REFERENCE

1.Fishkind WJ. Phaconet: fact-surge is a cause of the torn posterior capsule. Video Presentation, ASCRS Film Festival, May 20–24, 2000.

SUGGESTED READING

Seibel BS. Phacodynamics: Mastering the Tools and Techniques of Phacoemulsification Surgery. 3rd ed. Thorofare, NJ: Slack; 1999.