- Email: [email protected]
Feasibility of sleeveless bimanual phacoemulsification with the Millennium microsurgical system
laboratory science Feasibility of sleeveless bimanual phacoemulsification with the Millennium microsurgical system Rosa Braga-Mele, MD, FRCSC, Eugene Liu, MD, FRCSC Purpose: To assess the feasibility of sleeveless bimanual phacoemulsification using the Millennium Microsurgical System (Bausch & Lomb Surgical) by measuring wound temperature during phacoemulsification. Setting: In vitro laboratory. Methods: The Millennium system was used in 6 eye-bank eyes using pulse mode and 80-milllisecond and 160-millisecond phaco burst mode width intervals. Wound temperatures were measured, and the wounds were observed for thermal injury. Results: In pulse mode and the nonoccluded state at 100% power, the maximum temperature was 43.8⬚C. In the occluded state at 30% power, the maximum temperature was 51.7⬚C after 70 seconds of occlusion. In phaco burst mode with a 160-millisecond burst-width interval, the maximum temperature was 41.4⬚C (nonoccluded at 100% power). At 80% power, the maximum temperature was 53.2⬚C within 60 seconds of full aspiration occlusion with the footpedal fully depressed. With an 80-millisecond burst-width interval in the nonoccluded and occluded states (100% power, footpedal fully depressed for 3 minutes), there was no significant temperature rise. The maximum temperature was 33.6⬚C in the nonoccluded state and 41.8⬚C in the occluded state. In all instances, the corneal wound remained clear. No wound burn or contracture was noted. Conclusions: The demonstrated temperature rises were under clinically unusual parameters. Phacoemulsification with a sleeveless needle through a small stab incision can be safely performed with the Millennium system using conventional phaco burst mode settings within certain parameters. J Cataract Refract Surg 2003; 29:2199–2203 2003 ASCRS and ESCRS
C
ataract surgery and phacoemulsification techniques have advanced dramatically over the past 10 years. The development has been toward less traumatic surgery using ultrasound-assisted phacoaspiration
Accepted for publication March 10, 2003. Reprint requests to Rosa Braga-Mele, MD, FRCSC, Assistant Professor, University of Toronto, Mount Sinai Hospital Eye Clinic, 600 University Avenue, Toronto, Ontario, M5G 1X5, Canada. E-mail: rbragamele@ rogers.com. 2003 ASCRS and ESCRS Published by Elsevier Inc.
instead of vacuum-assisted phacoemulsification. Refinements in power modulations1 and control have led to reductions in the amount of ultrasonic energy delivered to the eye and, thus, less risk for injury to the corneal endothelium and the incision. Agarwal and coauthors2 report success using the phakonit method of bimanual lens extraction through a 0.9 mm incision with a sleeveless phacoemulsification needle. Recent research with the Sovereign system3 shows that microphaco using a bare phaco needle through a relatively small incision can be conducted with specific parameters. 0886-3350/03/$–see front matter doi:10.1016/S0886-3350(03)00330-4
LABORATORY SCIENCE: SLEEVELESS BIMANUAL PHACOEMULSIFICATION
Although currently no intraocular lens (IOL) will fit through a small stab incision, there are obvious advantages of lens extraction through 2 small incisions.4,5 First, irrigation through the side-port instrument can help move lens material toward the phacoemulsification needle tip; when irrigation is delivered through the sleeve, the irrigation fluid may create a current that pushes the lens material away from the needle tip. Separating irrigation and aspiration should theoretically direct loose pieces toward the aspiration port. Second, nuclear material can be approached from 2 incision sites if needed. Third, subincisional cortex can be more easily removed. Fourth, small stab incisions theoretically allow a tightly closed and stable anterior chamber, but in microphaco, flow is sometimes reduced and chamber stability may be in question. The feasibility of performing sleeveless bimanual phacoemulsification is dependent on the phacoemulsification needle remaining cool during the surgery. With a sleeve in place, a thermal barrier consisting of the irrigating fluid surrounded by the Teflon威 sleeve exists. With modern high-vacuum phacoemulsification and chopping techniques, the ultrasound time to perform phacoemulsification decreases. Adjuvant methods of cooling the wound such as using cooled irrigating solution or providing direct and constant irrigation externally to the incision site can be applied. This raises the question whether a sleeve is necessary to prevent corneal wound burns. The Millennium Microsurgical System (Bausch & Lomb Surgical) operates at a relatively low ultrasonic frequency of 28.5 kHz. This machine may produce less heat than others operating at higher frequencies since the amount of heat generated is proportional to the operating frequency.4 The current study was undertaken to assess the feasibility of performing sleeveless bimanual phacoemulsification with the Millennium system by measuring wound temperature during the procedure.
Materials and Methods Fresh human cadaver eye-bank eyes were used in the study. In each eye, 2 clear corneal uniplanar stab incisions 1.4 mm in width were made using a metal paracentesis blade. The width of the incision allowed the sleeveless phacoemulsification needle to be inserted without excessive tension on the wound. Irrigation was delivered through the first wound with a 20-gauge irrigation cannula. 2200
Figure 1. (Braga-Mele) Phaco tip with thermocouple.
A sleeve was cut at the hub and screwed on the phacoemulsification handpiece. This modified sleeve was used to secure a standard type-J thermocouple (accurate for 0⬚C to 76⬚C) to the phacoemulsification needle (Figure 1). The tip of the thermocouple was placed 2.0 mm behind the phacoemulsification needle tip; ie, the thermocouple was placed directly in the clear corneal wound and would thus measure wound temperature unequivocally. Because of the addition of the thermocouple, the wound was enlarged to 1.8 mm to allow the needle–thermocouple complex to fit within the clear corneal wound without excessive tension. The needle–thermocouple complex took up the entire width of the wound; thus, the egress of fluid from the wound was small and minimal. The thermocouple was plugged into a Fluke Hydra 2620A Data Acquisition Unit. The data were transmitted to a personal computer via an RS-232 connection and recorded using Fluke Hydra Logger version 3.0 software. Wound temperature was sampled at 3 points per second. Ambient room temperature was also measured for variance. The Millennium Microsurgical System with phaco burst technology was tested using the MicroFlow威 phacoemulsification needle (Bausch & Lomb Surgical), which has a 19gauge bore and a 1.07 mm outer diameter. The bottle height was 110 cm above the eye, and the vacuum was 180 mm Hg. Three modalities were tested: pulse mode at 5 pulses per second and phaco burst mode at 80-millisecond and 160-millisecond burst-width intervals. In phaco burst mode, the burst width is set by the surgeon. During the burst interval, the ultrasound power rises immediately to the maximum power set by the surgeon. This burst interval is initially followed by a 1.2-second quiet interval. As the footpedal is depressed, the quiet interval is reduced from 1.2 seconds to zero. When the footpedal is maximally depressed, the ultrasound is at maximum power continuously. End points were those used by Soscia and coauthors3: wound temperature greater than 45⬚C or whitening or contracture of the wound.
J CATARACT REFRACT SURG—VOL 29, NOVEMBER 2003
LABORATORY SCIENCE: SLEEVELESS BIMANUAL PHACOEMULSIFICATION
Figure 2. (Braga-Mele) Pulse mode 30% power with line occlusion.
Figure 3. (Braga-Mele) Burst mode at 160 milliseconds, 80% power, with line occlusion.
In pulse mode, the test was started with the power amplitude at 20% and ran for 3 minutes using the full 20% maximum power immediately (pedal engaged to maximum amount). If end point was not attained, the maximum power was increased by 10% increments. This was repeated for the nonoccluded and occluded (pinching the aspiration line) states. In phaco burst modalities with 80-millisecond and 160-millisecond burst-width intervals, the procedure was as follows: The maximum power was initially set at 15% of the available power. Testing began with the footpedal at the top of position 3. Entry into position 3 was identified by an audible click. A video overlay on-screen system allowed the surgeon to visualize the exact position of the footpedal within the range of position 3. At the top of position 3, the machine produced a burst of 15% power for 80 milliseconds followed by a quiet interval of 1.2 seconds. This position was held for 2 minutes. If end point was not attained, the foot pedal was depressed to the midpoint of foot position 3 (as indicated on the video overlay) for 2 minutes. At the midpoint of position 3, the burst duration remained at 80 milliseconds. However, the quiet interval was reduced to approximately 0.6 second. If end point was not attained, the footpedal was depressed fully to the end of position 3 for 2 more minutes. At this position, the machine delivered continuous ultrasound energy at 15% because the quiet interval was zero. This procedure was repeated with 10% increments in the maximum allowable phacoemulsification power until 100% power was reached or a temperature of 45⬚C or a wound burn occurred. The procedure was repeated using a 160-millisecond burst interval. The procedure was performed in the nonoccluded and occluded states for 80-millisecond and 160-millisecond quiet intervals.
The tests were performed twice in separate eyes to ensure reproducibility and validity. The wound was constantly irrigated externally with room-temperature balanced salt solution in all eyes to simulate the clinical setting of corneal irrigation during surgery. Throughout all procedures, the stability of the anterior chamber was monitored.
Results In pulse mode in the nonoccluded state, even at 100% power the temperature did not rise above 43.8⬚C. In the occluded state, the temperature rose to 51.7⬚C after 40 seconds of aspiration line occlusion at 30% power (Figure 2). The temperature returned to the preocclusion level of 30⬚C after 1 second. Although the temperature rose to a maximum of 51.7⬚C, the corneal wound remained clear and no wound burn or contracture was noted. In phaco burst mode with the burst-width interval preset at 160 milliseconds, no end point was reached in the nonoccluded state even at 100% power. The maximum temperature at this point was 41.4⬚C. At 80% power with the aspiration fully occluded, the temperature rose to 53.2⬚C within 60 seconds of occlusion when the footpedal was completely depressed (Figure 3). This did not create a visible wound burn or change, and once occlusion was broken, the temperature declined to 43.5⬚C within 0.6 second. In 1 set of eyes at 40% power, the temperature rose to 46.1⬚C during
J CATARACT REFRACT SURG—VOL 29, NOVEMBER 2003
2201
LABORATORY SCIENCE: SLEEVELESS BIMANUAL PHACOEMULSIFICATION
stable. The results were reproducible in the second set of eyes and were added to the results in the first eye; the mean results are reported. The external wound irrigation produced a 1.5⬚C to 2.0⬚C reduction in the wound temperature. This was determined during phacoemulsification when irrigation was interrupted and the temperature was noted to rise 1.5⬚C to 2.0⬚C and remain steady at this level; when irrigation was reinstated after 60 seconds, the wound temperature dropped to the previous level.
Discussion Figure 4. (Braga-Mele) Burst mode at 160 milliseconds, 40% power, with tip occlusion (vitreous).
the time vitreous occluded the phacoemulsification tip (Figure 4). In the burst-width interval preset at 80 milliseconds, in the nonoccluded and occluded states, at 100% power with the footpedal completely depressed for 3 minutes, there was no significant temperature rise and no wound burn (Figure 5). In the nonoccluded state, the temperature did not rise above 33.6⬚C; in the occluded state, the maximum temperature was 41.8⬚C. During the study, the ambient room temperature did not vary significantly and the chamber remained
Figure 5. (Braga-Mele) Burst mode at 80 milliseconds, 100% power, with line occlusion.
2202
Developments in technology have brought exciting advances in cataract surgery techniques. In this rapidly evolving field, surgeons aim to perform the least traumatic surgery by decreasing thermal energy delivered to the eye, wound size, and trauma to the cornea, thereby promoting more rapid visual recovery. Recent development has been toward small-incision sleeveless bimanual phacoemulsification, anticipating the advent of a smaller foldable, rollable, or injectable IOL. It was encouraging to find that the end points of 45⬚C, wound burn or wound contracture, were not reached in the nonoccluded state in the 3 modalities tested. In the phaco burst mode at the 80-millisecond burst-width interval, in the nonoccluded and fully occluded states, at 100% power with the footpedal completely depressed for 3 minutes, there was no significant temperature rise and no wound burn. In the nonoccluded state, the temperature did not rise above 33.6⬚C, and in the occluded state, the maximum temperature was 41.8⬚C. However, in the occluded state, the pulse mode and 160-millisecond burst mode created wound temperatures in excess of 45⬚C. In the pulse mode, the time the needle was in full occlusion (45 seconds) to produce a temperature rise was beyond what would normally happen during live surgery. Similar to Soscia and coauthors,3 we found that the phacoemulsification handpiece became extremely hot at higher temperatures but the wound did not burn. One possible reason was the constant flow and egress of fluid through the wound and around the needle. The wounds in the study had to be enlarged to accommodate the thermocouple, and this must be kept in mind when analyzing the tempera-
J CATARACT REFRACT SURG—VOL 29, NOVEMBER 2003
LABORATORY SCIENCE: SLEEVELESS BIMANUAL PHACOEMULSIFICATION
ture findings as a relatively leaky wound will allow egress of fluid around the wound and thus lower temperatures. One must also keep in mind that the thermocouple was in contact with the bare phaco needle and was thus probably measuring the phaco needle temperature and not the corneal temperature. Concurrently, one must note that cadaver eyes are generally kept at lower than body temperature. In this study, the eyes were at room temperature for a few hours before use, but because of the change from body temperature, the maximum temperature in real surgery could be higher or reached more quickly. Simultaneous temperature measurement using the thermocouple and infrared video thermal imaging6 may help address these questions. With respect to the temperature rise that occurred in the 160-millisecond burst mode at 80% power, the amount of power and time required to produce such a rise was higher than typical settings used in live surgery. It would be unusual to have sustained occlusion using burst mode at 80% power for 60 seconds. In 1 eye using the 160-millisecond burst mode, the temperature rose at 40% power. Reviewing the videotape footage of the experiment, we found that the posterior capsule in this eye had ruptured and the tip was fully occluded with vitreous. The presence of vitreous causes full occlusion at the distal tip of the needle as opposed to simulating occlusion by clamping the aspiration line. This appears to cause a rise in temperature at lower power than by clamping the aspiration line. During all other segments of the experiment, the posterior capsule was intact and vitreous was not found to occlude the tip. Our hypothesis for this finding is as follows: With clamping the aspiration line, a column of fluid remains within the lumen of the phacoemulsification needle. This small amount of fluid may act as a heat sink and retard the rise in the temperature of the needle. However, during true occlusion (at the tip), continued aspiration causes the lumen of the needle to empty. Without the small column of fluid to act as a heat sink, the needle and, secondarily, the wound temperature
will rise more quickly. Further studies of bare-needle phacoemulsification should look at simulating occlusion by closing the tip rather than clamping the aspiration tubing.
Conclusion In summary, the temperature rises that were demonstrated were mostly under clinically unusual parameters. One must take into account that this study was done in a laboratory setting and the results may be different in a clinical setting. However, we believe the study shows that phacoemulsification with a sleeveless needle through a small stab incision can be safely performed with the Millennium Microsurgical System using conventional phaco burst mode settings within certain parameters.
References 1. Fine IH, Packer M, Hoffman RS. Use of power modulations in phacoemulsification; choo-choo chop and flip phacoemulsification. J Cataract Refract Surg 2001; 27: 188–197 2. Agarwal A, Agarwal S, Agarwal A. Phakonit and laser phakonit: lens removal through a 0.9-mm incision. In: Agarwal A, Agarwal S, Sachdev MS, et al. Phacoemulsification, Laser Cataract Surgery and Foldable IOLs, 2nd ed. New Delhi, Jaypee Brothers, 2000; 204⫺216 3. Soscia W, Howard JG, Olson RJ. Bimanual phacoemulsification through 2 stab incisions; a wound-temperature study. J Cataract Refract Surg 2002; 28:1039–1043 4. Fine IH, Packer M, Hoffman RS. New phacoemulsification technologies. J Cataract Refract Surg 2002; 28:1054– 1060 5. Tsuneoka H, Shiba T, Takahashi Y. Ultrasonic phacoemulsification using a 1.4 mm incision: clinical results. J Cataract Refract Surg 2002; 28:81–86 6. Bissen-Miyajima H, Shimmura S, Tsubota K. Thermal effect on corneal incisions with different phacoemulsification ultrasonic tips. J Cataract Refract Surg 1999; 25:60–64 From the Department of Ophthalmology, University of Toronto, Toronto, Ontario, Canada. Neither author has a financial interest in any product mentioned.
J CATARACT REFRACT SURG—VOL 29, NOVEMBER 2003
2203
C
ataract surgery and phacoemulsification techniques have advanced dramatically over the past 10 years. The development has been toward less traumatic surgery using ultrasound-assisted phacoaspiration
Accepted for publication March 10, 2003. Reprint requests to Rosa Braga-Mele, MD, FRCSC, Assistant Professor, University of Toronto, Mount Sinai Hospital Eye Clinic, 600 University Avenue, Toronto, Ontario, M5G 1X5, Canada. E-mail: rbragamele@ rogers.com. 2003 ASCRS and ESCRS Published by Elsevier Inc.
instead of vacuum-assisted phacoemulsification. Refinements in power modulations1 and control have led to reductions in the amount of ultrasonic energy delivered to the eye and, thus, less risk for injury to the corneal endothelium and the incision. Agarwal and coauthors2 report success using the phakonit method of bimanual lens extraction through a 0.9 mm incision with a sleeveless phacoemulsification needle. Recent research with the Sovereign system3 shows that microphaco using a bare phaco needle through a relatively small incision can be conducted with specific parameters. 0886-3350/03/$–see front matter doi:10.1016/S0886-3350(03)00330-4
LABORATORY SCIENCE: SLEEVELESS BIMANUAL PHACOEMULSIFICATION
Although currently no intraocular lens (IOL) will fit through a small stab incision, there are obvious advantages of lens extraction through 2 small incisions.4,5 First, irrigation through the side-port instrument can help move lens material toward the phacoemulsification needle tip; when irrigation is delivered through the sleeve, the irrigation fluid may create a current that pushes the lens material away from the needle tip. Separating irrigation and aspiration should theoretically direct loose pieces toward the aspiration port. Second, nuclear material can be approached from 2 incision sites if needed. Third, subincisional cortex can be more easily removed. Fourth, small stab incisions theoretically allow a tightly closed and stable anterior chamber, but in microphaco, flow is sometimes reduced and chamber stability may be in question. The feasibility of performing sleeveless bimanual phacoemulsification is dependent on the phacoemulsification needle remaining cool during the surgery. With a sleeve in place, a thermal barrier consisting of the irrigating fluid surrounded by the Teflon威 sleeve exists. With modern high-vacuum phacoemulsification and chopping techniques, the ultrasound time to perform phacoemulsification decreases. Adjuvant methods of cooling the wound such as using cooled irrigating solution or providing direct and constant irrigation externally to the incision site can be applied. This raises the question whether a sleeve is necessary to prevent corneal wound burns. The Millennium Microsurgical System (Bausch & Lomb Surgical) operates at a relatively low ultrasonic frequency of 28.5 kHz. This machine may produce less heat than others operating at higher frequencies since the amount of heat generated is proportional to the operating frequency.4 The current study was undertaken to assess the feasibility of performing sleeveless bimanual phacoemulsification with the Millennium system by measuring wound temperature during the procedure.
Materials and Methods Fresh human cadaver eye-bank eyes were used in the study. In each eye, 2 clear corneal uniplanar stab incisions 1.4 mm in width were made using a metal paracentesis blade. The width of the incision allowed the sleeveless phacoemulsification needle to be inserted without excessive tension on the wound. Irrigation was delivered through the first wound with a 20-gauge irrigation cannula. 2200
Figure 1. (Braga-Mele) Phaco tip with thermocouple.
A sleeve was cut at the hub and screwed on the phacoemulsification handpiece. This modified sleeve was used to secure a standard type-J thermocouple (accurate for 0⬚C to 76⬚C) to the phacoemulsification needle (Figure 1). The tip of the thermocouple was placed 2.0 mm behind the phacoemulsification needle tip; ie, the thermocouple was placed directly in the clear corneal wound and would thus measure wound temperature unequivocally. Because of the addition of the thermocouple, the wound was enlarged to 1.8 mm to allow the needle–thermocouple complex to fit within the clear corneal wound without excessive tension. The needle–thermocouple complex took up the entire width of the wound; thus, the egress of fluid from the wound was small and minimal. The thermocouple was plugged into a Fluke Hydra 2620A Data Acquisition Unit. The data were transmitted to a personal computer via an RS-232 connection and recorded using Fluke Hydra Logger version 3.0 software. Wound temperature was sampled at 3 points per second. Ambient room temperature was also measured for variance. The Millennium Microsurgical System with phaco burst technology was tested using the MicroFlow威 phacoemulsification needle (Bausch & Lomb Surgical), which has a 19gauge bore and a 1.07 mm outer diameter. The bottle height was 110 cm above the eye, and the vacuum was 180 mm Hg. Three modalities were tested: pulse mode at 5 pulses per second and phaco burst mode at 80-millisecond and 160-millisecond burst-width intervals. In phaco burst mode, the burst width is set by the surgeon. During the burst interval, the ultrasound power rises immediately to the maximum power set by the surgeon. This burst interval is initially followed by a 1.2-second quiet interval. As the footpedal is depressed, the quiet interval is reduced from 1.2 seconds to zero. When the footpedal is maximally depressed, the ultrasound is at maximum power continuously. End points were those used by Soscia and coauthors3: wound temperature greater than 45⬚C or whitening or contracture of the wound.
J CATARACT REFRACT SURG—VOL 29, NOVEMBER 2003
LABORATORY SCIENCE: SLEEVELESS BIMANUAL PHACOEMULSIFICATION
Figure 2. (Braga-Mele) Pulse mode 30% power with line occlusion.
Figure 3. (Braga-Mele) Burst mode at 160 milliseconds, 80% power, with line occlusion.
In pulse mode, the test was started with the power amplitude at 20% and ran for 3 minutes using the full 20% maximum power immediately (pedal engaged to maximum amount). If end point was not attained, the maximum power was increased by 10% increments. This was repeated for the nonoccluded and occluded (pinching the aspiration line) states. In phaco burst modalities with 80-millisecond and 160-millisecond burst-width intervals, the procedure was as follows: The maximum power was initially set at 15% of the available power. Testing began with the footpedal at the top of position 3. Entry into position 3 was identified by an audible click. A video overlay on-screen system allowed the surgeon to visualize the exact position of the footpedal within the range of position 3. At the top of position 3, the machine produced a burst of 15% power for 80 milliseconds followed by a quiet interval of 1.2 seconds. This position was held for 2 minutes. If end point was not attained, the foot pedal was depressed to the midpoint of foot position 3 (as indicated on the video overlay) for 2 minutes. At the midpoint of position 3, the burst duration remained at 80 milliseconds. However, the quiet interval was reduced to approximately 0.6 second. If end point was not attained, the footpedal was depressed fully to the end of position 3 for 2 more minutes. At this position, the machine delivered continuous ultrasound energy at 15% because the quiet interval was zero. This procedure was repeated with 10% increments in the maximum allowable phacoemulsification power until 100% power was reached or a temperature of 45⬚C or a wound burn occurred. The procedure was repeated using a 160-millisecond burst interval. The procedure was performed in the nonoccluded and occluded states for 80-millisecond and 160-millisecond quiet intervals.
The tests were performed twice in separate eyes to ensure reproducibility and validity. The wound was constantly irrigated externally with room-temperature balanced salt solution in all eyes to simulate the clinical setting of corneal irrigation during surgery. Throughout all procedures, the stability of the anterior chamber was monitored.
Results In pulse mode in the nonoccluded state, even at 100% power the temperature did not rise above 43.8⬚C. In the occluded state, the temperature rose to 51.7⬚C after 40 seconds of aspiration line occlusion at 30% power (Figure 2). The temperature returned to the preocclusion level of 30⬚C after 1 second. Although the temperature rose to a maximum of 51.7⬚C, the corneal wound remained clear and no wound burn or contracture was noted. In phaco burst mode with the burst-width interval preset at 160 milliseconds, no end point was reached in the nonoccluded state even at 100% power. The maximum temperature at this point was 41.4⬚C. At 80% power with the aspiration fully occluded, the temperature rose to 53.2⬚C within 60 seconds of occlusion when the footpedal was completely depressed (Figure 3). This did not create a visible wound burn or change, and once occlusion was broken, the temperature declined to 43.5⬚C within 0.6 second. In 1 set of eyes at 40% power, the temperature rose to 46.1⬚C during
J CATARACT REFRACT SURG—VOL 29, NOVEMBER 2003
2201
LABORATORY SCIENCE: SLEEVELESS BIMANUAL PHACOEMULSIFICATION
stable. The results were reproducible in the second set of eyes and were added to the results in the first eye; the mean results are reported. The external wound irrigation produced a 1.5⬚C to 2.0⬚C reduction in the wound temperature. This was determined during phacoemulsification when irrigation was interrupted and the temperature was noted to rise 1.5⬚C to 2.0⬚C and remain steady at this level; when irrigation was reinstated after 60 seconds, the wound temperature dropped to the previous level.
Discussion Figure 4. (Braga-Mele) Burst mode at 160 milliseconds, 40% power, with tip occlusion (vitreous).
the time vitreous occluded the phacoemulsification tip (Figure 4). In the burst-width interval preset at 80 milliseconds, in the nonoccluded and occluded states, at 100% power with the footpedal completely depressed for 3 minutes, there was no significant temperature rise and no wound burn (Figure 5). In the nonoccluded state, the temperature did not rise above 33.6⬚C; in the occluded state, the maximum temperature was 41.8⬚C. During the study, the ambient room temperature did not vary significantly and the chamber remained
Figure 5. (Braga-Mele) Burst mode at 80 milliseconds, 100% power, with line occlusion.
2202
Developments in technology have brought exciting advances in cataract surgery techniques. In this rapidly evolving field, surgeons aim to perform the least traumatic surgery by decreasing thermal energy delivered to the eye, wound size, and trauma to the cornea, thereby promoting more rapid visual recovery. Recent development has been toward small-incision sleeveless bimanual phacoemulsification, anticipating the advent of a smaller foldable, rollable, or injectable IOL. It was encouraging to find that the end points of 45⬚C, wound burn or wound contracture, were not reached in the nonoccluded state in the 3 modalities tested. In the phaco burst mode at the 80-millisecond burst-width interval, in the nonoccluded and fully occluded states, at 100% power with the footpedal completely depressed for 3 minutes, there was no significant temperature rise and no wound burn. In the nonoccluded state, the temperature did not rise above 33.6⬚C, and in the occluded state, the maximum temperature was 41.8⬚C. However, in the occluded state, the pulse mode and 160-millisecond burst mode created wound temperatures in excess of 45⬚C. In the pulse mode, the time the needle was in full occlusion (45 seconds) to produce a temperature rise was beyond what would normally happen during live surgery. Similar to Soscia and coauthors,3 we found that the phacoemulsification handpiece became extremely hot at higher temperatures but the wound did not burn. One possible reason was the constant flow and egress of fluid through the wound and around the needle. The wounds in the study had to be enlarged to accommodate the thermocouple, and this must be kept in mind when analyzing the tempera-
J CATARACT REFRACT SURG—VOL 29, NOVEMBER 2003
LABORATORY SCIENCE: SLEEVELESS BIMANUAL PHACOEMULSIFICATION
ture findings as a relatively leaky wound will allow egress of fluid around the wound and thus lower temperatures. One must also keep in mind that the thermocouple was in contact with the bare phaco needle and was thus probably measuring the phaco needle temperature and not the corneal temperature. Concurrently, one must note that cadaver eyes are generally kept at lower than body temperature. In this study, the eyes were at room temperature for a few hours before use, but because of the change from body temperature, the maximum temperature in real surgery could be higher or reached more quickly. Simultaneous temperature measurement using the thermocouple and infrared video thermal imaging6 may help address these questions. With respect to the temperature rise that occurred in the 160-millisecond burst mode at 80% power, the amount of power and time required to produce such a rise was higher than typical settings used in live surgery. It would be unusual to have sustained occlusion using burst mode at 80% power for 60 seconds. In 1 eye using the 160-millisecond burst mode, the temperature rose at 40% power. Reviewing the videotape footage of the experiment, we found that the posterior capsule in this eye had ruptured and the tip was fully occluded with vitreous. The presence of vitreous causes full occlusion at the distal tip of the needle as opposed to simulating occlusion by clamping the aspiration line. This appears to cause a rise in temperature at lower power than by clamping the aspiration line. During all other segments of the experiment, the posterior capsule was intact and vitreous was not found to occlude the tip. Our hypothesis for this finding is as follows: With clamping the aspiration line, a column of fluid remains within the lumen of the phacoemulsification needle. This small amount of fluid may act as a heat sink and retard the rise in the temperature of the needle. However, during true occlusion (at the tip), continued aspiration causes the lumen of the needle to empty. Without the small column of fluid to act as a heat sink, the needle and, secondarily, the wound temperature
will rise more quickly. Further studies of bare-needle phacoemulsification should look at simulating occlusion by closing the tip rather than clamping the aspiration tubing.
Conclusion In summary, the temperature rises that were demonstrated were mostly under clinically unusual parameters. One must take into account that this study was done in a laboratory setting and the results may be different in a clinical setting. However, we believe the study shows that phacoemulsification with a sleeveless needle through a small stab incision can be safely performed with the Millennium Microsurgical System using conventional phaco burst mode settings within certain parameters.
References 1. Fine IH, Packer M, Hoffman RS. Use of power modulations in phacoemulsification; choo-choo chop and flip phacoemulsification. J Cataract Refract Surg 2001; 27: 188–197 2. Agarwal A, Agarwal S, Agarwal A. Phakonit and laser phakonit: lens removal through a 0.9-mm incision. In: Agarwal A, Agarwal S, Sachdev MS, et al. Phacoemulsification, Laser Cataract Surgery and Foldable IOLs, 2nd ed. New Delhi, Jaypee Brothers, 2000; 204⫺216 3. Soscia W, Howard JG, Olson RJ. Bimanual phacoemulsification through 2 stab incisions; a wound-temperature study. J Cataract Refract Surg 2002; 28:1039–1043 4. Fine IH, Packer M, Hoffman RS. New phacoemulsification technologies. J Cataract Refract Surg 2002; 28:1054– 1060 5. Tsuneoka H, Shiba T, Takahashi Y. Ultrasonic phacoemulsification using a 1.4 mm incision: clinical results. J Cataract Refract Surg 2002; 28:81–86 6. Bissen-Miyajima H, Shimmura S, Tsubota K. Thermal effect on corneal incisions with different phacoemulsification ultrasonic tips. J Cataract Refract Surg 1999; 25:60–64 From the Department of Ophthalmology, University of Toronto, Toronto, Ontario, Canada. Neither author has a financial interest in any product mentioned.
J CATARACT REFRACT SURG—VOL 29, NOVEMBER 2003
2203