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Comparison of actual vacuum pressures at the end of 3 phacoemulsification tips in swine eyes
LABORATORY SCIENCE
Comparison of actual vacuum pressures at the end of 3 phacoemulsification tips in swine eyes Sang Hoon Park, MD, Chul Young Choi, MD, Joon Mo Kim, MD, Hae Ran Chang, MD, Jae Yong Kim, MD, Myoung Joon Kim, MD, Hungwon Tchah, MD, Jae Chan Kim, MD
PURPOSE: To compare the actual vacuum pressure at the end of an aspiration bypass system (ABS) phaco tip and a conventional tip in conditions similar to those during human cataract surgery. SETTING: Kangbuk Samsung Hospital, Seoul, Korea. METHODS: A 4.0 mm diameter rubber eraser ball was inserted in a phacoemulsified swine eye and engaged to a phaco tip. With a vacuum pressure of 300 mm Hg, the eraser ball was pulled in the opposite direction with the phaco tip. The pulling power separating the eraser ball from the phaco tip was measured using the volume of water dripped into a container connected to the eraser ball. Measurements were taken with an Infiniti ABS tip and 2 conventional tips: Sovereign (conventional tip S) and Infiniti (conventional tip I). Measurements were taken alternatively at random in the same eye. RESULTS: The mean pulling power was 17.35 mL G 5.01 (SD) with conventional tip S and 16.85 G 4.45 mL with conventional tip I. The mean pulling power of the ABS tip was 13.35 G 4.32 mL, which was a mean 20.8% lower than that of conventional tip I (P Z .016) and 23.1% lower than that of conventional tip S (P Z .010). CONCLUSIONS: The actual vacuum pressure of the phaco tip was significantly influenced by the presence of the ABS hole. To compensate for the decrease in actual vacuum pressure, surgeons should be aware of the characteristics of the ABS tip being used and change the standard settings accordingly. J Cataract Refract Surg 2009; 35:917–920 Q 2009 ASCRS and ESCRS
Phacoemulsification, the most commonly used surgical technique for cataract extraction, has the advantages of
Submitted: October 1, 2008. Final revision submitted: January 13, 2009. Accepted: January 14, 2009. From the Departments of Ophthalmology, Kangbuk Samsung Hospital (Park, Choi, J.M. Kim, Chang), Sungkyunkwan University School of Medicine, and Intraocular Fluid Dynamics Study Group (IFDSG), and University of Ulsan College of Medicine (J.Y. Kim, M.J. Kim, Tchah), Asan Medical Center, Department of Ophthalmology, College of Medicine (Kim), Chung-Ang University, Seoul, Korea. No author has a financial or proprietary interest in any material or method mentioned. Presented at the XXVI Congress of the European Society of Cataract & Refractive Surgeons, Berlin, Germany, September 2008. Corresponding author: Chul Young Choi, MD, Department of Ophthalmology, Kangbuk Samsung Hospital, Sungkyunkwan University, School of Medicine, Seoul, Korea. E-mail: sashimi0@naver. com. Q 2009 ASCRS and ESCRS Published by Elsevier Inc.
a small incision, minimal induced astigmatism, and fast healing.1 As in other surgeries, complications can occur during phacoemulsification; these include iris prolapse, intraocular hemorrhage, and posterior capsule rupture. Posterior capsule rupture is probably the most common complication encountered by surgeons learning phacoemulsification. It can lead to vitreous prolapse or migration of nuclear fragments into the vitreous cavity, leading to an increased risk for retinal detachment and cystoid macular edema as well as virtually every other surgical complication.2 One way the posterior capsule can be ruptured is through surge. An aspiration bypass system (ABS) tip was introduced for phacoemulsification in 1998. Its purpose was to allow fluid to be drawn through the opening when the phaco tip was occluded by nuclear material. The ABS tip made the use of high vacuum and flow rates safe and improved chamber stability by decreasing surge.1,3,4 However, Payne et al.4 report that the ABS opening causes a 12.1% mean decrease in actual vacuum pressure at the phaco tip. Seibel5 recommends that 0886-3350/09/$dsee front matter doi:10.1016/j.jcrs.2009.01.007
917
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LABORATORY SCIENCE: VACUUM PRESSURES AT END OF PHACO TIPS
Figure 1. Vacuum-pressure measurement equipment.
Figure 2. Mean volume (mL) of dripped saline with each phaco tip. Significant P values are indicated.
surgeons using a flow pump should increase the flow rate by 15% to 20% over their standard setting for a non-ABS tip and those using a vacuum pump should increase the vacuum by 15% to 20%. The purpose of this study was to compare the actual vacuum pressure at the end of an ABS phaco tip and a conventional phaco tip with the same diameter using swine eyes in an environment similar to that encountered during human cataract surgery.
measurements were performed with each phaco tip alternatively at random; this test was repeated 20 times with 20 swine eyes. Comparisons were made using the Student t test with statistical significance set at P!.05.
MATERIALS AND METHODS To measure the vacuum pressure, rubber eraser balls, swine eyes, and vacuum pressure measuring equipment were prepared. First, a rubber eraser, a replacement for the nucleus of the lens, was shaped into a 4.0 mm diameter sphere and connected with 6-0 black silk. The swine eye was phacoemulsified to permit the eraser ball to enter. After a clear corneal incision (8.00 mm) was made at 180 degrees for the phacoemulsification incision (2.75 mm, clear corneal), the eraser ball was inserted and the phaco incision sutured at 4 points with 9-0 nylon. Vacuum pressures generated by 2 phacoemulsification machines, the Sovereign (Advanced Medical Optics) and the Infiniti (Alcon Laboratories), were tested with the same settings as follows: vacuum pressure, 300 mm Hg; aspiration flow rate, 26.0 mL/min; and bottle height, 76.0 cm. A 30-degree phaco tip with a 0.9 mm outer diameter was used with both machines. A conventional tip was used with the Sovereign (conventional tip S) and the Infiniti (conventional tip I), and an ABS tip was used with the Infiniti. A phaco tip was inserted in the swine eye and completely engaged on the eraser ball; the maximum preset vacuum pressure was maintained. The black silk connected to the eraser ball was then pulled in the opposite direction (180 degrees) with the phaco tip, and the pulling power separating the eraser ball from the phaco tip was measured (Figure 1). The pulling power was generated by dripping saline into a container connected to the eraser ball at a speed of 24.0 mL/min, and the volume of dripped saline was measured the moment the phaco tip was separated from the eraser ball. The vacuum pressure was determined based on the volume of saline separating the eraser ball from the phaco tip connected in a straight line. In the same swine eye, 3
RESULTS The mean measured volume of dripped saline was 17.35 mL G 5.01 (SD) with conventional tip S and 16.85 G 4.45 mL with conventional tip I. The mean volume of dripped saline with the ABS tip was 13.35 G 4.32 mL, which was lower by a mean of 20.8% than that with conventional tip I (P Z .016) and lower by a mean of 23.1% than that with conventional tip S (P Z .010). Figure 2 shows the mean volume of dripped saline for each phaco tip. Figure 3 shows the volume of saline dripped in each swine eye. The volume of dripped saline with the ABS tip was similar to or lower than that with the conventional tips in all swine eyes. Tests using the conventional tip S and conventional tip I showed no statistically significant differences (P Z .740). DISCUSSION Surge occurs the moment a nuclear fragment occluding the phaco tip is removed during phacoemulsification. When a phaco tip is occluded, the pressure gradient between the anterior chamber and the aspiration line builds. After the phaco tip occlusion breaks, the volume of fluid in the anterior chamber rushes into the aspiration line to neutralize the pressure gradient. Surge like this occurs more frequently when a surgeon uses relatively high vacuum and flow rates, causing temporary shallowing of the anterior chamber; this can lead to complications such as posterior capsule rupture, vitreous prolapse, nuclear fragment migration into the vitreous cavity, and corneal endothelial cell damage.1,6 Although the occurrence of surge is dependent on the characteristics of the eye
J CATARACT REFRACT SURG - VOL 35, MAY 2009
LABORATORY SCIENCE: VACUUM PRESSURES AT END OF PHACO TIPS
919
Figure 3. Volume (mL) of dripped saline in each swine eye.
(small anterior chamber volume, lax zonules, and postvitrectomy cases), it is also highly dependent on the characteristics and presets of the machine and correlates directly with the strength of the vacuum, compliance, and diameter of the aspiration line.7 To reduce the occurrence of surge, several methods and devices have been introduced to enable safe surgery using higher vacuum and flow rates.8,9 These include changes in bottle height and vacuum level, decreases in the internal diameter of the phaco tip, and the use of lower compliance aspiration lines, ABS tips, and filtering devices that limits fluid egress to prevent postocclusion surge (eg, Cruise Control, Staar). Aspiration bypass technology, developed by Cavitron, was first used in neurosurgical and general surgical units for more efficient aspiration of tumor masses. Pre-aspirator apertures of 2400.0 mm, located 5.0 mm from the end of the ultrasonic tip, were placed to aspirate surrounding saline into the tip. These apertures liquefy the relatively dry tumor aspirant and aid in its removal. Since 1985, all Cavitron ultrasonic surgical aspirator tips have been equipped with these apertures. More recently, Alcon Laboratories introduced the ABS tip, a single 175.0 mm hole drilled into the shaft of the tip 3.0 mm from the open tip end.3 The ABS tips allow surgeons to use higher vacuum and flow rates safely and efficiently and decrease the occurrence of surge. As long as the main port is not occluded, there is virtually no flow through the ABS opening. As soon as occlusion occurs, a vacuum starts developing inside the tip and the flow starts increasing through the ABS opening. This bypass flow decreases surge during occlusion,1,5 cools the incision site, and protects the wound from thermal injury with continuous fluid movement. However, the ABS opening uses continuous fluid movement during occlusion so that full occlusion is not possible and a constant small leak is created.4 Therefore, if a surgeon uses an ABS tip instead of a phaco tip without an ABS opening, he or she will note a decrease in the actual vacuum
pressure. In this study, the actual vacuum pressure in tests using the Infiniti machine with an ABS tip was lower by a mean of 20.8% than that using the Infiniti with a conventional tip and lower by a mean of 23.1% than that using the Sovereign machine with a conventional tip. However, this discrepancy between the actual vacuum pressure and the preset vacuum pressure may vary depending on the preset vacuum pressure and flow rate. Faster flow rates will cause higher fluidic resistance of the small ABS hole and a decrease in flow; thus, the actual vacuum pressure will be closer to the preset vacuum pressure.5 Furthermore, Payne et al.4 found that the actual vacuum pressure decreased by a mean of 12.1% when the preset vacuum pressure was 100 mm Hg. However, when the preset vacuum pressure was 650 mm Hg, the ABS hole decreased the actual vacuum pressure by only 1.1%. A higher preset vacuum will also cause the actual vacuum pressure to be much closer to the preset vacuum pressure. Payne et al.4 used a test chamber rather than an anterior chamber to measure the tip vacuum and simulated occlusion by clamping the aspiration tubing. They indirectly measured vacuum pressure in an environment without fluid flow, which is different from clinical situations. In contrast, we used the anterior chamber of a swine eye, which is similar to a human anterior chamber, and we generated the vacuum by embedding the phaco tip end with an eraser ball (similar to a surgical environment). We also measured the vacuum pressure under the influence of fluid flow, which affects the holding power of the phaco tip. Although we tested actual vacuum pressures in an environment similar to that of a human eye, our study has several limitations. First, we compared the pulling power separating the eraser ball from the phaco tip using water (mL) instead of the practical vacuum pressure unit (mm Hg) of a phaco machine. Second, although we sutured the 8.0 mm incision to prevent leakage at 4 points, leaks did occur and the amount
J CATARACT REFRACT SURG - VOL 35, MAY 2009
920
LABORATORY SCIENCE: VACUUM PRESSURES AT END OF PHACO TIPS
of leakage differed between eyes. However, it was impossible to create this environment with no leakage. This difference in leakage between eyes might have affected the fluidics of the anterior chamber and modified the holding power of the phaco tip. Third, a crack occurred when the rubber eraser ball was being held by the phaco tip with ultrasound because the ball was somewhat fragile. The degree of the crack was different for each eraser ball. This caused measurement errors when the test was repeated more than 4 to 5 times in each eye, which is why we chose to repeat the test 3 times in each eye. Fourth, differences in the shape and length of the incision tunnel might have modified the friction between the incision tunnel and the black silk, which might have affected the results in our study. All these factors might have caused differences between the swine eyes; nevertheless, every measurement using the ABS tip was similar to or smaller than that using the conventional tip in all swine eyes. In conclusion, the presence of an ABS hole had a greater effect on actual vacuum pressure at the end of the phaco tip than that reported previously. Therefore, to compensate for the decrease in actual vacuum pressure and take full advantage of the ABS tip, surgeons should be aware of the characteristics of the various phaco tips and modify their standard fluidic settings accordingly.
2. Osher RH, Cionni RJ, Burk SE. Intraoperative complications of phacoemulsification surgery. In: Steinert RF, ed, Cataract Surgery: Technique, Complications, and Management, 2nd ed. Philadelphia, PA, Saunders, 2004; 469–486 3. Davison JA. Performance comparison of the Alcon Legacy 20000 1.1 mm TurboSonics and 0.9 mm Aspiration Bypass System tips. J Cataract Refract Surg 1999; 25:1386–1391 4. Payne M, Georgescu D, Waite AN, Olson RJ. Phacoemulsification tip vacuum pressure: comparison of 4 devices. J Cataract Refract Surg 2006; 32:1374–1377 5. Seibel BS. Phacodynamics: Mastering the Tools and Techniques of Phacoemulsification Surgery, 4th ed. Thorofare, NJ, Slack, 2005; 170–171 6. Fishkind WJ, Neuhann TF, Steinert RF. The phaco machine: the physical principles guiding its operation. In: Steinert RF, ed, Cataract Surgery; Technique, Complications, and Management, 2nd ed. Philadelphia, PA, Saunders, 2004; 69–73 7. Zanini M, Savini G, Buratto L. Physical principles of phacoemulsification. In: Buratto L, Werner L, Zanini M, Apple D, eds, Phacoemulsification; Principles and Techniques, 2nd ed. Thorofare, NJ, Slack, 2003; 41–43 8. Wade M, Isom R, Georgescu D, Olson RJ. Efficacy of cruise control in controlling postocclusion surge with Legacy and Millennium Venturi phacoemulsification machines. J Cataract Refract Surg 2007; 33:1071–1075 9. Seibel BS. Phacodynamics: Mastering the Tools and Techniques of Phacoemulsification Surgery, 4th ed. Thorofare, NJ, Slack, 2005; 100–107
REFERENCES 1. Georgescu D, Payne M, Olson RJ. Objective measurement of postocclusion surge during phacoemulsification in human eye-bank eyes. Am J Ophthalmol 2007; 143:437–440
J CATARACT REFRACT SURG - VOL 35, MAY 2009
First author: Sang Hoon Park, MD Department of Ophthalmology, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea
Comparison of actual vacuum pressures at the end of 3 phacoemulsification tips in swine eyes Sang Hoon Park, MD, Chul Young Choi, MD, Joon Mo Kim, MD, Hae Ran Chang, MD, Jae Yong Kim, MD, Myoung Joon Kim, MD, Hungwon Tchah, MD, Jae Chan Kim, MD
PURPOSE: To compare the actual vacuum pressure at the end of an aspiration bypass system (ABS) phaco tip and a conventional tip in conditions similar to those during human cataract surgery. SETTING: Kangbuk Samsung Hospital, Seoul, Korea. METHODS: A 4.0 mm diameter rubber eraser ball was inserted in a phacoemulsified swine eye and engaged to a phaco tip. With a vacuum pressure of 300 mm Hg, the eraser ball was pulled in the opposite direction with the phaco tip. The pulling power separating the eraser ball from the phaco tip was measured using the volume of water dripped into a container connected to the eraser ball. Measurements were taken with an Infiniti ABS tip and 2 conventional tips: Sovereign (conventional tip S) and Infiniti (conventional tip I). Measurements were taken alternatively at random in the same eye. RESULTS: The mean pulling power was 17.35 mL G 5.01 (SD) with conventional tip S and 16.85 G 4.45 mL with conventional tip I. The mean pulling power of the ABS tip was 13.35 G 4.32 mL, which was a mean 20.8% lower than that of conventional tip I (P Z .016) and 23.1% lower than that of conventional tip S (P Z .010). CONCLUSIONS: The actual vacuum pressure of the phaco tip was significantly influenced by the presence of the ABS hole. To compensate for the decrease in actual vacuum pressure, surgeons should be aware of the characteristics of the ABS tip being used and change the standard settings accordingly. J Cataract Refract Surg 2009; 35:917–920 Q 2009 ASCRS and ESCRS
Phacoemulsification, the most commonly used surgical technique for cataract extraction, has the advantages of
Submitted: October 1, 2008. Final revision submitted: January 13, 2009. Accepted: January 14, 2009. From the Departments of Ophthalmology, Kangbuk Samsung Hospital (Park, Choi, J.M. Kim, Chang), Sungkyunkwan University School of Medicine, and Intraocular Fluid Dynamics Study Group (IFDSG), and University of Ulsan College of Medicine (J.Y. Kim, M.J. Kim, Tchah), Asan Medical Center, Department of Ophthalmology, College of Medicine (Kim), Chung-Ang University, Seoul, Korea. No author has a financial or proprietary interest in any material or method mentioned. Presented at the XXVI Congress of the European Society of Cataract & Refractive Surgeons, Berlin, Germany, September 2008. Corresponding author: Chul Young Choi, MD, Department of Ophthalmology, Kangbuk Samsung Hospital, Sungkyunkwan University, School of Medicine, Seoul, Korea. E-mail: sashimi0@naver. com. Q 2009 ASCRS and ESCRS Published by Elsevier Inc.
a small incision, minimal induced astigmatism, and fast healing.1 As in other surgeries, complications can occur during phacoemulsification; these include iris prolapse, intraocular hemorrhage, and posterior capsule rupture. Posterior capsule rupture is probably the most common complication encountered by surgeons learning phacoemulsification. It can lead to vitreous prolapse or migration of nuclear fragments into the vitreous cavity, leading to an increased risk for retinal detachment and cystoid macular edema as well as virtually every other surgical complication.2 One way the posterior capsule can be ruptured is through surge. An aspiration bypass system (ABS) tip was introduced for phacoemulsification in 1998. Its purpose was to allow fluid to be drawn through the opening when the phaco tip was occluded by nuclear material. The ABS tip made the use of high vacuum and flow rates safe and improved chamber stability by decreasing surge.1,3,4 However, Payne et al.4 report that the ABS opening causes a 12.1% mean decrease in actual vacuum pressure at the phaco tip. Seibel5 recommends that 0886-3350/09/$dsee front matter doi:10.1016/j.jcrs.2009.01.007
917
918
LABORATORY SCIENCE: VACUUM PRESSURES AT END OF PHACO TIPS
Figure 1. Vacuum-pressure measurement equipment.
Figure 2. Mean volume (mL) of dripped saline with each phaco tip. Significant P values are indicated.
surgeons using a flow pump should increase the flow rate by 15% to 20% over their standard setting for a non-ABS tip and those using a vacuum pump should increase the vacuum by 15% to 20%. The purpose of this study was to compare the actual vacuum pressure at the end of an ABS phaco tip and a conventional phaco tip with the same diameter using swine eyes in an environment similar to that encountered during human cataract surgery.
measurements were performed with each phaco tip alternatively at random; this test was repeated 20 times with 20 swine eyes. Comparisons were made using the Student t test with statistical significance set at P!.05.
MATERIALS AND METHODS To measure the vacuum pressure, rubber eraser balls, swine eyes, and vacuum pressure measuring equipment were prepared. First, a rubber eraser, a replacement for the nucleus of the lens, was shaped into a 4.0 mm diameter sphere and connected with 6-0 black silk. The swine eye was phacoemulsified to permit the eraser ball to enter. After a clear corneal incision (8.00 mm) was made at 180 degrees for the phacoemulsification incision (2.75 mm, clear corneal), the eraser ball was inserted and the phaco incision sutured at 4 points with 9-0 nylon. Vacuum pressures generated by 2 phacoemulsification machines, the Sovereign (Advanced Medical Optics) and the Infiniti (Alcon Laboratories), were tested with the same settings as follows: vacuum pressure, 300 mm Hg; aspiration flow rate, 26.0 mL/min; and bottle height, 76.0 cm. A 30-degree phaco tip with a 0.9 mm outer diameter was used with both machines. A conventional tip was used with the Sovereign (conventional tip S) and the Infiniti (conventional tip I), and an ABS tip was used with the Infiniti. A phaco tip was inserted in the swine eye and completely engaged on the eraser ball; the maximum preset vacuum pressure was maintained. The black silk connected to the eraser ball was then pulled in the opposite direction (180 degrees) with the phaco tip, and the pulling power separating the eraser ball from the phaco tip was measured (Figure 1). The pulling power was generated by dripping saline into a container connected to the eraser ball at a speed of 24.0 mL/min, and the volume of dripped saline was measured the moment the phaco tip was separated from the eraser ball. The vacuum pressure was determined based on the volume of saline separating the eraser ball from the phaco tip connected in a straight line. In the same swine eye, 3
RESULTS The mean measured volume of dripped saline was 17.35 mL G 5.01 (SD) with conventional tip S and 16.85 G 4.45 mL with conventional tip I. The mean volume of dripped saline with the ABS tip was 13.35 G 4.32 mL, which was lower by a mean of 20.8% than that with conventional tip I (P Z .016) and lower by a mean of 23.1% than that with conventional tip S (P Z .010). Figure 2 shows the mean volume of dripped saline for each phaco tip. Figure 3 shows the volume of saline dripped in each swine eye. The volume of dripped saline with the ABS tip was similar to or lower than that with the conventional tips in all swine eyes. Tests using the conventional tip S and conventional tip I showed no statistically significant differences (P Z .740). DISCUSSION Surge occurs the moment a nuclear fragment occluding the phaco tip is removed during phacoemulsification. When a phaco tip is occluded, the pressure gradient between the anterior chamber and the aspiration line builds. After the phaco tip occlusion breaks, the volume of fluid in the anterior chamber rushes into the aspiration line to neutralize the pressure gradient. Surge like this occurs more frequently when a surgeon uses relatively high vacuum and flow rates, causing temporary shallowing of the anterior chamber; this can lead to complications such as posterior capsule rupture, vitreous prolapse, nuclear fragment migration into the vitreous cavity, and corneal endothelial cell damage.1,6 Although the occurrence of surge is dependent on the characteristics of the eye
J CATARACT REFRACT SURG - VOL 35, MAY 2009
LABORATORY SCIENCE: VACUUM PRESSURES AT END OF PHACO TIPS
919
Figure 3. Volume (mL) of dripped saline in each swine eye.
(small anterior chamber volume, lax zonules, and postvitrectomy cases), it is also highly dependent on the characteristics and presets of the machine and correlates directly with the strength of the vacuum, compliance, and diameter of the aspiration line.7 To reduce the occurrence of surge, several methods and devices have been introduced to enable safe surgery using higher vacuum and flow rates.8,9 These include changes in bottle height and vacuum level, decreases in the internal diameter of the phaco tip, and the use of lower compliance aspiration lines, ABS tips, and filtering devices that limits fluid egress to prevent postocclusion surge (eg, Cruise Control, Staar). Aspiration bypass technology, developed by Cavitron, was first used in neurosurgical and general surgical units for more efficient aspiration of tumor masses. Pre-aspirator apertures of 2400.0 mm, located 5.0 mm from the end of the ultrasonic tip, were placed to aspirate surrounding saline into the tip. These apertures liquefy the relatively dry tumor aspirant and aid in its removal. Since 1985, all Cavitron ultrasonic surgical aspirator tips have been equipped with these apertures. More recently, Alcon Laboratories introduced the ABS tip, a single 175.0 mm hole drilled into the shaft of the tip 3.0 mm from the open tip end.3 The ABS tips allow surgeons to use higher vacuum and flow rates safely and efficiently and decrease the occurrence of surge. As long as the main port is not occluded, there is virtually no flow through the ABS opening. As soon as occlusion occurs, a vacuum starts developing inside the tip and the flow starts increasing through the ABS opening. This bypass flow decreases surge during occlusion,1,5 cools the incision site, and protects the wound from thermal injury with continuous fluid movement. However, the ABS opening uses continuous fluid movement during occlusion so that full occlusion is not possible and a constant small leak is created.4 Therefore, if a surgeon uses an ABS tip instead of a phaco tip without an ABS opening, he or she will note a decrease in the actual vacuum
pressure. In this study, the actual vacuum pressure in tests using the Infiniti machine with an ABS tip was lower by a mean of 20.8% than that using the Infiniti with a conventional tip and lower by a mean of 23.1% than that using the Sovereign machine with a conventional tip. However, this discrepancy between the actual vacuum pressure and the preset vacuum pressure may vary depending on the preset vacuum pressure and flow rate. Faster flow rates will cause higher fluidic resistance of the small ABS hole and a decrease in flow; thus, the actual vacuum pressure will be closer to the preset vacuum pressure.5 Furthermore, Payne et al.4 found that the actual vacuum pressure decreased by a mean of 12.1% when the preset vacuum pressure was 100 mm Hg. However, when the preset vacuum pressure was 650 mm Hg, the ABS hole decreased the actual vacuum pressure by only 1.1%. A higher preset vacuum will also cause the actual vacuum pressure to be much closer to the preset vacuum pressure. Payne et al.4 used a test chamber rather than an anterior chamber to measure the tip vacuum and simulated occlusion by clamping the aspiration tubing. They indirectly measured vacuum pressure in an environment without fluid flow, which is different from clinical situations. In contrast, we used the anterior chamber of a swine eye, which is similar to a human anterior chamber, and we generated the vacuum by embedding the phaco tip end with an eraser ball (similar to a surgical environment). We also measured the vacuum pressure under the influence of fluid flow, which affects the holding power of the phaco tip. Although we tested actual vacuum pressures in an environment similar to that of a human eye, our study has several limitations. First, we compared the pulling power separating the eraser ball from the phaco tip using water (mL) instead of the practical vacuum pressure unit (mm Hg) of a phaco machine. Second, although we sutured the 8.0 mm incision to prevent leakage at 4 points, leaks did occur and the amount
J CATARACT REFRACT SURG - VOL 35, MAY 2009
920
LABORATORY SCIENCE: VACUUM PRESSURES AT END OF PHACO TIPS
of leakage differed between eyes. However, it was impossible to create this environment with no leakage. This difference in leakage between eyes might have affected the fluidics of the anterior chamber and modified the holding power of the phaco tip. Third, a crack occurred when the rubber eraser ball was being held by the phaco tip with ultrasound because the ball was somewhat fragile. The degree of the crack was different for each eraser ball. This caused measurement errors when the test was repeated more than 4 to 5 times in each eye, which is why we chose to repeat the test 3 times in each eye. Fourth, differences in the shape and length of the incision tunnel might have modified the friction between the incision tunnel and the black silk, which might have affected the results in our study. All these factors might have caused differences between the swine eyes; nevertheless, every measurement using the ABS tip was similar to or smaller than that using the conventional tip in all swine eyes. In conclusion, the presence of an ABS hole had a greater effect on actual vacuum pressure at the end of the phaco tip than that reported previously. Therefore, to compensate for the decrease in actual vacuum pressure and take full advantage of the ABS tip, surgeons should be aware of the characteristics of the various phaco tips and modify their standard fluidic settings accordingly.
2. Osher RH, Cionni RJ, Burk SE. Intraoperative complications of phacoemulsification surgery. In: Steinert RF, ed, Cataract Surgery: Technique, Complications, and Management, 2nd ed. Philadelphia, PA, Saunders, 2004; 469–486 3. Davison JA. Performance comparison of the Alcon Legacy 20000 1.1 mm TurboSonics and 0.9 mm Aspiration Bypass System tips. J Cataract Refract Surg 1999; 25:1386–1391 4. Payne M, Georgescu D, Waite AN, Olson RJ. Phacoemulsification tip vacuum pressure: comparison of 4 devices. J Cataract Refract Surg 2006; 32:1374–1377 5. Seibel BS. Phacodynamics: Mastering the Tools and Techniques of Phacoemulsification Surgery, 4th ed. Thorofare, NJ, Slack, 2005; 170–171 6. Fishkind WJ, Neuhann TF, Steinert RF. The phaco machine: the physical principles guiding its operation. In: Steinert RF, ed, Cataract Surgery; Technique, Complications, and Management, 2nd ed. Philadelphia, PA, Saunders, 2004; 69–73 7. Zanini M, Savini G, Buratto L. Physical principles of phacoemulsification. In: Buratto L, Werner L, Zanini M, Apple D, eds, Phacoemulsification; Principles and Techniques, 2nd ed. Thorofare, NJ, Slack, 2003; 41–43 8. Wade M, Isom R, Georgescu D, Olson RJ. Efficacy of cruise control in controlling postocclusion surge with Legacy and Millennium Venturi phacoemulsification machines. J Cataract Refract Surg 2007; 33:1071–1075 9. Seibel BS. Phacodynamics: Mastering the Tools and Techniques of Phacoemulsification Surgery, 4th ed. Thorofare, NJ, Slack, 2005; 100–107
REFERENCES 1. Georgescu D, Payne M, Olson RJ. Objective measurement of postocclusion surge during phacoemulsification in human eye-bank eyes. Am J Ophthalmol 2007; 143:437–440
J CATARACT REFRACT SURG - VOL 35, MAY 2009
First author: Sang Hoon Park, MD Department of Ophthalmology, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea