- Email: [email protected]
Temperature profiles of sleeveless and coaxial phacoemulsification
LABORATORY SCIENCE
Temperature profiles of sleeveless and coaxial phacoemulsification Adi Abulafia, MD, Adi Michaeli, MD, Avner Belkin, MD, Ehud I. Assia, MD
PURPOSE: To study the temperature profile at the corneal wound during 2 sleeveless techniques versus 2 coaxial phacoemulsification techniques. SETTING: Department of Ophthalmology, Meir Medical Center, Kfar Saba and Ein-Tal Eye Center, Tel-Aviv, Israel. DESIGN: Experimental study. METHODS: Thirty-six porcine eyes were randomized into 4 groups: Group 1: conventional coaxial system (3.0 mm incision); Group 2: coaxial microincision cataract surgery (MICS) system (2.2 mm incision); Group 3: bimanual MICS (1.1 mm incision); Group 4: sleeveless tri-MICS (1.1 mm incision) using a 19-gauge anterior chamber maintainer as the sole fluid source. Temperature measurements were taken using a thermocouple and an infrared thermal imaging system. Measurements were taken in 2 settings; that is, with and without occlusion. RESULTS: With no occlusion, corneal burns did not occur in any group. However, corneal temperatures were lower with the sleeveless systems (Groups 3 and 4) than with the coaxial systems (Groups 1 and 2) (PZ.0003). When occlusion was induced, temperatures were kept constantly low in the sleeveless groups, whereas in the coaxial groups, temperatures increased rapidly, causing corneal burns within seconds. The mean temperature elevations at the incision sites were 39 C, 48.5 C, 13.6 C, and 11.3 C in Groups 1, 2, 3, and 4, respectively (P<.0001). CONCLUSIONS: Sleeveless phacoemulsification maintained lower tissue temperatures than sleeved coaxial methods. During occlusion, fluid flow around the naked tip of the sleeveless systems prevented heat accumulation and corneal burns. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2013; 39:1742–1748 Q 2013 ASCRS and ESCRS
As methods for performing cataract surgery have improved from intracapsular cataract extraction, to extracapsular cataract extraction, to conventional phacoemulsification, and at present, microincision cataract surgery (MICS), incision size has decreased. Microincision cataract surgery, with incisions ranging from 1.6 to 2.2 mm, is becoming increasingly popular because it is often associated with advantages, such as the use of a lower effective phaco power,1 a reduction in surgically induced astigmatism, and faster refractive stability.2 To reduce incision size using MICS techniques, the irrigation sleeve is separated from the phaco tip. In bimanual MICS, fluid enters the anterior chamber through a second handheld instrument, such as the irrigating chopper.3,4 With the tri-MICS (3-port) technique, the 3 functions (phaco tip, second hand 1742
Q 2013 ASCRS and ESCRS Published by Elsevier Inc.
instrument, and irrigation line) are further separated.A The 2 superior incisions are used for the naked phaco tip and a standard chopper, whereas a third incision, located inferiorly, is used for a purpose-designed anterior chamber maintainer (ACM) as the sole source of irrigation fluid (Figure 1). The ACM is inserted as the first step of surgery and provides continuous irrigation throughout the procedure. The sleeveless MICS technique has the advantage of accomplishing cataract surgery through very small clear corneal incisions (CCIs); nevertheless, many surgeons are reluctant to perform sleeveless surgery because of the concern of corneal burns (from the unprotected metal tip), which may lead to wound leak, astigmatism,5 and anterior chamber instability.6,7 Although the thermal safety of sleeveless phaco tips has been reported in several studies,3,8,9 controversy 0886-3350/$ - see front matter http://dx.doi.org/10.1016/j.jcrs.2013.02.056
LABORATORY SCIENCE: TEMPERATURE PROFILE OF SLEEVELESS AND COAXIAL PHACOEMULSIFICATION
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MATERIALS AND METHODS
Figure 1. The tri-MICS system. The superior incisions are used for a naked phaco sleeve and a standard chopper, whereas the inferior incision is used for an ACM.
exists as to whether it is as safe as coaxial systems in maintaining low temperatures at the incision site.6 Furthermore, the thermal profile of a new sleeveless technique (tri-MICS) has not been tested. The primary goal of this study was to evaluate the temperature profiles at the corneal wound in 2 sleeveless techniques versus 2 coaxial techniques of phacoemulsification cataract surgery during free aspiration and occlusion conditions. The secondary goal of the study was to validate the accuracy of infrared (IR) thermal imaging of corneal temperatures during phacoemulsification with direct temperature measurements taken by a thermocouple embedded in the cornea as a reference. Submitted: September 29, 2012. Final revision submitted: February 12, 2013. Accepted: February 14, 2013.
Thirty-six postmortem porcine eyes were kept at room temperature (w20 C) for approximately 2 hours before surgery. Eyes were randomized into 4 groups (Figure 2): Group 1: conventional coaxial system; Group 2: coaxial MICS system; Group 3: bimanual MICS system; and Group 4: tri-MICS system. Two surgical conditions were tested in each group; that is, without occlusion (5 eyes) and with occlusion (4 eyes). Phacoemulsification was performed in all eyes using the Infiniti vision system (Alcon Laboratories, Inc.). In Group 1, a conventional coaxial system was used with a 19-gauge sleeved Kelman tip through a 3.0 mm CCI. In Group 2, a coaxial MICS system was used with a microcoaxial sleeved Kelman 20-gauge tip through a 2.2 mm CCI. In Group 3, the bimanual MICS system was used with a sleeveless Kelman 20-gauge tip inserted through a 1.1 mm CCI and an irrigating chopper (IC-Duet, Microsurgical Technology) inserted through a second 1.1 mm CCI. In Group 4, a triMICS system was used with a sleeveless Kelman 20-gauge tip through a 1.1 mm CCI. A purpose-designed 19-gauge ACM with thin walls and a large 0.9 mm internal diameter (AVI-ACM, Advanced Visual Instruments, Inc.) was inserted through an inferior 1.1 mm CCI.
Experiment 1 (No Occlusion) In the first set of eyes, continuous phaco power of 70% was applied to the anterior chamber for 60 seconds. The phaco tip was placed in the center of the eye over the crystalline lens. No lens removal was performed. The fluid settings were vacuum level 200 mm Hg, aspiration rate 20 cc/min, and bottle height 80 cm. Balanced salt solution was used as the irrigating fluid.
Experiment 2 (Occlusion Applied) In the second set of eyes, continuous phacoemulsification was performed using the same parameters. Complete tip occlusion was simulated by clamping the aspiration line for 30 seconds.
Temperature Recording
From the Department of Ophthalmology (Abulafia, Belkin, Assia), Meir Medical Center, Kfar Saba, and the Ein-Tal Eye Center (Abulafia, Michaeli, Assia), the Department of Ophthalmology (Michaeli), TelAviv Medical Center, and the Sackler School of Medicine (Abulafia, Michaeli, Belkin, Assia), Tel-Aviv University, Tel-Aviv, Israel. Avi Grinblat, Advanced Visual Instruments, Inc., designed the designated 19-gauge AVI-ACM. Presented at the XXVIII Congress of the European Society of Cataract & Refractive Surgeons, Paris, France, September 2010, the ASCRS Symposium on Cataract, IOL and Refractive Surgery, San Diego, California, USA, March 2011, the ASCRS Symposium on Cataract, IOL and Refractive Surgery, Chicago, Illinois, USA, April 2012, and the XXX Congress of the European Society of Cataract & Refractive Surgeons, Milan, Italy, September 2012. Corresponding author: Adi Abulafia, MD, Sir Charles Gairdner Hospital, Department of Ophthalmology, Hospital Avenue, Nedlands, Perth 6009, Western Australia. E-mail: [email protected].
Simultaneous temperature recordings at the phaco incision site were taken using 2 measurement methods. In the direct contact measurement, a 20-gauge slit knife was used to create a corneal tunnel parallel to the phaco incision site. A thermocouple electrode connected to a temperature recorder (Therm 2420, Ahlborn Mess- und Regelungstechnik GmbH) was inserted (Figure 3). Temperature measurements were taken at baseline and every 15 seconds during phacoemulsification. In the noncontact measurement, continuous measurements were taken using an IR thermal imaging system (Infratec GmbH) (Figure 4). Data were retrieved and analyzed using digital software (Irbis3 Professional, Infratec GmbH). Corneal burns were defined by clinical observation of localized corneal whitening by 2 observers.
Statistical Analysis The correlation between the 2 temperature measurement systems was calculated by the following steps (using data
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LABORATORY SCIENCE: TEMPERATURE PROFILE OF SLEEVELESS AND COAXIAL PHACOEMULSIFICATION
Figure 2. The 4 study groups (MICS Z microincision cataract surgery).
collected from the nonoccluded set of eyes): Pearson correlation (r) for each surgical method; r2 for each surgical method, and average r2 for all methods; the final r extracted from the average r2 by the simple square root. After a high correlation between the 2 measurement methods was established, only IR measurements were taken in the second set of eyes (occlusion applied). To evaluate differences in temperature between the 4 surgical methods in the 2 settings (nonocclusion and occlusion), a general linear model with repeated measurements was used for pairwise comparison, where temperatures at each timepoint were adjusted by the baseline value. No a correction was performed.
Figure 3. The tri-MICS system used in a porcine eye. The thermocouple is seen in the cornea adjacent to the naked phaco tip. Fluid leakage can be seen around the naked phaco tip.
A 2-group analysis (a coaxial group that included Groups 1 and 2 versus a sleeveless group that included Groups 3 and 4) was performed using a general linear model with repeated measurements with the following explaining variables: method, time, and interaction between method and time.
RESULTS Temperature Measurement Technique A high correlation was found between the temperature values recorded by the 2 measurement methods (direct measurement by the contact thermocouple and indirect recording by the IR camera) (r Z 0.93, P!.001). However, because the IR recording provided
Figure 4. An IR image taken with a thermal imaging system. The maximum temperature was measured at the area surrounded by the yellow circle (porcine globe).
J CATARACT REFRACT SURG - VOL 39, NOVEMBER 2013
LABORATORY SCIENCE: TEMPERATURE PROFILE OF SLEEVELESS AND COAXIAL PHACOEMULSIFICATION
continuous real-time noncontact measurement of each point in the entire surgical field, the results of this method were used for statistical analysis. Experiment 1 (No Occlusion) Corneal burns did not develop in any group. However, in a 2-group analysis, the corneal temperatures were lower in the sleeveless groups (Groups 3 and 4) than in the coaxial groups (Groups 1 and 2) (PZ.0003). Table 1 shows the mean incision temperatures at baseline, mean incision temperature elevation, and mean maximum incision temperature. Temperatures were lower in Group 3 (bimanual MICS) than in Group 1 (conventional coaxial) and Group 2 (coaxial MICS) (PZ.081 and PZ.0035, respectively). Temperatures were statistically significantly lower in Group 4 (tri-MICS) than in Group 1 (coaxial) and Group 2 (coaxial MICS) (PZ.021 and PZ.0001, respectively). Temperatures were statistically significantly lower in Group 1 than in Group 2 (PZ.015). The differences in temperatures between Group 3 and Group 4 were not statistically significant, PZ.85 (Figure 5). Experiment 2 (Occlusion Applied) When applying occlusion, the results were more dramatic. Although temperatures were consistently low in the sleeveless groups, temperatures increased rapidly in the coaxial groups, causing corneal burns within a few seconds (Figure 6). Table 2 shows the mean incision temperatures at baseline, mean incision temperature elevation, and mean maximum incision temperature. Temperatures were statistically significantly lower in Group 3 and Group 4 than in Group 1 and Group 2 (P!.0001). Temperatures were statistically significantly lower in Group 1 than in Group 2 (coaxial MICS) (PZ.0075). The differences in temperatures between Groups 3 and 4 were not statistically significant (PZ.1) (Figure 7).
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The coaxial and sleeveless systems also differed in their temperature curve profiles. While the temperatures in the sleeveless groups (3 and 4) had almost stabilized after approximately 7 seconds, the temperatures in the coaxial groups continued to rise (P!.0001). Tissue temperatures using the coaxial systems reached a mean of 65 C to 70 C, levels often associated with clinical tissue burns. DISCUSSION Recent developments in cataract surgery technology have focused on reducing incision size to a minimum. This provides a safer surgery with almost instantaneous recovery, low postoperative astigmatism, high predictability of postsurgical refraction, and a low risk for postoperative complications. The conventional coaxial system, in which the metal tip and the irrigating line are inserted through the same incision, has limitations. A 1.6 to 1.8 mm incision is probably the smallest practical size. Beyond that size, the irrigation tubing will not be able to provide enough fluid to cool the corneal tissue and compensate for the fluid being continuously aspirated. Therefore, to perform phacoemulsification through a smaller incision, the irrigation and the vibrating tip must be separated. In the bimanual technique, the irrigation fluid is provided through a combined second hand instrument, most commonly an irrigating chopper. In the tri-MICS technique, the 3 functions (tip, irrigation, and surgical instrument) are separated
Table 1. Temperature at the incision site with no occlusion. Mean Incision Temperature ( C) Group 1: conventional coaxial 2: coaxial MICS 3: bimanual MICS 4: tri-MICS
Corneal At Baseline Elevation Maximum Burns 24.9
11.1
38.8
No
24.1 22.2 21.8
16.0 7.5 8.3
45.7 35.4 30.1
No No No
MICS Z microincision cataract surgery
Figure 5. Temperature rise over time (no occlusion applied) (MICS Z microincision cataract surgery). J CATARACT REFRACT SURG - VOL 39, NOVEMBER 2013
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LABORATORY SCIENCE: TEMPERATURE PROFILE OF SLEEVELESS AND COAXIAL PHACOEMULSIFICATION
Figure 6. Infrared image after 30 sec in the 4 groups (occlusion applied). Temperatures were extremely high in the coaxial groups, causing corneal burns, as opposed to the sleeveless groups. (Color scale is adjusted due to the high temperature.) Black indicates temperatures higher than given by the color scale (MICS Z microincision cataract surgery).
and continuous irrigation is provided by an ACM inserted through a third corneal incision. This allows use of any second hand instrument with a stable predetermined intraocular pressure (IOP) throughout surgery. Clinical experience has shown that the additional incision has no effect on corneal stability or postoperative astigmatism. Many surgeons are reluctant to use the bimanual or tri-MICS techniques because of the intuitive concern that a high-frequency vibrating metal tip will cause corneal tissue burns. The irrigation sleeve is believed to protect the cornea as a mechanical barrier and by providing continuous fluid flow over the shaft of the tip during surgery. Moderate to severe wound burns occur in about 1 in 1000 phacoemulsification cases.10 Corneal burns usually occur when the phaco tip is occluded by a nuclear fragment or by a viscous or dispersive
ophthalmic viscosurgical device (OVD). Although relatively rare, corneal burns may cause serious complications, such as induced cylinder and loss of corrected vision.5,11,12 Many studies have evaluated the thermal effect of the vibrating phaco needle.11,13–15 Although the thermal safety of sleeveless phaco tips has been reported in several studies,3,8,9 controversy exists as to whether it is as safe as the coaxial systems in
Table 2. Temperature at the incision site after applying occlusion. Mean Incision Temperature ( C) Group 1: conventional coaxial 2: coaxial MICS 3: bimanual MICS 4: tri-MICS
Corneal At Baseline Elevation Maximum Burns 24.1
39.0
63.1
Yes
22.1 21.2 20.9
48.5 13.6 11.3
70.6 34.8 32.2
Yes No No
MICS Z microincision cataract surgery
Figure 7. Temperature rise over time (occlusion applied). Corneal burn can occur when the tissue temperature exceeds 45 C (MICS Z microincision cataract surgery).
J CATARACT REFRACT SURG - VOL 39, NOVEMBER 2013
LABORATORY SCIENCE: TEMPERATURE PROFILE OF SLEEVELESS AND COAXIAL PHACOEMULSIFICATION
maintaining low temperatures at the incision site.6 The main purpose of the present study was to measure the temperature profile at the corneal wound site using various sleeveless and coaxial systems under free aspiration and occlusion conditions. In this study, under a continuous phaco power of 70% for 1 minute, no corneal burns were encountered in any of the 4 groups (no occlusion). This effective phaco power is far more than encountered in actual practice, even during hard cataract removal, and indicates that when the phaco tip is not occluded, both sleeved and sleeveless techniques provide a safe surgical environment. Nevertheless, in a 2-group analysis, the sleeveless group had a statistically significant lower temperature profile than the conventional coaxial group. This indicates that cooling the tip by the irrigation fluid is even more effective when the irrigation system is separated from the phaco tip. Apparently, fluid always leaks through the surgical wound around the phaco tip, even though the wound is only 1.1 mm, and less fluid flows around a sleeved tip than around a naked tip, especially when the incision is small and the opening is tight. This may explain why temperatures in the conventional coaxial group were lower than those in the coaxial MICS group. Furthermore, tissue burns can occur in a coaxial system when the phaco handpiece is tilted,8,15 especially in deep-set eyes. The sleeve is then pressed against the corneal tissue, which prevents fluid flow. When inducing occlusion, the results were more pronounced. Although temperatures in the sleeveless groups remained low, in the conventional coaxial group temperatures climbed rapidly, causing corneal burns within a few seconds. Although we planned to take temperature measurements for 60 seconds, we had to stop after 30 seconds because the handpiece was too hot to grasp and the tubing began to melt. When occlusion occurs, there is no aspiration; that is, no fluid flows through the lumen of the tip (from inside out) and the anterior chamber becomes full. Therefore, when IOP equals gravitational pressure, there is no flow in the irrigation tubing either (from outside in). In other words, when occlusion occurs and phaco energy is activated, heat production is at its maximum, whereas the cooling system is not functioning. Under complete occlusion, it takes only a few seconds to reach temperatures above 45 C, which are consistent with corneal burns.16 Fortunately, occlusion usually breaks before the temperature reaches a critical level. However, if the nucleus is very hard or if a dispersive OVD occludes the tip, tissue burns can occur.17,18 Fluid leakage around the tip is thus a positive byproduct of sleeveless phacoemulsification; that is, not only does it require one half the conventional coaxial incision size, it is also safer.
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The tri-MICS technique was associated with somewhat lower temperature elevation than the bimanual MICS, even though the difference was not statistically significant. In bimanual MICS, irrigation is usually activated when the footpedal is pressed to at least position 1 (irrigation) and only when the second instrument (irrigating chopper) is in the eye. In contrast, the continuous irrigation through the ACM of the tri-MICS system provides continuous flow of irrigation fluid and constant cooling, even when the phaco system is not activated. Furthermore, with the tri-MICS technique, any second hand instrument can be used, not limited to an irrigating device. A strong correlation was found between the 2 temperature measurement techniques; that is, direct contact using a thermocouple and the noncontact method using an IR thermal imaging system. This correlation was statistically significant (P!.001). Thermal imaging systems have been used in several ophthalmic studies6,13,15,16 to measure corneal temperature during phacoemulsification. Our results validate the accuracy of measurement with the IR camera in the surgical setting and confirm that this device can be effectively used to study real-time temperature changes during cataract surgery in in vivo clinical studies. As was shown in this study, the sleeveless phaco systems had better temperature profiles than the coaxial systems. Another concern using microincision techniques is introducing sufficient fluid to maintain a stable anterior chamber in the presence of high vacuum and a high aspiration rate. In a parallel study,B we found that most irrigating choppers and the AVI-ACM may provide at least comparable amounts of fluid as the coaxial systems. In other words, chamber stability and surgical safety of the sleeveless MICS techniques are at least as good as those of the coaxial MICS techniques. Sleeveless MICS is not yet popularized because current foldable intraocular lenses (IOLs) require a relatively large incision, usually 2.0 mm or larger. The history of cataract surgery shows that improved methods to remove the crystalline lens always preceded the development of IOLs for smaller incisions. Microincision (1.1 mm) phaco surgery is now clinically practical and proven safe and effective. However, it will probably bloom only when true MICS IOLs become available. In conclusion, sleeveless phacoemulsification techniques maintained a lower temperature at the incision site than coaxial systems, especially when the phaco tip became occluded. The separate irrigation system provided effective cooling through irrigation fluid leakage around the phaco tip at the incision site. A separate irrigation line (ACM) in the tri-MICS technique
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was the most effective way to maintain a low tissue temperature during phacoemulsification. WHAT WAS KNOWN Although thermal safety of sleeveless phaco tips has been reported, controversy exists as to whether it is as safe as the coaxial systems in maintaining low temperatures at the incision site. Furthermore, the sleeveless temperature profile during occlusion condition has not been thoroughly studied. Infrared thermal imaging systems are used routinely for evaluating corneal temperature during phacoemulsification; however, their validity has not been published in the English literature. WHAT THIS PAPER ADDS Sleeveless phacoemulsification was associated with a lower temperature elevation than coaxial systems during occlusion of the phacoemulsification tip. The modified sleeveless tri-MICS technique using an ACM as the sole source of irrigation fluid had a high safety profile. Remote measurement of tissue temperature using IR thermal imaging was as accurate as contact recording and provided significantly more information.
REFERENCES
8. Tsuneoka H, Shiba T, Takahashi Y. Feasibility of ultrasound cataract surgery with a 1.4 mm incision. J Cataract Refract Surg 2001; 27:934–940 9. Donnenfeld ED, Olson RJ, Solomon R, Finger PT, Biser SA, Perry HD, Doshi S. Efficacy and wound-temperature gradient of WhiteStar phacoemulsification through a 1.2 mm incision. J Cataract Refract Surg 2003; 29:1097–1100 10. Bradley MJ, Olson RJ. A survey about phacoemulsification incision thermal contraction incidence and causal relationships. Am J Ophthalmol 2006; 141:222–224 11. Majid MA, Sharma MK, Harding SP. Corneoscleral burn during phacoemulsification surgery. J Cataract Refract Surg 1998; 24:1413–1415 12. Khodabakhsh AJ, Zaidman G, Tabin G. Corneal surgery for severe phacoemulsification burns. Ophthalmology 2004; 111:332–334 13. Osher RH, Injev VP. Thermal study of bare tips with various system parameters and incision sizes. J Cataract Refract Surg 2006; 32:867–872 14. Olson MD, Miller KM. In-air thermal imaging comparison of Legacy AdvanTec, Millennium, and Sovereign WhiteStar phacoemulsification systems. J Cataract Refract Surg 2005; 31:1640–1647 15. 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 16. Jun B, Berdahl JP, Kim T. Thermal study of longitudinal and torsional ultrasound phacoemulsification; tracking the temperature of the corneal surface, incision, and handpiece. J Cataract Refract Surg 2010; 36:832–837 17. Floyd M, Valentine J, Coombs J, Olson RJ. Effect of incisional friction and ophthalmic viscosurgical devices on the heat generation of ultrasound during cataract surgery. J Cataract Refract Surg 2006; 32:1222–1226 18. Ernest P, Rhem M, McDermott M, Lavery K, Sensoli A. Phacoemulsification conditions resulting in thermal wound injury. J Cataract Refract Surg 2001; 27:1829–1839
OTHER CITED MATERIAL
1. Kurz S, Krummenauer F, Gabriel P, Pfeiffer N, Dick HB. Biaxial microincision versus coaxial small-incision clear cornea cataract surgery. Ophthalmology 2006; 113:1818–1826 J, Rodrıguez-Prats JL, Galal A, Ramzy M. Outcomes of 2. Alio microincision cataract surgery versus coaxial phacoemulsification. Ophthalmology 2005; 112:1997–2003 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. Soscia W, Howard JG, Olson RJ. Microphacoemulsification with WhiteStar; a wound-temperature study. J Cataract Refract Surg 2002; 28:1044–1046 5. Sugar A, Schertzer RM. Clinical course of phacoemulsification wound burns. J Cataract Refract Surg 1999; 25:688–692 6. Osher RH, Injev VP. Microcoaxial phacoemulsification. Part 1: laboratory studies. J Cataract Refract Surg 2007; 33:401–407 7. Girard LJ. Pars plana lensectomy by ultrasonic fragmentation: 1984–Part II: operative and postoperative complications–avoidance or management. Ophthalmic Surg 1984; 15:217–220
A. Assia EI, Abulafia A, Michaeli A. “Three-Port MICS Technique,” presented at the ASCRS Symposium on Cataract, IOL and Refractive Surgery, San Diego, California, USA, March, 2011 B. Assia EI, Abulafia A, Schochot Y, Michaeli A. “Tri–MICS: 3-Port Mini-Incision PhacodConcept and Clinical Experience,” presented at the XXVII Congress of the European Society of Cataract & Refractive Surgeons, Barcelona, Spain, September 2009. Abstract available at: http://escrs.org/abstracts/details. asp?confidZ2&sessidZ25&typeZfree&paperidZ459. Accessed February 27, 2013
J CATARACT REFRACT SURG - VOL 39, NOVEMBER 2013
First author: Adi Abulafia, MD Department of Ophthalmology, Meir Medical Center, Kfar Saba, Isreal
Temperature profiles of sleeveless and coaxial phacoemulsification Adi Abulafia, MD, Adi Michaeli, MD, Avner Belkin, MD, Ehud I. Assia, MD
PURPOSE: To study the temperature profile at the corneal wound during 2 sleeveless techniques versus 2 coaxial phacoemulsification techniques. SETTING: Department of Ophthalmology, Meir Medical Center, Kfar Saba and Ein-Tal Eye Center, Tel-Aviv, Israel. DESIGN: Experimental study. METHODS: Thirty-six porcine eyes were randomized into 4 groups: Group 1: conventional coaxial system (3.0 mm incision); Group 2: coaxial microincision cataract surgery (MICS) system (2.2 mm incision); Group 3: bimanual MICS (1.1 mm incision); Group 4: sleeveless tri-MICS (1.1 mm incision) using a 19-gauge anterior chamber maintainer as the sole fluid source. Temperature measurements were taken using a thermocouple and an infrared thermal imaging system. Measurements were taken in 2 settings; that is, with and without occlusion. RESULTS: With no occlusion, corneal burns did not occur in any group. However, corneal temperatures were lower with the sleeveless systems (Groups 3 and 4) than with the coaxial systems (Groups 1 and 2) (PZ.0003). When occlusion was induced, temperatures were kept constantly low in the sleeveless groups, whereas in the coaxial groups, temperatures increased rapidly, causing corneal burns within seconds. The mean temperature elevations at the incision sites were 39 C, 48.5 C, 13.6 C, and 11.3 C in Groups 1, 2, 3, and 4, respectively (P<.0001). CONCLUSIONS: Sleeveless phacoemulsification maintained lower tissue temperatures than sleeved coaxial methods. During occlusion, fluid flow around the naked tip of the sleeveless systems prevented heat accumulation and corneal burns. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2013; 39:1742–1748 Q 2013 ASCRS and ESCRS
As methods for performing cataract surgery have improved from intracapsular cataract extraction, to extracapsular cataract extraction, to conventional phacoemulsification, and at present, microincision cataract surgery (MICS), incision size has decreased. Microincision cataract surgery, with incisions ranging from 1.6 to 2.2 mm, is becoming increasingly popular because it is often associated with advantages, such as the use of a lower effective phaco power,1 a reduction in surgically induced astigmatism, and faster refractive stability.2 To reduce incision size using MICS techniques, the irrigation sleeve is separated from the phaco tip. In bimanual MICS, fluid enters the anterior chamber through a second handheld instrument, such as the irrigating chopper.3,4 With the tri-MICS (3-port) technique, the 3 functions (phaco tip, second hand 1742
Q 2013 ASCRS and ESCRS Published by Elsevier Inc.
instrument, and irrigation line) are further separated.A The 2 superior incisions are used for the naked phaco tip and a standard chopper, whereas a third incision, located inferiorly, is used for a purpose-designed anterior chamber maintainer (ACM) as the sole source of irrigation fluid (Figure 1). The ACM is inserted as the first step of surgery and provides continuous irrigation throughout the procedure. The sleeveless MICS technique has the advantage of accomplishing cataract surgery through very small clear corneal incisions (CCIs); nevertheless, many surgeons are reluctant to perform sleeveless surgery because of the concern of corneal burns (from the unprotected metal tip), which may lead to wound leak, astigmatism,5 and anterior chamber instability.6,7 Although the thermal safety of sleeveless phaco tips has been reported in several studies,3,8,9 controversy 0886-3350/$ - see front matter http://dx.doi.org/10.1016/j.jcrs.2013.02.056
LABORATORY SCIENCE: TEMPERATURE PROFILE OF SLEEVELESS AND COAXIAL PHACOEMULSIFICATION
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MATERIALS AND METHODS
Figure 1. The tri-MICS system. The superior incisions are used for a naked phaco sleeve and a standard chopper, whereas the inferior incision is used for an ACM.
exists as to whether it is as safe as coaxial systems in maintaining low temperatures at the incision site.6 Furthermore, the thermal profile of a new sleeveless technique (tri-MICS) has not been tested. The primary goal of this study was to evaluate the temperature profiles at the corneal wound in 2 sleeveless techniques versus 2 coaxial techniques of phacoemulsification cataract surgery during free aspiration and occlusion conditions. The secondary goal of the study was to validate the accuracy of infrared (IR) thermal imaging of corneal temperatures during phacoemulsification with direct temperature measurements taken by a thermocouple embedded in the cornea as a reference. Submitted: September 29, 2012. Final revision submitted: February 12, 2013. Accepted: February 14, 2013.
Thirty-six postmortem porcine eyes were kept at room temperature (w20 C) for approximately 2 hours before surgery. Eyes were randomized into 4 groups (Figure 2): Group 1: conventional coaxial system; Group 2: coaxial MICS system; Group 3: bimanual MICS system; and Group 4: tri-MICS system. Two surgical conditions were tested in each group; that is, without occlusion (5 eyes) and with occlusion (4 eyes). Phacoemulsification was performed in all eyes using the Infiniti vision system (Alcon Laboratories, Inc.). In Group 1, a conventional coaxial system was used with a 19-gauge sleeved Kelman tip through a 3.0 mm CCI. In Group 2, a coaxial MICS system was used with a microcoaxial sleeved Kelman 20-gauge tip through a 2.2 mm CCI. In Group 3, the bimanual MICS system was used with a sleeveless Kelman 20-gauge tip inserted through a 1.1 mm CCI and an irrigating chopper (IC-Duet, Microsurgical Technology) inserted through a second 1.1 mm CCI. In Group 4, a triMICS system was used with a sleeveless Kelman 20-gauge tip through a 1.1 mm CCI. A purpose-designed 19-gauge ACM with thin walls and a large 0.9 mm internal diameter (AVI-ACM, Advanced Visual Instruments, Inc.) was inserted through an inferior 1.1 mm CCI.
Experiment 1 (No Occlusion) In the first set of eyes, continuous phaco power of 70% was applied to the anterior chamber for 60 seconds. The phaco tip was placed in the center of the eye over the crystalline lens. No lens removal was performed. The fluid settings were vacuum level 200 mm Hg, aspiration rate 20 cc/min, and bottle height 80 cm. Balanced salt solution was used as the irrigating fluid.
Experiment 2 (Occlusion Applied) In the second set of eyes, continuous phacoemulsification was performed using the same parameters. Complete tip occlusion was simulated by clamping the aspiration line for 30 seconds.
Temperature Recording
From the Department of Ophthalmology (Abulafia, Belkin, Assia), Meir Medical Center, Kfar Saba, and the Ein-Tal Eye Center (Abulafia, Michaeli, Assia), the Department of Ophthalmology (Michaeli), TelAviv Medical Center, and the Sackler School of Medicine (Abulafia, Michaeli, Belkin, Assia), Tel-Aviv University, Tel-Aviv, Israel. Avi Grinblat, Advanced Visual Instruments, Inc., designed the designated 19-gauge AVI-ACM. Presented at the XXVIII Congress of the European Society of Cataract & Refractive Surgeons, Paris, France, September 2010, the ASCRS Symposium on Cataract, IOL and Refractive Surgery, San Diego, California, USA, March 2011, the ASCRS Symposium on Cataract, IOL and Refractive Surgery, Chicago, Illinois, USA, April 2012, and the XXX Congress of the European Society of Cataract & Refractive Surgeons, Milan, Italy, September 2012. Corresponding author: Adi Abulafia, MD, Sir Charles Gairdner Hospital, Department of Ophthalmology, Hospital Avenue, Nedlands, Perth 6009, Western Australia. E-mail: [email protected].
Simultaneous temperature recordings at the phaco incision site were taken using 2 measurement methods. In the direct contact measurement, a 20-gauge slit knife was used to create a corneal tunnel parallel to the phaco incision site. A thermocouple electrode connected to a temperature recorder (Therm 2420, Ahlborn Mess- und Regelungstechnik GmbH) was inserted (Figure 3). Temperature measurements were taken at baseline and every 15 seconds during phacoemulsification. In the noncontact measurement, continuous measurements were taken using an IR thermal imaging system (Infratec GmbH) (Figure 4). Data were retrieved and analyzed using digital software (Irbis3 Professional, Infratec GmbH). Corneal burns were defined by clinical observation of localized corneal whitening by 2 observers.
Statistical Analysis The correlation between the 2 temperature measurement systems was calculated by the following steps (using data
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LABORATORY SCIENCE: TEMPERATURE PROFILE OF SLEEVELESS AND COAXIAL PHACOEMULSIFICATION
Figure 2. The 4 study groups (MICS Z microincision cataract surgery).
collected from the nonoccluded set of eyes): Pearson correlation (r) for each surgical method; r2 for each surgical method, and average r2 for all methods; the final r extracted from the average r2 by the simple square root. After a high correlation between the 2 measurement methods was established, only IR measurements were taken in the second set of eyes (occlusion applied). To evaluate differences in temperature between the 4 surgical methods in the 2 settings (nonocclusion and occlusion), a general linear model with repeated measurements was used for pairwise comparison, where temperatures at each timepoint were adjusted by the baseline value. No a correction was performed.
Figure 3. The tri-MICS system used in a porcine eye. The thermocouple is seen in the cornea adjacent to the naked phaco tip. Fluid leakage can be seen around the naked phaco tip.
A 2-group analysis (a coaxial group that included Groups 1 and 2 versus a sleeveless group that included Groups 3 and 4) was performed using a general linear model with repeated measurements with the following explaining variables: method, time, and interaction between method and time.
RESULTS Temperature Measurement Technique A high correlation was found between the temperature values recorded by the 2 measurement methods (direct measurement by the contact thermocouple and indirect recording by the IR camera) (r Z 0.93, P!.001). However, because the IR recording provided
Figure 4. An IR image taken with a thermal imaging system. The maximum temperature was measured at the area surrounded by the yellow circle (porcine globe).
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continuous real-time noncontact measurement of each point in the entire surgical field, the results of this method were used for statistical analysis. Experiment 1 (No Occlusion) Corneal burns did not develop in any group. However, in a 2-group analysis, the corneal temperatures were lower in the sleeveless groups (Groups 3 and 4) than in the coaxial groups (Groups 1 and 2) (PZ.0003). Table 1 shows the mean incision temperatures at baseline, mean incision temperature elevation, and mean maximum incision temperature. Temperatures were lower in Group 3 (bimanual MICS) than in Group 1 (conventional coaxial) and Group 2 (coaxial MICS) (PZ.081 and PZ.0035, respectively). Temperatures were statistically significantly lower in Group 4 (tri-MICS) than in Group 1 (coaxial) and Group 2 (coaxial MICS) (PZ.021 and PZ.0001, respectively). Temperatures were statistically significantly lower in Group 1 than in Group 2 (PZ.015). The differences in temperatures between Group 3 and Group 4 were not statistically significant, PZ.85 (Figure 5). Experiment 2 (Occlusion Applied) When applying occlusion, the results were more dramatic. Although temperatures were consistently low in the sleeveless groups, temperatures increased rapidly in the coaxial groups, causing corneal burns within a few seconds (Figure 6). Table 2 shows the mean incision temperatures at baseline, mean incision temperature elevation, and mean maximum incision temperature. Temperatures were statistically significantly lower in Group 3 and Group 4 than in Group 1 and Group 2 (P!.0001). Temperatures were statistically significantly lower in Group 1 than in Group 2 (coaxial MICS) (PZ.0075). The differences in temperatures between Groups 3 and 4 were not statistically significant (PZ.1) (Figure 7).
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The coaxial and sleeveless systems also differed in their temperature curve profiles. While the temperatures in the sleeveless groups (3 and 4) had almost stabilized after approximately 7 seconds, the temperatures in the coaxial groups continued to rise (P!.0001). Tissue temperatures using the coaxial systems reached a mean of 65 C to 70 C, levels often associated with clinical tissue burns. DISCUSSION Recent developments in cataract surgery technology have focused on reducing incision size to a minimum. This provides a safer surgery with almost instantaneous recovery, low postoperative astigmatism, high predictability of postsurgical refraction, and a low risk for postoperative complications. The conventional coaxial system, in which the metal tip and the irrigating line are inserted through the same incision, has limitations. A 1.6 to 1.8 mm incision is probably the smallest practical size. Beyond that size, the irrigation tubing will not be able to provide enough fluid to cool the corneal tissue and compensate for the fluid being continuously aspirated. Therefore, to perform phacoemulsification through a smaller incision, the irrigation and the vibrating tip must be separated. In the bimanual technique, the irrigation fluid is provided through a combined second hand instrument, most commonly an irrigating chopper. In the tri-MICS technique, the 3 functions (tip, irrigation, and surgical instrument) are separated
Table 1. Temperature at the incision site with no occlusion. Mean Incision Temperature ( C) Group 1: conventional coaxial 2: coaxial MICS 3: bimanual MICS 4: tri-MICS
Corneal At Baseline Elevation Maximum Burns 24.9
11.1
38.8
No
24.1 22.2 21.8
16.0 7.5 8.3
45.7 35.4 30.1
No No No
MICS Z microincision cataract surgery
Figure 5. Temperature rise over time (no occlusion applied) (MICS Z microincision cataract surgery). J CATARACT REFRACT SURG - VOL 39, NOVEMBER 2013
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LABORATORY SCIENCE: TEMPERATURE PROFILE OF SLEEVELESS AND COAXIAL PHACOEMULSIFICATION
Figure 6. Infrared image after 30 sec in the 4 groups (occlusion applied). Temperatures were extremely high in the coaxial groups, causing corneal burns, as opposed to the sleeveless groups. (Color scale is adjusted due to the high temperature.) Black indicates temperatures higher than given by the color scale (MICS Z microincision cataract surgery).
and continuous irrigation is provided by an ACM inserted through a third corneal incision. This allows use of any second hand instrument with a stable predetermined intraocular pressure (IOP) throughout surgery. Clinical experience has shown that the additional incision has no effect on corneal stability or postoperative astigmatism. Many surgeons are reluctant to use the bimanual or tri-MICS techniques because of the intuitive concern that a high-frequency vibrating metal tip will cause corneal tissue burns. The irrigation sleeve is believed to protect the cornea as a mechanical barrier and by providing continuous fluid flow over the shaft of the tip during surgery. Moderate to severe wound burns occur in about 1 in 1000 phacoemulsification cases.10 Corneal burns usually occur when the phaco tip is occluded by a nuclear fragment or by a viscous or dispersive
ophthalmic viscosurgical device (OVD). Although relatively rare, corneal burns may cause serious complications, such as induced cylinder and loss of corrected vision.5,11,12 Many studies have evaluated the thermal effect of the vibrating phaco needle.11,13–15 Although the thermal safety of sleeveless phaco tips has been reported in several studies,3,8,9 controversy exists as to whether it is as safe as the coaxial systems in
Table 2. Temperature at the incision site after applying occlusion. Mean Incision Temperature ( C) Group 1: conventional coaxial 2: coaxial MICS 3: bimanual MICS 4: tri-MICS
Corneal At Baseline Elevation Maximum Burns 24.1
39.0
63.1
Yes
22.1 21.2 20.9
48.5 13.6 11.3
70.6 34.8 32.2
Yes No No
MICS Z microincision cataract surgery
Figure 7. Temperature rise over time (occlusion applied). Corneal burn can occur when the tissue temperature exceeds 45 C (MICS Z microincision cataract surgery).
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maintaining low temperatures at the incision site.6 The main purpose of the present study was to measure the temperature profile at the corneal wound site using various sleeveless and coaxial systems under free aspiration and occlusion conditions. In this study, under a continuous phaco power of 70% for 1 minute, no corneal burns were encountered in any of the 4 groups (no occlusion). This effective phaco power is far more than encountered in actual practice, even during hard cataract removal, and indicates that when the phaco tip is not occluded, both sleeved and sleeveless techniques provide a safe surgical environment. Nevertheless, in a 2-group analysis, the sleeveless group had a statistically significant lower temperature profile than the conventional coaxial group. This indicates that cooling the tip by the irrigation fluid is even more effective when the irrigation system is separated from the phaco tip. Apparently, fluid always leaks through the surgical wound around the phaco tip, even though the wound is only 1.1 mm, and less fluid flows around a sleeved tip than around a naked tip, especially when the incision is small and the opening is tight. This may explain why temperatures in the conventional coaxial group were lower than those in the coaxial MICS group. Furthermore, tissue burns can occur in a coaxial system when the phaco handpiece is tilted,8,15 especially in deep-set eyes. The sleeve is then pressed against the corneal tissue, which prevents fluid flow. When inducing occlusion, the results were more pronounced. Although temperatures in the sleeveless groups remained low, in the conventional coaxial group temperatures climbed rapidly, causing corneal burns within a few seconds. Although we planned to take temperature measurements for 60 seconds, we had to stop after 30 seconds because the handpiece was too hot to grasp and the tubing began to melt. When occlusion occurs, there is no aspiration; that is, no fluid flows through the lumen of the tip (from inside out) and the anterior chamber becomes full. Therefore, when IOP equals gravitational pressure, there is no flow in the irrigation tubing either (from outside in). In other words, when occlusion occurs and phaco energy is activated, heat production is at its maximum, whereas the cooling system is not functioning. Under complete occlusion, it takes only a few seconds to reach temperatures above 45 C, which are consistent with corneal burns.16 Fortunately, occlusion usually breaks before the temperature reaches a critical level. However, if the nucleus is very hard or if a dispersive OVD occludes the tip, tissue burns can occur.17,18 Fluid leakage around the tip is thus a positive byproduct of sleeveless phacoemulsification; that is, not only does it require one half the conventional coaxial incision size, it is also safer.
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The tri-MICS technique was associated with somewhat lower temperature elevation than the bimanual MICS, even though the difference was not statistically significant. In bimanual MICS, irrigation is usually activated when the footpedal is pressed to at least position 1 (irrigation) and only when the second instrument (irrigating chopper) is in the eye. In contrast, the continuous irrigation through the ACM of the tri-MICS system provides continuous flow of irrigation fluid and constant cooling, even when the phaco system is not activated. Furthermore, with the tri-MICS technique, any second hand instrument can be used, not limited to an irrigating device. A strong correlation was found between the 2 temperature measurement techniques; that is, direct contact using a thermocouple and the noncontact method using an IR thermal imaging system. This correlation was statistically significant (P!.001). Thermal imaging systems have been used in several ophthalmic studies6,13,15,16 to measure corneal temperature during phacoemulsification. Our results validate the accuracy of measurement with the IR camera in the surgical setting and confirm that this device can be effectively used to study real-time temperature changes during cataract surgery in in vivo clinical studies. As was shown in this study, the sleeveless phaco systems had better temperature profiles than the coaxial systems. Another concern using microincision techniques is introducing sufficient fluid to maintain a stable anterior chamber in the presence of high vacuum and a high aspiration rate. In a parallel study,B we found that most irrigating choppers and the AVI-ACM may provide at least comparable amounts of fluid as the coaxial systems. In other words, chamber stability and surgical safety of the sleeveless MICS techniques are at least as good as those of the coaxial MICS techniques. Sleeveless MICS is not yet popularized because current foldable intraocular lenses (IOLs) require a relatively large incision, usually 2.0 mm or larger. The history of cataract surgery shows that improved methods to remove the crystalline lens always preceded the development of IOLs for smaller incisions. Microincision (1.1 mm) phaco surgery is now clinically practical and proven safe and effective. However, it will probably bloom only when true MICS IOLs become available. In conclusion, sleeveless phacoemulsification techniques maintained a lower temperature at the incision site than coaxial systems, especially when the phaco tip became occluded. The separate irrigation system provided effective cooling through irrigation fluid leakage around the phaco tip at the incision site. A separate irrigation line (ACM) in the tri-MICS technique
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was the most effective way to maintain a low tissue temperature during phacoemulsification. WHAT WAS KNOWN Although thermal safety of sleeveless phaco tips has been reported, controversy exists as to whether it is as safe as the coaxial systems in maintaining low temperatures at the incision site. Furthermore, the sleeveless temperature profile during occlusion condition has not been thoroughly studied. Infrared thermal imaging systems are used routinely for evaluating corneal temperature during phacoemulsification; however, their validity has not been published in the English literature. WHAT THIS PAPER ADDS Sleeveless phacoemulsification was associated with a lower temperature elevation than coaxial systems during occlusion of the phacoemulsification tip. The modified sleeveless tri-MICS technique using an ACM as the sole source of irrigation fluid had a high safety profile. Remote measurement of tissue temperature using IR thermal imaging was as accurate as contact recording and provided significantly more information.
REFERENCES
8. Tsuneoka H, Shiba T, Takahashi Y. Feasibility of ultrasound cataract surgery with a 1.4 mm incision. J Cataract Refract Surg 2001; 27:934–940 9. Donnenfeld ED, Olson RJ, Solomon R, Finger PT, Biser SA, Perry HD, Doshi S. Efficacy and wound-temperature gradient of WhiteStar phacoemulsification through a 1.2 mm incision. J Cataract Refract Surg 2003; 29:1097–1100 10. Bradley MJ, Olson RJ. A survey about phacoemulsification incision thermal contraction incidence and causal relationships. Am J Ophthalmol 2006; 141:222–224 11. Majid MA, Sharma MK, Harding SP. Corneoscleral burn during phacoemulsification surgery. J Cataract Refract Surg 1998; 24:1413–1415 12. Khodabakhsh AJ, Zaidman G, Tabin G. Corneal surgery for severe phacoemulsification burns. Ophthalmology 2004; 111:332–334 13. Osher RH, Injev VP. Thermal study of bare tips with various system parameters and incision sizes. J Cataract Refract Surg 2006; 32:867–872 14. Olson MD, Miller KM. In-air thermal imaging comparison of Legacy AdvanTec, Millennium, and Sovereign WhiteStar phacoemulsification systems. J Cataract Refract Surg 2005; 31:1640–1647 15. 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 16. Jun B, Berdahl JP, Kim T. Thermal study of longitudinal and torsional ultrasound phacoemulsification; tracking the temperature of the corneal surface, incision, and handpiece. J Cataract Refract Surg 2010; 36:832–837 17. Floyd M, Valentine J, Coombs J, Olson RJ. Effect of incisional friction and ophthalmic viscosurgical devices on the heat generation of ultrasound during cataract surgery. J Cataract Refract Surg 2006; 32:1222–1226 18. Ernest P, Rhem M, McDermott M, Lavery K, Sensoli A. Phacoemulsification conditions resulting in thermal wound injury. J Cataract Refract Surg 2001; 27:1829–1839
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A. Assia EI, Abulafia A, Michaeli A. “Three-Port MICS Technique,” presented at the ASCRS Symposium on Cataract, IOL and Refractive Surgery, San Diego, California, USA, March, 2011 B. Assia EI, Abulafia A, Schochot Y, Michaeli A. “Tri–MICS: 3-Port Mini-Incision PhacodConcept and Clinical Experience,” presented at the XXVII Congress of the European Society of Cataract & Refractive Surgeons, Barcelona, Spain, September 2009. Abstract available at: http://escrs.org/abstracts/details. asp?confidZ2&sessidZ25&typeZfree&paperidZ459. Accessed February 27, 2013
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First author: Adi Abulafia, MD Department of Ophthalmology, Meir Medical Center, Kfar Saba, Isreal