Microcoaxial phacoemulsification

ARTICLE

Microcoaxial phacoemulsification Part 1: Laboratory studies Robert H. Osher, MD, Valentine P. Injev, PE, MBA

PURPOSE: To examine and compare the fluidic, thermal, and incision behaviors of 2.2 mm microcoaxial and sleeveless bimanual phacoemulsification. SETTING: Private practice, Cincinnati, Ohio, USA. METHOD: Fluidic performance of microcoaxial phacoemulsification and sleeveless bimanual microphacoemulsification was examined using a reduced-size irrigating sleeve and numerous irrigating choppers, respectively. Incision temperature during phacoemulsification, incision sealability after phacoemulsification, and incision leak were compared in cadaver eyes. Porcine eyes were used to determine whether a full-sized single-piece SN60AT intraocular lens (IOL) (AcrySof) could be inserted through a 2.2 mm incision. RESULTS: Fluidic comparison indicated greater irrigation flow and a more stable occlusion break response with the microcoaxial setup than with the sleeveless bimanual setup under the same test conditions. Incision temperature during phacoemulsification, incision sealability after phacoemulsification, and incision leakage tests indicated that the microcoaxial setup produced less temperature rise, better incision sealability, and less incision leakage. A full-sized SN60AT IOL could be inserted through a 2.2 mm incision. CONCLUSIONS: Laboratory results indicate that microcoaxial phacoemulsification through a 2.2 mm incision offers fluidic-, thermal-, and incision-related benefits over sleeveless bimanual microphacoemulsification. Moreover, a full-sized single-piece acrylic IOL could be safely implanted without enlarging the 2.2 mm incision. J Cataract Refract Surg 2007; 33:401–407 Q 2007 ASCRS and ESCRS

As cataract surgery evolves, ophthalmic surgeons are constantly in search of new technology that allows the operation to be performed effectively and safely through a smaller incision. Requisite is the injection of a high-quality intraocular lens (IOL) through an unenlarged incision that is competent at the conclusion of the procedure. Bimanual sleeveless phacoemulsification was introduced to serve this purpose, but the acceptance of this technique has been slow because of the suboptimal fluidics, compromised incision integrity, and the necessity in the United States of enlarging or adding another incision for the IOL. An alternate way of reducing incision size is by reducing the dimensions of the coaxial setup. The MicroSmooth Ultrasleeve (Alcon Surgical) was designed to facilitate coaxial phacoemulsification through a 2.2 mm incision, which allows implantation of a fullsize acrylic IOL. This in vitro cadaver eye study compared coaxial and sleeveless bimanual microphacoemulsification. It evaluated infusion flow rates, Q 2007 ASCRS and ESCRS Published by Elsevier Inc.

chamber stability (surge), incision temperature, incision leakage, and incision competency. In addition, it evaluated the feasibility of inserting a full-sized single-piece IOL through a 2.2 mm incision in pig eyes. MATERIALS AND METHODS All cadaver eyes were obtained within 72 hours post-mortem. Infusion flow rates Several types of irrigating choppers were obtained from different manufacturers. The bottle height was set at 100 cm. A stopwatch was used as the infusate was collected in a beaker for a 1-minute interval. The fluid outflow was measured and recorded. Incision temperature profiles Two beveled single-plane incisions, 1.2 mm and 2.2 mm in length, were placed in the peripheral cornea 0886-3350/07/$dsee front matter doi:10.1016/j.jcrs.2006.10.058

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in a cadaver eye approximately 2 to 3 clock hours apart. Parameters selected included an aspiration rate of 12 cc per minute, 0 mm Hg vacuum, continuous ultrasound at 50% power on the Sovereign machine (Advanced Medical Optics) and Infiniti machine (Alcon), and a bottle height of 90 cm. A 0.9 mm bare tip and a 1.1 mm flared tip with Ultrasleeve were placed through the 1.2 mm and 2.2 mm incisions, respectively. A third incision allowed additional infusion from an anterior chamber maintainer (ACM). Simultaneous power was applied to both systems, and the temperature was recorded at the 2 incision regions with a Flir Systems ThermaCam P60 infrared camera at 5-second intervals for 1 minute (Figure 1). The maximum temperature values were simultaneously measured from the 2 individual and incision-localized readouts of the thermal camera. The same test was repeated in a fresh cadaver eye using an equivalent duty cycle of 33%. The Sovereign machine was set in C/F mode (6 ms on, 12 ms off), and the Infiniti machine was set at 20 ms on and 40 ms off. These 2 modulated settings, often used in live surgery, provided duty-cycle equivalency; insignificant differences could be attributed to the modulation’s exact cycle frequency.1

Figure 1. Comparative thermal testing with simultaneous temperature recordings.

incision with 19-gauge irrigating chopper. The microcoaxial setup consisted of a 1.1 mm flared tip with the Ultrasleeve on an Infiniti handpiece. The qualitative grading scale for surge was based on the amount and duration of test chamber shallowing as follows: none, trace, mild, moderate, significant, and severe. The test was repeated using vacuums of 100 mm Hg, 200 mm Hg, 300 mm Hg, 400 mm Hg, and 500 mm Hg.

Postocclusion surge A shortened silicone test chamber filled with 0.85 g of fluid without air was securely placed over the 0.9 mm tip on the Sovereign handpiece. A 1.2 mm beveled slit was placed in the test chamber to allow the introduction of a 20-gauge or 21-gauge irrigating chopper. The bottle height was set at 78 cm, the aspiration rate at 25 to 26 cc/minutes, and the vacuum at 100 mm Hg. The preset vacuum was achieved by pinching off the aspiration line with a hemostat until the occlusion tone sounded. The hemostat was released, and the behavior of the test chamber was observed and recorded (Figure 2). Another setup used a 1.3 mm

Incision leak A 2.2 mm beveled single-plane incision was placed in the peripheral cornea of a cadaver eye, and the iris was extracted with a microforceps. The iris removal was necessary to prevent prolapse into the incision, which could alter outflow. The balanced salt solution (BSS) bottle was weighed and set at 65 cm. The scale was calibrated to zero with a digital force gauge (Imada Inc.). A 1.1 mm flared tip with Ultrasleeve on an

Accepted for publication October 31, 2006. From the University of Cincinnati College of Medicine (Osher) and a private practice (Osher), Cincinnati, Ohio, and Alcon Laboratories (Injev), Irvine, California, USA. Dr. Osher is a paid consultant to Alcon and Mr. Injev, an Alcon employee. Neither has a financial or proprietary interest in any material or method mentioned. Presented in part at the ASCRS Symposium on Cataract, IOL and Refractive Surgery, San Francisco, California, USA, March 2006. Corresponding author: Robert H. Osher, MD, 1945 CEI Drive, Cincinnati, Ohio 45343-5201, USA. E-mail: rhosher@cincinnatieye. com.

Figure 2. Postocclusion surge graded by collapse of the test chamber comparing the sleeveless bimanual and microcoaxial Ultrasleeve techniques.

MICROCOAXIAL PHACOEMULSIFICATION: LABORATORY STUDY

Infiniti handpiece was introduced, and irrigation was initiated as the handpiece was gently moved to simulate the typical maneuvering of the tip during cataract surgery. After 1 minute, the weight of the BSS bottle was remeasured, and the change represented incisional leakage. The same test was repeated in a fresh cadaver eye with 2, 1.2 mm incisions. After the bottle was recalibrated to zero and the iris was removed, a 20-gauge Fine-Nagahara irrigating chopper and a sleeveless 0.9 mm Sovereign ultrasound tip were introduced. Irrigation was activated, and similar handpiece movements were performed. After 1 minute, the leakage was determined by weighing the BSS bottle and recording the difference. The final test was performed in a third cadaver eye by removing the iris and making a 1.3 mm incision and a 1.2 mm incision. A 19-gauge Osher 1.0 mm  0.8 mm irrigating chopper (Duckworth & Kent) was introduced through the 1.3 mm incision, and a sleeveless 0.9 mm Sovereign ultrasound tip was introduced though the 1.2 mm incision. Incision leakage was then measured. The incision in each cadaver eye was sealed with Prism instant adhesive glue until watertight, and the test was repeated. The adhesive sealed the test incision, allowing the construction of a new incision in the same eye for a subsequent test. Incision sealing Two separate, beveled, single-plane incisions 2 to 3 clock hours apart were made in the peripheral cornea of the same cadaver eye. Through the 1.2 mm incision, a 0.9 mm bare tip connected to the Sovereign machine was inserted. Through the 2.2 mm incision, a 1.1 mm flared tip with Ultrasleeve connected to the Infiniti machine was introduced. A remote third incision was placed to allow insertion of an ACM (Figure 3). Each machine was set at 100% continuous power, 0 mm Hg vacuum, and 12 cc per minute aspiration rate. The Infiniti was set to a duty cycle of 20 ms on and 40 ms off. The Sovereign was set in the C/F mode. Simultaneous depression of both foot switches for 10 to 60 seconds was followed by inspection of each incision for leakage; the inspection was facilitated by fluorescein staining. The incisions were sealed with Prism instant adhesive, and the test was repeated 9 times using 4 cadaver eyes (at which point available virgin tissue was exhausted). Intraocular lens implantation Pig eyes were used to determine whether a full-sized single-piece SN60AT IOL (AcrySof) with a 6.0 mm optic could be inserted through a 2.2 mm incision. Multiple attempts to inject an IOL were made, loading the optic by folding only the leading haptic, only the trailing haptic, or folding both haptics and then

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Figure 3. Incision sealing test setup.

injecting through the cartridge bevel up or bevel down. The lens was folded as depicted in the diagram on the cartridge as well as opposite the depiction in the diagram. A Monarch C injector with bimanual screwing action was compared with an ASICO Royale injector requiring a single-handed plunger technique. Fixation of the globe near the incision was compared with countertraction exerted by an Osher nucleus manipulator (#6-402-1, Duckworth & Kent) through the side-port incision. Injection just outside the incision tunnel, within the incision tunnel, and just through the tunnel was evaluated. Speed of injection was varied. The incision was measured with calipers before and after the injections. RESULTS Infusion flow rate Figure 4 shows the infusion (irrigation) flow rates measured at a 100 cm bottle height. Compared with a standard 1.1 mm flared tip with a 1.1 mm sleeve, the Ultrasleeve reduced the flow rate from 115 cc per minute to about 80 cc per minute, representing a 30% reduction. However, the Ultrasleeve had 60% higher flow than 50 cc per minute through a 20-gauge irrigating chopper. Incision temperature Figure 5 shows the incision temperature measured over 1 minute with parameters conducive to tip heating. When the test was repeated with power modulation using a 33% duty cycle, both curves were reduced to a safe temperature range (Figure 6). Postocclusion surge Table 1 shows the occlusion break response. The microcoaxial setup produced a more stable response.

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Intraocular lens implantation

Figure 4. Irrigation flow rate at 100 cm bottle height.

The difference in surge became visually significant at 300 mm Hg and was more obvious at 400 mm Hg and 500 mm Hg. Incision leakage The difference in incision leakage was easy to observe because BSS was visibly refluxing from the 1.2 mm incision. In contrast, the Ultrasleeve seemed to seal the 2.2 mm incision. Table 2 shows the results at a bottle height of 65 cc and with the iris removed. Incision sealing

DISCUSSION Sleeveless bimanual microphacoemulsification has been heavily promoted for several years, yet most cataract surgeons have not embraced the technology because of significant drawbacks. The fluidics proved to be challenging because of limited infusion through an irrigating chopper, even when the bottle is raised. As a result of restricted infusion, the aspiration rate and vacuum levels must be lowered to avoid chamber instability and surge. Already compromised by a smaller phaco needle, the consequences of working

50

50

45

45

40 35

1.2mm

30

2.2mm

25 20 15

5

10 15 20 25 30 35 40 45 50 55

Time (sec.) Figure 5. Temperature rise using continuous ultrasound (50% continuous power; vacuum 0 mm Hg; aspiration 12 cc/min; bottle height 90 cm).

Temp. (deg. C)

Temp. (deg. C)

The results of incision integrity after up to 60 seconds of simultaneous ultrasound in the presence of an ACM were variable. When the handpiece was withdrawn, the 1.2 mm incision leaked (because the ACM was not turned off) in 5 of the 9 trials. The 2.2 mm incision leaked in 1 of the 9 trials. There was no leakage from either incision in 4 trials (Table 3).

Multiple failures were encountered before a reliable method of IOL insertion was found (Figure 7). The reliable method was as follows: The chamber and capsular bag were filled with a retentive ophthalmic viscosurgical device (OVD). The IOL was folded as depicted in the diagram on the cartridge. With an ASICO spring injector, the incision was entered with the bevel-down tip of the Monarch C cartridge. Counterpressure was applied using an Osher nucleus manipulator (#6-472-2, Duckworth & Kent) through a 1.0 mm side-port incision. The cartridge was advanced as far as possible into the incision without using excessive force. While countertraction was maintained, the plunger was depressed without hesitation and the leading edge of the IOL was delivered into the OVD-filled capsular bag. The nucleus manipulator was used to depress the trailing edge of the optic–haptic junction and was then withdrawn from the side-port incision. An Osher Y-hook (#MP205, Duckworth & Kent) was used to rotate the unfolding IOL into the capsular bag. Although differences in the pig and human eye may exist, the technique that was developed confirmed that a full-sized IOL could be implanted through an unenlarged incision compatible with microcoaxial phacoemulsification.

40 35

1.2mm

30

2.2mm

25 20 15

5

10 15 20 25 30 35 40 45 50 55 60

Time (sec.) Figure 6. Temperature rise using modulated ultrasound (1.2 mm incision set at 50% power in C/F mode and 2.2 mm incision set at 50% power with 20 ms on and 40 ms off; vacuum 0 mm Hg; aspiration 12 cc/min; bottle height 90 cm).

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Table 1. Occlusion break response. Surgical Outcome Occlusion Break from Specified Vacuum Level (mm Hg) & 78 cm Bottle Height 100 200 300 400 500

Microcoaxial (Infiniti with Ultrasleeve and 1.1 mm Flared ABS)

Bimanual with 21 G MST Open Front Irrigation Chopper Through 1.2 mm

Bimanual with 20 G Fine/Nagahara Irrigation Chopper Through 1.2 mm

Bimanual with 19 G D&K Osher 1.0 mm  0.8 mm Irrigation Chopper Through 1.3 mm

Trace Trace/mild Mild/moderate Moderate Significant

Trace Mild Significant Severe Severe

Mild Mild Moderate Severe Severe

Trace Trace Trace/mild Significant Severe

ABS Z Aspiration Bypass System; D&K Z Duckworth & Kent; G Z gauge; MST Z MicroSurgical Technologies

at lower levels of vacuum create a tradeoff in purchasing power and overall efficiency. Temperature is another factor that must be addressed. Studies have evaluated the thermal impact of a vibrating needle.1–5 Several assessed incision temperature using a bare ultrasound tip.6–7 Others show the benefits of reducing delivered thermal energy by using various surgical techniques.8–10 With bimanual sleeveless microphacoemulsification, the margin of safety against a thermal injury when a bare phaco needle is used within a tight corneal incision is narrow. WhiteStar technology (Advanced Medical Optics), which uses hyperpulse with duty cycle, has a thermo-protective effect. However, the primary source of cooling is aspiration through the needle, and a bare 0.9 mm needle without insulation that becomes plugged in an OVD can quickly result in thermal injury. In comparison, the coaxial setup has the additional insulation of the irrigating sleeve. Moreover,

the aspiration bypass port on the flared tip allows the bypass flow to cool the tip even when the tip is occluded. The use of a tip with bypass flow is only possible with a coaxial design. The integrity of the incision is another drawback of sleeveless bimanual microphacoemulsification. When a round metal tube is manipulated through a tight linear incision, a change in the wound architecture occurs that can cause damage (M.P. Weikert, MD, D.D. Koch, MD, ‘‘Phaco Wound Study: Alterations in Corneal Wound Architecture with Bimanual Microincisional Phacoemulsification,’’ Cataract & Refractive Surgery Today, June 2005 Supplement, pages 11–13; A.R. Vasavada, FRCS, ‘‘Phaco Tips and Corneal Tissue; Histomorphology and Immunohistochemistry Reveal the Effects of Sleeveless and Sleeved Tips,’’ Cataract & Refractive Surgery Today, June 2005 Supplement, pages 9–10). The resulting incision leakage further compromises chamber stability. Some advocates of sleeveless

Table 2. Coaxial setups and incision width and leakage results. Test 1 2 3 4 5 6 7 8

Setup

Incision Width (mm)

Microcoaxial with Ultrasleeve Bimanual with Fine/Nagahara irrigating chopper and 0.9 mm US tip Microcoaxial with Ultrasleeve Bimanual with Fine/Nagahara irrigating chopper and 0.9 mm US tip Bimanual with Fine/Nagahara irrigating chopper and 0.9 mm US tip Microcoaxial with Ultrasleeve Bimanual with 19 G D&K Osher irrigating chopper and 0.9 mm US tip Microcoaxial with Ultrasleeve

2.2 1.2 for both

0 1

2.2 1.2 for both

1 3

1.2 for both

3

2.2 1.3 for both

0 2

2.2

0.5

D&K Z Duckworth & Kent; G Z gauge; US Z ultrasound

Incision Leakage (cc/min)

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MICROCOAXIAL PHACOEMULSIFICATION: LABORATORY STUDY

Table 3. Sealing comparisons. Test 1

2 3 4 5 6 7 8 9

1.2 mm MICS Setup

2.2 mm Ultrasleeve Setup

Time of US Power (Sec)

Sovereign in C/F mode; 100% power; 0 mm Hg vac; 12 cc/min flow rate (0.9 mm bare tip; 1.2 mm incision) Same setup as test 1 Same setup as test 1 Same setup as test 1 Same setup as test 1 Same setup as test 1 Same setup as test 1 Same setup as test 1 Same setup as test 1

Infiniti in burst mode; 20 ms on and 40 ms off; 100% power; 0 mm Hg vac, 12 cc/min flow rate (1.1 mm flared tip; 2.2 mm incision) Same setup as test 1 Same setup as test 1 Same setup as test 1 Same setup as test 1 Same setup as test 1 Same setup as test 1 Same setup as test 1 Same setup as test 1

30

Outcome

1.2 mm incision leaked 2.2 mm incision did not leak

42 10 15 20 30 60 30 45

Same as test 1 No leak with either setup No leak with either setup No leak with either setup No leak with either setup Same as test 1 Same as test 1 Same as test 1

MICS Z microincision cataract surgery; US Z ultrasound; vac Z vacuum

bimanual microphacoemulsification recommend a third incision for the IOL because they cannot depend on the competency of the primary incision.11 Other surgeons suggest an additional incision for an ACM to improve chamber stability.12 However, when the cumulative lengths of the incisions are added together, the sum may exceed 5.0 mm, undermining the concept of microphacoemulsification. In the United States, the IOL option remains a problem for surgeons using the sleeveless bimanual technique because the Food and Drug Administration has not approved an IOL that can be inserted though a sub-2.0 mm incision. Therefore, it is necessary to enlarge the incision or create a separate incision. Outside the U.S., several small-incision IOLs are being used; however, concern has been raised that a sub2.0 mm IOL may not have the equivalent quality of a full-sized IOL. Thus, the potential benefit of a reduced incision diminishes.

Figure 7. Intraocular lens insertion test in a pig eye.

Another challenge of sleeveless bimanual microphacoemulsification is the learning curve necessary for the surgeon to become proficient and comfortable with the technique. In contrast, a clinical study has shown that the technique for performing microcoaxial phacoemulsification is very similar to the contemporary phaco technique (R.H. Osher, MD, ‘‘Coaxial Microphacoemulsification: Science and Clinical Results,’’ presented at the ASCRS Symposium on Cataract, IOL and Refractive Surgery, San Francisco, California, USA, March 2006).13 The Ultrasleeve is 1.8 mm in diameter and was developed for coaxial phacoemulsification using a 1.1 mm or 0.9 mm flared tip through a 2.2 mm incision. It is a translucent, thin-walled silicone sleeve with large irrigating ports. A similar sleeve for sub-2.0 mm phacoemulsification surgery has been reported (T. Akahoshi, MD, ‘‘Phaco Prechop and Sub 2.0 mm Coaxial Phacoemulsification,’’ presented at the ASCRS Symposium on Cataract, IOL and Refractive Surgery, San Francisco, California, USA, March 2006). Our laboratory investigation showed preliminary advantages of coaxial phacoemulsification with the Ultrasleeve over the use of a bimanual bare tip. The fluidics are more favorable, with flow rates approximately 60% higher than those measured with a broad range of 20-gauge irrigating choppers. The temperature profile also seems favorable. Power modulation in microcoaxial phacoemulsification provides an important thermo-protective effect, and incorporating duty cycle adds greater safety. It also appears that the microcoaxial 2.2 mm incisions may leak less than the sleeveless 1.2 mm incision and remain more competent at the end of a procedure. Although this behavior is difficult to assess with a high degree of confidence in

MICROCOAXIAL PHACOEMULSIFICATION: LABORATORY STUDY

a cadaver eye, our laboratory results suggest that the coaxial incision should have fluidic benefits and better sealability. In vivo chamber stability and incision integrity were evaluated in the clinical sequel to this study.13 Perhaps one of the most important advantages of the microcoaxial phacoemulsification technique is that a full-sized IOL with consistent centration, optical quality, and low posterior capsule opacification rates can be injected without enlarging the incision or making a separate incision. It appears as though the surgeon who wishes to perform microphacoemulsification may be able to choose other sophisticated options in acrylic IOL technology, including macular protection, aberration reduction, toric correction, and multifocality. Traditionally, new technology that permits cataract surgery through a smaller incision has been accompanied by advances in IOL design and insertion technique. Microcoaxial phacoemulsification will inevitably result in innovations in IOL insertion as contemporary cataract surgery continues to evolve toward a less invasive, safer operation. REFERENCES 1. Osher RH, Injev VP. Thermal study of bare tips with various system parameters and incision sizes. J Cataract Refract Surg 2006; 32:867–872 2. 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 3. Mackool RJ, Sirota MA. Thermal comparison of the AdvanTec Legacy, Sovereign WhiteStar, and Millennium phacoemulsification systems. J Cataract Refract Surg 2005; 31: 812–817

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4. 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 5. Majid MA, Sharma MK, Harding SP. Corneoscleral burn during phacoemulsification surgery. J Cataract Refract Surg 1998; 24:1413–1415 6. 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 7. Soscia W, Howard JG, Olson RJ. Bimanual phacoemulsification through 2 stab incisions; a wound temperature study. J Cataract Refract Surg 2002; 28:1039–1043 8. DeBry P, Olson RJ, Crandall AS. Comparison of energy required for phaco-chop and divide and conquer phacoemulsification. J Cataract Refract Surg 1998; 24:689–692 9. Wong T, Hingorani M, Lee V. Phacoemulsification time and power requirements in phaco chop and divide and conquer nucleofractis techniques. J Cataract Refract Surg 2000; 26: 1374–1378 10. 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 11. Fine IH, Hoffman RS, Packer M. Optimizing refractive lens exchange with bimanual microincision phacoemulsification. J Cataract Refract Surg 2004; 30:550–554 12. Lu DC, Davis EA, Hardten DR, Lindstrom RL. Bimanual sleeveless microphacoemulsification using the ‘‘tilt and tumble’’ technique. In: Boyd S, Dodick J, Freitas LL, eds, New Outcomes in Cataract Surgery. El Dorado, Panama, Highlights of Ophthalmology, 2005; 1–14 13. Osher RH. Microcoaxial phacoemulsification. Part 2: clinical study. J Cataract Refract Surg 2007; 33:408–412

First author: Robert H. Osher, MD