GUILLOTINE PERFORMANCE: DUTY CYCLE ANALYSIS OF VITRECTOMY SYSTEMS Octaviano Magalhaes Jr, MD, MBA,*† Lawrence Chong, MD,*‡ Charles DeBoer, BS,* Prashant Bhadri, PHD,* Ralph Kerns, MS,* Aaron Barnes, MS,* Sophia Fang, BS,* Paulo Schor, MD,† Mark Humayun, MD, PHD*‡
Purpose: To evaluate the duty cycle of different vitrectomy cutters and classify their blade movement. Methods: A precise weighing (0.01 g) high speed (2 samples/s) balance was used to study the 20-gauge and 25-gauge Bausch & Lomb Lightning-Millenium (St. Louis, MO), the 20-gauge (1500 cpm) and the 25-gauge Alcon Accurus (Fort Worth, TX), the 20-gauge Alcon Innovit, and the 23-gauge DORC (Netherlands) cutters. The weight of balanced saline solution (BSS) was recorded in real time using LabView software and then translated into a graph of volume removed versus time. Variable cut rates and vacuum pressures were analyzed in vitreous and BSS. A high-speed (400 frames/s) camera was used to record cutting for each condition. Results: Three types of duty cycle were investigated: parabolic incomplete (pneumatic), sinusoid (electric), and trapezoid (double pneumatic). The parabolic incomplete and trapezoid had a decreased duty cycle at 1500 cuts per minute when it was compared to 600 cuts per minute. The sinusoid had no statistical difference between cut rates. Conclusions: Systems showed different performances of duty cycle. This new classification will be useful for improved understanding of vitrectomy in these different systems. RETINAL CASES & BRIEF REPORTS 3:64 – 67, 2009
From *Eye Concepts, Doheny Retina Institute, Doheny Eye Institute, Los Angeles, California; †Paulista School of Medicine, Federal University of Sa˜o Paulo, Brazil; and ‡Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles.
and pneumatic) (Figures 1 and 2). The dual pneumatic cutter has a gear-driven inner tube that produces limited rotary motion (Figure 3).3 The duty cycle3 of the cutter is the percentage of time during its use that the port is open. The different drive mechanisms produce different duty cycle curves and cycle rates. The purpose of this article is to evaluate the duty cycles of different vitrectomy cutters and classify their blade movement.
T
he electric-powered nondisposable vitreous cutters initially described by Machemer et al1 used a continuous rotational motion. O’Malley and Heintz2 later introduced an axial cutter they called the Ocutome (Berkeley Bioengineering, Berkeley, CA). A significant number of systems currently combine this technology with different drive mechanisms (electric
Methods Using a precise (to 0.01 g) high-speed (2 samples/s) Ohaus balance (Pine Brook, NJ) we evaluated the performance of six cutters: the 20- and 25-gauge electric Bausch & Lomb Lightning-Millennium (St Louis, MO), the 20- and 25-gauge pneumatic Alcon Accurus (Fort Worth, TX), the 20-gauge dual pneumatic Alcon
Doheny Eye Institute receives royalties from Bausch & Lomb Inc. for devices developed by Eye Concepts. Reprint requests: Octaviano Magalha˜es Jr, MD, MBA, REVER Consultores em Retina e Vitreo, Rua Mato Grosso, 306 cj 509/510 Sa˜o Paulo–SP 01239-040, Brazil; e-mail: [email protected]
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Fig. 1. Pneumatic parabolic incomplete cutter. Graphs displacement (D) ⫻ time (t) (see text).
Fig. 2. Electric sinusoid cutter. Graphs displacement (D) ⫻ time (t) (see text).
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Fig. 3. Double pneumatic trapezoid cutter. Graphs displacement (D) ⫻ time (t). Air discharges move a piston laterally in the handpiece. The piston is coupled to a rotary drive mechanism. First, an air discharge increases the pressure (P1) under a silicone piston and moves it laterally. The piston has a common gear to a plastic device tied to the inner tube. This mechanism produces a partial reciprocating movement. A reverse movement is then produced by the opposite air discharge (P2).
Innovit, and the 23-gauge pneumatic Dutch Ophthalmic Research Center (DORC) (Zuidland, the Netherlands). The cutters were investigated in balanced saline solution. Weight was recorded in real time using LabView data acquisition software and converted into a graph of volume removed versus time. Different cut rates (600, 800, 1000, 1200, 1500, and maximum) at the same vacuum pressure (500 mmHg) were analyzed. A high-speed (400 frames/s) camera (Dalsa 1M75, Waterloo, Ontario, Canada) was used to record the blade movement and analyze the duty cycles. Results Three types of duty cycle were investigated: parabolic incomplete (pneumatic), sinusoid (electric), and trapezoid (double pneumatic).
The parabolic incomplete had a decreased duty cycle at 1500 cuts per minute (cpm) (0.31 mL/s 20 gauge Alcon and 0.04 mL/s 25 gauge Alcon) compared to 600 cpm (0.62 mL/s 20 gauge Alcon and 0.11 mL/s 25 gauge Alcon) (P ⫽ 2.89 ⫻ 10–17 [20 gauge], and 6.78 ⫻ 10–11 [25 gauge]). No statistical difference was found between the cut rates of the sinusoid (0.32 mL/s 20 gauge B&L at 1500 cpm, 0.13 mL/s 25 gauge B&L at 1500 cpm, 0.29 mL/s 20 gauge B&L at 600 cpm, 0.10 mL/s 25 gauge B&L at 600 cpm) (P ⫽ 0.12 [20 gauge] and 0.19 [25 gauge]). The trapezoid 20 gauge INNOVIT-Alcon showed difference between 600 cpm and the rest of the cut speeds (0.56 mL/s at 600 cpm, and 0.42 mL/s at 1500 cpm; P ⫽ 1.3 ⫻ 10– 8). The DORC 23-gauge system showed reduced duty cycle and incomplete aperture opening at 1500
Table 1. Balanced Saline Solution Velocity at Different Cut Rates (600 and 1500 cpm) Probe Alcon pneumatic 20-gauge Alcon pneumatic 25-gauge Alcon Innovit 20-gauge B&L electric 20-gauge B&L electric 25-gauge DORC pneumatic 23-gauge
Velocity at 600 cpm, mL/sec
Velocity at 1500 cpm, mL/sec
P Values
0.62 0.11 0.56 0.29 0.10 0.15
0.31 0.04 0.42 0.32 0.13 0.012
2.89 ⫻ 10–17 6.78 ⫻ 10–11 1.3 ⫻ 10–8 0.12 0.19 1.2 ⫻ 10–12
B&L ⫽ Bausch & Lomb; DORC ⫽ Dutch Ophthalmic Research Center.
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cpm, leading to significant reduction in the flow of BSS (0.012 mL/s) compared to 600 cpm (0.15 mL/s) (P ⫽ 1.2 ⫻ 10–12) (Table 1). Discussion A basic understanding of cutter engineering is needed to appreciate the significance of duty cycle in cutters. The pneumatic probe (Figure 1) operates on the concept of air discharge from the vitrectomy machine. The movement of the diaphragm under increased pressure moves the inner tube in the axial direction. A counterforce by the coil provides a complete parabolic (harmonic) movement without the top restriction. At reduced cut rates (600 cpm), a separated interval parabola’s movement is observed. With increased cut speeds (1500 cpm), a smooth parabolic motion is observed. These cutters demonstrate the same closed time profile independent of speed. However, as speed is increased, the open time profile is reduced. This corresponds to a reduced duty cycle at high speed. The electric probe (Figure 2) operates with a motor and cam mechanism that drives the inner tube. The
constant sinusoidal motion of the inner tube produces equal closed and open time, independent of cut rates (Figure 2). The dual pneumatic probe (Figure 3) cutter works under an intermittent air discharge produced by the pneumatic machine. The air pulses move a piston back and forth, which drives the tip in a reciprocating rotary motion. The duty cycle has an ascending close movement and a descending open movement with a trapezoidal characteristic. As the cut velocity increases, the top of the trapezoidal curve is reduced, becoming triangular. In conclusion, we present systems showing different duty cycle performances. This new classification will be useful for improved understanding of vitrectomy in these different systems. References 1.
2.
3.
Machemer R, Buettner H, Parel JM. Vitrectomy, a pars plana approach. Instrumentation. Mod Probl Ophthalmol 1972;10: 172–177. O’Malley C, Heintz RM. Vitrectomy via the pars plana: a new instrument system. Trans Pac Coast Oto-Ophthalmol Soc Annu Meet 1972;53:121–137. Charles S. An engineering approach to vitreoretinal surgery. Retina 2004;24:435–444.
Purpose: To evaluate the duty cycle of different vitrectomy cutters and classify their blade movement. Methods: A precise weighing (0.01 g) high speed (2 samples/s) balance was used to study the 20-gauge and 25-gauge Bausch & Lomb Lightning-Millenium (St. Louis, MO), the 20-gauge (1500 cpm) and the 25-gauge Alcon Accurus (Fort Worth, TX), the 20-gauge Alcon Innovit, and the 23-gauge DORC (Netherlands) cutters. The weight of balanced saline solution (BSS) was recorded in real time using LabView software and then translated into a graph of volume removed versus time. Variable cut rates and vacuum pressures were analyzed in vitreous and BSS. A high-speed (400 frames/s) camera was used to record cutting for each condition. Results: Three types of duty cycle were investigated: parabolic incomplete (pneumatic), sinusoid (electric), and trapezoid (double pneumatic). The parabolic incomplete and trapezoid had a decreased duty cycle at 1500 cuts per minute when it was compared to 600 cuts per minute. The sinusoid had no statistical difference between cut rates. Conclusions: Systems showed different performances of duty cycle. This new classification will be useful for improved understanding of vitrectomy in these different systems. RETINAL CASES & BRIEF REPORTS 3:64 – 67, 2009
From *Eye Concepts, Doheny Retina Institute, Doheny Eye Institute, Los Angeles, California; †Paulista School of Medicine, Federal University of Sa˜o Paulo, Brazil; and ‡Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles.
and pneumatic) (Figures 1 and 2). The dual pneumatic cutter has a gear-driven inner tube that produces limited rotary motion (Figure 3).3 The duty cycle3 of the cutter is the percentage of time during its use that the port is open. The different drive mechanisms produce different duty cycle curves and cycle rates. The purpose of this article is to evaluate the duty cycles of different vitrectomy cutters and classify their blade movement.
T
he electric-powered nondisposable vitreous cutters initially described by Machemer et al1 used a continuous rotational motion. O’Malley and Heintz2 later introduced an axial cutter they called the Ocutome (Berkeley Bioengineering, Berkeley, CA). A significant number of systems currently combine this technology with different drive mechanisms (electric
Methods Using a precise (to 0.01 g) high-speed (2 samples/s) Ohaus balance (Pine Brook, NJ) we evaluated the performance of six cutters: the 20- and 25-gauge electric Bausch & Lomb Lightning-Millennium (St Louis, MO), the 20- and 25-gauge pneumatic Alcon Accurus (Fort Worth, TX), the 20-gauge dual pneumatic Alcon
Doheny Eye Institute receives royalties from Bausch & Lomb Inc. for devices developed by Eye Concepts. Reprint requests: Octaviano Magalha˜es Jr, MD, MBA, REVER Consultores em Retina e Vitreo, Rua Mato Grosso, 306 cj 509/510 Sa˜o Paulo–SP 01239-040, Brazil; e-mail: [email protected]
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Fig. 1. Pneumatic parabolic incomplete cutter. Graphs displacement (D) ⫻ time (t) (see text).
Fig. 2. Electric sinusoid cutter. Graphs displacement (D) ⫻ time (t) (see text).
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Fig. 3. Double pneumatic trapezoid cutter. Graphs displacement (D) ⫻ time (t). Air discharges move a piston laterally in the handpiece. The piston is coupled to a rotary drive mechanism. First, an air discharge increases the pressure (P1) under a silicone piston and moves it laterally. The piston has a common gear to a plastic device tied to the inner tube. This mechanism produces a partial reciprocating movement. A reverse movement is then produced by the opposite air discharge (P2).
Innovit, and the 23-gauge pneumatic Dutch Ophthalmic Research Center (DORC) (Zuidland, the Netherlands). The cutters were investigated in balanced saline solution. Weight was recorded in real time using LabView data acquisition software and converted into a graph of volume removed versus time. Different cut rates (600, 800, 1000, 1200, 1500, and maximum) at the same vacuum pressure (500 mmHg) were analyzed. A high-speed (400 frames/s) camera (Dalsa 1M75, Waterloo, Ontario, Canada) was used to record the blade movement and analyze the duty cycles. Results Three types of duty cycle were investigated: parabolic incomplete (pneumatic), sinusoid (electric), and trapezoid (double pneumatic).
The parabolic incomplete had a decreased duty cycle at 1500 cuts per minute (cpm) (0.31 mL/s 20 gauge Alcon and 0.04 mL/s 25 gauge Alcon) compared to 600 cpm (0.62 mL/s 20 gauge Alcon and 0.11 mL/s 25 gauge Alcon) (P ⫽ 2.89 ⫻ 10–17 [20 gauge], and 6.78 ⫻ 10–11 [25 gauge]). No statistical difference was found between the cut rates of the sinusoid (0.32 mL/s 20 gauge B&L at 1500 cpm, 0.13 mL/s 25 gauge B&L at 1500 cpm, 0.29 mL/s 20 gauge B&L at 600 cpm, 0.10 mL/s 25 gauge B&L at 600 cpm) (P ⫽ 0.12 [20 gauge] and 0.19 [25 gauge]). The trapezoid 20 gauge INNOVIT-Alcon showed difference between 600 cpm and the rest of the cut speeds (0.56 mL/s at 600 cpm, and 0.42 mL/s at 1500 cpm; P ⫽ 1.3 ⫻ 10– 8). The DORC 23-gauge system showed reduced duty cycle and incomplete aperture opening at 1500
Table 1. Balanced Saline Solution Velocity at Different Cut Rates (600 and 1500 cpm) Probe Alcon pneumatic 20-gauge Alcon pneumatic 25-gauge Alcon Innovit 20-gauge B&L electric 20-gauge B&L electric 25-gauge DORC pneumatic 23-gauge
Velocity at 600 cpm, mL/sec
Velocity at 1500 cpm, mL/sec
P Values
0.62 0.11 0.56 0.29 0.10 0.15
0.31 0.04 0.42 0.32 0.13 0.012
2.89 ⫻ 10–17 6.78 ⫻ 10–11 1.3 ⫻ 10–8 0.12 0.19 1.2 ⫻ 10–12
B&L ⫽ Bausch & Lomb; DORC ⫽ Dutch Ophthalmic Research Center.
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cpm, leading to significant reduction in the flow of BSS (0.012 mL/s) compared to 600 cpm (0.15 mL/s) (P ⫽ 1.2 ⫻ 10–12) (Table 1). Discussion A basic understanding of cutter engineering is needed to appreciate the significance of duty cycle in cutters. The pneumatic probe (Figure 1) operates on the concept of air discharge from the vitrectomy machine. The movement of the diaphragm under increased pressure moves the inner tube in the axial direction. A counterforce by the coil provides a complete parabolic (harmonic) movement without the top restriction. At reduced cut rates (600 cpm), a separated interval parabola’s movement is observed. With increased cut speeds (1500 cpm), a smooth parabolic motion is observed. These cutters demonstrate the same closed time profile independent of speed. However, as speed is increased, the open time profile is reduced. This corresponds to a reduced duty cycle at high speed. The electric probe (Figure 2) operates with a motor and cam mechanism that drives the inner tube. The
constant sinusoidal motion of the inner tube produces equal closed and open time, independent of cut rates (Figure 2). The dual pneumatic probe (Figure 3) cutter works under an intermittent air discharge produced by the pneumatic machine. The air pulses move a piston back and forth, which drives the tip in a reciprocating rotary motion. The duty cycle has an ascending close movement and a descending open movement with a trapezoidal characteristic. As the cut velocity increases, the top of the trapezoidal curve is reduced, becoming triangular. In conclusion, we present systems showing different duty cycle performances. This new classification will be useful for improved understanding of vitrectomy in these different systems. References 1.
2.
3.
Machemer R, Buettner H, Parel JM. Vitrectomy, a pars plana approach. Instrumentation. Mod Probl Ophthalmol 1972;10: 172–177. O’Malley C, Heintz RM. Vitrectomy via the pars plana: a new instrument system. Trans Pac Coast Oto-Ophthalmol Soc Annu Meet 1972;53:121–137. Charles S. An engineering approach to vitreoretinal surgery. Retina 2004;24:435–444.
