Comparison of occlusion break responses and vacuum rise times of phacoemulsification systems

Standard equipment, including a Foxboro pressure/vacuum transducer box (Invensys Systems, Inc., Plano, TX) and a digital storage oscilloscope (Classic 6000; Gould Instrument Systems, Cleveland, OH), was used for assessments of occlusion break surge and vacuum rise time. The infusion bottle height was set at the same actual elevation (90 cm) above the transducer for all systems tested to avoid potential differences in display height of the different systems. To eliminate variability due to differences in selected aspiration orifice cross-section areas, the same phacoemulsification handpiece (OZil®; Alcon Laboratories), phacoemulsification tip type (30^oR, 0.9 mm, nonaspiration bypass system; Alcon Laboratories), and matching infusion sleeve type were used for all testing [13]. The fittings for irrigation and aspiration tubing on each PEA system used a standard Luer interface that enabled attachment of a single tip/handpiece configuration to all systems. This setup ensured that resistance, which is influenced by the area of the aspiration orifice, was identical among PEA systems. After each system was tuned and primed, the infusion fitting was tied to the infusion Luer connector on the OZil ultrasound handpiece. The aspiration fitting of the system was connected to the corresponding fitting located at the back of the handpiece.

Phacoemulsification systems and their respective fluidics and consumables are summarized in Table 1. Occlusion break surge was assessed using Centurion, Infiniti® (Alcon Laboratories), and WhiteStar® Signature (Abbott Medical Optics [AMO], Santa Ana, CA) phacoemulsification systems. Because flow rate cannot be directly controlled in a venturi pump system, occlusion break surge testing was performed using only peristaltic pump systems. Vacuum rise times were evaluated for Centurion, Infiniti, WhiteStar Signature, and Stellaris® Vision Enhancement System (Bausch & Lomb, Rochester, NY).

The magnitude of the occlusion break surge was assessed using a published test protocol [13]. To ensure reproducibility of results, 6 fluidic packs (ie, cassettes and tubing) were tested per system, with each pack tested 3 times. Cassettes were primed to remove entrapped air, and the ultrasound tip and infusion sleeve were installed on the handpiece with the aspiration line attached. The oscilloscope was calibrated to the transducer; the vertical amplitude scale was set to 100 mV per division, and the horizontal time scale was set to 200 milliseconds per division. For testing systems with gravity fluidics, the irrigation bottle was placed at a height of 90 cm above the transducer midpoint. The Centurion system was also tested with Active Fluidics across target IOP settings ranging from 40 to 65 mmHg (equivalent to a bottle height of approximately 54–88 cm H₂O; Table 1). Centurion system default parameters (vacuum rise = 0; IOP ramp = 1.0; irrigation factor = 1.0) were used for testing; modifications to these settings can be made directly from the front panel of the PEA system.All systems were tested at preset aspiration vacuum limits of 200, 300, 400, 500, and 600 mmHg, with an aspiration flow rate of 30 cc/minute for the peristaltic systems. The handpiece, transducer, and tubing were positioned at the system target patient eye level, and the test setup (Figure 2A), including tubing, test adapter, handpiece, test chamber assembly, and transducer box, was primed by activating the system’s foot pedal before each experiment. Aspiration flow was started by activating the foot pedal, and the tubing portion between the aspiration tubing test adapter and the handpiece was occluded using needle-nose pliers. Occlusion was released when the preset vacuum limit was reached. The simulated occlusion break surge event was captured with the oscilloscope; surge area, which accounts for both amplitude and duration of the surge, was determined from the area under the surge curve and above the datum line corresponding to positive chamber pressure of 20 mmHg.

Vacuum rise times were evaluated using a minimum of 3 packs per system, with packs primed on the respective phacoemulsification systems. The oscilloscope vertical amplitude scale was set to 500 mV per division, and the horizontal time scale was set to 1 second per division. The equipment setup for vacuum rise testing is depicted in Figure 2B. As described elsewhere [13], testing of phacoemulsification systems was performed at a bottle height of 90 cm for gravity-fed fluidics and target IOP of 65 mmHg for Active Fluidics (Centurion only; Table 1).

Vacuum rise times were evaluated at preset vacuum pressure limits of 400 and 600 mmHg for all systems. With the exception of Stellaris, which does not allow control of aspiration flow rate, all systems were tested at aspiration flow rates of 30 and 60 cc/minute. Occlusion was formed by clamping the irrigation line within 1 inch of the Luer connector, and aspiration flow was started with the foot pedal. Vacuum was allowed to build for approximately 8 seconds before the system was vented by releasing the foot pedal; vacuum pressure level was recorded at 0.5, 1, 1.5, 2, 3, 4, 5, and 6 seconds.

Occlusion break surge increased with increasing aspiration vacuum for all phacoemulsification systems, with the smallest surge areas observed at 200 mmHg and largest surge areas observed at 600 mmHg. Across the aspiration vacuum pressure range tested, there was a significant difference in surge area between systems (2-way ANOVA, P < 0.05). Centurion produced substantially less occlusion break surge with gravity and Active Fluidics settings than the Infiniti and WhiteStar Signature; surge was highest with the WhiteStar Signature (Figure 3). At 400 mmHg, mean ± SD occlusion break surge areas were: WhiteStar Signature, 2.0 ± 0.28 mmHg∙second; Infiniti, 1.1 ± 0.12 mmHg∙second; Centurion (Active Fluidics, IOP target 65 mmHg), 0.2 ± 0.06 mmHg∙second; and Centurion (gravity fluidic), 0.1 ± 0.07 mmHg∙second. The difference in surge area produced by the 3 systems tested was largest at 600 mmHg. Surge areas were: WhiteStar Signature, 4.8 ± 0.45 mmHg∙second; Infiniti, 4.1 ± 0.37 mmHg∙second; Centurion Active Fluidics, 1.3 ± 0.15 mmHg∙second; and Centurion gravity fluidics, 1.4 ± 0.12 mmHg∙second. Centurion active (IOP target 65 mmHg) and gravity (90 cm H₂O) fluidics performed similarly across the range of aspiration vacuum pressures tested.

At each preset aspiration vacuum pressure tested, occlusion break surge area predictably increased with decreasing Centurion Active Fluidics IOP target settings (Figure 4). This was most evident at higher aspiration vacuum pressures (ie, 400, 500, and 600 mmHg). Surge areas were similar with Active Fluidics target IOP settings of 50, 55, and 65 mmHg and gravity fluidics (90 cm H₂O) at 200 and 300 mmHg (ranges, 0.04–0.06 and 0.05–0.13 mmHg, respectively). At 600 mmHg, all Centurion Active Fluidics target IOP settings achieved smaller occlusion break surge areas (Figure 4) than the gravity fluidics of Infiniti or WhiteStar Signature (Figure 3). With Active Fluidics, surge areas were 3.6 ± 0.37 mmHg with target IOP 40 mmHg; 2.7 ± 0.21 mmHg with target IOP 50 mmHg; 2.1 ± 0.37 mmHg with target IOP 55 mmHg; and 1.3 ± 0.15 mmHg with target IOP 65 mmHg.

With the vacuum limit preset to 400 mmHg, Infiniti had the fastest vacuum rise of the 4 systems tested during occlusion at flow rates of 30 and 60 cc/minute; the Stellaris, which does not enable flow rate control, had the slowest (Figure 5). Infiniti exceeded the preset vacuum limit at both tested flow rates (30 cc/minute, –410 mmHg; 60 cc/minute, –404 mmHg; both at 0.5 second). With gravity fluidics, Centurion demonstrated a rate of vacuum rise similar to that of Infiniti and did not exceed the preset vacuum limit (30 cc/minute, –399 mmHg; 60 cc/minute, –400 mmHg; 0.5 second each). At a flow rate of 60 cc/minute, vacuum rise times to 400 mmHg were similar between phacoemulsification systems with controllable flow rates.With the vacuum limit preset to 600 mmHg, Infiniti and WhiteStar Signature demonstrated the fastest initial vacuum rise during occlusion (Figure 6). No system reached the vacuum limit of 600 mmHg at 30 or 60 cc/minute. The maximum vacuum reached at a flow rate of 30 cc/minute was greatest with Infiniti (–595 mmHg, 1.5 seconds), followed by WhiteStar Signature (–593 mmHg, 5.0 seconds), Centurion with gravity fluidics (–587 mmHg, 2.0 seconds), and Centurion with Active Fluidics (–582 mmHg, 2 seconds). At 60 cc/minute, maximum vacuums achieved were –598 mmHg (Infiniti, 0.5 second), –595 mmHg (WhiteStar Signature, 1.5 seconds), –588 mmHg (Centurion with gravity fluidics, 1 second), and –583 mmHg (Centurion with Active Fluidics, 1.5 seconds). Stellaris reached –591 mmHg at 2 seconds.