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Original research
Impact of a handpiece with a built-in fluidics pressure sensor on phacoemulsification: a multicentre prospective comparative study
  1. Antoine P Brézin1,
  2. Dominique Monnet1,
  3. François Lignereux2,
  4. Pascal Rozot3,
  5. Lea Jilet4,
  6. Hendy Abdoul4
  1. 1Université Paris Cité, Ophtalmologie, Hôpital Cochin, Paris, France
  2. 2Institut Ophtalmologique Sourdille Atlantique, Nantes, France
  3. 3Clinique Juge, Marseille, France
  4. 4Université Paris Cité, URC Paris Centre, Paris, France
  1. Correspondence to Dr Antoine P Brézin; antoine.brezin{at}


Objective We assessed whether the immediate pressure adjustments provided by a phacoemulsification handpiece with a built-in pressure sensor (Active Sentry, AS) could decrease the amount of energy delivered in the eye during cataract surgery.

Methods and analysis The Study of Active Sentry in Cataract Surgery was a multicentre prospective clinical trial. The Centurion system (Alcon Labs) was used and we compared phacoemulsifications performed with the AS handpiece with procedures using a sensor placed in the phacoemulsifier (non-AS). The primary outcome measure was the cumulative dissipated energy (CDE) used during the procedures. The secondary outcome measures were the total, longitudinal and torsional ultrasound (US) times, the duration of the surgery and the amount of fluid used during the surgeries.

Results The study analysed 1432 (800 AS and 632 non-AS) procedures. The mean patient age was 72.4±10.0 years. The median CDE was respectively 6.3 (IQR 3.5–9.9) and 6.7 (IQR 4.5–11.5) with and without AS (p=0.0001). The median US time was, respectively, 48.0 s (IQR 34.0–68.0) and 55.0 s (IQR 38.0–80.0) with and without AS (p<0.0001). Torsional and longitudinal US times were reduced with AS. The median duration of the procedure was, respectively, 9.0 min (IQR 7.0–12.0) and 10.0 min (IQR 7.0–13.0) (p=0.0002) with and without AS. The median balanced salt solution volume used was 52.0 cm3 (IQR 41.0–72.0) and 57.0 cm3 (IQR 42.0–81.0) with and without AS (p=0.0018).

Conclusion The phacoemulsifications performed with a pressure sensor built in the handpiece delivered less energy in the eye and were shorter.

Trial registration number NCT04732351.

  • Treatment Surgery
  • Clinical Trial
  • Cataract

Data availability statement

Data are available upon reasonable request.

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  • Modern phacoemulsification machines aim to prevent pressure surges.

  • When pressure surges are controlled, surgeons can privilege vacuum over ultrasound usage during phacoemulsification.

  • Reducing the energy used during cataract surgery prevents corneal endothelial cell damage.

  • Shorter surgeries improve the comfort of the patients during the procedures.


  • Placing a pressure sensor directly in the phacoemulsification handpiece allowed surgeons to decrease the amount of energy delivered in the eye during cataract surgery.

  • This technology contributed to decreasing the duration of ultrasound usage and the overall length of the procedures.


  • The quicker reaction time provided by a handpiece with a built-in pressure sensor had a favourable effect on all the parameters recorded during the procedures.

  • This technology could become the norm for all future phacoemulsification machines.


In the 60 years since the invention of phacoemulsification, tremendous progress has been made in the machines used for cataract surgery.1 The three main domains of the technological advances have been a reduction of the diameter of the tips of the handpieces and hence in the incision size, an improved delivery of the energy required for the emulsification of the lens and an optimised control of the fluids irrigating the anterior segment of the eye during the procedure. The reduction of the size of the handpieces has made suture-free incision the norm and decreased the astigmatism induced by the surgery.2 Decreasing the amount of energy required to emulsify the lens has limited the potential to damage corneal endothelial cells or the posterior capsule.3 In addition, optimising the circulation of fluids in the eye has resulted in a more stable anterior chamber and less posterior capsule movement during occlusion breaks.4 This prevention of pressure surges has been an important factor to limit the risk of posterior capsule rupture (PCR).

The progress has been made possible by various improvements aiming to shorten the response time to keep the intraocular pressure unchanged during the procedure. Until recently, the pressure sensor used in all phacoemulsifiers was in the generator itself. Recently, a handpiece with built-in sensor has been developed with the aim of further reducing the risk of pressure surges. We hypothesised that this development would allow surgeons to privilege vacuum over the delivery of energy during phacoemulsification. Hence, we compared procedures performed with a handpiece-based sensor (Active Sentry (AS); Alcon Labs, Fort Worth, USA) versus a traditional generator-based sensor. The study’s main outcome measure was the cumulative dissipated energy (CDE) used during phacoemulsification.

Materials and methods

The Study of Active Sentry in Cataract Surgery was registered at (registration number: NCT04732351). Informed consents were collected from the participating patients. Six surgeons from five centres (four public hospitals and two private centres) participated in the study. The study compared consecutive procedures performed with the Centurion (Alcon Labs) phacoemulsifier equipped with the AS system and those performed using the same phacoemulsifier without this system. Consecutive procedures in adult patients were included. Investigators operating in two rooms alternated during sessions between an AS and a non-AS phacoemulsifier. Patients were assigned to either room by the operating room staff without the surgeons being involved in the process. Patients with dilated pupils <5 mm and/or zonular defects and/or corneal opacities were excluded. The data recorded at the preoperative visit included the decimal best corrected visual acuity, the axial length and the anterior chamber depth measured with the IOLMaster biometer (Carl Zeiss Meditec, Jena, Germany). The nuclear grade of the cataract was graded by the surgeons at the preoperative visit from 0 to 3, according to the WHO nuclear grading recommendation.5 At the end of each surgery, the procedure log was recovered. The primary outcome measure was the CDE. The other outcome measures were the time of ultrasound (US) usage and the respective use of torsional and longitudinal energy. The total duration of the surgery was also recorded as well as the volume of balanced salt solution (BSS) used during the procedure. These outcome measures were used to compare the AS and non-AS groups. Additionally, we analysed how the cataract grade influenced each of these parameters.

Statistical analysis

Based on the data of a pilot study in Cochin Hospital, the mean CDE was estimated at 10.31 in AS group and 12.88 in non-AS group with an SD of 9.74. We anticipated that a total of 446 procedures (223 procedures per group) were needed to demonstrate a difference of three points between the two groups, with 90% statistical power and a two-sided alpha risk of 0.05. We first planned to include a total of 2500 procedures in order to explore CDE measures in different subgroups based on nuclear cataract grade.

An intention-to-treat analysis based on all the patients assigned to either group was performed. Missing data for CDE, which is the primary endpoint, were imputed with Markov chain Monte Carlo method using PROC MI ANALYZE procedure. Age, sex and group (AS vs non-AS) variables were used for multiple imputation models. Quantitative variables were compared between with the use of Student’s t-test. Multivariable linear regression models were used to analyse the primary endpoint taking in account patient’s group, age and nuclear cataract grade. The statistical analysis was carried out at the Cochin Hospital clinical research unit—Assistance Publique-Hôpitaux de Paris —France, according to the prespecified analysis plan. An interim analysis was planned at 1000 patients and adjusted for multiplicity test with p=0.54% (O’Brien-Fleming method). The final analysis was performed with unilateral test and p=4.92%. All analyses were performed using SAS V.9.4 (Copyright 2016 by SAS Institute).

Trial oversight and trial stopping

The primary analysis was realised in February 2022 on 1000 enrolled procedures. The sponsor and the scientific committee decided to stop the trial on March 2022 as the results demonstrated a significative diminution of CDE in AS group versus non-AS group (p<0.0001).


We analysed 1432 procedures of which 800 (55.9%) were performed with AS and 632 (44.1%) without (non-AS) (figure 1). The patient demographics are shown in table 1.

Table 1

Demographics and baseline characteristics

Figure 1

Study flow chart. CDE, cumulative dissipated energy; US, ultrasound.

The mean patient age was 72.4±10.0 years, the nuclear grades of the cataracts were 0–1 in 532 (37.2%), 2 in 693 (48.4%) and 3 in 185 (12.9%) cases. Of the 1432 procedures analysed in the study, 1425 (99.5%) were performed by four investigators (AB, DM, PR and FL) who alternated during their sessions between an AS and a non-AS phacoemulsifier. At baseline, there was no significant difference between the AS and non-AS groups. The differences between the parameters of the phacoemulsifications in both groups are shown in table 2.

Table 2

Cumulative dissipated energy (CDE) in the study population

The mean CDE was lower with AS (8.0±7.19) than without (9.3±8.47) (p=0.0001). This significant difference was evident when we examined all procedures, as well as when we compared the subgroups based on nuclear cataract grade. For grade 0–1 cataracts, the mean CDE was 5.3±3.85 (n=304) and 5.8±3.96 (n=228) in the AS and non-AS groups, respectively (p=0.0257) (table 3).

Table 3

Cumulative dissipated energy (CDE) according to the cataract nuclear grades

For grade 2 cataracts, the mean CDE was 7.7±4.91 (n=374) and 9.8±7.99 (n=319) in the AS and non-AS groups, respectively (p=0.0004). For grade 3 cataracts, which comprised only 185 (12.9%) of the procedures, the mean CDE was 16.6±12.77 (n=107) and 17.7±12.30 (n=78) in the AS and non-AS groups, respectively (p=0.1229).

The average and median parameters recorded in each group are summarised in table 4.

Table 4

Duration of the procedure, US time, longitudinal/torsional energy and BSS volume

Less US time was used in the AS group (55.7±38.66 s) than in the non-AS group (63.6±37.83 s) (p<0.0001). Overall, the duration of surgery was shorter with AS (9.8±4.47 min) than without (11.0±9.22) (p=0.0002). Less longitudinal US energy was used with AS (49.3±206.19) than without (74.4±239.25) (p<0.0001). The use of torsional US energy was also decreased with AS (661.4±647.77) compared with without AS (725.0±627.76) (p=0.0074). Moreover, the BSS volume used during the procedure in the AS group (58.6±25.38 cm3) was less than in the non-AS group (63.3±28.59 cm3) (p=0.0018). No PCR during the phacoemulsification was recorded in either group.


Our study results showed that phacoemulsification procedures performed using a handpiece with a built-in pressure sensor decreased the energy delivered in the eye and shortened US use. Both longitudinal and torsional energy were spared, but the reduction was even more marked for the latter. Sparing energy delivered in the anterior chamber is known to be beneficial to avoid endothelial cell loss. When comparing the two types of energy—longitudinal and torsional—it has also been proven that the longitudinal emulsification is more deleterious.3 6 7 Moreover, a recent prospective study analysed the impact of phacoemulsification parameters on central retinal thickness following cataract surgery. Reducing the CDE correlated with a significant lower retinal volume change between the preoperative measures and those 3 months after surgery.8

The Centurion phacoemulsifier applies pressure directly to the irrigation bag, while older systems use a gravity-based fluidic system that is more prone to fluctuations in intraocular pressure.9 Even before the AS handpieces became available, this allowed to increase the vacuum used during phacoemulsification. A randomised study of 158 cases showed that the CDE was significantly lower with a 600 mm Hg vacuum setting than with 350 mm Hg.10 Similarly, the quicker procedures with the AS handpiece can be explained by the fact that surgeons used less time to emulsify the lens while trusting the phacoemulsifier to prevent surges during occlusion break. This mechanism can also account for the reduced volume of BSS used with the AS handpiece. Shorter procedures have been shown to improve patients’ comfort during the surgery.11 Although this was not assessed during the study, a reduction in the duration of the procedure and the prevention of pressure variations may improve the patients’ perception of the phacoemulsification.

Our study excluded complex cases such as zonular deficiencies, small pupils or corneal opacities, which might have resulted in more favourable results than if we had included all cataract types.12 Moreover, although some cases were partially or completely performed by residents, the great majority of procedures were performed by trained surgeons performing a high volume of cataract surgery. These factors could explain the lack of any PCR in our study; as previous reports have shown, the rate of PCR decreases with the number of cases performed by surgeons.13 14 Although we believe that the AS handpiece is safer than traditional handpieces, the lack of PCR in either group did not allow us to validate this claim.

A limitation of our study was that it was comparative but not randomised. Yet, the surgeons were not involved in the process assigning patients to an AS or a non-AS phacoemulsifier during their sessions. The absence of a significant difference at baseline between the AS and non-AS groups confirmed the lack of a selection bias. The phacoemulsification settings (infusion pressure, aspiration rate, maximum vacuum) were not standardised. This aimed at reflecting real-life conditions where surgeons are free to use their settings according to their technique. Differences in the average amount of energy used by the investigators were observed (data not shown), which probably reflected heterogeneous phacoemulsification techniques. One of our study limitations was the lack of recording of the techniques used during the procedures. Previous reports have shown that surgeons predominantly using chop methods tend to use less energy than those using mostly a divide and conquer technique.15 16

The CDE, which was our study’s main outcome measure, is one of the most used parameters to assess the amount of energy recorded during phacoemulsification.17 18 It is displayed automatically by the Centurion phacoemulsifier and it quantifies the total energy dissipated at the wound site in foot pedal position 3, calculated as a US time with an average US power. Hence, it is expressed in seconds instead of the standard energy unit of joules. The CDE has been designed with the goal of normalising the energy delivered in the eye in different modes, including torsional and longitudinal phacoemulsifications. As in other studies, we used the CDE to assess the energy used in different subgroups, which guaranteed a valid comparison between the phacoemulsification systems. A previous study comparing 103 phacoemulsification procedures performed with the AS handpiece and 101 performed without found that the mean CDE for soft and hard cataracts was 5.6 and 4.8 vs 9.3 and 9.4 for the AS versus the non-AS groups, respectively.19 The relatively small number of procedures in that study probably explained why statistically significant differences were not observed, but trends similar to our observations were reported. Cataract grade and older patients’ age have already been shown to be important predictors of high CDE.20 In our study, grade 3 cataracts represented only 12.9% of the total number of cases and this did not allow to demonstrate with statistical significance that the CDE could be reduced in this group when using AS. Our study showed a reduction of the BSS volume used during the procedure with the AS handpiece, although it remains to be proven that this is a factor reducing endothelial cell damage.21

Altogether, our study demonstrated that an improvement in the monitoring of intraocular pressure during phacoemulsification is an added step in the progress of the technology used for cataract surgery. Whether this can be implemented in a large number of phacoemulsifiers and their handpieces remains to be seen. Cataract surgery is one of the most performed procedures worldwide and the technological advances in phacoemulsification are critical to make it one of the safest.22

Data availability statement

Data are available upon reasonable request.

Ethics statements

Patient consent for publication

Ethics approval

This study involves human participants and was approved by the Personal Protection Committee (Grenoble University IRB number: 2020-A03-232-37) on 27 April 2021 and followed the tenets of the Declaration of Helsinki. Participants gave informed consent to participate in the study before taking part.



  • Presented at Presented at the European Society of Cataract and Refractive Surgery (ESCRS) Meeting, Milan, Italy, 16–20 September 2022, and at the American Academy of Ophthalmology (AAO) Meeting, Chicago, USA, 1–4 October 2022.

  • Contributors AB was the study’s principal investigator and drafted the manuscript. DM, PR and FL were study investigators. LJ and HA participated in the study design and performed the statistical analyses. All coauthors reviewed the final manuscript. AB accepts full responsibility for the work, had access to the data, and controlled the decision to publish.

  • Funding Supported by an investigator-initiated trial grant funded by Alcon (IIT number: 57203277).

  • Competing interests AB, DM, FL and PR are consultants for Alcon.

  • Patient and public involvement Patients and/or the public were involved in the design, or conduct, or reporting, or dissemination plans of this research. Refer to the Methods section for further details.

  • Provenance and peer review Not commissioned; externally peer reviewed.