Impact of a handpiece with a built-in fluidics pressure sensor on phacoemulsification: a multicentre prospective comparative study

Introduction

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 ClinicalTrials.gov (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.

Results

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.

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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.

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).

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.

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.

Discussion

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