INTRODUCTION
Cathleen M. McCabe, MD: Phacoemulsification, introduced in the late 1960s, is still the gold standard for cataract surgery.1 Thanks to innovations in technology and techniques, phacoemulsification continues to evolve. Yet, one of the issues we surgeons have historically encountered in the OR is that limitations in the operating systems we use compel us to operate at a high IOP to ensure efficient aspiration flow and vacuum in order to maintain a stable anterior chamber. Meanwhile, recent studies have suggested benefits associated with operating at a more physiologic IOP, including the ability to avoid unduly impacting the ocular structures. Dr. Rauen, what are the goals of operating at more physiological IOP?
Matthew P. Rauen, MD: There are two main objectives when performing phacoemulsification with physiologic IOP: we want to maintain normal pressure within the eye. We want to do so while also maintaining the anatomic relationships within the eye.
Dr. McCabe: Are there perhaps misconceptions about maintaining physiologic IOP that may be barriers to making it the standard for performing cataract surgery?
Zaina Al-Mohtaseb, MD: Any new technique or thought process around cataract surgery takes time to become the new standard. And I think the primary reason new ideas—like the concept of operating at more physiological IOP—take time to become the new standard is that surgeons are hesitant to change their routine unless they are assured that the new way of doing things is safe. For instance, one of the concerns with physiologic IOP is that anterior chamber stability may be compromised. But in my experience, I have not found that to be the case: cataract surgery at a more physiological IOP is just as safe as before, with a few additional benefits.
John A. Hovanesian, MD: Safety is a prime concern, and I would add that cataract surgeons are also concerned about their efficiency in the OR and the accuracy of the procedures. Surgeons may be concerned that operating at a more physiological IOP may negatively impact these variables, when in fact, it may actually improve efficiency and accuracy because we end up with a more quiet eye at the end of the case.2,4,7
WHAT IS PHYSIOLOGIC IOP?
Dr. McCabe: For many years, limitations in phacoemulsification systems required us to operate at a high IOP, but we now have the technology to operate at more physiological IOP when using Centurion with Active Sentry (Alcon). How does this system work?
Dr. Al-Mohtaseb: The key to our discussion today is that technology has evolved to allow us to consider the benefits of lowering IOP, which, frankly, isn’t possible with traditional irrigation systems that use gravity to regulate fluidics pressure. What makes Active Sentry unique is that it uses compression plates to adjust pressure on the balanced salt solution (BSS) irrigating bag (Figure 1). Functionally, the system detects changes in the eye in real time and rapidly compensates for any post-occlusion surge by adjusting the supply of BSS to the aspiration line. These capabilities allow us to lower the IOP while keeping the chamber stable,2 maintaining efficiency,3,4 and completing the procedure with a good safety profile.
Figure 1. Centurion with Active Sentry Technology.
Dr. Hovanesian: Having a sense for when pressure drops, as well as when subsequent post-occlusion surge and a leaking wound occurs is crucial. Older-generation machines weren’t as precise, and there wasn’t a good way to measure IOP. With those systems, we would increase the pressure inside the eye by raising the bottle to the height of the room—and I’ve heard stories from colleagues who cut a hole in the ceiling of their OR so they could achieve higher bottle height. What we are discussing now with Active Sentry is a more ideal fluidics system that allows us to put into the eye only the amount of fluid we need without increasing pressure any higher than needed, which in turn increases the safety of the procedure.5
Dr. McCabe: For the sake of a definition, what numbers should we associate with physiologic IOP?
Dr. Rauen: The short answer is that it is a lot lower than where most surgeons currently operate. Prior to introducing Centurion and Active Fluidics in my surgeries, I was operating at upwards of 60 mm Hg. With those systems in place, however, we realized we could start to increase the vacuum and decrease the IOP, while still maintaining chamber stability and the safe and effective surgical experience we’ve come to know.2 From 60 mm Hg, first we went to 55 mm Hg and detected no differences, and almost immediately, we decreased to 50 mm Hg. We kept making stepwise changes in the pressure, and currently I operate at an infusion pressure of around 28 mm Hg. In my experience, it’s hard to detect any difference in the chamber stability at 28 mm Hg versus 38 mm Hg.
Dr. McCabe: When I started adjusting my IOP I was concerned I might have to significantly adjust my technique. However, I quickly found that not to be the case, and in fact, I didn’t have to do anything different.
Dr. Al-Mohtaseb: I took my time dialing in to a new IOP setting because I perform most of my complex cases on the Centurion with Active Sentry. My original setting was 65 mm Hg, and initially, I decreased the pressure by 5 mm Hg and performed a few cases at the new IOP to optimize my technique. For instance, I would perform half of my phaco chop at a lower pressure and then switch to a higher pressure for the last pieces of the nucleus. I truly didn’t notice much of a difference, which gave me confidence in experimenting with lower IOP settings. Eventually, over the course of a few weeks time, I got to where I am currently with IOP in the low 30s mm Hg.
Dr. Hovanesian: My experience with adopting Active Sentry was similar, in that as I became accustomed to operating at more physiological IOP, I realized I was not changing my technique and it wasn’t impacting my efficiency. I started at around 65 mm Hg with a previous machine, but over time, I’ve become comfortable operating with a pressure around 28 mm Hg (Tables 1 and 2). The only notable difference is that the eye is a little softer. When you’re manipulating with multiple instruments, you may sense the eyeball gives a bit more gently than it does at a high IOP, but it’s a good thing. It indicates that we’re doing something to the eye at a pressure to which it is accustomed.
Dr. McCabe: Every surgeon’s technique is going to be a little different. Some of us are heavier on the footpedal than others, which is not a bad thing, but I might advise surgeons newer to using Active Sentry to go a bit slower. I tend to be light on the footpedal, which gave me more confidence to keep decreasing IOP. I ended up at 28 mm Hg, too, interestingly enough.
SURGICAL EFFICIENCY
Dr. McCabe: One thing surgeons may have concerns about is whether operating at more physiological IOP has any effect on efficiency. Dr. Hovanesian, what has been your experience?
Dr. Hovanesian: The truth is, I wouldn’t consider operating at more physiological IOP if it added surgical time or impacted the efficiency of removing the lens. In my hands, using an infusion pressure close to 28 mm Hg has had no impact on either. Importantly, there is data to back that up, as studies have demonstrated that case, aspiration, and ultrasound times at a more physiological IOP of 28 mm Hg were like those at an IOP around 60 mm Hg.3,7
Dr. McCabe: My experience has been similar, in that there has been no change in efficiency as I have lowered the IOP.
Dr. Al-Mohtaseb: Any time we make changes to our surgical protocols, we want to be driven by the data, and there is certainly growing evidence pointing to the benefits of operating at more physiological IOP. For instance, studies have shown decreased fluid usage at more physiological IOP,4,5 which can help to reduce postoperative corneal swelling3,4 and increase patient comfort.7
Dr. Rauen: In our center, we have documented that we have fewer fluid leaks at a lower IOP.4 Ideally, we are going to achieve sealed incisions every time we operate, but in reality, fluid leakage is something we all experience. When we’re operating at a more physiologic IOP, the fluid leakage goes down. Less fluid leakage reduces fluid utilization.
Dr. McCabe: Another variable that operating at more physiological IOP would seem to impact is the amount of turbulence in the eye during a case. Many surgeons orient the sleeve to avoid irrigating onto the endothelium because it can have deleterious effects, including inducing swelling of the cornea.8,9 It makes intuitive sense that reducing turbulence would be beneficial for the physiology of the eye.
ANTERIOR CHAMBER STABILITY
Dr. McCabe: How stable is the anterior chamber at a more physiological IOP?
Dr. Al-Mohtaseb: This is something I was concerned about when I started thinking about lowering my IOP. My initial thought was that a high pressure was necessary to maintain a stable and large chamber that’s easier to operate in. But after doing some research, that’s not necessarily the case. Suzuki and colleagues looked at the responsiveness of Centurion with Active Sentry, Centurion with Ozil, Infiniti, and Constellation (all from Alcon)—which represent both gravity and active fluidics systems—to occlusion breaks that were generated by pinching the aspiration tube.2 They found that the anterior chamber was most stable with the Centurion with Active Sentry, exhibiting only a 7% change ratio in anterior chamber depth, compared to 74% with Constellation (Figure 2).2
Figure 2. Anterior chamber stability with lower IOP settings.
Dr. McCabe: To me, those data really emphasize the safety of operating at low IOP settings. There is a common perception that we want the anterior chamber to be rock solid and steady, when in truth, we just need it to be steady and stable.
PATIENT COMFORT
Dr. McCabe: Does operating at more physiological IOP have any implications for patients’ comfort?
Dr. Rauen: Our experience is that operating at more physiological IOP can have an impact on patients’ comfort, and there is already data to back that assertion. In one study, patients (n = 40) were randomized to undergo surgery with either a high (80 mm Hg) or more physiological (30 mm Hg) IOP using the Centurion Active Sentry system.7 The results were quite interesting: patients that had surgery at an IOP of 30 mm Hg reported no pain, but about 80% of patients in the 80 mm Hg group reported some level of pain (Figure 3). There is additional evidence from a study by Liu et al, in which patients had less pain perception at more physiological IOP (30 mm Hg) when compared to higher IOPs (59 mm Hg) (Figure 4).10
Figure 3. Patients experienced less pain perception during cataract surgery with more physiological IOP. The rate of aspiration and vacuum, 45 cc/min and 450 mm Hg, respectively was identical between groups.
Figure 4. Patient pain level in eyes with lower corneal endothelial cell density.
My question is: If we can perform cataract surgery at a more physiological IOP safely and efficiently, why wouldn’t we embrace it? Surgery at physiologic IOP reduces pain perception and increases comfort.
Dr. McCabe: Cataract surgery has become so routine for us that we tend to think of it being straightforward and comfortable for patients, but there are instances where patients express discomfort. For example, I’m thinking about the high myope, where posterior displacement of the iris-lens diaphragm is common.
Dr. Rauen: In my experience, patients today are demanding more from their outcome and putting greater emphasis on their experience during surgery. And to me, that means we should take advantage of everything we can to make patients more comfortable and satisfied with their experience, and that includes their perception of pain. We are currently doing a study to determine patient discomfort with infusion pressures of around 65 mm Hg compared to 24 mm Hg. The study is ongoing, but so far, as we have interacted with patients during surgery, we are getting fewer reports of patients with the lower IOP, and we have also noticed that we have been able to reduce supplemental pain medicine or anxiolytic during the case. Another thing I have noticed is that the interaction with the patient after surgery is much more energetic if they have less medication—and some of the “wow” factor is muted with high amounts of medication.
CORNEAL HEALTH
Dr. McCabe: What does the data tell us about more physiological IOP and the health of the cornea?
Dr. Al-Mohtaseb: As a cornea specialist, this is dear to my heart. Studies show that operating at more physiological IOP levels results in a lower rate of corneal swelling at day 1 and week 1 in patients with normal corneas (Figure 5).3,4,11 Now, put that in the context of real-world practice, where a lot of surgeons are performing premium cataract surgery on the second eye about 1 week after the first. If we can get the patient happy on the first postoperative day, that is a huge boost going into the second eye surgery, especially with a premium IOL.
Figure 5. Less corneal swelling was seen at a more physiological IOP.
There is additional evidence to consider. For instance, Kokubun and Rauen showed that a more physiological IOP provided better endothelial cell protection.3,4 Compared to operating at a higher IOP, lower IOP surgeries resulted in significantly higher endothelial cell density at day 1 and day 4 (Figure 6),3 as well as month 14 and month 3.4 Rauen also found a significantly smaller drop in endothelial cell density at 1 month (-1.7% with more physiological IOP vs -12.3% with high IOP).4 Again considering this data in the context of real-world practice, the ability to protect the endothelium is important for all patients, but especially so for patients with glaucoma or Fuchs dystrophy who may already have a compromised endothelium.10
Figure 6. Endothelial cell protection was better with a more physiological IOP.
ANTERIOR SEGMENT INFLAMMATION
Dr. McCabe: Dr. Rauen, you did a study looking specifically at markers of inflammation in relation to operating IOP. What did you find?
Dr. Rauen: In short, we found evidence that optimizing the fluidics may blunt the inflammatory response. Specifically, we found more cell and flare with the high IOP settings compared to operating at more physiological IOP.4 In real-world practice, steroids may be prescribed to address inflammation, but inflammation is associated with discomfort and compromised vision. Why wouldn’t we want to embrace a technique that can possibly blunt the inflammatory response?
Dr. McCabe: It makes intuitive sense that less inflammation after surgery means the eye was quieter during surgery.
Dr. Rauen: I completely agree. Having technology that allows the ability to operate at more physiological IOP lets us control one more variable that might generate inflammation and impact corneal health.
ANTERIOR VITREOUS FACE AND RETINA
Dr. McCabe: Dr. Hovanesian, what are the differences in anterior hyaloid membrane (AHM) integrity with high and lower IOP levels?
Dr. Hovanesian: Phacoemulsification has the potential to increase the presence of Berger’s space, or the space located between the posterior capsule of the lens and the anterior hyaloid of the vitreous. The presence of Berger’s space has a couple of implications. For instance, lens fragments can migrate into the space, potentially increasing the risk of intraocular inflammation.12,13 As well, Berger’s space may allow for greater motility of the AHM, which in turn, may increase traction at the vitreous base, potentially leading to retinal detachment.12 In short, in an ideal world, we wouldn’t be blowing open Berger’s space, and there is evidence that there is a dramatic difference in the creation of Berger’s space at a low versus high IOP. Scarfone and colleagues showed that 42% of eyes operated on at an IOP of 80 mm Hg had a measurable Berger’s space using anterior segment OCT, compared to 7.5% of eyes operated on at an IOP of 30 mm Hg.7
Dr. McCabe: Does IOP have any impact on retinal structures?
Dr. Hovanesian: We know from studies that a high IOP can reduce retinal blood flow,14 potentially impact recovery of visual acuity,15 increase macular thickness,16 and reduce macular density.17 Additionally, Dr. Rauen studied how the size of the foveal avascular zone, as visualized on OCT angiography, was impacted by an infusion pressure of 60 and 28 mm Hg.4 The study found a significantly smaller foveal avascular zone in eyes operated under higher IOP conditions at 1 week postoperative (Figure 7). This is one more item to include in the column of safer surgery when we operate at a more physiological IOP.
Figure 7. The changes in retinal blood flow and the macula at higher and lower IOP settings.
CONCLUSION
Dr. McCabe: In my thinking, operating at a more physiological IOP means we are trying to keep the eye in homeostasis, which is something we were ignoring for a long time. As we have discussed today, there is a lot of evidence to support a shift in mindset, and to lower IOP while performing phacoemulsification. With the Centurion with Active Sentry, we have the technology that makes it feasible to lower IOP while maintaining a stable anterior chamber, and while maintaining the conditions that contribute to the safety we have become accustomed to in performing cataract surgery.
Dr. Rauen: I appreciate that you are framing this as a change in mindset. Lowering operating IOP actually does not require any change in technique, as infusion pressure does not impact anterior chamber stability. And so, if all the evidence is pointing us to the notion that operating at more physiological IOP has a variety of benefits for safety and efficiency, then why wouldn’t we want to adopt this new operating environment?
Dr. Al-Mohtaseb: Of all the benefits associated with operating at a more physiological IOP, the most exciting aspect to me is that it potentially increases patient comfort and reduces perception of pain during the procedure. Furthermore, we have seen evidence that the day 1 outcome is better when operating at a more physiological IOP, and that is a huge win for our patients.
Caution: Federal (USA) law restricts this device to sale by, or on the order of, a physician.
As part of a properly maintained surgical environment, it is recommended that a backup IOL injector be made available in the event the AutoSert® IOL Injector Handpiece does not perform as expected.
Indication: The CENTURION® Vision system is indicated for emulsification, separation, irrigation, and aspiration of cataracts, residual cortical material and lens epithelial cells, vitreous aspiration and cutting associated with anterior vitrectomy, bipolar coagulation, and intraocular lens injection. The AutoSert® IOL Injector Handpiece is intended to deliver qualified AcrySof® intraocular lenses into the eye following cataract removal.
The AutoSert® IOL Injector Handpiece achieves the functionality of injection of intraocular lenses. The AutoSert® IOL Injector Handpiece is indicated for use with the AcrySof® lenses SN6OWF, SN6AD1, SN6AT3 through SN6AT9, as well as approved AcrySof® lenses that are specifically indicated for use with this inserter, as indicated in the approved labeling of those lenses.
Warnings: Appropriate use of CENTURION® Vision System parameters and accessories is important for successful procedures. Use of low vacuum limits, low flow rates, low bottle heights, high power settings, extended power usage, power usage during occlusion conditions (beeping tones), failure to sufficiently aspirate viscoelastic prior to using power, excessively tight incisions, and combinations of the above actions may result in significant temperature increases at incision site and inside the eye, and lead to severe thermal eye tissue damage.
Good clinical practice dictates the testing for adequate irrigation and aspiration flow prior to entering the eye. Ensure that tubings are not occluded or pinched during any phase of operation.
The consumables used in conjunction with ALCON® instrument products constitute a complete surgical system. Use of consumables and handpieces other than those manufactured by Alcon may affect system performance and create potential hazards.
AEs/Complications: Inadvertent actuation of Prime or Tune while a handpiece is in the eye can create a hazardous condition that may result in patient injury. During any ultrasonic procedure, metal particles may result from inadvertent touching of the ultrasonic tip with a second instrument. Another potential source of metal particles resulting from any ultrasonic handpiece may be the result of ultrasonic energy causing micro abrasion of the ultrasonic tip.
ATTENTION: Refer to the Directions for Use for the accessories/consumables and Operator’s Manual for a complete listing of indications, warnings, cautions and notes.
1. Gurnani B, Kaur K. Phacoemulsification. [Updated 2023 Jun 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; January 2024. https://www.ncbi.nlm.nih.gov/books/NBK576419/
2. Suzuki H, Igarashi T, Takahashi H. Effect of a new phacoemulsification and aspiration handpiece on anterior chamber stability. J Cataract Refract Surg. 2023;49:91-96.
3. Kokubun T. Verification for the usefulness of normal tension cataract surgery. Paper presented at the: 126th Annual Meeting of the Japanese Ophthalmological Society; 2022; Osaka, Japan.
4. Rauen MP, Joiner H, Kohler RA, O’Connor S. Phacoemulsification using an Active Fluidics System at Physiologic versus High IOP: Impact on Anterior and Posterior Segment Physiology. J Cataract Refract Surg. 2024;50(8):822-827.
5. Beres H, de Ortueta D, Buehner B, Scharioth GB. Does low infusion pressure microincision cataract surgery (LIPMICS) reduce frequency of post-occlusion breaks? Romanian Journal of Ophthalmology. 2022;66:135-139.
6. Phacoemulsification Systems’ Occlusion Break Surge Performance Report – Surge
Tool App (2020).
7. Scarfone HA, Rodriguez EC, Rufiner MG, et al. Vitreous-lens interface changes after cataract surgery using active fluidics and active sentry with high and low infusion pressure settings. J Cataract Refract Surg. 2024;50(4):333-338.
8. Vasavada V, Raj SM, Praveen MR, et al. Real-time dynamic intraocular pressure fluctuations during microcoaxial phacoemulsification using different aspiration flow rates and their impact on early postoperative outcomes: a randomized clinical trial. J Refract Surg. 2014;30(8):534-540.
9. Vasavada AR, Praveen MR, Vasavada VA, et al. Impact of high and low aspiration parameters on postoperative outcomes of phacoemulsification: randomized clinical trial. J Cataract Refract Surg. 2010;36(4):588-598.
10. Liu Y, Hong J, Chen X. Comparison of the clinical outcomes of Centurion active fluidics system with a low IOP setting and gravity fluidics system with normal IOP setting for cataract patients with low corneal endothelial cell density. Front Med (Lausanne). 2023;10:1294808.
11. Rauen M. Phacoemulsification at high IOP and physiologic IOP: impact on anterior segment physiology. Paper presented at ASCRS 2023; San Diego.
12. Anisimova NS, Arbisser LB, Shilova NF, et al. Anterior vitreous detachment: risk factor for intraoperative complications during phacoemulsification. J Cataract Refract Surg. 2020;46(1):55-62.
13. Lin W, Luo J, Li P, et al. Anterior vitreous detachment and retrolental material during cataract surgery: incidence and risk factors, with pathological evidence. J Cataract Refract Surg. 2023;49(6):578-583.
14. Takhtaev, Y. V. et al. The effect of preset intraoperative intraocular pressure during phacoemulsification on the blood flow velocity in the central retinal artery. Ophthalmology Journal. 12, 5-12 (2019).
15. Liu, J. et al. Microvascular Changes in Macular Area After Phacoemulsification and Its Influencing Factors Assessed by Optical Coherence Tomography Angiography. Ther Clin Risk Manag. 17, 405-414, doi:10.2147/TCRM.S309679 (2021).
16. Chen, D. et al. Effect of simulated dynamic intraocular pressure on retinal thickness measured by optical coherence tomography after cataract surgery. Int J Ophthalmol 5, 687-693, doi:10.3980/j.issn.2222-3959.2012.06.07 (2012).
17. Wang J. et al. Effect on ocular blood flow after cataract surgery with different fluidics systems in high myopia cases. Asia-Pacific Association for Cataract & Refractive Surgeons (APACRS) (Singapore, 2021).
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