Does Further Lowering Intraoperative Intraocular Pressure Reduce Surgical Invasiveness in Active-Fluidics Eight-Chop Phacoemulsification? A Fellow-Eye Comparative Study

Background: Active-fluidics phacoemulsification can maintain anterior chamber stability at lower intraoperative intraocular pressure (IOP) levels. However, whether reducing IOP alone—without additional stabilizing technologies such as the Active Sentry handpiece—can decrease surgical invasiveness during Eight-Chop phacoemulsification remains unclear. Methods: In this prospective fellow-eye comparative study, 56 non-diabetic patients (112 eyes) underwent Eight-Chop technique phacoemulsification using the Centurion Vision System with active fluidics. One eye was randomly assigned to a standard-IOP setting (55 mmHg; high-IOP group) and the fellow eye to a reduced-IOP setting (28 mmHg; low-IOP group). Intraoperative parameters—including operative time, phaco time, aspiration time, cumulative dissipated energy (CDE), and irrigation volume—were recorded. Postoperative outcomes included aqueous flare (laser flare photometry), corneal endothelial cell density (CECD) and CECD loss, corneal morphology (central corneal thickness [CCT], coefficient of variation [CV], percentage of hexagonal cells [PHC]), and IOP. Linear mixed-effects models with patient ID as a random effect were used for all paired-eye comparisons. Results: Lowering the intraoperative IOP did not reduce surgical invasiveness. Phaco time was significantly longer in the low-IOP group (16.2 ± 5.22 s vs. 13.9 ± 4.40 s; p = 0.001), and aspiration time was also longer (75.0 ± 18.3 s vs. 69.0 ± 17.9 s; p = 0.033). No significant differences were found in operative time (5.08 ± 1.10 min vs. 4.82 ± 1.13 min; p = 0.082), CDE (5.93 ± 1.87 vs. 5.56 ± 1.90; p = 0.099), or irrigation volume (26.6 ± 7.71 mL vs. 25.2 ± 7.35 mL; p = 0.214). Postoperative outcomes were similarly comparable. Aqueous flare showed no significant differences at any time point (e.g., day 1: 14.8 ± 5.10 vs. 14.5 ± 4.76 ph/ms; p = 0.655). Mean CECD loss remained small in both groups and did not differ significantly (7 weeks: −0.82 ± 1.05% vs. −0.98 ± 1.16%, p = 0.460; 19 weeks: −0.93 ± 1.38% vs. −1.28 ± 1.69%, p = 0.239). Corneal morphological parameters (CCT, CV, PHC) and postoperative IOP also showed no significant differences between settings. Conclusions: In this fellow-eye comparative study, lowering intraoperative intraocular pressure from conventional to near-physiologic levels under active-fluidics control did not reduce surgical invasiveness during Eight-chop phacoemulsification. No additional benefits were observed in terms of endothelial cell preservation, postoperative inflammation, or overall surgical performance. These findings indicate that, when chamber stability is already ensured by a low-invasive fragmentation strategy, further reduction in intraoperative IOP alone does not confer measurable short-term clinical advantages.