Cataracts affect more than 24 million Americans over the age of 40, with approximately 4 million surgeries performed annually. Cataract removal is reported as the most common surgical procedure in the United States.¹ Since the advent of phacoemulsification in 1967, cataract extraction with intraocular lens insertion has become one of the safest and most predictable surgeries.² Historically, titration of fluidics for phacoemulsification required height-regulated irrigation along with static air pressure systems to produce high infusion and elevated intraocular pressure (IOP) levels, often 2 to 3 times physiological levels, to prevent post-occlusion surge and chamber collapse.³ However, there is a growing trend toward performing cataract surgery at more physiologic infusion pressure, with potential benefits for efficiency and patient safety.

The Risks of High IOP During Cataract Surgery

High IOP during cataract surgery has been associated with a range of negative postoperative complications. These include persistent postoperative inflammation, corneal edema and Descemet’s folds,^4,5 greater loss of endothelial cell density at 1 month and 3 months postoperative,⁶ along with possible disruption of the anterior vitreous face.⁷ In patients with history of trauma or pseudoexfoliation, operating at high IOP can lead to unnecessary trampolining of the lens and further damage to the zonules with increased chance of lens subluxation. In the posterior pole, elevated IOP has been shown to reduce both retinal and choroidal blood flow, increasing the risks of transient ocular ischemia and ganglion cell loss, along with increased macular thickness at 1 week postoperative positively correlated with prolonged infusion time.^8-13 Though rare, cases of ischemic optic neuropathy and maculopathy have also been reported, although direct causation remains unclear.^14-16

Technological Advancements Improving Chamber Stability

Recent advancements have significantly enhanced chamber stability during phacoemulsification. One of these is the introduction of torsional ultrasound in 2008, which, combined with longitudinal motion, reduced the likelihood of tip clogging and surge.¹⁷ Active fluidics systems, primarily the Centurion Vision with Active Sentry handpiece (Alcon Laboratories, Inc) applies pressurized infusion in conjunction with QuickValve technology to dynamically control fluid flow and monitor IOP fluctuations, thus reducing anterior chamber variability and minimizing complications such as surge and collapse.^18-23 Compared to gravity-dependent systems, Active Fluidics technology has been shown to result in fewer adverse corneal events, including decreased corneal edema.^24-25

Benefits of Operating at Physiologic IOP

In addition to advancements in phacoemulsification machines, operating at physiologic IOP, compared to high IOP, has been shown to improve both patient safety and surgical efficiency.²⁶ Osher’s “slow-motion” phacoemulsification, which uses lower infusion pressure, aspiration, and ultrasound energy, has been shown to improve postoperative corneal clarity while reducing complications.²⁷ Lower IOP minimizes flow turbulence, ultimately improving the safety of the cornea, with recent literature revealing statistically significant endothelial cell protection with reduced postoperative inflammation and corneal edema, improving intraoperative intracameral view without increasing surgical time or ultrasound energy.^28-29

Physiologic IOP settings reduce overinflation of the anterior chamber, thereby limiting zonular stress and the risk of capsule tears. This approach also equilibrates flow, allowing nuclear fragments to “float” instead of being subjected to aggressive irrigation flow, reducing the risk of posterior complications such as lens drop, retinal tears and endophthalmitis.²⁶ Additionally, lower fluid turbulence improves pupil stability in patients with intraoperative floppy iris syndrome.³⁰ Anecdotal evidence suggests that physiologic IOP settings may reduce procedural discomfort, particularly in high myopes and vitrectomized patients, who are prone to “lens-iris diaphragm retropulsion” syndrome.^31-33 Finally, in patients with advanced glaucoma, physiologic IOP during phacoemulsification may also decrease the chance of “nerve snuff” or “wipeout syndrome.” Although optic neuropathy after cataract surgery is rare, this diagnosis is known to ophthalmologists in patients having unexpected poor visual outcome after cataract surgery and may be underdiagnosed. Chamber stability and avoiding IOP fluctuations are necessary in patients with history of optic nerve compromise and should be protected intraoperatively.^34-35

Considerations and Limitations

Despite its advantages, operating at physiologic IOP does present certain limitations. Lower IOP settings can reduce anterior chamber depth, limiting the available “working space” for the surgeon. In cases requiring additional space, such as eyes with unstable anterior chambers, mature lens bulge, or high posterior pressure, higher IOP settings may be necessary. When chamber stability is inadequate while operating at lower IOP, higher “supraphysiologic” IOP of 23 mmHg to 34 mmHg can be utilized during sculpting and cortex removal and “sub-high” IOP (35 mmHg to 44 mmHg) during chopping, nuclear disassembly, and phacoaspiration.²⁶ However, while the intraoperative working space between the endothelium and lens may seem larger and thus “safer” at more traditional higher IOP, emerging evidence does suggest equivalent or improved postoperative outcomes with no change in surgeon efficiency.

Another concern with operating at low IOP is that reduced fluid flow may decrease mobilization of lens fragments, especially to the novice learner. However, studies confirm little or no apparent difference in surgical predictability between low and high IOP settings when operating in routine elderly eyes having a normal axial length of 22 mm to 26 mm.²⁹

When changing surgical technique from traditional high IOP to a lower, more physiologic IOP, the recommendation among experts is to gradually adjust IOP in small incremental changes, typically decreasing by 5 mmHg to 10 mmHg, and testing over several cases. Surgeons must challenge themselves periodically to refine their techniques and improve efficiency, while also keeping a backup program to compare results and maintain flexibility.

Conclusion

For most patients undergoing cataract surgery, the risks associated with high IOP, including prolonged inflammation, endothelial injury, and ocular ischemia, support the recommendation to operate at physiologic IOP. This approach is particularly beneficial for patients with compromised optic nerves, such as those with severe glaucoma, where chamber stability and avoidance of IOP fluctuations are critical.

Studies confirm that operating at physiologic IOP, especially when utilizing advanced fluidics technology for dynamic monitoring of IOP and more consistent intraoperative IOP, results in a reduction in surge events, lower fluid usage, lower total aspiration time, and lower cumulative dispersed energy. Thisenhances intraoperative surgeon and postoperative patient clarity, reduces procedural discomfort, and preserves both surgical efficiency and safety. While there are scenarios where higher IOP settings may be appropriate, the trend toward physiologic IOP promises improved outcomes for patients and surgeons alikeand is another progressive breakthrough in the advancement of cataract surgery. GP

Shivani S. Kamat, MD, is an associate professor in the department of ophthalmology at the University of Texas Southwestern Medical Center in Dallas, where she leads the glaucoma service and is the director of the glaucoma fellowship. She is a consultant and speaker for AbbVie, Alcon, Glaukos, New World Medical, and Nova Eye. Dr. Kamat can be reached at  Shivani.Kamat@utsouthwestern.edu.

Mohamed R. Mohamed, MD, is a glaucoma fellow at the University of Texas Southwestern Medical Center in Dallas, and holds another doctorate degree in sports rehabilitation and physical therapy. He reports no disclosures.

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