Differential Intraocular Pressure Phacoemulsification

One crucial factor in ensuring safe phacoemulsification is the intraocular pressure (IOP), or bottle height, at which the procedure is conducted. We introduce the concept of differential IOP phacoemulsification – a strategy that adjusts IOP based on specific situations and surgical stages to optimize patient outcomes. Performing phacoemulsification at higher IOP levels offers the benefit of maintaining a stable anterior chamber by counteracting fluid outflow and dynamic pressure fluctuations, thereby preventing chamber shallowing. DISADVANTAGES OF HIGH INTRAOCULAR PRESSURE SETTINGS OR HIGH BOTTLE HEIGHT Performing phacoemulsification at high IOP can present significant risks, particularly in patients with advanced glaucoma, as it may contribute to wipe-out syndrome. In addition, patients with elevated baseline IOP, increased anterior chamber depth, or longer axial length may experience more discomfort during the procedure. High IOP can also be linked to fluid misdirection syndrome. In cases of high myopia or prior vitrectomy, elevated bottle height or IOP can overly deepen the anterior chamber, increasing the risk of lens–iris diaphragm retropulsion syndrome and complicating the surgical process. Prolonged high IOP during phacoemulsification is associated with greater occurrence of Descemet’s membrane folds, heightened anterior segment (AS) inflammation, and more severe corneal edema. In patients with pseudoexfoliation syndrome, elevated IOP can cause excessive anterior chamber deepening. This, combined with high fluid pressure and chamber fluctuations, places additional strain on weakened zonules, increasing the risk of anterior hyaloid face disruption, even when the posterior capsule remains intact. LOW INTRAOCULAR PRESSURE PHACOEMULSIFICATION SETTINGS Robert Osher described the use of slow-motion phacoemulsification as a solution to the challenges associated with high bottle heights. Adopting low IOP settings during phacoemulsification addresses many of the limitations of high IOP procedures. Achieving optimal fluidics at low IOP involves careful titration, requiring the surgeon to balance fluid inflow and outflow. The outflow is determined by a combination of aspirated fluid and leakage through incisions. At a fixed bottle height, fluid inflow and leakage remain constant, while aspiration flow rate (AFR) and vacuum are the adjustable parameters. In cases involving hard cataracts during chopping and phacoaspiration, a high vacuum is essential for securing the nucleus. In these scenarios, reducing the vacuum is not feasible, but lowering the flow rate while maintaining high vacuum can minimize surge. For softer cataracts or steps where firm nucleus stabilization is less critical, surge can be managed by lowering the vacuum while keeping the flow rate constant. Chamber stability can be tested by positioning the handpiece about 6″ above the patient’s eye and evaluating chamber maintenance under various fluid settings. In addition, intraoperative stability can be enhanced by adjusting fluid settings based on real-time chamber conditions. Modern gravitational fluidic systems have become more efficient at lower bottle heights due to advancements in surge control. Meanwhile, active fluidics offer faster responses to pressure fluctuations, enabling stable chamber conditions even at physiological IOP levels. LOW INTRAOCULAR PRESSURE SETTINGS I divide low IOP phacoemulsification into: Physiological IOP settings - IOP 18 mmHg - 22 mmHg; AFR 23 cc/min to 26 cc/min Supraphysiological IOP settings - IOP 23 mmHg to 34 mmHg; AFR 23–35 cc/min Subhigh IOP settings - IOP 35 mmHg - 44 mmHg; AFR 40–45 cc/min [Figure 1]. Figure 1: Low intraocular pressure settings. IOP: Intraocular pressureHOW DO LOW INTRAOCULAR PRESSURE SETTINGS HELP? Low IOP settings reduce the amount of fluid entering the eye, preventing excessive deepening of the anterior chamber and maintaining a lower pressure gradient between the anterior and posterior segments. This setup enhances corneal endothelial protection by minimizing turbulence within the anterior chamber, helping to retain the ophthalmic viscosurgical device (OVD) and reduce direct trauma to the corneal endothelium. Proper calibration of both the primary and side-port incisions with their corresponding instruments is essential for maintaining chamber stability at low IOP. This prevents excessive fluid outflow through the incisions, ensuring a stable surgical environment. PHYSIOLOGICAL INTRAOCULAR PRESSURE SETTINGS’ APPLICATIONS Posterior polar cataracts with preexisting posterior capsular defects Posterior polar cataracts with preexisting capsular defects can be identified through slit-lamp examination, AS optical coherence tomography (AS-OCT), and direct visualization under the operating microscope. Using physiological IOP settings with a low flow rate and vacuum ensures stable chamber conditions, avoiding excessive deepening of the anterior chamber or posterior bulging, which helps minimize the risk of extending the capsular defect. Lower fluid infusion prevents excess fluid from entering the vitreous, reducing the risk of vitreous hydration and spontaneous rupture of the anterior vitreous face. The reduced turbulence at a low flow rate also lowers the chance of vitreous aspiration. The minimal pressure gradient between the anterior and posterior segments allows nuclear fragments to remain in the AS without being pushed back. Proper planning and execution are essential for successful surgery, with the size of the posterior capsular rent remaining unchanged before and after the procedure [Figure 2].Figure 2: (a) Posterior capsular defect at the start of surgery of the patient of posterior polar cataract, (b) Posterior capsular defect at the end of the surgery of the same patientIntraoperative posterior capsular rupture during sculpting Low IOP settings are particularly useful in managing intraoperative posterior capsular rupture (PCR). In a case where PCR occurred during sculpting [Figure 3], surgical parameters were adjusted to physiological IOP with reduced flow rates. This minimized vitreous hydration and prevented the vitreous from being drawn toward the phaco tip. Nuclear fragments remained suspended without being pushed back, allowing for their safe removal and avoiding further extension of the capsular defect [Figure 4].Figure 3: Posterior capsule punch while sculptingFigure 4: Posterior capsular rupture size same at the end of surgeryAdvanced glaucoma and wipe-out syndrome risk Operating under physiological IOP settings prevents intraoperative IOP from exceeding normal levels, effectively eliminating the risk of wipe-out syndrome in patients with advanced glaucoma. Surgery is concluded at low IOP after confirming secure wound closure [Figure 5].Figure 5: Physiological intraocular pressure settings in advanced glaucoma patientPreexisting posterior capsular rupture in patients with prior antivascular endothelial growth factor injections Patients with a history of intravitreal antivascular endothelial growth factor injections may develop cataracts rapidly. Posterior capsular defects in these cases can be detected through slit-lamp examination and AS-OCT. Similar to posterior polar cataracts with preexisting defects, phacoemulsification in these patients is managed using low IOP settings. Proper technique and careful parameter adjustment reduce the risk of nuclear fragment dislocation into the posterior segment. Patients with zonulopathy In patients with zonular weakness, low IOP and low fluidic parameters create a stable chamber environment, reducing stress on the remaining zonules. This approach minimizes fluid inflow, preventing vitreous hydration and decreasing the risk of vitreous prolapse into the tip. In addition, the likelihood of spontaneous rupture of the anterior vitreous face and fluid misdirection is significantly reduced, contributing to safer surgical outcomes. APPLICATION OF PHYSIOLOGICAL/SUPRAPHYSIOLOGICAL INTRAOCULAR PRESSURE SETTINGS Anterior capsular tear In cases involving anterior capsular tears, the challenge is to safely complete phacoemulsification or decide on a timely conversion to manual small-incision cataract surgery (MSICS) or extracapsular cataract extraction (ECCE). Utilizing low IOP settings, the flap motility sign, and cautious surgical techniques helps manage these cases effectively. Stable chamber conditions with low IOP reduce the risk of preequatorial tears progressing into wraparound tears. In addition, low IOP settings provide sufficient time for the surgeon to convert to MSICS or ECCE if a tear extends, thus preventing nucleus drop. Phacoemulsification in high myopes and vitrectomized eyes For patients with high myopia or vitrectomized eyes, low IOP settings and reduced parameters are essential. Decreased fluid inflow helps prevent excessive anterior chamber deepening, thereby reducing the likelihood of lens–iris diaphragm retropulsion syndrome. This approach allows the surgery to proceed smoothly, with patients experiencing less intraoperative discomfort. Phacoemulsification in patients on tamsulosin or similar medications Patients using alpha-1 antagonist drugs, such as tamsulosin, are at high risk for intraoperative floppy iris syndrome (IFIS). Low IOP settings, combined with protocols designed to manage IFIS, help maintain stable chamber conditions. By reducing fluid turbulence and pressure fluctuations, this technique preserves pupil size throughout the surgery, from start to finish [Figure 6].Figure 6: (a) Pupil size at the start of surgery of the patient on alpha-1 antagonist drug (Tamsulosin), (b) Same pupil size at the end of the surgery of the same patient on alpha-1 antagonist drug (Tamsulosin)Posterior polar cataracts without preexisting posterior capsular defects Posterior polar cataracts have a significant risk of posterior capsule rupture. Maintaining stable chamber conditions with physiological or slightly elevated IOP settings prevents unnecessary anterior chamber deepening and posterior capsule bulging, mitigating the risk of rupture. CORNEAL ENDOTHELIAL PROTECTION IN LOW INTRAOCULAR PRESSURE PHACOEMULSIFICATION Protecting corneal endothelial cells during low IOP phacoemulsification involves minimizing the impact of lens fragments on the endothelium due to reduced turbulence and better retention of the OVD in the anterior chamber. This approach significantly decreases endothelial trauma. CHALLENGES OF LOW INTRAOCULAR PRESSURE PHACOEMULSIFICATION Operating at near-physiological IOP levels can lead to a shallower anterior chamber and reduced capsular bag volume, limiting working space. In patients with dense cataracts or short axial lengths, this reduced space may increase the risk of trauma to surrounding tissues, particularly the corneal endothelium [Figure 7].Figure 7: Low intraocular pressure settings and corneal endothelial cell protection/damage. IOP: Intraocular pressureOPTIMIZING INTRAOCULAR PRESSURE SETTINGS: THE SOLUTION A subhigh IOP approach can address these challenges. Using an IOP of up to 44 mmHg (equivalent to a 60 cm bottle height) provides sufficient working space while keeping the IOP below the central retinal artery closing pressure. This strategy balances moderate fluidics with controlled turbulence, ensuring safer surgical conditions without compromising anterior chamber stability. USE OF SUBHIGH INTRAOCULAR PRESSURE SETTINGS Subhigh IOP settings are particularly useful during chopping and phacoaspiration in cases involving hard cataracts with increased lens thickness or in shorter eyes. These settings provide additional working space, allowing for more controlled and efficient surgical steps. DIFFERENTIAL INTRAOCULAR PRESSURE PHACOEMULSIFICATION Each surgical case presents unique challenges, and the choice of IOP settings plays a crucial role in managing these variations. Physiological IOP settings are ideal for cases with preexisting posterior capsule rupture or zonulopathy. They are also essential in situations where an increase in IOP could jeopardize a compromised optic nerve head. In specific, complex cases, both physiological and supraphysiological IOP settings can be used depending on the surgeon’s preference. These settings minimize fluid turbulence and maintain stable chamber conditions, preventing the anterior chamber from becoming excessively deep due to increased fluid inflow. For cases requiring more working space, subhigh IOP settings are appropriate. This category of low IOP settings offers an optimal balance for certain stages of surgery, such as chopping and phacoaspiration. In contrast, physiological or supraphysiological IOP settings can be applied during delicate steps such as sculpting and cortex removal, where stability and control are paramount. For challenging cases such as hard cataracts with increased lens thickness or short axial length, a combination of physiological/supraphysiological IOP settings and subhigh IOP settings may be beneficial. This approach allows for precise management throughout the surgical process [Figure 8].Figure 8: Differential intraocular pressure settings. OVD: Ophthalmic viscosurgical device. IOP: Intraocular pressureCONCLUSION It is essential to tailor IOP settings to the specific needs of each patient, using the appropriate settings at different stages of surgery to optimize outcomes. Surgeons should ensure that their phacoemulsification equipment is equipped with a full range of IOP settings, enabling them to adjust quickly and efficiently for improved patient care.