Surgeons should use IOP settings in phaco to their advantage
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Differential IOP phacoemulsification is a new concept from Rohit Om Parkash, MBBS, MS, and a video on the topic won the film festival award at this year’s American Society of Cataract and Refractive Surgery meeting.
In this column, I invite Rohit Om Parkash, MBBS, MS, and Tushya Om Parkash, MBBS, MS, to explain this topic.
Amar Agarwal, MS, FRCS, FRCOphth
OSN Complications Consult Editor
One of the most important aspects in safe phacoemulsification is the IOP or the bottle height at which phacoemulsification is performed.
We present use of differential IOP phacoemulsification, a new paradigm wherein different IOPs are used in different situations and in different steps to maximize patient outcomes.
Disadvantages of high IOP settings or high bottle height
High IOP phacoemulsification gives the advantage of a stable anterior chamber by compensating for anterior chamber shallowing by the outflow of fluid and dynamic pressure losses.
But high IOP phacoemulsification can lead to wipeout syndrome in advanced glaucoma patients. Phacoemulsification is painful in patients with higher baseline IOP, larger anterior chamber depth or greater axial length.
High IOP during phacoemulsification can also be associated with fluid misdirection syndrome.
In high myopes and vitrectomized eyes, use of high bottle height or high IOP during phacoemulsification makes the surgical procedure difficult, with undue deepening of the anterior chamber resulting in higher incidence of lens-iris diaphragm retropulsion syndrome.
There is an association of increased Descemet’s folds, greater anterior segment inflammation and more edematous corneas with use of prolonged high IOP during phacoemulsification.
In patients with pseudoexfoliation syndrome, high IOP usage predisposes to deepening of the anterior chamber. The combination of deepened anterior chamber, high fluid pressure and chamber fluctuations puts stress on the already compromised zonules.
There is more predisposition to disruption of the anterior hyaloid phase even in the presence of an intact posterior capsule.
Low IOP phacoemulsification
Use of low IOP settings during phacoemulsification seems to be the answer to the drawbacks of high IOP phacoemulsification. Setting up fluidics at low IOP requires titrating of fluidics. The surgeon needs to create a balance of fluid entering and exiting the eye. The amount of fluid exiting the eye is the combination of fluid being aspirated and the fluid leakage through the incisions. For a given bottle height, the fluid inflow and leakage are constant. The variable parameters of aspiration are aspiration flow rate (AFR) and vacuum.
In the chopping and phacoaspiration steps of hard cataracts, high vacuum is required to firmly hold the nucleus. Vacuum cannot be decreased in such situations. Surge can be decreased by reducing flow rate while maintaining high vacuum.
In softer cataracts or in surgical steps in which firm holding of the nucleus is not that important, surge can be decreased by lowering vacuum settings while maintaining flow rate settings.
The stable chamber settings of fluidics can be determined by keeping the handpiece 6 inches above the patient’s eye and checking for maintenance of the test chamber by using different fluid settings. Furthermore, intraoperative chamber stability at each step can be enhanced by titrating fluid settings while looking for chamber stability.
Gravitational fluidic systems have become more effective than before at lower bottle heights due to advanced surge control measures. However, active fluidics have improved response time to pressure fluctuations. Subsequently, stable chamber settings are achievable at physiological IOP settings.
Low IOP settings
In my practice, I divide low IOP phacoemulsification into:
- Physiological IOP settings: IOP 18 mm Hg to 22 mm Hg; AFR 23 cc/min to 26 cc/min.
- Supraphysiological IOP settings: IOP 23 mm Hg to 34 mm Hg; AFR 23 cc/min to 35 cc/min.
- Sub-high IOP settings: IOP 35 mm Hg to 44 mm Hg; AFR 40 cc/min to 45 cc/min (Figure 1).
Source: Rohit Om Parkash, MBBS, MS, and Tushya Om Parkash, MBBS, MS
How do low IOP settings help?
With low IOP settings, the fluid entering the eye decreases. There is no undue deepening of the anterior chamber. There is a low pressure difference between the anterior and posterior segments. Corneal endothelial protection is provided by less turbulence in the anterior chamber, resulting in retention of ophthalmic viscosurgical device and less direct trauma to the corneal endothelium.
Calibrating of both primary and side-port incisions with their respective instruments is important for increasing chamber stability at low IOP settings as it prevents undue efflux of fluid through the incisions.
Application of physiological IOP settings
1. Posterior polar cataracts with preexisting posterior capsular defects: Posterior polar cataracts with preexisting cataracts can be diagnosed by slit lamp examination, anterior segment OCT and direct visualization on the operating microscope. With physiological IOP settings, there are stable chamber settings using a low flow rate with vacuum. There is neither undue deepening of the anterior chamber nor posterior bulging. The setting decreases the chances of extension of the posterior capsular defect. Low infusion of fluid does not push more fluid into the vitreous, thereby not hydrating the vitreous. The probability of spontaneous rupturing of the anterior vitreous phase is minimized. A low flow rate decreases turbulence and reduces predisposition to vitreous aspiration. The minimal pressure difference between the anterior and posterior segments makes the nuclear fragments float in the anterior segment without being pushed back. Appropriate planning with execution invariably helps complete the case. The surgeon can see that the size of posterior capsular rent remains the same before and after surgery (Figure 2).
2. Phaco punch of posterior capsule: Low IOP settings help in cases of intraoperative posterior capsule rupture. This patient had posterior capsular punch during sculpting (Figure 3). Once the posterior capsular punch occurred, parameters were decreased to physiological IOP settings with low IOP and flow rate. There was negligible vitreous hydration, and vitreous was not being drawn to the tip. Nuclear fragments were floating without being pushed back. Fragments were successfully taken out safely. There was no extension of the posterior capsular defect (Figure 4).
3. Advanced glaucoma with predisposition to wipeout syndrome: Physiological IOP settings do not allow intraoperative IOP to rise above physiological IOP and practically eliminate the possibility of wipeout syndrome. The case is closed with low IOP following confirmation of wound sealing (Figure 5).
4. Preexisting posterior capsule rupture in patients with a history of anti-VEGF intravitreal injections: These patients have a history of fast onset of cataract. Slit lamp examination and anterior segment OCT are used to ascertain the posterior capsule defect. Physiological low IOP settings are used and managed on similar phacoemulsification principles as posterior polar cataracts with preexisting posterior capsule defects. Judicious use of technique and settings helps decrease the incidence of posterior dislocation of nuclear fragments.
5. Patients with zonulopathy: In patients with zonulopathy, low IOP and low fluidics are used. Low parameters result in stable chamber settings. The combination of stable chamber settings, reduced fluid pressure and a less inflated anterior chamber reduces stress to the intact zonules. There is decreased fluid inflow to hydrate the vitreous. A low flow rate decreases the possibility of drawing vitreous to the tip. Low IOP settings reduce the probability of spontaneous rupture of the anterior vitreous phase and cause lesser fluid misdirection as well.
Application of physiological/supraphysiological IOP settings
1. Anterior capsular tear: In patients with anterior capsular tears, the challenge lies in completing phacoemulsification or timely conversion to manual small-incision cataract surgery (MSICS) or extracapsular cataract extraction (ECCE). A combination of low IOP settings, use of flap motility sign and safe phacoemulsification techniques is employed. With low IOP and stable chamber settings, the chances of pre-equatorial tears extending to wraparound tears decrease. Furthermore, low IOP settings help the surgeon avoid a nucleus drop by providing ample time to convert to MSICS or ECCE when the tear extends to become a wraparound tear.
2. Phacoemulsification in high myopes/vitrectomized eyes: In these patients, low IOP settings with low parameters are used. With decreased inflow, there is less deepening of the anterior chamber. Subsequently, the probability of lens-iris diaphragm retropulsion syndrome is minimized. The case proceeds as a normal case with decreased pain score felt by the patients.
3. Phacoemulsification in patients with tamsulosin and similar drugs: There is a strong predisposition to intraoperative floppy iris syndrome (IFIS) in patients using alpha-1 antagonist drugs. Low IOP settings are used in conjunction with IFIS-preventing surgical protocols. Stable chamber settings with low fluidics decrease fluid stream turbulence and pressure variance in the anterior chamber. Pupil size remains the same at the start and end of surgery (Figure 6).
4. Posterior polar cataracts with no preexisting posterior capsular defects: Posterior polar cataracts have a strong predisposition to posterior capsule rupture. Stable chamber settings with physiological or supraphysiological IOP settings prevent an undue deepening of the anterior chamber and posterior bulging of the posterior capsule.
Corneal endothelial protection in low IOP
Let’s understand a few concepts of corneal endothelial cell protection during low IOP phacoemulsification. Corneal endothelial protection is provided by minimal impact of lens fragments with the corneal endothelium because of low turbulence and better retention of ophthalmic viscosurgical device in the anterior chamber.
Shortcomings of low IOP phacoemulsification
Low IOP phacoemulsification around physiological IOP involves decreased anterior chamber depth and bag volume. Low IOP settings are associated with reduced working space. In hard cataracts with increased lens thickness and in short eyes, reduced anterior chamber depth predisposes to more trauma to the surrounding tissues, especially the corneal endothelium (Figure 7).
What is the answer?
Sub-high IOP settings can be used. In these patients, IOP up to 44 mm Hg or 60 cm bottle height is used. At the sub-high IOP settings, IOP is much below the closing pressure of the central retinal artery. With sub-high IOP settings, working space is increased. Moderate fluidics are used, and turbulence in the anterior chamber is not high.
Application of sub-high IOP settings
Sub-high IOP settings can be used during chopping and phacoaspiration in hard cataracts with increased lens thickness and in shorter eyes.
Differential IOP phacoemulsification
All cases are different. We can use physiological IOP settings in the presence of preexisting posterior capsule rupture and in cases with zonulopathy. Additionally, physiological IOP settings are mandatory when we do not want IOP to rise in compromised optic nerve heads.
Physiological or supraphysiological IOP settings can be used as per the surgeon’s convenience in special case scenarios. These settings produce minimal fluid turbulence and provide stable chamber settings. The anterior chamber is not unduly deepened by more fluid entering the eye.
The sub-high IOP category of low IOP settings is used in procedures and steps when we need more working space.
The combination of physiological/supraphysiological IOP settings and sub-high IOP settings can be used in hard cataracts with increased lens thickness and in short eyes. Physiological or supraphysiological settings are used during sculpting and cortex removal. Sub-high IOP settings can be used during chopping and phacoaspiration (Figure 8).
In conclusion, we should use IOP settings to our advantage. Our armamentarium should have phaco programming of all IOP settings in our machine settings for ready use to help improve patient outcomes.
- For more information:
- Amar Agarwal, MS, FRCS, FRCOphth, director of Dr. Agarwal’s Eye Hospital and Eye Research Centre, is the author of several books published by SLACK Books, sister company of Healio publisher Ocular Surgery News, including Phaco Nightmares: Conquering Cataract Catastrophes, Bimanual Phaco: Mastering the Phakonit/MICS Technique, Dry Eye: A Practical Guide to Ocular Surface Disorders and Stem Cell Surgery and Presbyopia: A Surgical Textbook. He can be reached at aehl19c@gmail.com; website: www.dragarwal.com.
- Rohit Om Parkash, MBBS, MS, of Dr. Om Parkash Eye Institute, Punjab, India, can be reached at drrohitop@gmail.com.
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