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At Issue: Fluidics and cataract surgery
At Issue posed the following question to a panel of experts: “How important is fluidics today for performing modern phacoemulsification, including microincision cataract surgery?”
Changing perspective, practice
Jorge L. Alio, MD, PhD: Recent advances in fluidics and a better understanding of how we need to work with the different types of energies that are created around the phaco tip have changed our perspective on and practice of phacoemulsification. Recently, the need to do surgery through microincisions seems to be mandatory, as this is the normal evolution of the technique. Microincisions are leading us to a more controlled environment and a better knowledge and understanding of our technology, influencing industry to create better instruments and new IOLs.
Concerning surgical performance, fluidics has become an extremely important issue. We now know that by making fluidics better, we can decrease the total surgical time in a very effective way, decreasing the use of ultrasonic energy inside the eye.
The use of high vacuum (up to 600 mm Hg), which is possible with the Alcon Infiniti phacoemulsification system, has increased our capability of working with this type of energy (vacuum only) to perform, in many cases, up to 90% of the total work of cataract removal. To do this, we must have an extremely well-controlled environment with non-leaking incisions that create a stable anterior chamber. Immediate detection of changes in anterior chamber pressure should be corrected by overflow with the irrigation tip. To do that, we need elastic machines that have no surge at all and special sensors to detect these changes in the anterior chamber fluid dynamics. Fluidics has become an important part of our phacoemulsification practice. It is also a main issue in laser cataract surgery.
Recent improvements in the knowledge and technology in fluid dynamics in cataract surgery have led to enormous progress in our practice.
Eliminating ultrasound
Noel Alpins, MD: The evolution of phacoemulsification into the modern era has brought the progressive minimization of ultrasound time to approach its lowest possible level – zero — potentially eliminating ultrasound altogether from the small- and microincision procedure. This process has been achieved only by the mastery of fluidics to control the stability of the anterior chamber associated with the higher flow and vacuum settings necessary.
Fluidics management can be understood as a balancing act among multiple variables. In essence, the greater the vacuum and the faster the rise time to achieve it, the less the amount of ultrasound and total fluid use required to remove the lens.
When the total ultrasound power used is below a minimum threshold, it becomes safe for the cornea to no longer require an irrigating sleeve to protect it from heat generated by the ultrasonic needle. Bimanual separate irrigation and aspiration is thus enabled.
The multiple variables can be grouped either under infusion, which depends on both the bottle height and tubing diameter, or outflow, with its components of aspiration flow rate and vacuum, wound leakage, tip profile and lumen size, tubing diameter and compliance. The net effect of these various components is observed as anterior chamber depth and can be gauged by IOP. Varying any single parameter will change the overall dynamics.
Delegating all these functions to the default values in the technology without necessarily comprehending their interrelationships is not a recipe for a smooth transition to microincision surgery. The new technologies have elevated micromanagement of fluidics to a level that makes bimanual microincision surgery possible for all savvy cataract surgeons.
Bimanual is ideal situation
I. Howard Fine, MD: Fluidics is paramount in the performance of modern phaco. Most of the modern phacoemulsification systems have anti-surge mechanisms available, which stabilize the anterior chamber in an effective way. However, I have found the most useful anti-surge device, usable on all machines, is the Cruise Control by STAAR Surgical, which creates inordinately stable anterior chambers.
It is true that some of the phaco tips that have narrow throats have provided anti-surge protection, and the addition of noncompliant components to modern phacoemulsification systems have also contributed to anti-surge protection. Perhaps the best fluidics are achievable in bimanual microincision phaco because this is closer to the ideal situation, that of a completely closed system. Bimanual microincision phaco is associated with dramatically less fluidic change through the eye and less incisional outflow from the eye. It has the added advantage that all of the fluid comes in through one incision and out the other. This allows the incoming stream of fluid to mobilize lens fragments, and since there are no competing currents around the phaco tip, lens fragments are removed more efficiently.
The use of power modulation has created a situation in which we are using dramatically less ultrasound energy and removing cataracts primarily with fluidics.
Less power needed
Richard L. Lindstrom, MD: Fluidics is a key issue in phacoemusification today. Current phaco techniques can be characterized as “phaco-aspiration,” with sonic, ultrasonic, laser or waterjet assist. Minimal power is usually needed for the progressively softer average nucleus the American ophthalmologist is usually called on today to remove. The 20/200 brunescent nucleus of 20 years ago has been supplanted by the softer nucleus of refractive lensectomy or today’s less mature yet visually significant cataract. Thus, quality fluidics is paramount to today’s phaco surgeon. Newer machines allow higher vacuum levels with acceptable surge. This is achieved in some machines by improved “surgeon control” as exemplified by the Bausch & Lomb Millennium Dual Linear System and in others by advanced “machine control” as exemplified by the Advanced Medical Optics Sovereign. Both approaches, along with high frequency pulse or burst mode and lower power settings, allow today’s surgeon to remove a nucleus with much less effective power than was used in the past. This results in clearer first day corneas and more rapid visual rehabilitation. These advanced fluidics will also enhance our ability to safely perform bimanual microincision phacoemulsification, likely the procedure of the future.
Manipulator-infuser, pump important
Giuseppe Panzardi, MD: After many years, we find ourselves still talking about fluid dynamics, a problem that has been greatly resolved in traditional phacoemulsification.
With bimanual phaco, the fluid dynamic becomes a problem once again. In fact, the moment the sleeve is removed, so is the infusion system. The irrigating solution now has to enter laterally with a new instrument, the manipulator-infuser.
This instrument, beyond ensuring the flow of liquid, allows the mobilization of the nucleus and the management of the fragments. However, for the instrument to be manageable, it must be thin, and therefore its water capacity is reduced as compared with the phaco tip’s sleeve. It then becomes necessary to also decrease the dimension of the tip the greater the dimension of the manipulator-infuser. More simply, we can say that the manipulator-infuser must be the same dimension as the tip (both 0.7 mm or 0.8 mm or so) and cannot be smaller in any way.
Another important element to consider is the type of pump used for the procedure. For the bimanual procedure, the venturi pump has proven to be the clear winner. The low effusion of the microtip permits the use of more vacuum without alteration to the chamber, and the capture and emulsification of the fragments is much faster compared to the peristaltic pump since occlusion is not necessary.
The form and precision of the incisions that must be maintained for stability of the chamber take on great importance, allowing for more manageable movement of the instruments.
Fluid dynamics essential
Khiun Tjia, MD: Fluid dynamics play a major role in optimizing efficiency.
The attractive forces of vacuum and high aspiration flow counteract the repulsive forces of ultrasound to keep the lens material in close contact with the phaco tip during emulsification.
A problem in modern microincision surgery is that the irrigation flow is significantly reduced from a normal 60 to 80 mL/min to 25 to 40 mL/min. This makes reduction of surge flow volume on occlusion break even more important than with conventional phaco surgery, when a high irrigation flow can partially compensate for surge flow.
To achieve this reduction in surge flow, the compliance of the pump and tubing should be as low as possible.
A very rigid tubing, such as the Max-Vac cassettes of the Alcon Legacy, was a big step forward in this respect. Other manufacturers also have improved (or are currently improving) their tubing. A very low compliance cassette (such as the Bausch & Lomb Millennium Concentrix) is also mandatory.
The recently introduced Alcon Infiniti combines the low compliance of the Max-Vac tubing with a virtually zero compliance cassette. The anterior chamber stability, even with high vacuum settings, is remarkable. This will set a new standard in modern phacoemulsification surgery.
Other components can also contribute to enhance the characteristics of the fluid dynamics: Dynamic rise time (variable flow setting on occlusion) is an innovation to facilitate efficient ultrasound energy delivery.
Another tool to influence fluid dynamics is the modern phaco tip. A smaller lumen of the shaft has a higher resistance to outflow after occlusion break. A bigger head of the phaco tip gives a larger holding surface during occlusion.
Ultrasound modulation (both time and power modulation are important) optimizes ultrasound energy efficiency. Fluid dynamics, however, are the essential backbone for the ongoing process of modernizing phacoemulsification.
This process will surely lead to further innovations and improvements, to the benefit of both surgeons and patients.
For Your Information:
- Jorge L. Alio, MD, PhD, is a professor and chairman of ophthalmology and the medical director of the Instituto Oftalmologico de Alicante in Spain. He can be reached at Avda, Denia 111, 03015 Alicante, Spain; +34-965-150-025; fax: +34-965-151-501; e-mail: jlalio@oftalio.com. Dr. Alio has no financial interest in any of the products mentioned in his response nor is he a paid consultant for the companies mentioned.
- Noel Alpins, MD, can be reached at NewVision Clinics, 7 Chesterville Road, Cheltenham, Victoria, Australia, 03192; +61-3-9584-6122; fax: +61-3-9585-0995; e-mail: alpins@newvisionclinics.com.au. Dr. Alpins has no financial interest in any of the products mentioned in his response nor is he a paid consultant for the companies mentioned.
- I. Howard Fine, MD, can be reached at Drs. Fine, Hoffman & Packer, LLC, 1550 Oak St., Suite 5, Eugene, OR 97401 U.S.A.; +1-541-687-2110; fax: +1-541-484-3883; e-mail: hfine@finemd.com; Web site: www.finemd.com. Dr. Fine is a paid consultant for Advanced Medical Optics, Bausch & Lomb, Pfizer Ophthalmics and iScience. He receives travel and research support from Alcon, Eyeonics and STAAR Surgical.
- Richard L. Lindstrom, MD, is the chief medical editor of Ocular Surgery News. He can be reached at Minnesota Eye Associates, 710 E. 24th Street, Suite 106, Minneapolis, MN 55404 U.S.A.; +1-612-813-3600; fax: +1-612-813-3660; e-mail: rllindstrom@mneye.com. Dr. Lindstrom has a financial interest in Bausch & Lomb, Advanced Medical Optics, STAAR, Becton Dickinson, TLCVision, Midwest Surgical Services and Minnesota Eye Consultants.
- Giuseppe Panzardi, MD, can be reached at Clinic Villa Donatello, Piazzale Donatello 14, 50132 Firenze, Italy; +39-055-50975; fax: +39-055-482503; e-mail: kryq@libero.it. Dr. Panzardi has no financial interest in the subject of his response.
- Khiun Tjia, MD, can be reached at Heerderweg 14, 8161 BM EPE, Zwolle, Netherlands; +31-578-621-727; fax: +31-578-629-940; e-mail: k.tjia@isala.nl. Dr. Tjia has no financial interest in the subject of his response.