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High-vacuum bimanual phaco attainable with STAAR's Cruise Control
Stable chambers with 400 mm Hg vacuum are possible with this new disposable flow restrictor.
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Bimanual phaco goes by several names coined by its innovators – Phakonit (Agarwal), Micro Phaco (Olson) and MICS – Micro-Incision Cataract Surgery (Alio). Although preceded by other “cold” modalities such as laser phaco and sonics, it was the introduction of WhiteStar technology (Advanced Medical Optics) 2 years ago that jumpstarted the growing interest in bimanual phaco.
This was the first time we could utilize ultrasound from an existing machine to perform cold phaco for nuclei of all densities. Bimanual phaco is now being performed with the Millennium (Bausch & Lomb) and the Infiniti (Alcon) machines as well.
While these power modulations solved the problem of incisional burn from a sleeveless phaco needle, we quickly learned that bimanual fluidics would be the next challenge. The main problem has been the reduced irrigation inflow caused by eliminating the coaxial infusion sleeve.
Because chamber stability is an issue with current 20-gauge instrumentation, several different strategies have been adopted. The incisions must be tight enough to avoid leakage around the instrument shafts. Mini-keratomes have been specifically designed to create reproducible incisions of either 1 mm or 1.2 mm. Strategies to increase irrigation flow include bottle height extenders, use of an additional chamber maintainer and positive pressure pumps. Examples of the latter would be Agarwal’s modified air pump and the forced infusion provided by the Accurus (Alcon).
Like Drs. I. Howard Fine and Randy Olson, I have found that the Microsurgical Technologies (MST) 20-gauge Duet irrigating choppers provide the best inflow of comparable devices. The MST shaft design gives an impressive inflow rate of 40 cc/min at 30 in of bottle height and is available with an assortment of interchangeable chopper tips. I designed and use the MST Chang horizontal irrigating chopper tip, modeled after the original Chang horizontal microfinger chopper (Katena).
Cruise Control
Until now, there have not been any innovations for the aspiration side of the bimanual fluidic equation. To avoid surge and chamber instability, most bimanual surgeons have reduced their vacuum limits to the 100- to 200-mm Hg range.
In May, STAAR Surgical introduced its disposable Cruise Control device, which can be used with any phaco machine. After hearing Dr. Fine discuss this during the American Society of Cataract and Refractive Surgery meeting, I began working with this product when it became available.
While the Cruise Control does allow me to work at higher vacuum settings for standard coaxial phaco with the Sovereign machine (AMO), it was when I started using it for bimanual phaco that I realized that this is the definitive and ideal application for this product.
The Cruise Control is a disposable, flow-restricting (0.3-mm internal diameter) device that is placed in between the phaco handpiece and the aspiration tubing of any phaco machine. The goal is similar to that of the flare tip (Alcon): combining a standard phaco tip opening with a narrower shaft to provide more grip with less surge.
Vacuum settings
Remember that the aspiration vacuum setting determines the holding power of the phaco tip. If pieces keep falling off, then we need to raise the vacuum in order to increase our grip. Superior holding power provided by high vacuum increases our control for maneuvers such as chopping, separating partially cleaved segments and elevating quadrants and fragments out of the capsular fornices. However, post-occlusion surge limits how high we can safely set our vacuum limit. This is the excessive surge of outflow that occurs when the occlusion is broken at high vacuum levels. A sudden chamber collapse is dangerous and usually means that our vacuum setting is too high.
Equipment manufacturers have introduced many strategies to control surge and permit the use of higher vacuum settings. One such innovation was the flared phaco tip design. At a given vacuum setting of 300 mm Hg, for example, you can reduce surge by narrowing the shaft of the phaco needle, which restricts flow. However, this also reduces holding power, which at any given vacuum setting decreases as the area of the tip opening is reduced. As Dr. Barry Seibel likes to point out, this is true of both vacuum cleaner attachments (a smaller mouth means less holding force) and phaco tips.
The idea of the flare tip is to provide the holding power of a 19-gauge tip (a larger tip diameter and area mean greater holding power at a given vacuum setting, for example 300 mm Hg), with the surge protection of a narrower 20-gauge needle shaft. One inherent drawback with this funneled design is internal needle clogging. This is because brunescent nuclear material can become stuck at the site of the bottleneck within the needle. In addition, a flared needle tip is unsuitable for a micro phaco incision.
Within the Cruise Control device, the 2-cm long flow restrictor is placed behind a mesh filter that traps all of the nuclear emulsate. This prevents the narrow 0.3-mm lumen from becoming clogged like the bottleneck within a flare tip. However, like the flare tip design, this flow restrictor significantly reduces surge without reducing the diameter of the tip opening (thus maintaining the same holding power). In fact, the Cruise Control shaft is much narrower than a flared phaco tip shaft and provides far greater surge suppression.
The design of the Cruise Control also creates a non-linear flow limiter. This means that it has no effect on regular aspiration flow below 50 cc/min, but limits any unwanted flow surge above 60 cc/min. Indeed, surge can momentarily reach 300 cc/min when occlusion breaks from a 400-mm Hg vacuum level.
| Bimanual phaco instrumentation and settings |
| aMST Duet irrigating handpiece with Chang horizontal chopper tip (interchangeable tips) Sovereign with WhiteStar: 20-gauge phaco tip, 30-degree bevel |
Advantages
Bimanual phaco is the ideal application for the cruise control device because this is the one situation where current technology cannot give us high enough vacuum performance without surge. Surprisingly, I found that I was able to perform bimanual phaco on soft, medium and dense nuclei with an aspiration flow rate of 26 cc/min and a maximum vacuum setting of 400 mm Hg with very stable chambers in a series of 35 consecutive cases. I lower the vacuum to 200 mm Hg for the epinucleus. These are my same vacuum settings for coaxial phaco with the Sovereign machine using a 20-gauge phaco tip. Without the Cruise Control device, such high vacuum settings have not been safely attainable using the Sovereign machine for bimanual phaco.
I believe this will be a great advance for the field of bimanual phaco because the inability to use higher vacuum until now has been a significant disadvantage. Because of the larger handle and shaft, the tight incision and the tethering effect of the irrigation tubing, the irrigating chopper is much more difficult to manipulate than standard choppers. Thus, the high vacuum-aided ability to carry pieces into the center of the chamber with the phaco tip is a significant advantage because it reduces the maneuvers required of the chopper.
Because it is slower, I do not believe that bimanual phaco currently offers any major benefit to surgeons over coaxial phaco. However, we are all intrigued by the future possibilities and have been experimenting with new ways to improve this procedure. Thanks to the MST Duet irrigating handpieces on the inflow side and the Cruise Control flow restrictor on the aspiration side, I am delighted to report that the gap in fluidic performance between bimanual and coaxial phaco has now been considerably narrowed.
Schematic diagram of Cruise Control Flow Limiter and the STAAR Cruise Control flow limiter connected to the phaco handpiece. | ||
Bimanual phaco using Cruise Control, with overlay demonstrating 400-mm Hg vacuum. | Chang horizontal chopper tip for MST Duet bimanual set. | |
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For Your Information:
- David F. Chang, MD, a clinical professor at the University of California, San Francisco, and in private practice in Los Altos, CA, can be reached at 762 Altos Oaks Dr, Suite 1, Los Altos, CA 94024; (650) 948-9123; fax: (650) 948-0563; e-mail: dceye@earthlink.net. Dr. Chang is a consultant for Advanced Medical Optics. He has no financial interest in any products mentioned in this article.
- STAAR Surgical, manufacturer of the Cruise Control device, can be reached at 1911 Walker Ave, Monrovia, CA 91016; (626) 303-7902; fax: (626) 358-9187.