Historically, until the development of transversal movement of the phaco needle, we have had fluidics-driven phaco systems. Phaco systems that were limited to longitudinal movement of the phaco needle commonly became locked or “occluded” on a component of the cataract, which then caused a buildup in vacuum. When this was released with a break in occlusion, it caused chamber instability or “surge” and the potential for damages to the internal structures in the eye. Identifying this buildup of vacuum or “occlusion recognition” limited systems to peristaltic pumps and their ability to rapidly reverse the pump and lower stored energy in the tubing to minimize surge on occlusion breaks. Although this minimized surge, it also limited the overall efficiency of phaco by working at lower vacuum levels, delaying acquiring the next segment, and maximizing the repulsion effect associated with longitudinal phaco needle movement.
With the advent of blended phaco combining simultaneous transversal and longitudinal needle movement available with the ELLIPS FX (Abbott Medical Optics, AMO, Santa Ana, Calif.), everything has changed. Transversal phaco energy dispersion has two main advantages: It essentially eliminates high-grade occlusion events and repulsion of the nucleus. Therefore, today we don’t have to worry as much about surge and its potential consequences, so it releases surgeons to look beyond the limits of peristaltic fluidics. While the vast majority of surgeons in the U.S. currently use peristaltic, I believe that most phaco within the next 3-5 years will move to 100% venturi fluidics.
Currently, surgeons who use transversal phaco will need a system that will give them a choice in fluidics, either peristaltic or venturi, and the only commercially available system at present is the AMO Signature system with the dualpump technology. The dual-pump technology allows surgeons to use 100% peristaltic or 100% venturi or to shift on the fly.
There are advantages early in phaco to using peristaltic. Surgeons can very finely control the different components of peristaltic because they have vacuum, fluid flow, and rise time, the speed at which they start to build vacuum, which has value in the initial groove and chop with excellent stability when not a lot of material is removed from the eye and the nucleus is still intact. So surgeons may want to use peristaltic for the initial sculpting and removal of the cortical material along with “lollipoping” the nucleus to chop. Surgeons may even wish to use peristaltic with the removal of the first chop segment in order to draw it to the center.
Venturi fluidics has a great advantage in segment removal as it doesn’t require occlusion to generate vacuum so the holding ability is better at lower vacuum levels, and its ability to acquire new nuclear components is superior to that of peristaltic. Venturi will also “extend” surgeons’ reach in the eye, allowing them to spend more time in the center of the pupil and allow pieces to freely come to the tip of the phaco needle, reducing the potential for damage to the iris or capsular bag. A significant percentage of vitreoretinal surgeons likes venturi because of the consistent vacuum at low levels. Therefore, as soon as the segment is separated from its capsular attachment, converting over to venturi with the Signature system simply requires a side movement or yaw of the foot pedal because it’s a dual linear design. Converting to venturi allows the surgeon followability and improvement in terms of reacquiring segments, which is not characteristic of peristaltic. Peristaltic can slow the procedure down because once a segment is lost, the surgeon has to go and get it, reacquire it, and then
begin the phaco again. With venturi, followability is significantly enhanced, and surgeons’ ability to reacquire and access the next segment is improved. When venturi fluidics is optimally used, there is no other place for the segments to go but to the phaco needle. During the irrigation/aspiration phase, there is no comparison to venturi fluidics, which by extending surgeons’ reach and working at lower vacuum make this component of cataract removal more efficient and safer.
It is a tremendous advancement to have dual-pump technology because surgeons are finally able to blend the fluidics between peristaltic and venturi and do it on the fly. The system is designed to allow surgeons to automatically move between the two types of fluidics on demand when they want. Ultimately, most surgeons will probably see the advantages of venturi as their primary fluidics modality; however, there are certain cases where peristaltic will still have a role to play.
Dr. Nixon is senior staff ophthalmologist, Royal Victoria Hospital, Barrie, Ontario, Canada. He can be reached at 705-737-3737 or firstname.lastname@example.org.