Raviv T. Yan D., Top 10 questions in phaco fluidics. Ocular Surgery News Education Lab. Healio.com
1.How does a fluidics system impact the safety and efficacy of cataract surgery?
Fluidics is the main modality in phacoemulsification for controlling movement within the eye during cataract surgery. Vacuum generates the holding force to break apart the nucleus and flow rate brings the nucleus to the phaco tip. When a surgeon is working with an advanced fluidics system, he or she can achieve better outcomes more efficiently and reduce the risk for fluidics-related complications, such as rupture of the posterior capsule.
2.How does a peristaltic pump work?
A peristaltic pump’s primary function is to set a constant flow rate and maintain that flow rate until it reaches a preset vacuum limit. As it pumps fluid (usually with rollers), a peristaltic pump builds up vacuum only when the phaco tip becomes occluded. When the vacuum limit is reached, the rollers slow and the vacuum is maintained until emulsification, and then the process of occlusion and vacuum rise repeats. The peristaltic pump provides for good holdability and is advantageous for the chopping portion of the procedure.
3.How does a venturi pump work?
A venturi pump is vacuum based; it generates vacuum and pumps out air with a cassette. The phaco aspiration tubing is connected to a drainage cassette, and that is where the vacuum level is created. The venturi pump is able to create a preset vacuum level without occlusion of the phaco needle tip, and the outflow rate depends on the chosen vacuum level.
4.How does a dual-pump system work?
A dual-pump system features the ability to switch from a flow-based peristaltic pump to a vacuum-based venturi pump instantaneously in the same case during different steps of the phaco procedure. With this type of system, surgeons can instantly change pumps using a single machine, allowing them to customize their settings depending on which pump they prefer for each phase of surgery. Typically, surgeons prefer the peristaltic pump for nuclear disassembly (chopping, cracking) and the venturi pump for quadrant removal and irrigation and aspiration (I&A).
5.Which pump should I use when performing laser cataract surgery?
In femtosecond laser cataract surgery, the lens is prefragmented by the laser, which often allows the surgeon to proceed directly to quadrant removal. Although the peristaltic pump can be utilized, the tiny segments may occlude the tip and slow down the procedure. The venturi pump is preferable as its fluidics are better suited to draw in the small precut cubes without tip occlusion. Laser lens fragmentation allows for less ultrasound utilization with fluidics being the primary modality for lens removal.
6.Which cutting modality is most efficient—transversal or longitudinal?
Transversal mode produces a side-to-side motion, whereas longitudinal mode produces an in-and-out motion. Transversal movement tends to be more efficient because a left-to-right cutting action can “shave” apart the nucleus as opposed to fracturing the nucleus with longitudinal movement. It is comparable to thinly slicing a hard block of parmesan cheese with a cheese slicer (transversal cutting) versus cutting the block down the middle with a knife (longitudinal cutting).
7.What is the difference between holdability and followability?
Holdability describes the ability of the phaco tip to hold onto the lens and keep it stationary, which is advantageous when surgeons need to hold the lens in place for chopping.
Followability describes the ability of the phaco pump to continuously draw the lens fragments to the phaco tip as emulsification occurs. Followability is advantageous for surgeons because it allows them to use the fluid stream to draw in peripheral lens fragments.
8.What fluidics setting should I use for removal of a soft cataract?
For a dense cataract?
Either the venturi or peristaltic pump would be effective for removal of a soft nucleus. Surgeons prefer the venturi pump’s fluidics for removal of a soft lens. They can utilize a low vacuum rate of approximately 150 mm Hg and safely draw in the soft fragments without requiring occlusion, which may risk phacoemulsifying through a segment into a potential capsule. For dense cataracts, some surgeons find it is best to impale and chop with the peristaltic pump and then use the venturi pump to remove the segments.
9.What incision size and needle size should I use for the most efficient cataract surgery?
A 21-guage needle creates a smaller incision, while a 20-guage needle creates a slightly larger incision. A larger incision reduces clogging at the phaco tip and requires lower vacuum settings, which reduces the risk for post-occlusion surge. However, larger incisions tend to be less water-tight and can induce more astigmatism.
While incision and needle size largely depend on the surgeon’s preference, many surgeons have moved away from the “smaller is better” philosophy. The incision must be large enough to allow for a safe and efficient cataract surgery, including insertion of the IOL. The optimal incision size is usually between 2.2 mm to 2.4 mm. Some surgeons think that fluidics is compromised when the incision is less than 2.2 mm and that it is not worth the trade-off in efficiency and safety.
10. I am new to using a dual-pump system. How do I get started?
For surgeons who are accustomed to performing phaco with the peristaltic pump, it is best to gradually introduce them to the venturi pump. The surgeon should first try the venturi pump with irrigation and aspiration. As the surgeon becomes more comfortable with it, he or she can transition to epinucleus removal, and finally to the quadrant removal portion of the procedure. Chopping should still be performed with the peristaltic pump. Surgeons can divide the nucleus into the desired number of fragments within the capsular bag before removing the first segment. Then they can begin to pull the first segment out of the bag with the high holdability of the peristaltic pump. Once it has reached the iris plane, they can switch to the venturi pump to efficiently remove all of the segments with high followability.
David B. Yan, MD, FACS
- Assistant Professor
Department of Ophthalmology and
University of Toronto
Tal Raviv, MD
- Founder and Medical Director
Eye Center of New York
Clinical Associate Professor of Ophthalmology
New York Eye and Ear Infirmary
New York Medical College