Venturing Into Venturi

Just over a decade ago, most cataract surgeons operated entirely with manual incisions, and a large proportion of them would have performed phacoemulsification with a balanced salt solution (BSS) irrigation and aspiration using a peristaltic pump controlled with a foot pedal. Today, for many, it’s a different story. If a femtosecond laser is used, it can not only perform the rhexis, but also pre-fracture the clouded lens, making it far easier to aspirate the lens fragments. Often, only minimal phaco power is required. As surgical technology evolves, so do our techniques. I converted to femtosecond laser-assisted cataract surgery, and by combining it with a Venturi pump for lens removal, I’ve found a successful method that I now employ in all of my cataract surgery cases.

Back to basics

Let’s go back to basics in terms of fluidics and vacuum in phaco systems. In order to aspirate lens fragments, you need two things: BSS irrigation and vacuum for aspiration. Peristaltic pumps are flow-based – they use rollers to compress the phaco outflow tubing, creating flow and vacuum. You can set the parameters beforehand, but you only get the maximal preset vacuum when the phaco needle tip is occluded with cataract material. Tip occlusion doesn’t result in immediate vacuum generation, either. Rather, the vacuum builds relatively slowly, the peristaltic pump rollers slow, and the outflow level decreases. It’s a nice, conservative way of aspirating the lens fragments, but it’s not the fastest method out there. That title belongs to vacuum-based pumps such as Venturi or mechanical ones based on a rotary vane or diaphragm-based design. Venturi pumps exploit the Venturi effect, where a vacuum is generated by forcing pressurized air over an opening; mechanical pumps utilize either the rotary vane or diaphragm type. These configurations all operate in the same manner – the vacuum is stored in a reservoir, which can be utilized almost instantaneously by the surgeon, under the control of a foot pedal – irrespective of whether or not the phaco tip is occluded. It’s therefore faster, and vacuum, irrespective of occlusion, means that you’re far less likely to need to chase lens fragments – more often than not, they come to you. Pairing a Venturi pump with a femtosecond laser that can perform lens fragmentation can make for a fast and effective method of phacoemulsification that requires minimal phaco (ultrasound) energy, minimizing the potential for corneal endothelial damage.

My own conversion

If you’re accustomed to using peristaltic aspiration in your practice, switching to Venturi will take some adjustment. Anticipating my own conversion to laser cataract surgery, I began using AMO’s WHITESTAR Signature System for my manual procedures about four months before I transitioned to femtosecond laser-assisted surgery, as it allowed me to switch between peristaltic and Venturi aspiration modes. At first, I only used the peristaltic pump mode, which I set to the familiar parameters I was already using for my quick chop technique. After I was comfortable with the machine’s peristaltic function, I started trying the Venturi pump mode, still using the same phaco tip, sleeve and vacuum power that I was accustomed to in peristaltic mode. This let me determine the differences between the two pump modes with respect to lens removal and vacuum function. I quickly discovered it isn’t phaco tip occlusion that the Venturi pump mode depends on – it’s the surgeon controlling the foot pedal. Once the tip was in place, holdability was totally under my control without the limitations of peristaltic presets. I have over 25 years of experience using a peristaltic pump, but that was a new twist for me.

When I first began femtosecond laser procedures in cataract surgery, I tried using my quick chop technique to impale and split the lens, with the pump in peristaltic mode. But because the lens was no longer the same solid consistency, I had trouble gaining purchase on it. Even if you deeply sculpt the lens, it’s still difficult to divide; you’re pushing on the wall of the central sculpted area, but the fragmented lens doesn’t offer the same level of resistance. That’s what led me to develop my Femto Chop technique. Knowing how important it was to pre-chop the lens – especially for freeing and removing the first quadrant – I found that the Venturi mode was more effective than the peristaltic mode for aspirating the cataract.

Scott Femto Chop

Today, I do all of my cataract surgeries with the femtosecond laser, and I’ve had the opportunity to perform around 3,000 such procedures. Over time, I’ve developed what I believe is a highly efficient chop technique that exploits the benefits of femtosecond laser treatment and takes advantage of maximal Venturi vacuum to minimize the need for ultrasound energy.

To begin, I use the Catalys (AMO) femtosecond laser system to perform a 4.9 mm capsulotomy using customized settings, which results in a treatment time of less than one second. The speed of treatment helps minimize the potential effect of patient eye movement. By placing pressure on the center of the capsule (the “dimple-down” technique), I can confirm that the capsule is completely cut.

In a temporal approach, the Scott Femto Chop (Duckworth and Kent, Baldock, UK) or a Koch Chop is placed nasally in the segmentation line and a Bechert nucleus rotator is placed temporally just inside the capsulotomy border. I bring them toward the center of the lens. When they meet in the middle, I use both instruments to apply lateral force, moving them away from each other until the nucleus splits in two. Then I can split the lens into quarters.

Next, I insert the phaco tip and then reinsert the chop through the paracentesis. High Venturi vacuum and the chop help me to move each quadrant centrally towards the phaco tip, so that I can aspirate the cataract. As each quadrant is aspirated, the remaining lens acts as a safety barrier to separate the tip from the posterior capsule. If it becomes necessary, I might reduce vacuum and use 1 percent phaco energy on the last quadrant – but about 80 percent of cases use zero phaco energy. I use the technique I’ve just described for most of my cases, but I do have other methods for soft or very dense cataracts.

After removing the cataract, I use a “Venturi sweep” technique to aspirate the cortex. Starting subincisionally, I place the port slightly posterior to the capsulotomy border, facing the femto-cut cortex. Once the aspiration port engages the cortex, it is “swept,” or moved circumferentially, along the capsulotomy border, removing the subincisional cortex. Then I rotate the port so that it’s facing up and slightly forward, continuing the sweep and removal of the remaining cortex.

It’s particularly noteworthy that my technique doesn’t include hydrodissection. Once the lens has been fractured – by the chop technique and by pneumodissection from the secondary gas created by the femto treatment – the interface between it and the cortex is disrupted, rendering hydrodissection unnecessary.

Femtosecond laser-assisted methods will continue to evolve. The key step to zero phaco is splitting the lens into two or more pieces before attempting to remove it. Femtosecond technology allows us to provide effective treatment of both routine and complex cases, and it gives us excellent and consistent outcomes. If we also take advantage of Venturi vacuum technology, we can speed up the aspiration process to really capitalize on the advantages provided by the laser’s fragmentation capabilities. In fact, femtosecond lens treatment and Venturi vacuum complement each other so well that I would say they were made for each other.

Wendell J. Scott is a partner at Mercy Eye Specialists, and is associated with the Mercy Medical Research Institute in Springfield, MO, USA.