Cataract Surgery Is Rush Hour

Performing cataract surgery – particularly in dense cataracts – is a bit like being Jackie Chan in his highest-grossing Hollywood movie, Rush Hour. Alongside having to fight the Triad leader’s henchmen on his own, Chan has to make sure he doesn’t damage the priceless Ming vase he’s just saved from crashing to the floor. Although we surgeons aren’t involved in armed combat, we do adopt similar tactics to Chan – staying acutely aware of the dangers that surround us, prepared to respond to any threat within milliseconds, and handling priceless objects with the utmost care.

Training to take the pressure
 

Just like Chan, to achieve excellence, we have to train for years. Just like Chan, we need to practice our skills almost daily to stay at the highest level of our game. But while Chan employs the empty hand, the clenched fist, and a swift hip movement to deliver a roundhouse kick to a henchman’s torso, we surgeons battle cataracts with a steady hand and phacoemulsification machine: a highly sophisticated instrument that enables us to do what we do, day-in, day-out, safely and effectively.

Like Chan, we cataract surgeons are usually under a lot of pressure. Long to-do lists mean that efficiency is a priority during surgery – without which a patient’s vision may be at stake. Although “quick” and “excellent” are not adjectives often used in conjunction, for a cataract surgeon, they are the key to successful outcomes.

The perils of phacoemulsification
 

When fighting at the edge of a rooftop, if Chan misjudges a punch and misses the target – or even if he kicks the enemy too hard – the momentum could propel him over the edge. Here, his skill is finessed aggression, where there is a fine line to walk between success and disaster. I view phacoemulsification in much the same way. Although we need to liquefy the lens with ultrasound energy from the phaco tip as quickly and efficiently as possible, we don’t want to deliver too much, as this can cause excessive damage to the corneal endothelium as well as causing “shattering” – where the lens fragment “explodes” into many small pieces – each of which needs to be found and removed with care. This is a slow process, but if we miss any of them, we risk focal inflammation, corneal edema, and raised intraocular pressure (IOP).

The lens fragments are removed through aspiration, but this also removes fluid from the anterior chamber, depressurizing the eye, something that can have disastrous consequences. Our partner here isn’t Chris Tucker, it’s the phaco machine’s fluidics system, which tries to keep the IOP constant by adding fluid into the anterior chamber as lens fragments and fluid is being aspirated away.

Fluidics first
 

Similar to racing drivers boring people with talk about tire compounds, cataract surgeons are mostly occupied with talk of fluidics. Although not as fun as Chris Tucker in the late nineties, keeping IOP within the right range is essential, and a process that has evolved over the years.

Traditionally, we exploited gravity: raise a bag of balanced salt solution (BSS) in the air, and the height determines the pressure inside of the eye. Simple and easy, but not nearly as responsive as it could be. The Alcon Centurion machine took a different approach called “Active Fluidics” – in short, place the BSS in a flexible bag that is acted upon by plates inside the machine to vary the pressure on the BSS – and therefore the eye – to the appropriate level at each step of the surgery. The Alcon Infiniti system has a peristaltic pump, the Bausch + Lomb Stellaris has a Venturi pump, and the Johnson & Johnson Signature has both Venturi and peristaltic pumps to achieve this (see Table 1). There has been considerable debate regarding which fluidics approach, Venturi or peristaltic, is better. The consensus is that Venturi pumps are faster and more efficient, but peristaltic pumps are safer and more stable – we’re almost back to the battle between “quick” and “better” – but in practice, the reality is far more complicated than that. The most recent approach to fluidics is taken by the Zeiss QUATERA 700 system, which uses symmetric pumps. The QUATERA 700 can constantly measure infusion and aspiration volumes (including leakage through the corneal incisions) in real time –  a very precise way of maintaining IOP.

Fast feet
 

One – if not the largest – aspect of being as efficient and excellent as possible during cataract surgery is how familiar and comfortable the surgeon is with the phacoemulsification machine. Why? Most of it comes down to how the phaco machine handles occlusion breaks. We’ve all been there: there is a fragment of the nucleus in front of the phaco tip, you’re deploying phaco energy to liquefy the fragment, and you’re aspirating to remove the debris. But while the phaco tip is occluded, a vacuum builds up in the tip and the tubing, and if there’s a large pressure difference once the tip clears, ocular fluid can rush in, causing IOP to drop – and with it – a shallowing of the anterior chamber. Further, the iris, or even the posterior capsule, can vault towards the phaco tip, both of which can become damaged if they come into close proximity or contact with the tip. To counter this effect, you tend to lift your foot from the foot pedal as you get close to the point of occlusion break to reduce the amount of vacuum applied, thus minimizing the effect of the occlusion break when it inevitably happens.

Although this caution is completely warranted, if you are too cautious and reduce the vacuum too much, you lose the piece from the tip – and it floats away. You have to go and grab it back again, slowing the process down, and this can happen time after time during the procedure – especially when you’re at the start of the cataract surgery learning curve. Suddenly, we’re Jackie Chan, fighting on the rooftop again. However, if you feel comfortable that you won’t have a big surge after the occlusion break, you don’t feel that urge to back off and, subsequently, don’t need to have your foot always at the limit, ready to drop the vacuum as fast as your foot-eye coordination permits.

A large market
 

Clearly, the dynamics of these fluidics systems play an important role in cataract surgery. And so it’s interesting to see how manufacturers take different engineering approaches – both to make their fluidics systems work (see Table 1) and to handle the rapid pressure changes during occlusion breaks, which really determines how comfortable a surgeon is using a given system.

Throughout my career as a cataract surgeon, I have used several phacoemulsification machines. I started my training with the AMO (now Johnson & Johnson) Signature system, and since then, I have used the Alcon Infiniti and Centurion platforms, as well as the Bausch + Lomb Stellaris, and, most recently, I have used the Zeiss QUATERA 700 system. I would like to share my experiences with you.

Take your pick
 

I want to stress that all of them are perfectly fine instruments – all have pros and cons. I tend to use Signature with its peristaltic pump-based fluidics, but this system feels like it is slow to build vacuum to perform aspiration, and is slower to move things around inside than platforms like Infiniti and Stellaris, which use peristaltic and Venturi pump, respectively. Though ultra-rapid vacuum generation might cause anterior chamber instability when my phaco tip is unoccluded, fast vacuum generation is great for when I want to grab the nucleus, cut it, rotate it, and then grab it again. In general terms, I feel that the Centurion keeps IOP more stable than the Stellaris. Although I have had limited experience with the system to date, the Zeiss QUATERA 700 system (with its real-time volume measurement symmetric pump fluidics concept) worked well. Alongside stabilizing IOP, the system also removes surge from the procedure (and some of the drama) and alleviates the need for fast foot action on the foot pedal.

The trade-off here is once again between speed and stability – and it can take quite a while for each surgeon to optimize the settings for their own preferences and safety margins.

Ultrasound deployment
 

If the surgeon is comfortable that the anterior chamber will remain stable throughout phacoemulsification, the next consideration is the efficacy of the ultrasound energy delivery from the phaco tip. Low energy delivery simply makes it slower and harder to liquefy the lens and leads to longer phacoemulsification times. Too much energy risks damaging several ocular structures, most notably the corneal endothelium. This issue is most apparent in dense cataracts; trying to liquefy very hard nuclei fragments can require the delivery of a great deal of ultrasound energy into the anterior chamber. Inevitably, this extra energy leads to more corneal edema the next day. If we are to stick with our Rush Hour analogy (and why not?), the equivalent action scene would be when, after all Chan’s remarkable efforts, someone destroys the Ming vase anyway.

Ultrasound energy has historically been delivered to the tip by longitudinal motion – back and forth (like a chain punch in Kung Fu). This however, can cause problems with followability, as the energy is pushing fragments away. On the other hand, longitudinal energy delivery is great for chopping up the nucleus. Some manufacturers have developed phaco tips that can also deliver ultrasound energy through lateral motion (for example, Alcon’s OZil torsional handpieces on Infiniti). This is less efficient at chopping but makes for far better followability – and switching between the two helps you to optimize the ultrasound energy delivered. The Signature system comes with “Ellips Transversional Ultrasound,” where the phaco tip applies the ultrasound energy through an ellipsoid motion, again reducing the repelling forces generated with longitudinal tip motion, and increasing followability. The Zeiss QUATERA 700 system uses traditional longitudinal phaco tips; but takes a different approach to optimizing the ultrasound delivery. It exploits its sophisticated fluidics system to give users a “Power on Demand” setting, which only allows ultrasound delivery when the tip is occluded, minimizing the energy delivered into the eye. I have found that this helps with followability and decreased shattering – and, from an ergonomic perspective, it means I don’t have to move my foot to stop the ultrasound deployment.

You may be thinking, in light of all of these concepts, what does this mean for me, day to day? With Stellaris, I am usually very fast, but sometimes when I am struggling with a dense nucleus, shattering occurs. With Centurion, because I can change the movements by which the ultrasound energy is delivered through the phaco tip, I tend to deliver less ultrasound energy than with Stellaris – and through experience – I am able to minimize the amount of shattering, although this is never eliminated. With the QUATERA 700, I am stable and fast, exercise good energy deployment, and don’t experience much shattering at all.

Experience counts – until now?
 

Ultimately, though, what has counted most for me in the past is the amount of experience I have had with an instrument. Despite what I wrote earlier about the trade-off between peristaltic and Venturi pumps, I find myself to be more efficient with the Infiniti system’s peristaltic pump, compared with either the Signature’s peristaltic pump or the Stellaris’ Venturi pump. Why? I have no doubt that it is because the Infiniti is the machine that I have the most experience with. Put another way, I have had the time to optimize it to match my style of surgery. (I am sure Jackie Chan would prefer sparring with a trusted and long-time partner rather than a new kid on the block.)

I mostly work with the Centurion today: it is a stable, fast, and efficient machine, but I still feel like I’m learning to optimize it – mainly the deployment of ultrasound. What most impressed me about QUATERA 700 is how easy it was to change the fluidics and ultrasound parameters to suit my style – and I felt I was highly efficient after just a few surgeries – being comfortable with the fluidics, attractability, holdability, and the ultrasound delivery.

Many other elements are important for efficient and excellent cataract surgery, such as how the information from the biometers and imaging are integrated together – even down to the image overlays on the surgical microscope. These all help make the surgeon’s life easier, eliminate mistakes like transcription errors, and deliver excellence – day-in, day-out. Each system has its pros and cons, its idiosyncrasies, and its learning curves. But with every new generation of instruments, the cons become smaller, the oddities become less… odd, and the learning curve gets a little shorter and straighter.

It is heartening to see the continued, iterative advances made to this crucial technology, but when you put all of these relatively marginal gains together, I think it adds up to a real difference. As Jackie Chan gets older, doing what he does is not going to get any easier. With phacoemulsification, at least, it will be interesting to see how technological advances close the distance between “quick” and “better.”