Eyeworld

Breaking down peristaltic vs. venturi Bearing in mind the differences and synergism between flow and vacuum, peristaltic and venturi pumps are just different styles of pump. The peristaltic pump is generally considered to be safer because the nature of the pump dictates that flow and vacuum are separate param- eters—they are measured separately and can be con- trolled separately. Flow occurs when the needle is unocclud- ed; vacuum occurs when the needle is occluded and there is resistance to flow. Meanwhile, with the venturi pump, the vacuum is always active; it is the param- eter that you control with your foot pedal. The pull on the fluid is the same whether the needle is occluded or whether flow is occurring. While flow is a con- sequence of using the venturi vacuum, there is no way of measuring flow when using a venturi pump. So which is better? They are both good for different situations during surgery. At occlusion, the vacu- um created by each system is the same—the vacuum force created at the tip of the needle during occlusion is the same whether it is created by a peristaltic or venturi pump. The difference is in how flow is generated (venturi) versus how flow is measured (peristaltic). With the flow generated using the venturi pump, the only flow regulation is mechanical—i.e., the lumen size of the needle. The peristaltic pump, on the other hand, regulates the flow directly. However, the venturi pump is generally regarded as more efficient as it creates more attraction—higher flow—at low levels of vacuum. The creation of this vacuum is furthermore not dependent on the state of occlusion. This style of pump is therefore efficient for any size material, and is exceptionally efficient for material that cannot form an occlusion—wispy cor- tex and viscoelastic. Still, the peristaltic pump has the advantage over ven- turi in terms of emulsification. When the needle is occluded, whether partially or completely, the hold of the vacuum estab- lishes the transfer of power from the needle to the material. Now, as power is applied, material is removed and the occlusion is broken. Flow then reattracts the material to rees- tablish occlusion while vacuum holds the material to subject it to the forces of power. The Signature Pro (Abbott Medical Optics, Abbott Park, Illinois) has both vacuum sys- tems available for on-demand, middle-of-the-case switching. This allows surgeons to opti- mize their surgery by making use of each system's advan- tages over the other whenever appropriate. Dealing with occlusion break surge In addition to having two styles of pump in one system, the Signature Pro has automatic occlusion sensing technology. When complete occlusion takes place with a dense frag- ment, flow stops and vacuum builds—this is the system working to restore flow. With vacuum at its highest level, the occlusion breaks and flow is immediately restored. Given the tiny volume of the anterior chamber, at the point of an occlusion break, the chamber evacuates, creating a post-occlusion surge. This is a bigger problem for the venturi vacuum, in which the blunting of the surge is dependent on reaction time and the speed of the surgeon's foot on the pedal. On the other hand, because the peristaltic pump allows measurement of flow, the reduction of flow is de- tected and the vacuum reduced appropriately. The Signature Pro's automatic occlusion sens- ing technology replaces the surgeon's reaction time and foot speed with the speed of a modern computer. The system automatically cuts the vacuum, resulting in a significantly less precipitous drop in intraocu- lar pressure, from a drop of around 60 mm Hg without the automatic sensing technology to a drop of just around 25 mm Hg. This essentially reduces post-occlusion surge to zero. CASA After examining our assump- tions, setting aside ego and given a thorough understand- ing of flow and vacuum, how then do we proceed to advance our surgery? We always want to move our surgery forward and take it to the next step, but how do we do that? In order to do better with our surgery, we have to be able to measure something, then we have to monitor what we are measuring; we have to have a basis for comparison. For years the only option was to keep a paper log and digital video recordings of all your cases. All the information gathered would then have to be converted, tabulated, and encoded into a spreadsheet—a cumbersome process to say the least. Now, with the Signature Pro, we have the Cataract Analysis and Settings App (CASA), the first mobile analytics tool in phaco. CASA wirelessly connects to your Apple operating system device and allows you to download all the performance metrics and parameters you could want or need to analyze your surgical performance, including phaco time, case time, and turnover time. With all the metrics the app allows you to analyze, in addition to the performance of the surgery, you can also measure the efficiency of the system and workflow in place in your surgery center. It is a fantastic tool for keeping track of what you are actually doing as opposed to what you only think you are doing. When something hap- pens during surgery, emotions can dictate what you think just happened, and it is only when you review the video—which you can watch in slow motion— that you can see what actually happened, what you actually did, and how you can do better. This should become an essential part of the cataract surgeon's evolution. Sponsored by Abbott Medical Optics 5

• Cover