Choosing the Right Gauge
Learn more about the use of varying instrument sizes in vitreoretinal surgery.
Dr. Chang: Let's move on to micro-incision surgery in 23-gauge and 25-gauge. What is the percentage breakdown in your cases between 23-gauge and 25-gauge?
Dr. Corcostegui: I use 25-gauge in very few cases. I perform about 50% of my cases with 23-gauge. For the other 50% of my cases, I use 20-gauge because I inject silicone oil. These are proliferative vitreoretinopathy (PVR) cases, very difficult diabetic retinopathy cases.1,2 I still use 20-gauge because it makes removing silicone oil easier. Injecting silicone oil is very difficult when using 23-gauge.
Dr. Packo: A couple of weeks ago, I sutured a 20-gauge cannula to the eye and I thought: "I wonder if I remember how to do this?" I still use 20-gauge, as you said, Dr. Corcostegui, in very difficult PVR cases, because I prefer to have the ability to work in the vitreous base in that way. But I have made this transition, as many surgeons have done. I started out using 25-gauge heavily, and then I realized that, with proper wound construction, you can close a 23-gauge wound as well as, if not better than, a 25-gauge wound.3
When comparing metal cannula vs. our current polyamide cannulas with 25-gauge, I find the 23-gauge closes beautifully now. I use 23-gauge for most of the cases I perform. For a simple macular pucker, I am still comfortable using 25-gauge, just like you said, taking advantage of a smaller hole. Why not make a smaller hole? That is why I am anxious to try the new 25+ gauge instrumentation, too, because it adds that level of comfort back that the 23-gauge gave us. But 23-gauge is primarily what I use now.
Dr. Charles: I use 25-gauge for all cases, with two exceptions: I enlarge one wound for the 20-gauge fragmenter when there is a dislocated nucleus after I have completed the vitrectomy with 25-gauge, and I enlarge one wound for intraocular foreign body forceps because foreign bodies do not come in 25-gauge. They are always bigger than that. Silicone oil removal, as well as injection, works very well with a 25-gauge system, and we have evolved techniques to do that nicely, so I use it for all cases.
Professor Tano: I started out using 25-gauge, but I am mainly using 23-gauge now.4 In some cases, I use 27-gauge, which facilitates non-vitrectomizing vitreous surgery.5
|The ideal transition from traditional 20-gauge vitrectomy to micro-incisional vitrectomy would be to start with macular epiretinal membrane or macular hole cases, particularly in pseudophakic eyes.|
— Harry Flynn, MD
Dr. Williams: Like the others, I am very much case-dependent. So, if it is a straightforward pucker or a macular hole, I am very comfortable using 25-gauge. I like the 25-gauge forceps that are available now. For more advanced cases, in which I need to get out to the periphery, I typically go with 23-gauge. Then, for the very difficult cases, including trauma or severe PVR, I fall back on 20-gauge. I cannot say exactly what percentages of my cases are being done with 23-gauge or 25-gauge. It sort of depends on what shows up on my doorstep that day. The nurses know not to pull any particular gauge until I have told them what I want to do in each case.
Dr. Flynn: We all like the new micro-incisional instrumentation, but we also want the best outcomes for our patients. Our patients certainly are more comfortable and the procedures take less time, in my opinion, with micro-incision surgery.
About 4 years ago, I made the transition to 25-gauge surgery, but we had limited forceps and other ancillary 25-gauge equipment. We became more comfortable with 25-gauge surgery as the disposable line of forceps, DSP, became available.
When I made the transition to 23-gauge surgery in 2007, all of the ancillary 23-gauge instruments were available.
The ideal transition from traditional 20-gauge vitrectomy to micro-incisional vitrectomy would be to start with macular epiretinal membrane or macular hole cases, particularly in pseudophakic eyes. With 23-gauge surgery, we have outstanding ancillary equipment that allows a one-step incision entry, reducing the risk of inadvertent contact with the crystalline lens. Early on with 25-gauge, we had a two-step approach. With the new 23-gauge trocar and cannular system, the entry system is excellent and we are all very comfortable with the current ancillaries.
Dr. McCuen: Well, I agree that the selection of the instrumentation system is very case dependent. I started with 25-gauge but rapidly moved to 23-gauge when it became available because of the advantages it offered. Although I still use 20-gauge for a number of cases, I have come to realize that the ancillary equipment allows approaches such as bi-manual surgery, increasing my use of 23-gauge. But for the most complex cases, I still rely on 20-gauge. However, that is changing and is likely to continue to evolve, especially as 23-gauge becomes more similar to 20-gauge surgery in terms of the ancillary equipment.
Dr. Chang: I have changed many of my 20-gauge cases to 23-gauge because the cutter is so much better — the port is closer to the tip and the cutting speed is higher. RP
|Managing Intraocular Pressures|
|Dr. Chang: We've transitioned from a manual gravity infusion system to an automated IV pole used by the previous machines. Now most of us use Vented Gas Forced Infusion (VGFI) to maintain stable IOP. One of the technological advancements in the Constellation Vision System will be integrated pressurized infusion, IOP control and the infusion flow limit function. Could the panel discuss the benefits and suggest how this might change the way we operate?|
Dr. Packo: In the Practices and Trends (PAT) survey of the American Society of Retinal Specialists, we asked the same question a few times: At what pressure do surgeons like to operate? The most common answer was the 35 mmHg to 40 mmHg range. Most surgeons are picking higher than normal IOPs at which to operate. We have moved to these levels gradually, not knowing what was really happening because the eye would get too soft and we would see corneal striae and possibly more bleeding if we were operating at a low pressure.
The problem was that when you hit the pedal, the pressure was not 35 mmHg. We have never measured it before or paid attention to it, but when you hit the pedal during conventional surgery, the pressure drops significantly. With a 20-gauge system, even though the VGFI is set at 35 mmHg, you could be down to a pressure of 15 mmHg in the eye, or even lower. This is where the IOP control is going to help. It will respond faster than we can to the low pressure.
Now when we hit the pedal, the pressure will stay where we want it. I think we will experiment. I think we will learn that by backing off to a lower pressure, we can keep the level closer to what is meant for the human eye, at around 20 mmHg, and still get the job done without the eye becoming too soft as we operate.
Dr. Charles: I think Dr. Packo's points are excellent, but I would like to add to them. Simplistically, people tend to think that the VGFI represents IOP. It only does if there is no flow. It represents the infusion pressure, the force that drives the flow down this restricted line. What matters is the IOP, not the infusion level. Because this machine can now calculate Ohm's law on the fly by measuring flow and recording resistance, it can calculate the losses in the line and compensate for them. That's how the Constellation controls IOP.
Dr. Chang: Knowing the pressure in the eye is very important. Even with settings of 25 mmHg on the Accurus, I have seen the central retinal artery pulsate. To me, this indicates that you have to keep aspirating at the same time that the flow is coming in.