Carl Awh, MD: Human Experience of Hypersonic Vitrectomy

Carl Awh, MD, Tennessee Retina:

Hypersonic vitrectomy is a new technology that uses ultrasound to drive the vitrectomy probe. So unlike the traditional pneumatic guillotine type cutter, where you have a tube within a tube moving up and down, this uses a single tube with a small port in the end of it, and the tube is oscillating at around 1.7 million cycles per minute, so for a very effective fast cut rate. And what we're seeing with this technology is that at the tip of the device we're sort of almost liquefying the vitreous.

There have been electron microscopy studies that show that the collagen fibers that we normally see in vitreous are just pulverized, they're tiny little dots after they pass through this, so we call this effect hypersonic liquefaction. And it appears to occur right at the outer borders of the port, that's also interesting because it means we're not really pulling the vitreous into the port to cut it off, like a guillotine type cutter has to do, but it happens at the surface of the port so maybe that results in less traction than with a traditional cutter.

We're able to move the port to different parts of the probe tip so that's going to free us up for other sorts of designs in the future, we've even experimented with some curved probes, however, the only surgeries done so far have been with a straight probe.

Something very different about this, is that the parameters that we adjust to affect how the probe performs are very different. So traditionally we vary infusion pressure, vacuum and cut rate, that indirectly also affects duty cycle. These are things that all retina specialists understand affect how our cutter works, but with the hypersonic vitrector, we vary stroke — and stroke is the distance that the tip is oscillating. So it's oscillating at anywhere from 0 to 60 microns, so a really tiny movement. It's really not perceptible when you look at it under the microscope, the tip doesn't look like anything's happening, it's just that when you're activating it, suddenly it's liquefying or cutting tissue at the port.

And we're seeing that our ability to influence flow is really very powerfully affected by stroke. So if at very low settings of stroke, we can have extremely low, predictable flow, but at high settings of stroke we actually have higher flow than with a pneumatic cutter. So this really expands the the range of this cutter, and may allow us to do some things differently. Right now we're not trying to do much differently, we're just trying to see if we can use this device safely, in the way that we're used to, and that's our initial human experience.