Hypersonic vitrectomy: Exploring novel way of vitreous removal

Hypersonic vitrectomy is a new method of removing the vitreous in which ultrasonic power is used to actuate the vitrectomy probe. 

This article was reviewed by Carl C. Awh, MD 

Hypersonic vitrectomy is a new method of removing the vitreous in which ultrasonic power is used to actuate the vitrectomy probe.

Thus far, this technology has been used in more than 200 cases performed by 17 surgeons to treat myriad vitreoretinal pathologies, according to Carl C. Awh, MD.

He highlighted cases in which a 23-gauge hypersonic vitrectomy probe was able to quickly remove thick, chronic vitreous hemorrhage resulting from proliferative diabetic retinopathy; to fragment and remove an entire dislocated dense nucleus; and to aspirate 1,000 centistoke silicone oil from the vitreous cavity. This display may raise the question about whether it is now time to replace the tried-and-true guillotine cutter.

Related: 'Hypersonic' vitrectomy overcomes flaws of traditional systems 

Though hypersonic vitrectomy has proven to be excellent in most situations and has expanded capabilities-such as the ability to perform lensectomy and remove silicone oil-it is not always the equal of current guillotine cutters, said Dr. Awh, president of Tennessee Retina, Nashville, TN.

“I find that, in some cases, it does not work as well as my guillotine cutter,” said Dr. Awh, noting that the device sometimes seems to have suboptimal cutting power.

As an example, he described a phenomenon of what he calls “stranding,” when strands of native collagen are revealed during hypersonic vitrectomy. These strands are eventually severed by the hypersonic vitrectomy probe. There seems to be no peripheral traction created and no iatrogenic breaks created, but the appearance of the strands is disconcerting, he noted. Dr. Awh said he would prefer that the hypersonic cutter cut them more effectively.

Similarly, he has observed that while the hypersonic probe can cut fibrovascular membranes, it does not always accomplish this task as efficiently as a guillotine cutter. Despite these reservations, Dr. Awh predicts significant improvements in the performance of hypersonic vitrectomy.

Related: Vitreous history in the making 
Fluidics of vitrectomy
Dr. Awh discussed recent observations about the fluidics of vitrectomy. Ultra-high-speed video demonstrates that even a hypersonic vitrectomy probe with a constantly open port does not have completely uninterrupted inflow.

Although there is net inflow, longitudinal oscillations of the probe and the inertial lag of the fluid column within the lumen of the probe result in the egress of a tiny amount of fluid during the “upstroke” of the hypersonic probe.

This effect is best visualized in a fluid medium and when no active vacuum is being applied. This effect is not visible during vitrectomy due to the dampening effect of vitreous and to the net ingress of vitreous and fluid when active vacuum is applied.

Related: Vitrectomy for floaters can be safe, effective 

However, this effect is one of the main reasons that ultra-high-speed video demonstrates turbulence at the tip of the probe. This turbulence is present with all types of vitrectomy cutters and is greater with guillotine cutters.

With the hypersonic vitrectomy probe, a reduction in gauge size and changes in port geometry can reduce turbulence, which should result in cutters with more predictable and stable fluidics.

Handpiece modifications
Cases performed to date with hypersonic vitrectomy have been with a device operating at a frequency of 31 kHz, or 1.8 million “cuts” per minute, he noted. The next-generation device will operate at frequencies up to 41 kHz with an increase to 2.5 million cuts per minute.

The increased frequency will result in increased flow, but Dr. Awh points out that this will not be the most valuable difference. 

Related: Comprehension of vitrectomy fluidics underlies safe and effective surgery

“Shear stress, that is, cutting power, increases in a quadratic relationship to frequency, such that increased frequency equals increased cutting power and increased flow,” he said. 

The downside to taking two steps forward is the one step back due to increased turbulence that may result from increased frequency.

To address this concern, the next-generation device will incorporate adaptive frequency control to adjust the frequency instantaneously in response to changes in tissue behavior.

“Hypersonic vitrectomy has the potential to provide performance superior to current state-of-the-art guillotine vitrectomy cutters,” Dr. Awh concluded.

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Carl C. Awh, MD
E: carlawh@gmail.com
Dr. Awh is a consultant to Bausch + Lomb.