‘Hypersonic’ vitrectomy overcomes flaws of traditional systems

March 12, 2018

Using ultrasonic power to actuate a vitrectomy probe (hypersonic vitrectomy) allows for a “smooth steady flow of vitreous into a port that is oscillating at 1.7 million cycles per minute,” according to Carl C. Awh, MD.

Reviewed by Carl C. Awh, MD

Using ultrasonic power to actuate a vitrectomy probe (hypersonic vitrectomy) allows for a “smooth steady flow of vitreous into a port that is oscillating at 1.7 million cycles per minute,” said Carl C. Awh, MD.

This effect termed “hypersonic liquefaction” (Vitesse, Bausch & Lomb) may provide numerous advantages over conventional guillotine vitrectomy cutters because of fundamental differences in the mechanics of the devices, Dr. Awh said. The ever-increasing cut rates of guillotine vitrectomy cutters have improved flow by decreasing the viscosity of aspirated vitreous, but further improvements will be limited by constraints of cut rate and duty cycle.1

The hypersonic vitrectomy probe does not “cut” vitreous or tissue in a conventional manner. Instead, the device virtually liquefies tissue as it enters a port oscillating at 1.7 million cycles per minute.

Dr. Awh, of Tennessee Retina, Nashville, TN, said the liquefaction “occurs at the outer margins of the port. There appears to be no cutting by other portions of the tip, and different port geometries and locations are possible.”

The port, much smaller than that of conventional guillotine cutters, remains constantly open, allowing continuous and uninterrupted vitreous flow, he said.

No inner needle

Emulsified material is pulled into the probe and out of the eye with conventional vacuum. Dr. Awh pointed out that unlike guillotine cutters, the hypersonic vitrector has no inner needle, resulting in a larger inner lumen which improves the flow.

Flow is also influenced by a variable new to most vitreous surgeons– “stroke,” a term used to describe the distance of longitudinal oscillation of the tip, which ranges from 0 µm to 60 µm.

Dr. Awh differentiated flow comparisons of the hypersonic vitrector with a guillotine cutter. The flow curves associated with different stroke settings showed that the hypersonic vitrector may be capable of predictable flow at rates similar or superior to the guillotine cutter, Dr. Awh said.

“The effect of stroke seems to be much greater than that of cut rate,” he added. “In particular, we can create extremely low levels of flow that are quite predictable.”

First human cases

The first human cases were performed in India in the summer of 2017 (22 procedures in 20 patients performed by Paulo E. Stanga, MD, who helped develop the system; Anusha Venkatarman, MD; and Amar Agarwal, MD). Dr. Awh has performed 23 of the 46 cases done in the United States. The initial clinical results in these 46 cases with the Vitesse device have been encouraging, Dr. Awh said.

Dr. Awh’s first cases were “fairly routine,” with a combination of macular holes, epiretinal membranes (ERM), retinal detachments, retained lens cortex, vitreomacular traction (VMT), and retained silicone oil.

“I've had two complications–one small retinal break in an area of detached retina out of eight cases for retinal detachment, and one case of pitting the IOL during a posterior capsulotomy out of nine cases where I did a capsulotomy,” Dr. Awh said. He added that in both instances, he now realizes he had the stroke setting too high.

While creating a posterior vitreous detachment during surgery for VMT, Dr. Awh said he was able to generate “tremendously high suction” at the port because the port was so small. “It’s very easy to engage the vitreous,” he said. “We don't get as large a bite of it, but we grasp it quite firmly.”

In another case (with a thick ERM), Dr. Awh stripped the ERM and left it tethered to the macula along the inferior temporal arcade.

“With low vacuum and low stroke, I was able to ‘nibble’ down the membrane,” he said, and anticipates being able to use the device to perform “very controlled” dissections.

Grasping power

Because the small port of the device produces “very effective grasping power,” Dr. Awh uses it as a tool to strip thick membranes. This may reduce the need for forceps in certain cases.

An additional benefit of the hypersonic system over a conventional guillotine is that the latter cannot remove silicone oil without clogging. Dr. Awh has used the system to remove both 1,000 and 5,000 cSt silicone oil. The probe quickly removed silicone oil from the vitreous cavity of an eye.

“By positioning the port of the probe at the interface of the oil and the infusion fluid, we probably created an admixture of oil and fluid that has much less viscosity and comes easily out of the eye,” Dr. Awh said.

Vitesse is “the first major vitreous removal innovation in 40 years,” according to Bausch + Lomb, and was designed to work with the company’s Stellaris Elite Vision Enhancement System. Guillotine vitreous cutters aspirate vitreous fibers into their port and then cut them once inside the vitrector needle.

Smaller gauge cutters have many benefits, but this comes at a reduction in the vitreous flow rate through the vitrector needle. In a hypersonic system1, low amplitude ultrasonic motion of the tip is used to create oscillating, high-speed vitreous liquefaction and flow near the outer surface of the port. Because there is only one needle rather than two, “there is no chance of trapping vitreous strands between the port edge and the needle.”1

Disclosures:

Carl C. Awh, MD
P: 615-983-6000
E: carlawh@gmail.com
This article was adapted from a presentation that Dr. Awh delivered at the Retina Subspecialty Day preceding the 2017 American Academy of Ophthalmology meeting. Dr. Awh is a consultant to Bausch + Lomb.

References:

1. Stanga PE, Pastor-Idoate S, Zambrano I, Carlin P, McLeod D (2017) Performance analysis of a new hypersonic vitrector system. PLoS ONE 12(6): e0178462. https://doi.org/10.1371/journal.pone.0178462