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New tool provides pressure-free vitreoretinal cutting
Dielectric breakdown in an aqueous medium produces an electron cascade and provides a means for precise tissue cutting.
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KOLOA, Hawaii — The Pulsed Electron Avalanche Knife (PEAK) is a new method for vitreoretinal cutting and membrane dissection. The tool uses electrical pulses rather than laser light for the generation of plasma micro streamers for the microdissection of tissue and liquid media.
Mark Blumenkranz, MD, described the PEAK here at Retina 2001, presented with Hawaii 2001, the Royal Hawaiian Eye Meeting, sponsored by Ocular Surgery News in conjunction with the New England Eye Center. The device was a collaborative effort on behalf of Dr. Blumenkranz, Daniel Palanker, MD, of Stanford University, Steve Sanslow and Michael Marmor. Their work was supported in part by a research grant from Carl Zeiss.
“In view of the generally complicated nature and high cost of laser-based instrumentation, we’ve been searching for ways to emulate these mechanisms by non-laser methodology,” said Dr. Blumenkranz, chairman of the ophthalmology department at Stanford University School of Medicine.
“Being as cavitation bubbles result from fast and localized heating, it is logical to consider overheating a conductive medium with a short pulsive electric current,” he explained.
In addition, high-temperature plasma can also be generated in a liquid medium using a dielectric breakdown induced by short pulses.
“Our preliminary research indicates that these sub-microsecond, discharged-induced cavitation bubbles have identical dynamics to those induced by fiber-delivered lasers and have the potential for application in vitreoretinal surgery,” he said.
Dr. Palanker designed a probe comparable in size and other dimensions to intraocular probes for illumination and cutting based upon the principle of dielectric breakdown in aqueous medium, Dr. Blumenkranz reported. This resulted in the production of an electron cascade producing very high voltage threshold energies in a spatially and temporally confined region, in turn leading to the creation of means for precise tissue cutting.
The method
The method relies on a thin platinum wire sealed in a tapered glass pipette with a diameter varying between 0.7 mm and 2.2 mm at the tip, connected to the output of a high-voltage generator.
“Nanosecond pulses of high voltage are applied to the intraocular microelectrodes to produce plasma or streamers that emanate from the tips of the probe. These streamers can produce either electrical breakdown of tissue or cavitation bubbles, functioning much in the way an erbium YAG laser may,” Dr. Blumenkranz said.
Using this type of precise cutting, it is possible to either transect or shave tissue.
“It is also possible to use lower discharge energies in the range of 0.05 mJ to shave off surface layers of tissue. This produces a very subtle or refined cut,” he said.
The shaft of insulated material in the conductive tip may either be non-illuminated or illuminated, and the probe may either be straight or bent at a right angle so as to permit oblique tissue dissection. It is controlled by a small laptop computer-sized console that produces high voltage sparks, which are then controlled either in terms of repetition rate or power by a foot pedal.
“In addition to cutting very thin structures such as retina, thicker tissue such as iris and sclera can also be cut, layer by layer, using higher energy settings. On average, the total energy deposited is less than 3 J, and the average accumulative energy density in the posterior pole would be less than 25 J/mL, which minimizes the creation of free radicals,” Dr. Blumenkranz said.
Very precise cuts
The system has been tested on chick chorioallantoic membrane, a highly vascularized tissue simulating the retina.
“We are able to produce a very precise cut and at the same time not damage the closely adjacent underlying vascularized tissues,” Dr. Blumenkranz said.
Using the device in lower energy mode, it is possible to produce a small water jet that in turn, produces movement of a blood column along a normal vessel without damaging the vessel wall itself or producing a hole, bleeding or defect.
“One might imagine how this type of technique could be applied to the direct treatment of retinal vascular occlusive disease, where a thrombus might be able to be massaged or displaced distally,” he said.
It is also possible, using slightly higher energy, to create slightly more damage to the vascular wall in such a fashion that a controlled aneurysm can be created.
“The potential utility of this may be in facilitating canalization of very small vessels, or in producing changes in permeability of the vascular wall that may facilitate drug therapy,” he said.
PEAK requires neither pressure nor traction, according to Dr. Blumenkranz, so in that regard it is inherently much more accurate and much more reliable and precise than any mechanical methods.
For Your Information:
- Mark Blumenkranz, MD, can be reached at 300 Pasteur Drive, Boswell A 157, Stanford, CA 94305-5308; (650) 725-0231; fax: (650) 498-5834; e-mail: mark.blumenkranz@stanford.edu. Drs. Blumenkranz and Palanker are paid consultants for Carl Zeiss.