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Precision and Safety of the Pulsed Electron Avalanche Knife in Vitreoretinal Surgery

Jason M. Miller, MSc; Daniel V. Palanker, PhD; Alexander Vankov, PhD; Michael F. Marmor, MD; Mark S. Blumenkranz, MD
Arch Ophthalmol. 2003;121(6):871-877. doi:10.1001/archopht.121.6.871.
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Background  We have developed a new surgical instrument, called the pulsed electron avalanche knife (PEAK; Carl Zeiss Meditec, Jena, Germany), for precise, "cold, "and tractionless dissection of tissue in liquid media.

Objective  To evaluate the 3-dimensional damage zone induced by the PEAK compared with 2 other standard intraocular surgical instruments, diathermy and retinal scissors.

Methods  Damage zone and minimum safe distance were measured in vitro on chick chorioallantoic membrane and in vivo on rabbit retina with the use of propidium iodide staining.

Results  The PEAK produced a paracentral zone of cellular structure disruption surrounding a crater and a peripheral zone of structurally intact but abnormally permeable cells. The instrument induced a damage radius that varied from 55 to 300 µm for the range of voltages and pulses typically used during surgery. For comparison, damage radius for microsurgical scissors was 50 µm, and for diathermy, 400 to 850 µm. The PEAK also damaged tissue up to 1.4 mm away by the creation of water flow that formed at the tip of convex probes during collapse of a cavitation bubble. Concave probes, which prevent formation of the water jet, eliminated this effect.

Conclusions  The PEAK operated well within accept-able safety limits and may greatly facilitate both posterior segment surgeries (eg, membrane dissection and sheathotomy) and anterior segment procedures (eg, capsulotomy, nonpenetrating trabeculectomy, and iridectomy).

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Figure 1.

Propidium iodide staining of cuts on chick chorioallantoic membrane (CAM) produced with microsurgical scissors(A) and with the pulsed electron avalanche knife at 2.75 k V (B). While damage zones are similar, the pulsed electron avalanche knife offers tractionless dissection with increased maneuverability and precision.

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Figure 2.

Propidium iodide–stained damage zones induced by 1 pulsed electron avalanche knife pulse at 5 k V (A) and by 0.5 seconds of diathermy (B) at a standard retinal surgery setting(see Table 1).

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Figure 3.

Radius of the damage zone created by pulsed electron avalanche knife (PEAK) pulses applied in contact with chick chorioallantoic membrane. For comparison, we plot the maximum radius of the vapor bubble at each respective voltage, as well as the damage zone produced by microsurgical scissors and by diathermy at a standard (25/70) retinal surgery setting (see Table 1). The typical range of voltages used by PEAK during retinal surgery is 2 to 5 k V. A, Results from 1 pulse. B, Results from 50 pulses.

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Figure 4.

Depth of damage for different levels of diathermy and pulsed electron avalanche knife (PEAK) (50-pulse regimen) application. Diathermy was operated at a setting of 25/70 (see Table 1). Maximum radius of the PEAK vapor bubble produced in isotonic sodium chloride solution at each respective voltage is also shown. The typical range of voltages used by PEAK during retinal surgery is 2 to 5 k V.

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Figure 5.

Collapse of cavitation bubbles on convex (A-C) and concave (D-F) pulsed electron avalanche knife probes. Delay between the pulse and the flash is shown in the corner of each frame. The shapes of the tips are clearly seen in the right frames of each series(C and F), during the final stages of the collapse. Collapse on a convex tip produces a forward-propagating water jet (C; direction of the flow is shown by an arrow). On the concave tip, the bubble collapses toward the probe without generation of a water jet (F).

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Figure 6.

Minimum safe distance for application of 50 pulses on chick chorioallantoic membrane (CAM) with the use of convex and concave tips with and without the inner shell membrane (SM) and for diathermy on "naked" chorioallantoic membrane. Maximum radius of the vapor bubble at respective voltages is plotted for comparison. The typical range of voltages used by the pulsed electron avalanche knife during retinal surgery is 2 to 5 k V.

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