Pulsed Electron Avalanche Knife (PEAK) for intraocular surgery

PURPOSE. To develop a better and more economical instrument for precise, tr actionless, "cold" cutting during intraocular surgery. The use of highly lo calized electric fields rather than laser light as the means of tissue diss ection was investigated. METHODS. A high electric field at the tip of a fine wire can, like lasers, initiate plasma formation. Micrometer-length plasma streamers are generated when an insulated 25 micron (mum) wire, exposed to physiological medium at one end, is subjected to nanosecond electrical pulses between 1 and 8 kV i n magnitude. The explosive evaporation of water in the vicinity of these st reamers cuts soft tissue without heat deposition into surrounding material (cold cutting). Streamers of plasma and the dynamics of water evaporation w ere imaged using an inverted microscope and fast flash photography. Cutting effectiveness was evaluated on both polyacrylamide gels, on different tiss ues from excised bovine eyes, and in vivo on rabbit retina. Standard histol ogy techniques were used to examine the tissue. RESULTs. Electric pulses with energies between 150 and 670 muJ produced pla sma streamers in saline between 10 and 200 mum in length. Application of el ectric discharges to dense (10%) polyacrylamide gels resulted in fracturing of the gel without ejection of bulk material. In both dense and softer (6% ) gels, layer by layer shaving was possible with pulse energy rather than n umber of pulses as the determinant of ultimate cutting depth. The instrumen t made precise partial or full-thickness cuts of retina, iris, lens, and le ns capsule without any evidence of thermal damage. Because different tissue s require distinct energies for dissection, tissue-selective cutting on com plex structures can be performed if the appropriate pulse energies are used ; for example, retina can be dissected without damage to the major retinal vessels. CONCLUSIONS. This instrument, called the Pulsed Electron Avalanche Knife (P EAK), can quickly and precisely cut intraocular tissues without traction. T he small delivery probe and modest cost make it promising for many ophthalm ic applications, including retinal, cataract, and glaucoma surgery. In addi tion, the instrument may be useful in nonophthalmic procedures such as intr avascular surgery and neurosurgery.