LASER MEDICINE S SURGERY NEWS - VOLUME 1 NUMBER 2

ThS4 Cuting Vitreal Mem-branes In a Wet Field with aC02 Laser, R. F. Bonner and S.M. Meyers, National Institute ofHealth. Two prototype in-travitreal C02 laser probes wereused to cut vitreal membranesin rabbits with short pulses(300usec

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200msec) of infraredenergy. The threshold energydensity for cutting was em-pirically determined as a func-tion of pulse length and com-pared with theoretical calcula-tions. Hazards associated withsuch surgery were alsoexplored.

ThS1 Target Specific SelectiveEffects of Laser Irradiation ofTissue, J. A. Parrish, HarvardMedical School. Specificdamage by selectively ab-sorbed, pulsed lasers can bepredicted based on physicalmodels. The likely modes ofselective alterations includelocalized thermal denaturation,vaporization, and shock wavegeneration. Excimer, dye, cop-per vapor, ruby, YAG, andnitrogen lasers are used to pro-vide evidence for time resolvedspatial confinement of thermalalteration of specific targets(selective photopyrolysis).(Invited Paper)

ThS2 Laser Angioplasty inAnimals and Humans, Daniel S.J. Choy, Simon H. Stertzer,Eugene Wallsh, Jean-MichelLoubeau, Philippe Quilichi,Heidrun Rotterdam, Lenox HillHospital, William Marienberg,Tri Boro Animal Hospital, andIvan Kaminow, Bell Labor-atories. We report on in vitroand in vivo experiments inanimals and humans on suc-cessful recanalizatlon ofvessels obstructed by thrombusor atherosclerotic plaque usingargon-laser energy introducedpercutaneously through a lasercatheter.(Invited Paper)

CURRENT LASER OPHTHALMOLOGY

Members of the American Society for Laser Medicine should be familiar with the currentinterest in the YAG laser in ophthalmology, not only as an example of the effect of shortpulses but to determine how it can be applied to individual areas. As an introduction, hereis a piece by Janet Pierce Frye, at Duke University Medical Center, entitled "New Laser WillSave Cataract Patients From Additional Operations" (see also the abstracts from CLEO '83):

A new laser at Duke University Medical Center can literally cut membranesin the eye without surgery and will save many cataract patients fromadditional operations.

"The reason the Neodymium YAG laser has become important in ophthalmologyis because of a type of cataract surgery called 'extracapsular surgery,'"said Dr. Michael Cobo, assistant professor of ophthalmology at the Duke EyeCenter. "In this type of surgery, part of the membrane of the lens is leftintact (when the lens is removed) to protect the retina. When an intraocularlens is implanted, the membrane helps stabilize the lens.

"The only trouble is that while the membrane stays clear for a period oftime, in about half of the patients it will eventually cloud and decreasevision. Then the membrane must be opened and/or partially removed to allowlight to pass through. In the past, this has required additional surgery."

The new laser allows the eye surgeons to cut the membrane, when necessary,without having to open the eye surgically. In a matter of seconds, the laserwill put a hole in the membrane so light can get through.

Previously, the surgery to open up the membrane took place in the operatingroom and required local anesthesia. With the YAG laser, it is performed by a

staff surgeon in an examining room in the Eye Center and no anesthetic isrequired.

"This allows us to make it a very simple outpatient procedure," Cobo said."Because it's non-invasive—you don't enter the eye with surgical instruments—there is no risk of infection or secondary problems from the surgery."

Although the YAG. laser was developed in the United States for military andindustrial purposes, he said, it was first used for this type of eye surgeryin Europe in 1979. It has been used in this country for surgery since mid-1982, he said.

"The concept of using this laser as a surgical cutting tool is new," Cobosaid. "It's not a difficult technique, but it's a very exciting conceptbecause by using these laser 'scissors,' we may be able to treat disease ina different manner than we've been accustomed to.

"If you can use it in the retina and vitreous (of the eye), you may be

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LASER MEDICINE & SURGERY NEWS - VOLUME 1 NUMBER 2

able to cut membranes that are presently inaccessible or very difficult to

operate on. Of course, this idea is theoretical at this point."The cost of a YAG laser is more than four times the cost of a so-called

"burning" laser, the type currently used at the Duke Eye Center to treatretinal detachment.

Using the new YAG laser, which is on loan from Méditée Inc., Dukesurgeons also will be conducting research on new applications of the laserto other eye problems.

MODE-LOCKED VS. Q-SWITCHEDFOR

THE YAG LASER IN OPHTHALMOLOGY

Since the introduction of the YAG ophthalmic laser program from France, there has been muchargument and debate (more heat than light!) over mode-locked vs. Q-switched.

According to the laser physicist, R.J. Rockwell, Jr., who has had long experience arguingwith physicians who wanted to use diffuse biological control rather than quantitative controls,very few basic and control studies have been done. Theoretically if it is nonlinear, mode-locked impulses would have some higher outputs than the nanosecond impacts of the Q-switchedimpacts, and have some picosecond spikes as well. Dr. Hugh Beckman of Detroit, President-Elect of the American Society for Laser Medicine and Surgery, claims that the "Q-switched isadequate for the job and more versatile." Furthermore, of the present available instruments,the Q-switched machines outnumber the mode-locked by 20 to 1.

So, the debate continues with no true definite knowledge of whether the results show muchdifference or not. As usual, more controlled investigative studies are needed.

If the lens is nicked during YAG laser therapy, the operator has not been trained well.In San Diego at present, there is a portable trucking device delivering the ophthalmic YAGlaser to laser ophthalmology treatment centers.

In our early experiments, using picoseconds with ruby and nanoseconds with ruby, SEM(scanning electron microscopy) studies were done to determine the effects on tissue adjacentto the target area.

LASER GYNECOLOGY

Dr. Helmut Schellhas has called attention to the new developments in laser gynecology: thecomparative studies of cold knife and laser conization for preinvasive and early invasivecarcinoma of the uterine cervix (Aeta Obstétrica et Gynecologica Scandinavica, Suplement 114,Goran Larson, Lund, 1983). Laser conization, even as an outpatient procedure, reduced thefrequency of early complications. In short-term, follow-up studies, laser conization gavegood "cure rates." "Laser conization is a method," Dr. Schellhas observes, "which—not leastfor economical reasons—probably will replace cold knife conization in the future."

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The Newsletter welcomes Laser Beam, a Publication of the Gynecologic Laser Society,.Inc.This will be published three times a year by Cecil Wright, M.D., and will be a valuablesource for laser gynecology. We hope there will be exchanges of mutual information.

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Medicare has recently approved payment for the first laser surgery outside the area ofophthalmology. This important official document is reproduced on the next page.

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