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Tissue response to injury caused by the electrosurgical scalpel, the hemostatic Shaw scalpel, the CO2 laser, and a standard steel scalpel have been compared. Subcutaneous incisions in pigs were evaluated histologically at 1, 4, 7, 14, and 22 days postincision. The least damage was produced by the standard steel scalpel at all time periods. Epithelial migration started on day 1 for the standard steel scalpel, on day 4 for the Shaw scalpel, and only on day 7 for the electrosurgical scalpel and laser knives. Lateral thermal necrotic zones were found for all three thermal knives. Tensile testing showed no significant differences in the early postincision tissue strength. By day 14 wounds made with the standard steel scalpel were stronger than those made with the Shaw and electrosurgical scalpel. These findings indicate that thermal injury delays the wound healing process.

The erythrocyte magnesium content was determined using two different analytical systems (atomic absorption spectrometry and the laser microprobe mass analyzer) with specimens from 18 patients with normal renal function and from 10 patients with chronic renal insufficiency. There was a good correlation (r = 0.73) between the two analytical systems. Additionally, the laser microprobe mass analyzer was used to determine the aluminum content of plasma and erythrocytes in specimens from patients who ingested moderate quantities of aluminum hydroxide for several months. Results showed a significant elevation of the plasma aluminum concentration, but a normal erythrocyte aluminum content. The laser microprobe mass analyzer may be useful in studies of mineral metabolism in humans.

Three cases of bleeding ulcers in childhood are described. In children with considerably increased operative risk, laser coagulation has proved a valuable additional therapeutic concept after failure of conservative treatment of stress ulcer bleeding. Advantages and technical problems of this new method are discussed.

The authors have developed a CW YAG laser for transpupillary coagulation. The effects of CW YAG coagulation on the retina, retinal vessels, and fovea were compared with those produced by the krypton red and argon green lasers. To produce threshold coagulative lesions in monkeys and rabbits, we needed five to ten times more energy with the CW YAG than with the krypton red or argon green lasers. Nerve fiber damage was observed only when coagulating retinal vessels with the argon green laser. At the parameters used, none of the lasers damaged the sensory retina of the fovea. The CW YAG may be used as a new mode of laser coagulation in the treatment of retinal diseases.

There are many kinds of abnormally coloured skin lesions, or naevi, which cannot be successfully treated by using conventional techniques. From experience gained in treating over 6,700 patients in the last 6 years, we find that the visible light ruby and argon lasers are useful in the treatment of naevi. However, to use the laser effectively and safely, both skill and knowledge are necessary so that it can become an additional and effective tool in the management of certain dermatological conditions.

An argon-ion laser, coupled to a flexible fiberoptic endoscope, was used to photocoagulate experimentally produced bleeding gastric ulcers in dogs. Argon-ion laser phototherapy rapidly and effectively achieved hemostasis in all bleeding ulcers. Bleeding arteries up to 2 mm in diameter were photocoagulated. Intact normal gastric mucosa was exposed to laser energy for varying periods of time to determine if transmural photothermal injury occurred. Exposure for greater than 15 seconds at 1.0 w of throughput power caused microscopical evidence of transmural injury. Healed, laser-treated ulcers could not be differentiated from nontreated control ulcers or normal stomach one month after injury. The Beer law and the heattransfer factors relating to soft tissues are discussed. The coupled argon-ion laser-endoscope may be a safe tool to treat self-limited superficial bleeding gastric lesions.

The aim of the present study was to test the hypothesis that ultrasonic propagation properties in skin and wound tissue would correlate with material properties such as collagen content, water content, and tensile strength of those tissues. Both ultrasonic speed and ultrasonic attenuation coefficient were directly correlated with tissue collagen content, [r = 0.80 and r = 0.56, respectively (p less than 0.001)]. In addition, ultrasonic speed and attenuation coefficient were inversely correlated with tissue water content, [r = -0.57 and r = -0.73, respectively (p less than 0.001)]. Tensile strength also correlated very significantly with ultrasonic speed (r = 0.90, p less than 0.001), and significantly with attenuation coefficient (r = 0.58, p less than 0.001). The results demonstrate the feasibility of using ultrasound for noninvasively determining the material properties of biologic tissues including healing cutaneous wounds.

Relative merits of different laser wavelengths for macular photocoagulation are analyzed in terms of light scattering and light absorption in hemoglobin, melanin, and macular xanthophyll. Disadvantages of inner retinal damage in the macula caused by the blue-green argon photocoagulators in standard clinical use are discussed, along with advantages of argon green and krypton yellow light. Results of treatment of subretinal neovascularization in disciform macular degeneration are presented. A repetitive treatment, close follow-up protocol was employed with the objectives of closing neovasculature and preserving central visual field. In 74 successive patients treated with monochromatic argon green radiation, neovasculature was closed in 93%, central visual field loss was reduced or stabilized in 76%, and visual acuity was improved or stabilized in 70%. Results were analyzed in terms of location and size of the neovascular membrane, and it was found that best results were obtained with neovascularization farther than 600 microns from the foveola and smaller than 2 mm2. In 17 patients with neovascular membranes more than 600 microns from the foveola, neovasculature was closed in 100%, central visual field loss was reduced or stabilized in 94%, and visual acuity was improved or stabilized in 88%. Similar results were obtained with monochromatic krypton yellow radiation.

A technique for treating primary open angle glaucoma by argon laser photocoagulation is described. Its elective action on the trabeculum and on trabecular "collapse" in the absence of any trabecular perforation suggested the name of "trabecular retraction" for this procedure. Its efficacy depends on very good visibility of the trabeculum through 360 degrees, on perfect focalization of the point of impact to 50 mu, and on the application of one hundred or so impacts distributed throughout 360 degrees. Any pretrabecular obstacle must be eliminated. Mean pressure drap obtained is 10 mmHg. Complications are minimal and results comparable or superior to those of surgery.

Various tracheobronchial obstruction indications have been treated with laser yag neodyme with flexible fibre introduced into a bronchofibroscope. Experience covers 44 patients who underwent 75 photocoagulation sessions under local or general anaesthesia. Inoperable tracheo-bronchial tumours are the most frequent and spectacular indications. Malignant tumour, cylindromas, carcinomas and benign tumours are the best indications. Tracheal stenoses were treated in association with instrumental dilatation. The other indications proposed are resections of granulomas, resection of suture threads, extraction of peripheral foreign bodies and control of major haemorrhages. No complications were observed. The immediate effectiveness of this new technique is considerable. Long-term development depends on the aetiology of tracheobronchial stenosis.

Forty of 59 patients with a circumscribed choroidal hemangioma have been treated by photocoagulation since 1972 because of visual impairment due to secondary nonrhegmatogenous retinal detachment involving the fovea. An attempt was made in every case to bring about resolution of the subretinal fluid, but no attempt was made to destroy the tumor. The treatment techniques used were xenon arc photocoagulation and less intense argon laser photocoagulation. At least a temporary reduction or resolution of subretinal fluid occurred after treatment in most of the eyes, but subsequent reaccumulation of subretinal fluid was noted in many cases. Unfortunately, only 22.5% of the treated eyes retained visual acuity of 6/12 or better after an average follow-up of four years.

We evaluated the effects of Nd:YAG laser energy directly applied to ocular tissue through a fiberoptic and a sapphire tip. All ocular tissue could be easily cut with the maximum 4 watts of energy. The coagulated borders extended 20 to 200 mu into the healthy tissue depending on the speed with which the cutting was performed.

Contact lenses for anterior and posterior segment laser applications are described. Commercially available lenses are classified according to design, application, manufacturer and cost.

The conditions for an optimal ophthalmic coagulating system are derived from the absorption spectra of xanthophyll, melanin and hemoglobin. Coagulation is effected by a dye laser with two dyes. The continuously tunable range of 570 nm to 680 nm opens up new horizons in photocoagulation of the retina.

Argon laser intraocular photocoagulation is now available during vitreous surgery, to treat retinal breaks and to give panretinal photocoagulation. Twenty patients, including phakic patients with gas-filled eyes, were treated using a new operative contact lens without complication. This intraoperative technique allows controlled rapid application of laser lesions at a safe distance from the retina, and eliminated the need for attempting treatment through the often hazy media of an irritated postoperative eye. A group of five rhesus monkeys were treated with various power settings to assess the histopathologic features of these laser lesions.

The photoelectric activity of different parts of lipid bilayer containing bacteriorhodopsin was investigated by moving a small actinic light spot across the Plateau-Gibbs border and the bimolecular part of this reconstituted model membrane. The results give direct evidence that bacteriorhodopsin incorporated into the bimolecular region of the lipid membrane is responsible for the photoelectric activity of this system. A technique for scanning the photoelectric activity of a modified bimolecular lipid membrane is described in detail.