The year 1986 marks the twentieth anniversary of the use of the laser in clinical medicine.

The use of laser in medicine has grown rapidly in the past decade. Medical specialties such as ophthalmology, dermatology and podiatry now use lasers as standard surgical tools. Recently new technology has led to the development of hand-held surgical lasers that are highly portable, compact in size and easily manipulated. This technology breakthrough has opened the medical fields of orthopedic and cardiac surgery to the use of lasers with positive clinical results.

Nanosecond pulses from CO2 TEA lasers, (A= 10,600nm,T = 3ns, 4Ons and 200ns), HF lasers (X= 2,744nm,1'= 300ns) and excimer lasers (N= 193nm,T= 15ns) were focussed (either through cylindrical quartz lens or 0.001" thick Beryllium-copper mask etched with slits of various widths) onto the corneas of enucleated dog eyes. Pulse energies were measured with a pyroelectric or disc calorimeter, placed behind the mask. The mask unit area and the number of pulses were varied to determine energy parameters required for ablation of different depths of corneal tissue. Ultrastructural studies of corneal incisions made with knife were compared with those made by laser pulses.

Fiber optic delivery of argon ion laser energy and Nd-YAG laser energy were compared by the performance of open laser endarterectomy in the rabbit arteriosclerosis model. In Group I, 6 open laser endarterectomies were performed with an argon ion laser (488 nm and 514.5 nm) with the laser beam directed through a 400 pm quartz fiber optic. In Group II, 6 open laser endarterectomies were performed with a Nd-YAG laser (1.06 pm) with the laser beam directed through a 600 pm quartz fiber optic. Gross and light microscopic examination revealed smooth endarterectomy surfaces with tapered end points in Group I. In Group II, the endarterectomy surfaces were uneven and perforation occurred at 5/6 end points. Although energy could be precisely delivered with each laser by fiber optics, satisfactory results could only be achieved with the argon ion laser because argon ion energy was well absorbed by atheromas. Successful intravascular laser use requires a strong interaction between wavelength and atheroma as well as a precise delivery system.

A solid state Er:YAG laser operating at 2.94μm, which is at the absorption peak of biological tissue, was used to ablate calcified and uncalcified atherosclerotic plaque in human arteries. The experiments were done in vitro. The laser radiation was passed through a flexible zirconium fluoride glass fiber, with virtually no loss, onto human aortas in saline solution. A low threshold for ablation and clean cuts with no charring compare favorably with excimer laser studies of tissue ablation.

In this study, we have developed a concept of wound closure by laser welding and studied the wound healing process. In the first set of experiments, six-millimeter long, full-thickness incisions were made in the skin on the back of hairless mice. Control wounds were closed with interrupted 5-0 prolene suture. The experimental wounds were approximated and closed by laser welding using a Nd:YAG (1.06 μm) laser. Selected wounds were excised for histopathology, transmission electron microscopy, tensile strength determination and assay of type I collagen specific messenger-RNA. The laser welded wounds demonstrated rapid healing with good cosmetic results. The tensile strength was identical both for laser welded and sutured wounds at 7, 16, and 21 days. A significant increase of type I collagen specific mRNA was noted in both specimens at 4, 10 and 16 days, but a higher level was recorded in the sutured specimens at day 16 (2652 vs. 911 U/pg total RNA). We further initiated a comparative study to identify the laser which would be most suitable for skin welding. For this purpose argon, Nd:YAG (1.06 μm and 1.32 μm) and CO₂ lasers were used to weld skin. Wound healing, tensile strength and collagen analyses were performed. The results indicated that both argon and Nd:YAG (1.32 μm) lasers achieved the most effective closure. These results suggest that laser welding provides an efficient method for closing skin wounds. The laser welding has clear advantages over conventional suturing techniques, being sterile, non-tactile, not requiring introduction of foreign materials into the wound, and providing improved cosmetic results.

Lasers have gained considerable use in the field of dermatology for treatment of a variety of cutaneous lesions. In this overview, we are discussing the current applications of argon, CO₂ and Nd:YAG lasers in dermatology. We are also exploring the future prospects of laser research in the field of cutaneous biology.

Clinical observations have suggested that low energy lasers might stimulate wound healing. To understand the mechanism of the biostimulation, we have previously examined the effects of low energy lasers on collagen production by human skin fibroblasts and reported an increase of collagen synthesis in vitro (J. Am. Acad. Derm. 11:1142-1150, 1980. To examine the effects of low energy lasers in vivo, hairless mice were experimentally wounded, sutured and subjected to laser irradiation by He-Ne laser with a power output of 1.56 mW, and an energy fluence of 1.22 J/cm². Experimental wounds were subjected to laser treatment every other day, for a total duration of 2 months; control wounds remained untreated. Specimens from the wounds were then examined for histology, tensile strength and total collagen content. Results demonstrated a considerable improvement of the tensile strength of the laser-irradiated wounds at 1 and 2 weeks. Furthermore, the total collagen content was significantly increased at 2 months when compared to control wounds. These results suggest a beneficial effect of He-Ne laser on wound healing in vivo.

Tne feasibility of welding thin-walled microvessels by laser has been established. This report summarizes our experience using laser welding to repair thick-walled, large-diameter, 4 to 8 mm canine veins and arteries using CO₂, Nd:YAG and argon lasers. Welding of venotomies is uniformly successful using CO₂ and Nd:YAG lasers, and Nd:YAG venotomies appear to veal more rapidly than sutured controls. Arterial welding has been accomplished with the Nd:YAG and argon laser. Our preliminary experience shows promise for welding both large diameter veins and arteries using lasers. Laser welding may represent an alternative for repair of small and large diameter vessels with several advantages compared to conventional suture techniques.

CO₂ laser beam delivery through a flexible waveguide has many potential clinical (and some industrial) applications. We have developed a pair of 75cm long, hollow flexible waveguides with square lumen cross-sections of 3/4mm X 3/4mm and limm X 1/2mm respectively; both sizes have a 11/2mm outside diameter. The larger waveguide has a transmission efficiency of 80%; the smaller a transmission efficiency of 70%. Both waveguides will handle more than 30 watts of power. The device is fabricated from two aluminum substrate halves onto which a dielectric optical coating has been applied. The two halves are then assembled into the completed unit. We have also fabricated a short "nozzle" extension tip with tapered lumen which can produce an output spot size as small as .3mm. Gas flow through the waveguide lumen in conjunction with the disposable, nozzletips ensure that the interior of the waveguide is kept free from backstreaming smoke and debris. While this device does not have the flexibility of a wet noodle, we believe it has immediate applications in many topical and endoscopic procedures.

The use of laser energy for recanalizing blood vessels has been investigated by several groups. Various lasers were shown to be capable of vaporizing obstructive tissue under certain conditions. However, vessel perforation and inability to create sufficiently large channels are major technical limitations of laser angioplasty. These limitations appear to be related to the delivery system employed in these studies. An open-end fiber-optic laser delivery system, reportedly utilized by various investigators, has certain design deficiencies that could be responsible for the high incidence of vessel perforation and inability to create a large channel. Understanding of these limitations, and of the thermal nature of laser tissue interaction has motivated the author to develop a fiberoptic laserprobe that overcomes the difficulties imposed by open-end fiberoptic delivery systems. The proposed laserprobe contains emitted laser radiation and distributes thermal energy evenly around probe surface while permitting tactile feedback. This probe was shown to substantially reduce the incidence of vessel perforation and to increase the rate of angiographic success in two animal models and in man.

Since their introduction in 1985, Contact Laser Probes have been used to deliver energy from the Nd:YAG laser in a variety of surgical applications in several clinical laser centers in the United States and in Japan. The aim was to evaluate the ability of this new delivery system to improve the present applications of cutting, evaporation and coagulation carried out in many centers with a variety of non-contact lasers the most commonly used being CO₂, Argon, and YAG.

Optical dosimetry has been investigated in a tissue phantom, consisting of an aqueous suspension of uniform polystyrene spheres plus methylene blue as a chromophore. The rate of light absorption by the dye was measured for different concentrations of dye and scatterers, using the photosensitized inactivation of an enzyme as a sensitive internal actinometer. The optical penetration depth of each sample was measured with a fiber optic probe technique. The results are in good agreement with the predictions of the diffusion model, and the high scattering limit of Kubelka-Munk theory.

Continuing investigations of copper(II) and iron(II) protoporphyrin complexes show that variations in solvent polarity, number of coordinating ligands and spin state for iron(II) can induce changes in the electronic relaxation rates of the protoporphyrin complexes studied. Picosecond biphasic kinetic behavior indicates that intermediate energy levels are present in both copper(II) and iron(II) complexes.

Small foveal retinal lesions are often difficult to detect with conventional ophthalmoscopy, as well as the visual functions effects of such damage. In order to improve conventional ophthalmoscopy of such lesions we have adapted computer image analysis techniques to quantify the spatial and temporal characteristics of such lesions. Our methodology incorporates conventional statistical tests of significance for plotting gray scale differences along common retinal landmarks. Preliminary data indicates that punctate retinal lesions in the fovea vary over time somewhat differently than similar size lesions placed parafoveally. Such temporal variations in gray scale distribution may aid in explanation of visual functional affects of such lesions.

This report describes instrumentation used to non-invasively quantitate lens changes and to moniter the development of cataract formation. Quasi-elastic light scattering spectroscopy is used to investigate quarternary lens protein structural changes and lens autofluorescence measurements are used to moniter changes in lens fluorophore concentration. These measurements can be used to investigate the mechanisms of cataract development and to identify those patients showing an accelerated progression in cataracto-genesis.

Quasi-elastic light scattering is a useful method to determine the size distribution of sub-micron particles in fluids. We have applied this technique to measure in vivo changes in the association of human lens protein constituents that occur with aging and cataractogenesis. The autocorrelation function of the scattered light has been analyzed by a two component exponential where each component is characterized by an intensity and decay rate. Each pair of parameters is associated with one of two major protein components in the lens. These parameters have been determined as a function of age and position within normal, clear lenses. In cataractous lenses the intensity and decay rate parameters show anomalous behavior, when compared to normal lenses, even in clear regions of the lens which are some distance from the cataract. Our results seem to be consistent with the model of progressive aggregation of the lens proteins as detected in vitro by other biochemical methods. Our studies suggest that quasi-elastic light scattering spectroscopy is a useful probe of the protein modifications that occur both in normal and cataractogenic human lenses.