Clinicopathologic study of healing excimer laser radial excisions

Four radial linear excisions were created by an argon fluoride (193 nm) excimer laser in the edematous cornea of a blind eye of a diabetic human patient. Partial thickness corneal trephinations were performed at 3, 7, and 18 months after surgery for histopathologic examination. At 3 months, a wide gap in Bowman's layer permitted extension of an epithelial plug to a depth of 0.35 mm; at 7 and 18 months, the depth of the epithelial plug was decreased to 0.29 mm and 0.01 mm, respectively. With wound healing, excision width decreased and the two cut ends of Bowman's layer were almost reapposed by 18 months, suggesting wound contraction. Linear excisions with the excimer laser appear to be wider than incisions made with a diamond blade, but the pattern of wound maturation appears to be similar.     

Arterial response to excimer and argon laser irradiation in the atherosclerotic swine

Injury associated with laser-induced tissue ablation may be reduced by using pulsed energy delivery at low repetition rates, as opposed to using continuous wave energy delivery. This study was designed to examine the similarities and differences between these two systems as regards the healing process, and to examine whether one is superior to the other. In order to test this postulate, the healing response of normal and atherosclerotic aorta were examined after exposure in vivo to argon and excimer (XeCl 308 nm) laser radiation in hypercholesterolemic swine. Swine were fed hyperlipidemic diets for eight months following balloon denudation of the descending aorta. Following general anaesthetic, the descending aorta was isolated and laser burns were made on both normal and atherosclerotic intima using a continuous wave argon laser delivered through a 50 diameter quartz fibre, and a XeCl excimer laser carried through a 1 mm diameter fibre. Energy levels of 3 to 5 J were applied with the argon laser. The pulse duration for the excimer laser was 30 ns and craters were produced using 10 to 60 pulses at a repetition rate of 20 Hz and an energy density of 2 J cm^–2.Forty-eight hours after laser application, craters created by both lasers were filled with thrombus material. Argon burns were surrounded by thermal and acoustic injury which was not seen with excimer burns. Three weeks after laser application all crater surfaces were reconstituted. Unlike the excimer burns, argon craters demonstrated necrosis well beyond the crater margins and were characterized by multinucleate giant-cell reaction surrounding char debris. By nine weeks both excimer and argon laser burns were covered by fibrous tissue but could be distinguished by the fact that char debris and subjacent tissue injury arose with the argon burns.The results suggest that both lasers can be used to remove focal atherosclerotic plaque from arteries without inducing excessive thrombogenicity. Rapid healing is observed with both; however, damage to surrounding tissue is significantly greater with a continuous energy delivery laser as opposed to pulsed energy delivery.Work supported in part by: Heart and Stroke Foundation of Ontario, Grant-in-Aid No. 5-17     

Intraoperative coronary artery endarterectomy with excimer laser

Compared with continuous-wave lasers, excimer lasers exhibit several in vitro advantages: nonthermal ablation process and linear relation between the number of pulses and the depth of the crater. A 308 nm, 20 nsec pulse duration, 1 to 5 repetition rate laser was specifically designed for clinical application. At the time of cardiopulmonary bypass in 10 symptomatic patients, before bypass grafting, a 1 mm diameter core specifically ultraviolet-tipped fiberoptic scope was introduced via the coronary arteriotomy and placed upstream (seven patients) and downstream (three patients) in contact with the stenosis. Laser power was increasingly delivered up to the clearing of the stenosis or occlusion. Quality of angioplasty was controlled by calibration of the neolumen, cardioplegic solution output through the laser-treated segment, and an eighth day or sixth month coronary arteriogram. In the first three patients studied on the eighth day, all laser-treated coronary artery segments showed an early parallel-linked patent neolumen despite competitive bypass graft flow. In the patients studied after 6 months, all recanalized segments were patent except one; in one patient the venous graft was occluded, but the upstream laser angioplasty was patent. The main limitation of the method lies in the fact that laser coronary recanalization is confined to the fiber core diameter. We conclude that (1) excimer laser angioplasty may be safe and efficient during surgical procedure and (2) as catheter flexibility remains the most critical problem, we are now assuming an appropriate tool with a multifiber system that is suitable for intraoperative as well as percutaneous routes.     

Scattered UV irradiation during VISX excimer laser keratorefractive surgery

PURPOSE: To evaluate the potential occupational health hazards associated with scattered ultraviolet (UV) radiation during photorefractive keratectomy (PRK) using the VISX Star S3 excimer laser. SETTING: The Laser Vision Center, National Naval Medical Center, Bethesda, Maryland, USA. METHODS: Intraoperative radiometric measurements were made with the Ophir Power/Energy Meter (LaserStar Model PD-10 with silicon detector) during PRK treatments as well as during required calibration procedures at a distance of 20.3 cm from the left cornea. These measurements were evaluated using a worst-case scenario for exposure, and then compared with the American Conference of Governmental Industrial Hygeinists (ACGIH) Threshold Value Limits (TVL) to perform a risk/hazard analysis. RESULTS: During the PRK procedures, the highest measured value was 248.4 nJ/pulse. During the calibration procedures, the highest measured UV scattered radiation level was 149.6 nJ/pulse. The maximum treatment time was 52 seconds. Using a worst-case scenario in which all treatments used the maximum power and time, the total energy per eye treated was 0.132 mJ/cm2 and the total UV radiation at close range (80 cm from the treated eye) was 0.0085 mJ/cm2. With a workload of 20 patients, the total occupational exposure at 80 cm to actinic UV radiation in an 8-hour period would be 0.425 mJ/cm2. CONCLUSIONS: The scattered actinic UV laser radiation from the VISX Star S3 excimer laser did not exceed occupational exposure limits during a busy 8-hour workday, provided that operating room personnel were at least 80 cm from the treated eye. While the use of protective eyewear is always prudent, this study demonstrates that the trace amounts of scattered laser emissions produced by this laser do not pose a serious health risk even without the use of protective eyewear.     

Early and late arterial healing response to catheter-induced laser, thermal, and mechanical wall damage in the rabbit

Pulsed lasers are being promoted for laser angioplasty because of their capacity to ablate obstructions without producing adjacent thermal tissue injury. The implicit assumption that thermal injury to the artery is to be avoided was tested. Thermal lesions were produced in the iliac arteries and aorta of normal rabbits by a) electrical spark erosion, b) the metal laser probe, and c) continuous wave neodymium-yttrium aluminum garnet (Nd-YAG) laser energy through the sapphire contact probe. High-energy doses were used to induce substantial damage without perforating the vessel wall. Thermal lesions (n = 77) were compared with mechanical lesions (n = 22) induced by oversized balloon dilation. Medial necrosis was induced by all four injury methods. Provided no extravascular contrast was observed after the injury, all damaged segments were patent after 1 to 56 days. The progression of healing with myointimal proliferation was remarkably similar for all injuries. At 56 days, the neointima measured up to 370 microns. In conclusion, provided no perforation with contrast extravasation occurred, the normal rabbit artery recovered well from transmural thermal injury. The wall healing response is largely nonspecific.     

Effects of excimer laser on healing of articular cartilage in rabbits

This study examined healing of 1.0 mm diameter defects in rabbit knee articular cartilage for as long as 14 weeks after creation of the defects by either laser or drilling. The purpose of the research was to determine the effects of laser debridement of cartilage on the intrinsic biomechanical properties of the repair tissue. We therefore imitated chondral shaving and subchondral abrasion of cartilage by creating partial-thickness and full-thickness cartilage defects of standardized size with both excimer laser and drilling. Light and scanning electron microscopic examinations of the repair tissue showed that healing of osteochondral defects created by laser may be delayed compared with defects created by drilling, for at least 6 weeks postoperatively. Even though there initially was a considerable delay in healing in the laser group, neither laser nor drilling had any appreciable effects on the mechanical properties of the repair tissue, as demonstrated by biomechanical testing at 14 weeks. Specifically, the repair cartilage in the defects in the laser group had the following material properties (mean ± SD): aggregate modulus, 0.40 ± 0.24 MPa; Poisson's ratio, 0.37 ± 0.08; permeability, 3.72 ± 4.28 × 10^?15 m⁴/N.s; and thickness, 0.20 ± 0.06 mm. The corresponding values for the defects in the drilling group were 0.39 ± 0.23 MPa, 0.34 ± 0.09, 3.82 ± 3.44 × 10^?15 m⁴/N.s, and 0.22 ± 0.09 mm. The repair tissue from both types of defects was pooled, and the values were compared with those for contralateral (control) tissue. The control tissue had a 51% greater aggregate modulus (0.59 ± 0.18 MPa, p = 0.0001), 34% less Poisson's ration (0.23 ± 0.25, p = 0.0001), 48% less permeability (1.94 ± 0.96 × 10^?15 m⁴/N.s, p = 0.0001), and was 29% thicker (0.27 ± 0.08 mm, p = 0.0001). Thus, as evidenced by biomechanical testing at 14 weeks, neocartilage in both superficial and osteochondral defects, created by either laser or a drill, exhibited structural integrity inferior to that of normal control tissue.     

Photoacoustic injury and bone healing following 193nm excimer laser ablation.

The argon-fluoride excimer laser was investigated as a cutting-ablating tool for bone surgery. A total of 52 rats were divided into two experimental groups and two control groups. In one experimental group cortical bone defects were made; in another experimental group defects penetrating into the medullary space were performed. In the two control groups similar defects were achieved using water-cooled carbide burs. The rats were sacrificed on each of the 3, 7, 10, 20, 30, and 40 postoperative day. The cortical bone, the medullary space, and the extrabony tissue were examined by means of light microscopy. In both experimental groups, bone damage, represented by osteocyte destruction, extended to 1,050-1,450 microns ahead from the irradiated site, and bone healing was very much impaired. In the control groups no histological changes could be identified and bone healing appeared to be within normal limits. We believe this extensive bone damage, following 193 nm irradiation, to be a result of photoacoustic waves propagating in the bone following each pulse. In view of our results we feel that excimer lasers presently in use are not suitable for bone surgery. This problem of photoacoustic damage can be overcome in one of two ways: by designing a CW excimer laser or by reducing the pulse width to the picosecond regime.     

Temperature changes using excimer laser irradiation in a cochlear model

The excimer laser-ArF has certain characteristics that render it ideal for the performance of stapedotomy. These include the short wavelength of the emitted laser beam (193 nm), its high water absorption rate, the ability of pin-point focusing and its capability of operating in a pulse mode. In an effort to measure the temperature changes of the labyrinthine fluids in the inner ear during excimer laser irradiation, a cochlear model with the dimensions of the normal vestibule was designed. In this model cerebrospinal fluid (CSF) was used as a substitute for the labyrinthine fluids. Our study showed that the number of pulses needed to created the stapedotomy fenestra to the bony plate were 112–132. The temperature elevation of the CSF during laser irradiation showed only a slight increase of 0.1–0.4°C. The results of this study are very encouraging for the future use of the excimer laser in clinical situations. Part of this paper was presented at the ‘Lasers in Medicine Facing 1992’ Congress, Amsterdam, Netherlands, 1991.     

Photobiomodulation of wound healing via visible and infrared laser irradiation

Fibroblast cells are known to be one of the key elements in wound healing process, which has been under the scope of research for decades. However, the exact mechanism of photobiomodulation on wound healing is not fully understood yet. Photobiomodulation of 635 and 809 nm laser irradiation at two different energy densities were investigated with two independent experiments; first, in vitro cell proliferation and then in vivo wound healing. L929 mouse fibroblast cell suspensions were exposed with 635 and 809 nm laser irradiations of 1 and 3 J/cm² energy densities at 50 mW output power separately for the investigation of photobiomodulation in vitro. Viabilities of cells were examined by means of MTT assays performed at the 24th, 48th, and 72nd hours following the laser irradiations. Following the in vitro experiments, 1 cm long cutaneous incisional skin wounds on Wistar albino rats (n = 24) were exposed with the same laser sources and doses in vivo. Wound samples were examined on 3rd, 5th, and 7th days of healing by means of mechanical tensile strength tests and histological examinations. MTT assay results showed that 635 nm laser irradiation of both energy densities after 24 h were found to be proliferative. One joule per square centimeter laser irradiation results also had positive effect on cell proliferation after 72 h. However, 809 nm laser irradiation at both energy densities had neither positive nor negative affects on cell viability. In vivo experiment results showed that, 635 nm laser irradiation of both energy densities stimulated wound healing in terms of tensile strength, whereas 809 nm laser stimulation did not cause any stimulative effect. The results of mechanical tests were compatible with the histological evaluations. In this study, it is observed that 635 nm laser irradiations of low energy densities had stimulative effects in terms of cell proliferation in vitro and mechanical strength of incisions in vivo. However, 809 nm laser irradiations at the same doses did not have any positive effect.     

Corneal wound healing in monkeys 18 months after excimer laser photorefractive keratectomy

Excimer laser keratomileusis (photorefractive keratectomy, direct corneal ablation) for myopic corrections of 2.00 diopters (n = 1), 4.00 D (n = 4), and 8.00 D (n = 3) was performed on eight corneas of four Rhesus monkeys. All animals were followed for 18 months. The ablations healed normally and no epithelial erosions occurred. Serial slit-lamp microscope examinations revealed that a variable amount of corneal haze developed in all animals; this haze progressively faded during the follow-up period. Histopathology revealed an epithelium of normal thickness, basement membrane abnormalities, increased number and activity of stromal keratocytes, and a variable amount of newly secreted extracellular matrix in the anterior stroma. These findings suggest that excimer laser keratomileusis induces a mild wound healing response in the anterior cornea which displays considerable individual variability and persists up to 18 months.     

French experience in intra-operative XeCl excimer laser coronary artery endarterectomy

We present the results of 15 XeCl laser coronary artery endarterectomies performed in 13 patients during CABG surgery. The results are very encouraging but they show that the development of new and more efficient laser catheter delivery systems with a better proportion of optical active surface at the distal tip of the multifibre catheters is necessary to reduce the longterm and mid-term rates of restenosis.     

Stimulation of the healing of aseptic wounds using laser irradiation

On the basis of experimental studies conducted on 535 albino Wistar rats and clinical observations over 125 patients, and from complex appraisal of morphological, biochemical, and tensiometric data the conclusion is drawn that optimal operative cutting of tissues is achieved by means of far infrared carbon dioxide laser beam with a wavelength of 10.6 microns. Comparison of these characteristics showed the strength of the postoperative scar to be much less in intraoperative tissue cutting with a steel scalpel or high-energy beam of an AIG laser with a wavelength of 1.06 microns. Low-intensity laser radiation increased the strength of the postoperative scar in the early periods in all groups. Tissue cutting with a high-energy carbon dioxide laser beam with a wavelength of 10.6 microns in combination with pre- and postoperative exposure of the zone of the incision to low-intensity 0.89 micron wavelength laser beam considerably increases the strength of the postoperative scar and is the method of choice in the treatment of aseptic wounds.     

Experimental study of application of excimer laser to laser angioplasty

The possible application of excimer laser to laser angioplasty was studied. In the first experiment, the ablative effects of excimer laser at wavelengths of 248 nm and 308 nm on the pig myocardium were examined in vitro at an air-tissue interface. Crater depth increased with total delivered energy and energy per pulse. Very clear cuts could be observed by histological examination. There was no evidence of thermal damage at a wavelength of 248 nm, at 10 pps. Above 10 pps, a thin bordering zone of suspicious thermal damage was noted with the wavelengths of 248 nm and 308 nm. Thermal damage increased with pulse repetition rate. In the second experiment, the effects of excimer laser irradiation on blood were examined. Five vials, each of which contained 3 ml of blood, were exposed to 37.5 mJ laser beam at 10 pps in repetition rate for 10, 20, 30, 40, 50 seconds. One vial was left untreated as a control. No change in hematocrit value was observed after excimer laser irradiation. In contrast, the level of plasma free hemoglobin rose progressively with each increased duration of exposure. This result indicates that the lysis of erythrocytes does not occur in the laser-exposed cells. However, the damage to erythrocyte membrane took place as it was evidenced by progressive hemoglobin leakage into plasma. In the third experiment, the excimer laser was coupled to a 400 microns quartz optical fiber and the laser energy transmitted through the fiber was measured. At a wavelength of 308 nm, pulse energies up to 9 mJ were noted at the tip of the fiber. At a wavelength of 248 nm, the fiber tip was destroyed. In the fourth experiment, acute and chronic healing responses of normal canine arteries to excimer laser irradiation were studied in 4 mongrel dogs. The artery healed completely at the 18th day after the excimer laser irradiation. There was no evidence of thrombus formation and intimal hyperplasia in these arteries. The results suggest the applicability of excimer laser to laser angioplasty.     

Effect of helium-neon and infrared laser irradiation on wound healing in rabbits

We examined the biostimulating effects of helium-neon laser radiation (HeNe; 632.8 nm), pulsed infrared laser radiation (IR; 904 nm), and the two combined on skin wound healing in New Zealand white rabbits. Seventy-two rabbits received either 1) no exposure, 2) 1.65 J/cm2 HeNe, 3) 8.25 J/cm2 pulsed IR, or 4) both HeNe and IR together to one of two dorsal full-thickness skin wounds, daily, for 21 days. Wound areas were measured photographically at periodic intervals. Tissue samples were analyzed for tensile strength, and histology was done to measure epidermal thickness and cross-sectional collagen area. Significant differences were found in the tensile strength of all laser-treated groups (both the irradiated and nonirradiated lesion) compared to group 1. No differences were found in the rate of wound healing or collagen area. Epidermal growth was greater in the HeNe-lased area compared to unexposed tissue, but the difference was not significant. Thus, laser irradiation at 632.8 nm and 904 nm alone or in combination increased tensile strength during wound healing and may have released tissue factors into the systemic circulation that increased tensile strength on the opposite side as well.