The effect of indocyanine green pretreatment on the parameters of transscleral diode laser thermotherapy-induced threshold coagulation of the ciliary body

BACKGROUND AND OBJECTIVE: To study the effect of indocyanine green (ICG) pretreatment on threshold parameters of transscleral diode laser thermotherapy-induced threshold coagulation of the ciliary body. The procedure was termed 'cyclothermotherapy' based on the long duration (15-60 seconds) of diode laser application. STUDY DESIGN/MATERIALS AND METHODS: The right eyes of nine young adult New Zealand white rabbits underwent transscleral cyclothermotherapy (TCT, Group 1), TCT following ICG pretreatment (Group 2), and external manipulation of the ciliary body alone (Group 3). Rabbits were sacrificed after 24 hours; specimens were evaluated with gross examination and light microscopy. RESULTS: Thresholds were 30 J/cm2 (TCT) and 4.5 J/cm2 (TCT with ICG). Widespread structural damage was seen in the ciliary processes and the ciliary body in Groups 1 and 2. In Group 3, external manipulation of the ciliary body caused hemorrhage and structural damage confined to the ciliary processes. CONCLUSION: ICG pretreatment reduced the energy necessary to cause a threshold lesion with TCT in nonpigmented rabbits.     

Trans-scleral application of a semiconductor diode laser

We used a diode laser with an output power of 1 W through a fiberoptic light pipe (200 microns diameter) to deliver laser energy through the sclera of pigmented rabbits. Ciliary body destruction occurred with energy levels of 300-400 mW and exposure time of 0.5 sec. Retinal photocoagulation was achieved with energy levels of 200-500 mW in 0.5 sec. Histologic examination of acute lesions demonstrated thermal destruction of ciliary body processes and retina. Chorioretinal scar formation was observed clinically and histologically within 2-3 weeks. Our data indicate that the transscleral diode laser may be used for destruction of the ciliary body processes or peripheral retinal coagulation in pigmented eyes.     

A new contact neodymium:YAG laser for cyclophotocoagulation

A newly developed compact (40 kg), self-contained contact Neodymium:YAG laser produces high-peak, high-energy (800 mJ/pulse), short (1.0 millisecond) pulses with 1 to 3 pulses/exposure. Energy is delivered via a 320-microns cleaved quartz fiber optic probe. Cyclophotocoagulation was performed in five eyes of three medium-sized Dutch-pigmented rabbits. The eyes received exposures of 1 to 3 pulses/exposure. Energy delivered ranged from 100 to 800 mJ/pulse. Histopathology revealed ciliary body disruption and hemorrhage with no damage to overlying sclera. When used for transscleral cyclodiathermy in the rabbit, the laser created significant ciliary body disruption with minimal scleral injury.     

The effect of low-power laser light at different doses on gastric mucosa sensitized with methylene blue, haematoporphyrin derivative or toluidine blue

Helicobacter pylori has been associated with peptic ulcers, gastric cancer and various other gastroduodenal pathologies. Conventional antibiotic treatment is not entirely satisfactory, whereas photodynamic therapy (PDT) is a possible alternative. Although PDT has been shown to be effective in killing helicobacter on native gastric mucosa, the success of the technique will depend upon the mucosa underlying the bacteria remaining unharmed. This study examined the effect of increasing doses of low-power laser light on rat gastric mucosa, sensitized with either methylene blue (MB), haematoporphyrin derivative (HpD) or toluidine blue (TBO). No damage was detectable with any of the photosensitizers when a light dose of 250 Jcm^-2 was used. Mucosal damage was seen consistently with TBO (1 mg ml^-1) and a light dose of 500 J cm^-2. The same light dose of 500 J cm^-2 using MB caused inconsistent damage to the mucosa, whereas HpD had no effect even with the highest dose of laser light (500 J cm^-2). As the energy doses required to kill bacteria (50 and 200 Jcm^-2 for MB and TBO, respectively) are well below the levels shown to damage normal gastric mucosa, PDT forH. pylori should not be harmful to the underlying epithelium.     

Lasers in surgery and medicine reviewers. November 1, 1992 through October 31, 1993

Chloro-aluminum sulfonated phthalocyanine (CASPc) is a photo-chemically active dye employed in photodynamic therapy (PDT). CASPc is a potent generator of singlet oxygen when irradiated with 675 nm light and is also capable of fluorescence, allowing visualization of the dye in tissues. We devised an angiography system using CASPc fluorescence to determine its localization in experimental choroidal neovascularization in monkeys and then investigated the ability of CASPc to produce photochemical closure of neovascularization upon irradiation with 675nm laser light. Fluorescent imaging indicated that CASPc localized angio-graphically in areas of neovascularization for at least 24 hours. Irradiation with 675 nm laser light 5–30 minutes after CASPc injection produced complete closure of choroidal neovascularization with minimal damage to overlying retina. We conclude that CASPc localizes in neovascular choroidal vessels and that CASPc photodynamic therapy can produce closure of these choroidal vessels. © 1994 Wiley-Liss, Inc.     

Photodynamic therapy of C3H tumours in mice: Effect of drug/light dose fractionation and misonidazole

C3H mammary carcinomas transplanted to the feet of mice were treated with haematoporphyrin derivative (HPD) or Photofrin II(PII) and laser light at 630 nm. While fluence rates lower than 100 mW cm⁻² gave minimal hyperthermic effects, a slight but significant growth delay was observed in unsensitized tumours exposed to a fluence rate of 150 mW cm⁻² which induced tumour temperatures in the range 40–50°C. Different modes of fractionation of the light fluence and of the HPD dose were tested but were found to give poorer rather than better results than the application of a single light exposure 24 h after intraperitoneal injection of HPD. Different PII doses were applied together with different light fluences, keeping the product of the drug dose and light fluence constant. In the dose range 6.25–50 mg/kg body weight the resulting effect on tumours was constant, allowing for a slight effect of hyperthermia at the highest light fluences, and possibly a photodegradation of PII. Misonidazole given before photodynamic treatment (PDT) slightly reduced the effect of PDT on the tumour growth. When given after PDT, however, misonidazole improved the therapeutic results significantly.     

Spot size reduction in coupling of laser to micromanipulator in laser microsurgery by fiberoptic link

Background and Objective: In coupling laser with micromanipulator through fiberoptics, the resulting diameter of the spot is limited by the laws of geometrical optics, because of the high numerical aperture (N.A.) of fiberoptic radiation. A new method for the reduction of spot size diameter is suggested. Study Design/Materials and Methods: The output of a 2 mW He-Ne laser was couped via fiberoptic link, the fiberoptic output light collected by a single lens collimator and directed to the input of the micromanipulator. Results: The spot size can be considerably reduced by the introduction of an aperture which reduces the numerical aperture (N.A.) of the fiberoptic. The resulting reduction in total power has little effect on the power density. Conclusion: This approach to the collimator design permits reduction in spot size without any significant changes in power density, thus avoiding damage to the tissue and obtaining optimum performance from the micromanipulator. © 1995 Wiley-Liss, Inc.     

Retinal and choroidal vessel closure using phthalocyanine photodynamic therapy

Chloro-aluminum sulfonated phthalocyanine (CASPc) is a photoactive dye capable of generating photochemical reactions when excited with 675 nm light. We used CASPc to produce photochemical closure of retinal medullary ray vessels and choroidal vessels in normal rabbits. Irradiation prior to CASPc injection produced no photographic, angiographic, or histologic lesions in any eyes. Identical irradiation of medullary ray and choroidal vessels after CASPc injection produced complete vessel closure in all eyes. Histopathologic examination showed marked thrombosis of medullary ray and choroidal vessels, with minimal damage to contiguous tissues including the neurosensory retina. We conclude that CASPc can produce profound closure of normal retinal and choroidal vessels with minimal deleterious effect on surrounding tissues. © 1994 Wiley-Liss, Inc.     

Photodynamic therapy of experimental tumours with Zn(II)-phthalocyanine and pulsed laser irradiation

The effectiveness of a pulsed dye laser (673 nm) for photodynamic therapy (PDT) of tumours in the presence of Zn(II)-phthalocyanine (ZnPc) was evaluated using Lewis lung carcinoma-bearing mice. The tumours were irradiated with different pulse energies (from 0.4 to 10 mJ) at a constant fluence of 0.6 J cm^–2 at 24 h after administration of 0.25 mg kg^–1 body weight liposome-incorporated ZnPc. Maximal PDT effect, as evaluated by changes in mean tumour diameter, animal survival time and histological evaluation of tumour necrosis, was observed after 3.0 mJ pulse energy irradiation which appears to yield a deeper light penetration and a more efficient sensitizer excitation when compared with lower or higher pulse energies. Electron microscopic analysis of photo-treated tumour indicates preferential damage to malignant tissue as compared to endothelial cells.     

In vivo uptake of liposomal benzoporphyrin derivative and photothrombosis in experimental corneal neovascularization

Background and Objective: Photodynamic therapy (PDT) has been used successfully to occlude neovascularizations experimentally. We evaluated the vasoocclusive potential of benzoporphyrin derivative (BPD), a new photosensitizer currently in clinical trials. Since liposomally formulated BPD strongly binds to endogenous low density lipoproteins (LDL) after i.v. injection, LDL act as carrier to deliver BPD preferentially to proliferating endothelial cells. Study Design/Materials and Methods: Corneal neovascularizations in rabbits were used as model. Time-dependent uptake and retention of liposomal BPD were measured in vivo by monitoring the laser-induced fluorescence (LIF). Photothrombosis was induced using a dye laser emitting at 692 nm. Results: A maximal BPD concentration was measured at 60–90 minutes postinjection determining the optimal time interval for treatment. Exposures as low as 10 J/cm² allowed complete and irreversible neovascular occlusion as documented angiographically. Histology revealed selective endothelial damage, adjacent corneal stroma, or iris vessels, remained intact. Identical results were obtained using BPD directly complexed with LDL suggesting use of a LDL-mediated pathway. Conclusion: We suggest BPD-PDT for a selective treatment of neovascular diseases. © 1995 Wiley-Liss, Inc.     

Differences between cytotoxicity in photodynamic therapy using a pulsed laser and a continuous wave laser: study of oxygen consumption and photobleaching

Oxygen consumption at the targeted site has a significant effect on dosimetry in photodynamic therapy (PDT). However, oxygen consumption in PDT using a pulsed laser as a light source has not been clarified. We therefore investigated the dependence of cytotoxicity on the oxygen consumption and the photosensitizer photobleaching of PDT using a pulsed laser by comparing with that using a continuous wave (CW) laser. Mouse renal carcinoma cells (Renca) were incubated with a second-generation photosensitizer, PAD-S31. The cells were then irradiated with either a 670-nm nanosecond pulsed light from the 3rd harmonics of a Nd:YAG laser-pumped optical parametric oscillator with a peak fluence rate of ~1 MW/cm² at 30 Hz or a 670-nm CW diode laser with a total light dose of 40 J/cm². Regardless of laser source, cytotoxic effects exhibited cumulative dose responses to the photosensitizer ranging from 12 to 96 g/ml. However, cytotoxic effect of PDT using the pulsed light was significantly less than that using the CW light with the photosensitizer concentrations of 24 and 48 g/ml under identical fluence rates. During PDT, the cells exposed to the pulsed light consumed oxygen more slowly, resulting in a lower amount of oxygen consumption when compared with PDT using CW light. In accordance with oxygen consumption, the pulsed light induced significantly less photobleaching of the photosensitizer than the CW light did. These results indicate that the efficiency of PDT using pulsed light is less when compared with CW light, probably being related to suppressed oxygen consumption during the pulsed light irradiation.     

Transscleral cyclophotocoagulation using a semiconductor diode laser in cadaver eyes.

We studied the effectiveness of semiconductor diode laser transscleral cyclophotocoagulation in cadaver eyes using the Miyake technique and light microscopy. Thermal lesions in the ciliary processes were induced with 0.7-second, 1200-mW, and 100- to 500-microns applications, 0.5 mm from the surgical limbus and defocused 1 mm posteriorly. An effective ciliary body reaction was observed grossly as tissue blanching, shrinkage, and pigment dispersion; and histologically, as coagulation necrosis and epithelial cell disruption. No damage to crystalline or intraocular lenses was evident. This successful application of diode laser transscleral cyclophotocoagulation in cadaver eyes suggests that it may prove useful in treating patients with glaucoma.     

Intrathoracic photodynamic therapy: A canine normal tissue tolerance study and early clinical experience

Surgery with intraoperative photodynamic therapy (PDT) has the potential to improve the treatment of pleural malignancies. Before embarking on such treatment in humans, however, thoracic tissue tolerance to PDT was studied. For each of three (1 week, 1 month, and 6 month) study end-points, one control (no Photofrin II [PII]) and four treated animals underwent thoracotomy 72 hours after I.V. injection (6 mg/ kg) PII. Red light (630 nm) was delivered (5–40 J/cm²) to the pleural surface (1 cm diameter) of selected thoracic organs. No clinical differences were observed between PDT and control dogs. The control showed no histological changes; however, in the treated animals focal areas of coagulation necrosis were found at 1 week which progressed to fibrosis at 1 month. The extent and depth of injury was proportional to light dose. The lung was the most sensitive; the chest wall was the most resistant. Myocardium had superficial damage, whereas coronary arteries appeared normal. The results provide the basis for proceeding to phase I human trials in the evaluation of PDT as an intraoperative adjuvant treatment in the management of pleural malignancies. © 1994 Wiley-Liss, Inc.     

Telerobotic contact transscleral cyclophotocoagulation of the ciliary body with the diode laser

To assess the feasibility of using the Robotic Slave Micromanipulator Unit (RSMU) to remotely photocoagulate the ciliary body for the treatment of glaucoma with the diode laser. In fresh unoperated enucleated human eyes, the ciliary body was destroyed either with a standard contact transscleral cyclophotocoagulation ‘by hand’ diode laser technique, or remotely using the RSMU. The treated sections were fixed in formalin, paraffin-embedded, and stained with hematoxylin and eosin. Histological evaluation was performed by a masked observer using a standardized grading system based on the amount of damage to the ciliary body to evaluate effectiveness of treatment. Both methods of contact transscleral cyclophotocoagulation showed therapeutic tissue disruption of the ciliary processes and both the non-pigmented and pigmented ciliary epithelium. Histology examination of remote robotic contact transscleral cyclophotocoagulation and “by hand” technique produced similar degrees of ciliary body tissue disruption. Remote diode laser contact transscleral cyclophotocoagulation of the ciliary body in fresh enucleated human eyes is possible with the RSMU. Therapeutic tissue disruption of the ciliary body was achieved. Additional study is necessary to determine the safety and efficacy of robotically-delivered cyclophotocoagulation in live eyes.     

Bactericidal effects of different laser wavelengths on periodontopathic germs in photodynamic therapy

 This study was an attempt to clarify whether the bactericidal effects of photodynamic therapy (PDT) are wavelength or dose-dependent. We also attempted to create an optimised protocol for a light-based bactericidal modality to eliminate periodontal pathogens. Cultures of Actinobacillus actinomycetemcomitans, Fusobacterium nucleatum, Porphromonas gingivalis, Prevotella intermedia, and Streptococcus sanguis, were exposed to a He-Ne laser (632.8 nm) with a 30 mW power output, a 100 mW diode laser at 665 nm, or a 100 mW diode laser at 830 nm, in the presence or absence of methylene blue (MB) as a photosensitiser. A control group was also used with exposure to MB alone without laser exposure. The cultures were analysed by viable counts. The results indicated that exposure to the 100 mW laser light could eliminate up to 40% of bacteria on average. In particular, the most effective killing occurred with exposure to laser light in combination with the MB photosensitiser. The results of kinetic studies indicated that the best PDT response rate was achieved with a 60 s (energy density 21.2 J/cm²) exposure to the 665 nm wavelength diode laser in the presence photosensitiser. In this condition, approximately 95% of A. actinomycetemcomitans and F. nucleatum, and 99–100% of the black-pigmented bacteria (P. gingivalis and P. intermedia) and S. sanguis were eliminated. These results showed that both wavelength and energy density are important factors, and that a low power laser of optimal wavelength and dosage, in combination with an appropriate photosensitiser, is a practical bactericidal modality. We concluded that using a diode laser of proper power and wavelength to deliver 60 s of irradiation could be a useful adjunct with mechanical debridement in the prevention of the re-colonisation of subgingival lesions by pathogenic microorganisms. Received: 29 November 2001 / Accepted: 18 June 2002     

Combination studies of hyperthermia induced by the neodymium: yttrium-aluminum-garnet (Nd:YAG) laser as an adjuvant to photodynamic therapy

Photodynamic therapy (PDT) and hyperthermia have been investigated as treatments for several types of tumors. Studies have been done to determine the efficacy of each modality individually and recently in combination with each other. In this study, 630-nm light was delivered by an argon-dye laser and hyperthermia was induced using an Nd:YAG laser. Both lasers offer the ability of delivering the beams through a quartz fiberoptic alone or simultaneously. This study examines the efficacy of the simultaneous administration of PDT and selective hyperthermia at 44.5 degrees C in tumor control in the spontaneous mammary tumor (SMT-F) in DBA mice. Hyperthermia alone (44.5 degrees C, 30 min) resulted in complete destruction of tumors, with no subsequent regrowth in 6.6% of the mice treated. PDT alone (5 mg/kg dihematoporphyrin ether; 135 J/cm) resulted in a cure rate of approximately 10%, and the simultaneous treatment of the modalities resulted in a 32.8% cure rate after 90 days. These values are indicative of a synergistic interaction.     

Wavelength-dependent effect of tetra(m-hydroxyphenyl)chlorin for photodynamic therapy in an ‘early’ squamous cell carcinoma model

The purpose of the present study was to correlate the wavelength of the irradiation source with the phototoxic activity of tetra(m-hydroxyphenyl)chlorin (mTHPC) in healthy and neoplastic mucosae. The hamster tumour model for early squamous cell carcinoma was used in these experiments. In vitro and in vivo studies have shown that mTHPC absorbs significantly at 652 nm (1, 2). This wavelength is used currently in clinical mTHPC photodynamic therapy (PDT) trials. In order to study the wavelength dependence of the phototoxic effect on normal and tumour tissues, irradiation tests were performed 4 days after injection of 0.5mg kg^-1 mTHPC. An argon-ion pumped dye laser was used as the light source. The light dose of 12 J cm^-2 was delivered at a light dose rate of 150 mW cm^-2. The wavelength was varied between 642.5 and 665 nm at 2.5-nm increments. The PDT damage was evaluated in serial Haematoxylin and Eosin stained sections using a tissue-damage scale. Light between 647.5 and 652.5 nm induced the highest damage to both the healthy and tumour mucosae. At wavelengths equal to or below 645 nm, and equal to or above 655 nm, tissue damage decreased. Wavelengths below 642 nm and above 660 nm did not induce any visible tissue damage. These results suggest that the in vivo optimal wavelength range for PDT with mTHPC is between 647 and 652 nm. This information is essential for selecting an appropriate light source.     

Immediate changes in subcellular structures of transplanted tumors following photodynamic and laser hyperthermic therapy

Background and Objective: To further understand the precise process of the tumor cell degeneration after photodynamic therapy (PDT), laser hyperthermic therapy (LH), and combined treatments using an Nd:YAG laser. It is important to examine initial morphological alteration of tumor cells after these treatments. Study Design/Materials and Methods: In this study, nude mice bearing HeLa cell tumors were treated with PDT, LH, and combined treatments of the two. Tumor tissues obtained immediately after these treatments were analyzed using electron microscopy and morphometry. Results: In the combined treatments, which produced more severe effects on tumor cells, morphological features of apoptosis such as cytoplasmic condensation, blebs, and apoptotic bodies appeared in the cells, although the typical alteration in the nuclear chromatin was not seen. Conclusion: Cytoplasmic alterations may proceed more rapidly than nuclear alterations in the cellular degeneration induced by the single or combined treatments of PDT and LH.     

Biological effect of low-power helium-neon (HeNe) laser irradiation

The functional effects (activation and cell damage) of low-power, continuous-wave HeNe laser irradiation were studied in different in vitro cultured cell lines. A characteristic dose-dependence was observed between 0.14 and 28.0 J/cm². The functional activation (increased phagocytic activity, immunoglobulin secretion) or cell destruction could not be detected after irradiation by normal monochromatic light of the same wavelength and energy output. The experiments suggested that low-power laser irradiation has a specific influence on the cells which depends on the coherent and polarized physical features of the laser light.     

Evaluation of a KTP (potassium-titanyl-phosphate) 532 nm laser for endovaporization of choroidal melanomas

BACKGROUND AND OBJECTIVES: The purpose of this in vitro study is to evaluate the use of the KTP (potassium-titanyl-phosphate) 532 nm laser for future use in endovaporization of large choroidal melanomas. STUDY DESIGN/MATERIALS AND METHODS: A KTP 532 nm green laser coupled to a 0.3 mm fiberoptic probe was used to perform in vitro studies on human cadaver eyes and on one enucleated melanoma eye. The specimens were examined by histological staining (Masson-Trichrome) and scanning electron microscopy (SEM). RESULTS: Histological analysis of sclera, choroid, retina, and melanoma revealed different zones of collateral thermal tissue damage. These zones were analyzed quantitatively. We determined the best suitable laser parameters and the time for sclera penetration. CONCLUSIONS: The KTP-laser showed good potential in intraocular vaporization of choroidal melanomas. However, great differences in laser absorption between sclera and melanoma can cause significant complications such as perforation.