[Transscleral laser therapy in the treatment of glaucoma]. / Lazernye transskleral'nye tekhnologii v lechenii glaukomy.

Nowadays glaucoma is one of the leading causes of irreversible blindness worldwide. The main goal in preservation of vision in glaucoma patients is reducing intraocular pressure (IOP), which is considered the main controlled risk factor for progression of glaucomatous optic neuropathy. The article discusses the effectiveness and safety of various transscleral laser technologies in the treatment of glaucoma. Modern transscleral laser technologies that affect the uveoscleral drainage and scleral hydro-permeability are less traumatic and more gentle making them promising in the treatment of patients with early stages of glaucoma, and not only in terminal glaucoma with pain syndrome resistant to conventional treatment ("last resort surgery").

[New biophotonics methods for improving efficiency and safety of laser modification of the fibrous tunic of the eye]. / Novye metody biofotoniki dlia povysheniia éffektivnosti i bezopasnosti lazernykh tekhnologii modifikatsii fibroznoi obolochki glaza.

The article describes a newly developed and tested diffractive optical element (DOE) that converts non-uniform radiation of the laser output into a homogeneous ring. The Gerchberg-Saxton algorithm is shown to be well suited for achieving annular intensity distribution. Testing this ring transducer on threshold-plasticity cornea demonstrated the reversibility of axisymmetric changes in the cornea. Atomic-Force microscopy of the area of maximum stresses in the corneal periphery showed no significant changes in the structure of the cornea when irradiated in the selected mode. Measurement of Young's modulus of the corneal surface areas after their irradiation also revealed no changes in the elastic properties, while examination of the corneal structure demonstrated the absence of significant structural changes in irradiated samples compared with intact ones.

[Hybrid (femtosecond laser-assisted) phaco surgery and the state of the macula]. / Gibridnaia (femtolazernaia) fakokhirurgiia i sostoianie makuliarnoi zony setchatki.

The review covers different aspects of the impact of femtosecond laser-assisted cataract surgery on the state of the macular zone of the retina. Literature search has revealed inconsistency of the published data and indicated the need for a more detailed study of this problem.

[The study of opportunity of aqueous humor filtration increase after nondestructive laser exposure of sclera in the site of pars plana projection (experimental study)].

Increase of scleral water permeability due to formation of porous structure after exposure of pulsed periodic radiation of erbium-glass optical fiber laser with wave length 1,56 pm was demonstrated in experimental study of cadaver human eyes in vitro and eyes of experimental animals (rabbits) in vivo. Simultaneous complex laser exposure of pars plana and ciliary processes results in summation of morphological changes that provide decrease of aqueous humor secretion, uveal drainage and extension of suprachoroid space. A base for new noninvasive technology of nondestructive laser exposure in glaucoma treatment is established.

[Effect of infrared laser radiation on sorption of dry cartilage and connective tissue preparations]. / Vliianie lazernogo izlucheniia infrakrasnogo diapazona na sorptsiiu vody sukhimi preparatami khriashchevoi i soedinitel'noi tkanei.

Cartilaginous and connective tissues were exposed to a moderate-intensity IR laser treatment with IR radiometric temperature control. The isotherms of water sorption by dry preparations of intact and laser-treated tissues were obtained and calculated in terms of well known models. It was shown that the sorption capacity of a monolayer of tissues decreases with increasing temperature during laser treatment. Changes in the supramolecular structure of the extracellular matrix of tissues (loss of regularity) upon IR laser exposure are discussed.

[Experimental and morphological as well as physical and chemical interaction of laser radiation of a close infrared range with the fibrous eye membrane]. / Eksperimental'no-morfologicheskie i fiziko-khimicheskie aspekty vzaimodeistviia lazernogo izlucheniia blizhnego infrakrasnogo diapazona s fibroznoi obolochkoi glaza.

Experimental-and-morphological as well as physical-and-chemical changes occurring in the eye fibrous coat tissues, i.e. the cornea and sclera, at non-ablation impact of fiber laser radiation (Er-glass) with a wavelength of 1.56 mcm were analyzed. Necrobiotic or necrotic changes occur in the tissues with regard for laser radiation capacity and impact duration; subsequently, the regenerative process involving a retraction of the sclera and a flattening of the cornea takes place in the end. When the cornea is heated by fiber laser radiation with a minimally possible intensity (up to 0.3 Wt), a temporary weakening is observed in the corneal rigidity. Should it be accompanied by a simultaneous occurrence of retraction forces coming from the sclera (at its coagulation), it can be used to change, in the clinical controllable mode, the corneal curvature radius.

Theramal, mechanical, optical, and morphologic changes in bovine nucleus pulposus induced by Nd:YAG (lambda = 1.32 microm) laser irradiation.

UNLABELLED: BACKGROUND AND OBJECTIVE To examine the biophysical effects of photothermal heating on herniated intervertebral discs during laser decompression surgery. STUDY DESIGN/MATERIALS AND METHODS: Ex vivo bovine nucleus pulposus specimens were irradiated with a Nd: YAG laser (lambda = 1.32 microm, 100 seconds exposure time, 9-31 W/cm(2), 4.8 mm spot diameter), whereas changes in tissue thermal, mechanical, and optical properties were monitored by using, respectively, infrared radiometry, tissue tension measurements, and diffuse reflectance from a HeNe probe laser. Morphologic changes and mass reduction were monitored by recording shape changes on video and weighing specimens before and after laser exposure. RESULTS: At power densities below 20 W/cm(2), evaporation of water and specimen volume reduction (shrinking) were consistently observed on video during irradiation. In contrast, above 20 W/cm(2), vapor bubbles formed within the specimen matrix and subsequently ruptured (releasing heated vapors). When radiometric surface temperature approaches approximately 60 to 70 degrees C (denaturation threshold for tissue), tissue tension begins to increase, which is consistent with observations of specimen length reduction. The onset of this change in tissue tension is also reflected in characteristic alterations in diffuse reflectance. With cessation of laser irradiation, a sustained increase in tissue tension is observed, which is consistent with changes in specimen length and volume. Higher laser power results in a faster heating rate and subsequently an accelerated tension change. Specimen mass reduction increased with irradiance from 19 to 72% of the initial mass for 9--31 W/cm(2), respectively. Irradiated specimens did not return to their original shape after immersion in saline (48 hours) in contrast to air-dried specimens (24 hours), which returned to their original shape and size. CONCLUSION: These observations suggest that photothermal heating results in irreversible matrix alteration causing shape change and volume reduction (observed on video and evidenced by the increase in tissue tension) taking place at approximately 65 degrees C. Inasmuch as high laser power results in vapor bubble formation and specimen tearing, the heating process must be controlled. Diffuse reflectance measurements provide a noncontact, highly sensitive means to monitor dynamically changes in tension of nucleus purposus.

[Holmium laser in chondrology: potentials and prospects]. / Vozmozhnosti i perspektivy primeneniia gol'mievogo lazera v khondrologii.

To study the mechanism of simulation of a cartilage, to define the optimum parameters and laser radiation regimens, the authors made a complex of in vitro experiments on the cartilages of the nasal septum in man and domestic animals and in vivo experiments on those of the concha in rabbits and pigs. Holmium laser radiation is shown to be the most suitable tool for formation of a cartilage. Evidence is provided for the possibility of irreversibly altering the shape of a cartilage during laser radiation. A procedure has been developed for non-invasive correction of the septum of the nose for its curvature. Restored or improved nasal respiration was observed in more than two thirds of the patients. Laser surgery is not of age-limited application, it is noninvasive, can be performed in the outpatient settings and requires no drug treatment in the postoperative treatment.

Proteoglycan synthesis in porcine nasal cartilage grafts following Nd:YAG (lambda = 1.32 microns) laser-mediated reshaping.

Mechanically deformed morphologic cartilage grafts undergo temperature-dependent stress relaxation during sustained laser irradiation resulting in stable shape changes. In this study, porcine nasal septal cartilage specimens were evaluated for viability by measuring the incorporation of Na2(35)SO4 into proteoglycan (PTG) macromolecules in whole tissue culture following laser-mediated reshaping. Synthesis rates of PTG were determined by scintillation counting lyophilized specimens and normalizing these values by total protein content. Positive controls were established by inducing chondrocyte apoptosis using prolonged exposure to nitric oxide (NO). In chondrocytes, apoptosis induced using NO resulted in significantly lower PTG synthesis rates compared to untreated native specimens. Cartilage specimens were irradiated with light emitted from a Nd:YAG laser (25 W/cm2, lambda = 1.32 microns) while recording simultaneously radiometric surface temperature, internal stress and back-scattered light intensity from a probe laser. Each specimen received one, two or three sequential laser exposures. The duration of each exposure was determined from real-time measurements of characteristic changes in back-scattered light intensity that correlate with accelerated stress relaxation. A 5 min time interval between each laser exposures allowed the cartilage specimen to return to thermal equilibrium. Average PTG synthesis rates decreased with successive laser exposures, though these were always higher than baseline rates established for NO-treated tissues, suggesting that laser-mediated cartilage reshaping acutely does not eliminate the entire population of viable chondrocytes. The reduction in PTG synthesis is correlated with the time-temperature-dependent heating profile created during laser irradiation, supporting our hypothesis that careful monitoring of laser dosimetry is required to ensure chondrocyte viability.

[Reestablishing of nasal respiration with Holmium laser in distortion of nasal septum in cartilaginous part]. / Vosstanovlenie nosovogo dykhaniia s pomoshch'iu izlucheniia gol'mievogo lazera pri iskrevlenii peregorodki nosa v khriashchevom otdele.

To study mechanisms of cartilage modelling, estimation of optimal parameters and regimens of laser radiation, the authors made in vitro and human experiments on nasal septum cartilages and in vivo experiments on cartilages of the floor of the auricle in rabbits and pig. Ho-laser radiation is thought the most appropriate tool for cartilage shaping. A method of non-invasive correction of the nasal septum cartilage in its distortion has been designed. 2/3 of the patients recovered or improved nasal respiration. Laser operation has no age restrictions, is non-invasive, can be made outpatiently, is not followed by pharmacological treatment.

Feedback-controlled laser-mediated cartilage reshaping.

OBJECTIVE: To demonstrate feedback-controlled laser-mediated cartilage reshaping using dynamic measurements of tissue optical properties and radiometric surface temperatures. DESIGN: Flat cartilage specimens were reshaped into curved configurations using a feedback-controlled laser device. MATERIALS: Fresh porcine nasal septum, stripped of perichondrium and cut into uniform strips (25 x 10 x 1.5-2.1 mm) with a custom guillotine microtome. INTERVENTIONS: Cartilage specimens secured in a cylindrical reshaping jig (2.5 cm in diameter) and irradiated with an Nd:YAG laser (lambda = 1.32 microns, 25 W/cm2, 50-Hz pulse repetition rate). During laser irradiation, radiometric surface temperature was measured along with changes in forward-scattered light from a diode probe laser (lambda = 650 nm, 5 mW), using a lock-in detection technique. Sequential irradiation of the specimen outer surface was made (3 laser passes). Characteristic changes in tissue temperature and light-scattering signals were used to terminate laser irradiation. RESULTS: Effective reshaping was accomplished for both thin (1.5-mm) and thick (2.1-mm) specimens. Following reshaping, specimens were stored in saline solution at 4 degrees C for 21 days. No return to the original flat configuration was noted during this period. CONCLUSIONS: The prototype device effectively reshapes flat native porcine cartilage into curve configurations. The use of optical and thermal signals provides effective feedback control for optimizing the reshaping process.

Stress Relaxation of Porcine Septal Cartilage During Nd:YAG (λ=1.32 µm) Laser Irradiation: Mechanical, Optical, and Thermal Responses.

Laser-assisted cartilage reshaping is mediated by thermally induced stress relaxation, and may be used to alter cartilage morphology for reconstructive surgical procedures in the upper airway and face without carving, morselizing, or suturing. Internal stress σ(t), integrated backscattered light intensity I(t) from a He-Ne probe laser (λ=632.8 nm), and radiometric surface temperature Sc(t) were measured during the reshaping of porcine nasal septal cartilage using a pulsed Nd:YAG laser (λ=1.32 µm). Internal stress and integrated backscattered light intensity were observed to increase, plateau, and then decrease in similar ways during laser irradiation. The plateau region occurred when the cartilage front surface temperature approached 65 °C. I(t) was utilized in a feedback control procedure to reshape cartilage specimens from a flat to a curved geometry. Immediately following laser irradiation, the tissues were rehydrated in normal saline for 15 min while wrapped around a small dowel. A stable shape change was retained for 21 days while the specimens were stored in normal saline at 5 °C. The backscattered light intensity signal mirrors underlying changes in internal stress, and further rate of change or slope of I(t) is nearly zero when the surface temperature reaches about 65 °C. Measurements of I(t) (or, equivalently, the fractional change in integrated backscattered light intensity ΔI(t)/I0) may be used to control the process of laser-assisted cartilage reshaping and minimize nonspecific thermal injury due to uncontrolled heating. © 1998 Society of Photo-Optical Instrumentation Engineers.

Biocompatibility of Laser-deposited Hydroxyapatite Coatings on Titanium and Polymer Implant Materials.

We have investigated the biocompatibility of calcium phosphate coatings deposited by pulsed laser ablation from hydroxyapatite (HA) targets onto polyethylene and Teflon substrates. It was found that the cell density, attachment, and morphology of primary rat calvaria osteoblasts were influenced by both the original polymer and by the nature of the apatite coatings. HA coatings on Teflon were found to have higher biocompatibility in terms of cell adhesion and spreading. In vivo studies of bone response to coatings deposited by KrF excimer and CO2 lasers on commercial Ti6A14V alloy implants show that both deposition techniques suppress fibrous tissue formation and promote osteogenesis. © 1998 Society of Photo-Optical Instrumentation Engineers.

Atomic force microscopic study of the surface morphology of apatite films deposited by pulsed laser ablation.

Atomic force microscopy (AFM) has been used to study the surface morphology of apatite films deposited on metallic and polyethylene substrates by laser ablation using KrF and transversely excited atmospheric CO2 lasers. The films are found to consist of a smooth apatite coating with macroparticles scattered on the surface. A wide variety of macroparticles, differing in size, shape and roughness, were found and analysed employing the high spatial resolution of AFM (< 1 nm). We have investigated the correlation between the apatite film morphology and the deposition conditions. Of particular importance are laser fluence, gas pressure, the nature of the target and the substrate temperature. We have explained these dependencies on the basis of a theoretical model which includes evaporation and a cluster-type laser ablation mechanism.

Thermal and diffusion processes in laser-induced stress relaxation and reshaping of cartilage.

The thermodynamic characteristics of the 'bound-to-free' phase transformation of water are studied by means of differential microcalorimetry and FTIR spectroscopy. This phase transition controls the stress relaxation and reshaping of cartilage which we have observed previously under moderate laser heating. It is shown that the FTIR spectrum of bound water in cartilage differs from that of free water in cartilage, and that both show differences to the FTIR spectrum of pure water. The proportion of bound water in cartilage is found to be of the order 4%. We have examined water liberation and absorption kinetics and found them to be controlled by diffusion through the tissue and also by the bound-to-free water transformation. The theoretical modelling and experimental data allowed calculation of diffusion coefficients and the activation energy for water transfer. The latter was found to be close to the heat of phase transformation of water. We have established that the drying and wetting processes in cartilage are reversible (fully or in a part, depending on the temperature of preliminary drying) and can be described by identical solutions of the diffusion problem, with coefficients of water diffusion being the same. The mechanism of water diffusion in cartilaginous tissue is also discussed.

[Photochemical reactions in bone tissue induced by excimer laser ultraviolet]. / O proiavleniiakh fotokhimicheskikh reaktsi'i v kostno'i tkani pod de'istviem ul'trafioletovogo izlucheniia eksimernogo lasera.

A phenomenological model of an increase in ultraviolet absorption in bone tissue induced by ultraviolet radiation of excimer laser has been developed. It is assumed that the increase in absorption is related to photochemical reactions in collagen. The model accounts for changes in the intensity of laser radiation due to its absorption inside the specimen. From the comparison of experimental and calculated results the parameters of the photochemical model were estimated. The temperature fields in the specimen were calculated with regard to laser-induced changes in absorption coefficient. The limits of applicability of the model are discussed.

[Possibilities of the use of surgical laser irradiation in spontaneous formation of cartilage tissue in ENT plastic surgery]. / Vozmozhnosti primeneniia izlucheniia khirurgicheskikh lazerov s tsel'iu proizvol'nogo formirovaniia khriashchevoi tkani v plasticheskoi LOR-khirurgii.

The experiments were made to study CO2-laser ability to promote spontaneous formation of nasal septum cartilage. Laser-induced changes in physical and histological characteristics of the cartilage tissue were followed up. Optimal regimens of radiation were selected which allowed to modify cartilage shape without impairment of its morphological and histological structure. In vivo tests were performed on rabbit auricular floor cartilage. The present shape of the cartilage remained stable. It is inferred that laser energy may be a promising tool in plastic ENT surgery.