Amount Of Laser Energy Research Articles

A Study of Visual Improvement and Variation in IOP Following Nd-YAG Laser Capsulotomy

AIM: To study the visual improvement and to correlate the effect of energy used and number of shots with post procedural IOP spike following Nd-YAG laser capsulotomy cases. MATERIALS AND METHODS: A total of 36 patients presented with pseudophakia with PCO attending ophthalmology outpaient department at Rajah Muthiah medical college hospital during the period of October 2020 - December 2022 were included in the study. Patients with glaucoma, Uveitis, high myopia, posterior segment disorders will be excluded from the study. The patient will be subjected to visual acuity testing, detailed slit lamp examination, IOP measurement using Non-contact tonometer pre and post laser procedure and detailed fundus examination done and results were interpreted. OBSERVATION: Among the total 36 participants, 31.4% belong to age group 56 to 65 years followed by 28.6% in the age group 66 to 75 years. 51.4% were males and 48.6% were females. Of the total participants 28.6% had visual acuity of 6/24 in the affected eye and 22.9% had visual acuity of 6/36 in the affected eye.one subject presented with visual acuity of hand movements (HM) only in the involved eye.The mean pre-operative intraocular pressure among the participants was 1.85±0.73. 45.7% had preoperative IOP of 13 to 16 mmHg and 34.3% had preoperative IOP of 8 to 12. The mean number of YAG shots among the participants was 1.96±0.81. 36.3% were provided with 5 to 8 YAG shots and 33.3% with 2 to 4.The mean IOP among the participants in the preop was 14.03±2.92. The mean IOP immediately after the intervention was 15.29±2.83.The mean IOP 20 mins after the intervention was 17.43±2.96.Our study shows that the change in mean IOP after ND YAG LASER administration was significant with P value of less than 0.05 and also our study shows improvement in post laser BCVA with significant P values CONCLUSION: The study concluded that all patients had good visual recovery. The post laser IOP raise is minimal and transient. It varies with amount of laser energy used. Hence recommended to use minimum possible laser energy and must be followed up for raised intraocular pressure changes. Keywords: Intraocular pressure, Neodymium: Yttrium Aluminium GARNET Capsulotomy.

Клинические результаты лечения открытоугольной глаукомы микроимпульсной транссклеральной циклофотокоагуляцией

Purpose. To evaluate treatment efficiency of open-angle glaucoma with micropulse transscleral cyclophotocoagulation, to determine the optimal total energy of laser exposure and to assess the stability of the glaucoma process after treatment. Material and methods. A prospective study was carried out. It included 34 (21 patients) with primary open-angle and pseudoexfoliative glaucoma of stages 1-3, which undergone micropulse transscleral cyclophotocoagulation. The patients were divided into subgroups 1 and 2, depending on the total amount of laser energy (100 J and 150 J, respectively). At different periods of observation, the intraocular pressure, best corrected visual acuity, visual fields, cup-to-disc ratio and the number of antiglaucoma drugs were determined. Results. In the general group, all operated patients achieved a decrease in IOP to a tolerant level, from a median value of 27 [25; 28] in the preoperative period, up to 17.5 [15; 20] at the end of the observation period. The number of used drugs decreased statistically significantly, from 3.0 [3.0; 3.0] to 2.0 [1.0; 2.0]. There was a statistically significant increase in the mean deviation of the retinal photosensitivity, from –4.85 [–8.25; –2.17] to –4.36 [–7.06; –2.37] after 18 months. Indicators of best corrected visual acuity and CDR remained stable throughout the observation period. In subgroup 2 (150J), a statistically more significant decrease in IOP level (p=0.033) and the number of used drugs (p=0.001) was achieved compared with subgroup 1 (100J). Conclusion. Micropulse transscleral cyclophotocoagulation is an effective and safe method of treating open-angle glaucoma in patients with early stages of the disease and high values of best corrected visual acuity. Using a total amount of energy in 150J contributes to a more pronounced decrease in IOP and a decrease in the number of applied drugs than an energy in 100J. Key words: open-angle glaucoma, pseudoexfoliative glaucoma, micropulse cyclophotocoagulation.

Free radical production by femtosecond laser lens irradiation in porcine eyes

To investigate the relationship between the generation of free radicals and femtosecond laser lens irradiation. AMO Laboratory, Tokyo, Japan. Exvivo studies. Hydroxyphenyl fluorescein (HPF) was injected into the anterior chamber of fresh 6-month-old porcine cadaver eyes (N=31). After laser irradiation, a plate reader was used to measure the fluorescence of the aqueous humor samples. Relative fluorescence units (RFU) were calculated by subtracting the average control value from the measured values of all the samples. Experiment 1: After determining the RFU in the 7 laser-irradiated eyes, the relationship with the amount of laser energy was then assessed. Experiment 2: To clarify the issue regarding the degree of attenuation of the fluorescence intensity, HPF was simultaneously injected into 2 eyes, with 1 eye irradiated and the other eye used as a control. After dividing the RFU of the laser-irradiated eye by the control RFU, the laser irradiation-control RFU ratio was calculated, and the relationship with the laser irradiation energy amount then assessed. There was a significant correlation between the femtosecond laser lens irradiation energy and the RFU in the aqueous humor (P<.05, analysis of variance). Femtosecond laser lens irradiation increases the quantity of free radicals in the aqueous humor, with the extent of the increase dependent on the amount of laser energy. These results suggest that excessive laser irradiation during femtosecond laser-assisted cataract surgery might cause corneal endothelial damage because of the free radicals created during the procedure.

Comparison of New Visual Disturbances after Superior versus Nasal/Temporal Laser Peripheral Iridotomy: A Prospective Randomized Trial

To determine whether laser peripheral iridotomy (LPI) location affects postoperative dysphotopsia symptoms. Multicenter, randomized, prospective, single-masked trial. Five hundred fifty-nine South Indian patients 30 years of age or older diagnosed as primary angle-closure suspects (PACSs) or with primary angle closure (PAC) or primary angle-closure glaucoma (PACG) in both eyes. Patients were randomized to either bilateral superior or bilateral nasal/temporal LPI. Occurrence of new visual disturbances was evaluated before and 2 weeks after LPI using a questionnaire based on the 7-item dysphotopsia symptoms described by Spaeth etal. New-onset dysphotopsia symptoms. Superior LPI (n= 285) and nasal/temporal LPI (n= 274) patients were matched for age (P= 0.6), gender (P= 0.7), and distribution of PACS versus PAC or PACG (P= 0.7). Similar initial laser energy settings were used in both groups (P= 0.3), although superior LPIs required more shots (P= 0.006) and greater total energy (P< 0.001) than nasal/temporal LPIs. No significant differences in postoperative anterior chamber reaction (P=0.7) or LPI area (P= 0.9) were noted between the 2 groups. No group differences were noted regarding the proportion of patients demonstrating 1 or more dysphotopsia symptoms before LPI (15.8% for superior vs. 13.9% for nasal/temporal; P= 0.1) or any individual dysphotopsia symptom (P > 0.2 for all). After LPI, 8.9% of all patients reported 1 or more new symptoms, the most common consisting of linear dysphotopsias, glare, and blurring in 2.7%, 4.3%, and 4.3% of patients, respectively. Patients undergoing superior LPI were not more likely to describe the new onset of 1 or more dysphotopsia symptoms as compared with patients undergoing nasal/temporal LPI (8.4% vs. 9.5%; P= 0.7), nor did the frequency of any new individual symptoms differ by group (P≥0.3 for all). In multivariate logistic regression analysis, neither LPI location nor LPI area nor total laser energy predicted higher odds of new postoperative dysphotopsias (P > 0.1 for all). Laser peripheral iridotomy likely is safe with respect to visual dysphotopsias regardless of location, LPI size, and amount of laser energy used.

Kinetic (particle-in-cell) simulation of nonlinear laser absorption in a finite-size plasma with a background inhomogeneous magnetic field

In this paper, the effect of an external inhomogeneous magnetic field on the high intensity laser absorption rate in a sub-critical plasma has been investigated by employing a relativistic electromagnetic 1.5 dimensional particle-in-cell code. Relying on the effective nonlinear phenomena such as phase-mixing and scattering, this study shows that in a finite-size plasma the laser absorption increases with inhomogeneity of the magnetic field (i.e., reduction of characteristic length of inhomogeneous magnetic field, λp) before exiting a considerable amount of laser energy from the plasma due to scattering process. On the other hand, the presence of the external inhomogeneous magnetic field causes the maximum absorption of laser to occur at a shorter time. Moreover, study of the kinetic results associated with the distribution function of plasma particles shows that, in a special range of the plasma density and the characteristic length of inhomogeneous magnetic field, a considerable amount of laser energy is transferred to the particles producing a population of electrons with kinetic energy along the laser direction.

Effect of the Thickness of a Diamond-Like Carbon Layer on the Local Temperature Increase in a Multilayered Structure Induced by Laser Heating

The present study concerns the effect of the thickness of the overcoating layer on the local temperature increase in the multilayered structure subject to laser heating. The numerical simulation indicates that the presence of the diamond-like carbon (DLC) layer on the top of multilayered structure enhances local temperature increase, compared with the same structure without the DLC layer. This enhancement gradually becomes significant with an increase in the thickness of DLC layer. The DLC layer only absorbs small amount of laser energy. However, the energy accumulates in the DLC layer due to its low thermal conductivity, resulting in significant temperature increase.

Quantitative Tradeoffs between Spatial, Temporal, and Thermometric Resolution of Nonresonant Raman Thermometry for Dynamic Experiments

The ratio of Stokes to anti-Stokes nonresonant spontaneous Raman can provide an in situ thermometer that is noncontact, independent of any material specific parameters or calibrations, can be multiplexed spatially with line imaging, and can be time resolved for dynamic measurements. However, spontaneous Raman cross sections are very small, and thermometric measurements are often limited by the amount of laser energy that can be applied without damaging the sample or changing its temperature appreciably. In this paper, we quantitatively detail the tradeoff space between spatial, temporal, and thermometric accuracy measurable with spontaneous Raman. Theoretical estimates are pinned to experimental measurements to form realistic expectations of the resolution tradeoffs appropriate to various experiments. We consider the effects of signal to noise, collection efficiency, laser heating, pulsed laser ablation, and blackbody emission as limiting factors, provide formulae to help choose optimal conditions and provide estimates relevant to planning experiments along with concrete examples for single-shot measurements.

Pilot study of the clinical efficacy of ejaculatory hood sparing technique for ejaculation preservation in Holmium laser enucleation of the prostate.

We explored the effectiveness of ejaculatory hood sparing technique to Holmium laser enucleation of the prostate (HoLEP) for ejaculation preservation. From June 2010 to July 2011, 52 sexually active patients with sufficient ejaculate underwent HoLEP. Twenty-six patients received the ejaulatory hood sparing technique during HoLEP (EH-HoLEP group). The other 26 patients underwent conventional HoLEP (conventional-HoLEP group). In the EH-HoLEP group, paracollicular and supracollicular tissue >1 cm proximal to the verumontanum was preserved. The mean follow-up period was 9.7 months (range 3-12). There was no significant difference in patient characteristics and perioperative parameters, including age, prostate volume, International Index of Erectile Function score, operation time, weight of the enucleated tissue and the amount of laser energy. Semen was unchanged, decreased or vanished in 4 (15.4%), 8 (30.8%) and 17 (53.8%) EH-HoLEP patients, respectively. In the conventional-HoLEP group, semen was unchanged, decreased or vanished in 0 (0.0%%), 7 (26.9%) and 19 (73.1%) patients, respectively. Overall success rate of ejaculation preservation was 46.2% in the EH-HoLEP group and 26.9% in the conventional-HoLEP group (P = 0.249). Application of an ejaculatory hood sparing technique to HoLEP could not improve the success rate for ejaculation preservation. This was likely due to the surgical characteristics of HoLEP, which enable complete removal of the apical tissue. In this condition, simply preserved ejaculatory hood tissue seems not to be sufficient to obviate retrograde ejaculation. For the maintenance of antegrade ejaculation, it is postulated that a part of apical tissue should be preserved as well.

The Influence of Er: YAG Laser, Alumi-num oxide and diamond bur on surface treatment of Aged Composite Resin to Repair Restoration

Aim of this study is to investigate the effect of Er: YAG Laser, the sand blasted with aluminum oxide and wearing with diamond bur as a surface treatment to the bond strength of repaired composite resin after aged. Materials and Methods: Sixty Teflon mold (4mm×2mm), of Tetric® Ceram prepared. The specimens were randomly separated into six groups and undergo the following surface treatments: G1 no treatment (control), G2-G4 treated with a different amount of laser energy (40, 60, 80 mJ Er: YAG laser respectively) under a 2Hz frequency, G5 wearing with diamond bur, and G6 sandblasted with 50μm aluminum oxide. All 6 groups divided into two subgroups,1st control,2ed etched with 37% phosphoric acid. Bonding material was applied and the second split of Teflon mold (4mm×1mm) placed onto the prepared specimen, filled with Tetric N-Ceram. The shear test was done using the Uni-versal testing machine. Results: Significant differences of all variables, laser 60,40mj surface treatment displayed superior shear strength (45.24, 45.03 MPa respectively), aluminum oxide showed low shear value (32.48 MPa). Phosphoric acid showed the highest shear value (40.47 MPa) in compare to the control one (31.62 MPa). Conclusions: Using of Er:YAG laser improve the shear value of repaired composite in comparing with a diamond bur and aluminum oxide. Conditioning aged composite surface with a phosphoric acid enhancing its adhesive result.

Laser Ablation of Ti-Al Alloy in Vacuum and Air Environments

The time-resolved optical emission spectroscopy of Ti-Al alloy plasma produced by the Nd:YAG high-power laser pulses with wavelength of 1064nm was investigated both in air and vacuum conditions. The comparative studies gave detailed insights that the plasmas produced in air were much hotter and denser. The quantitative descriptions indeed suggested that a cascade avalanche process would be happen followed by air plasma firstly, before the laser impacting the target surface. On the other hand, the laser energy may be considerably attenuated via hotter and denser plasma, the amount of laser energy on the target surface remarkably decreased in air condition. In addition, at high-power laser irradiance levels, there was an auto regulatory area near the target surface and the plasma parameters tend to be saturated

Effect of laser operating mode in paint removal with a fiber laser

The laser paint removal behavior with the continuous wave (CW) beam and repetitive pulses has been investigated using an Yb:fiber laser. The specific energy, which is defined as the amount of laser energy needed to remove unit volume of paint prior to the onset of substrate damage and is a measure of the process efficiency, was found to be dependent on the laser processing parameters. In CW mode the specific energy reduced with the increase of laser scan speed and corresponding increase of laser power. In case of repetitive pulsed mode the specific energy was found to depend on the pulse on-time as well as on the time interval between two successive pulses. At 1kHz repetition rate, the specific energy reduced with the increase of duty cycle and corresponding increase in scanning speed, but at relatively low frequencies of 50–150Hz and 50% overlap between two pulses specific energy was found to increase with increasing duty cycle. Irrespective of the mode of operation specific energy increased with the increase of average line energy. During the laser paint irradiation a plume of burning fume was formed over the surface and the variation in specific energy with laser processing parameters has been attributed to the absorption of laser radiation in the plume. Since the dimension of plume and fume particle density in it will depend on the laser energy absorbed in paint, the absorption loss in plume will depend on the laser parameters. This was confirmed by measuring the plume temperature for different laser processing conditions. Based on this and considering that the actual specific energy absorbed by paint should be constant, the absorption characteristic of plume was modeled applying Beer Lambert's law.

Predictive factors of success in selective laser trabeculoplasty (SLT) treatment

Purpose:Glaucoma is a progressive optic neuropathy that may lead to blindness. Reducing intraocular pressure (IOP) is the only known treatment to slow progression in glaucoma. IOP can be reduced by pharmaceutical treatment, laser and surgery. The aim of the present study was to assess predictive factors of success after selective laser trabeculoplasty (SLT) treatment.Methods:We used a retrospective chart review of eyes that underwent SLT between January 1, 2005 and December 31, 2005. The dependent variable was time to failure after SLT treatment. Failure after SLT was defined as any changes in the medical treatment, and/or a new SLT treatment was performed and/or the patient was sent for surgery. All patients were treated with 90° SLT. A multivariate regression analysis was performed to assess correlation between time to failure after SLT and age, gender, IOP before treatment, number of medications used, SLT number, amount of spots, laser energy used, grade of angle, pigmentation and diagnosis.Results:120 eyes of 120 patients were identified. The average time to failure after SLT was 18 months. The predictive factors identified were: age, IOP before SLT and dose.Conclusion:Predictive factors identified in our study were high baseline IOP, age and amount of laser energy used. Our study confirms previous results about baseline IOP as a predictive factor.

New Laser Fusion and Its Gain by Intense Laser

The feasibility of a new approach of laser fusion in plasma without implosion has been proposed and is discussed using an intense laser. The cross section of the nuclear reaction is increased by enhancing the penetrability of nuclei through the Coulomb barrier. In this approach, an intense laser field of more than 100 PW was required to distort the Coulomb barrier to obtain enough penetrability. An energy gain even with Deuterium-Deuterium (D-D) reaction can be obtained using this scheme in Deuterium plasma. A reactor with neutron and direct conversion of charged particle beam individually is proposed. Charged particles from D-D reaction are guided to the end of the reactor and are directly converted by a MHD scheme into electric energy. The energy recovery rate is high and requires a small amount of laser energy, which may make the energy cost cheaper than that of a fission reactor.

Transcanalicular diode laser-assisted dacryocystorhinostomy

Objective:We present a prospective, non-comparative case series study of 126 consecutive diode laser-assisted transcanalicular dacryocystorhinostomy (TCL-DCR) procedures on 122 patients. We analyzed success rate, procedure time and amount of laser energy needed for a 5 mm osteotomy.Materials and Methods:One hundred and twenty-two patients with nasolacrimal duct obstruction were included in the study. The procedure was performed under general anesthesia, and the nasal mucosa was anesthetized. An endoscope was used for examination of the lacrimal pathways. The site of osteotomy was determined with transillumination of the lateral nasal wall. We achieved osteotomy by applying laser energy via an optic fiber. We used a 980 nm diode laser with power of 10 Watts. We inserted a bicanalicular silicone stent as the last step. Success of procedure was absence of epiphora (subjective), or patency of the lacrimal drainage system on irrigation (objective).Results:We performed 126 successive endoscopic laser (EL-DCR) with bicanalicular intubation in 122 patients. The average procedure time was 12 min, and on average 245 Joules of laser energy was needed. The silicone stents were removed three to eight months after surgery. We observed absence of epiphora and a patent nasolacrimal duct on irrigation in 105 out of 126 treated eyes. Eighteen patients had epiphora despite a patent nasolacrimal duct on irrigation. This yields a success rate of 83.3%, with an average follow-up period of 12 months.Conclusions:The 980 nm EL-DCR with bicanalicular intubation is a new contribution to the field of lacrimal surgery. It is a minimally invasive quick procedure yielding a high success rate.

Measuring and Machining of Ripples on Silicon Surface with Femtosecond Pulse Laser

Experiments are carried out on a femtosecond laser micromachining system with the wavelength 775nm. The ablated patterns on Si (100) and Si (111) surfaces affected by femtosecond pulse laser parameters are presented. The periodic structure termed ripples on silicon surface is investigated. Two kinds of ripples on the ablated surface are observed by SEM. The whole ablation region indicates the ablated field of all amount of laser energy. The ablation region forms two circular areas. The cross section image of the ablated region is showed which is cut by FIB in the orthogonal direction of the line of the center ripples. The depth of ripples is measured. Adjusted the laser fluence as about 0.3~0.33J/cm2 and the pulse number as changeable from 1 to 50, the forming process of the ripples is observed and studied by AFM. Another experiment is done that the wave-plates are inserted into the space between the objective and sample, the result of the direction of ripples changed with the wave-plates of 1/2 or 1/4 is reviewed.

High sensitivity imaging Thomson scattering for low temperature plasma

A highly sensitive imaging Thomson scattering system was developed for low temperature (0.1-10 eV) plasma applications at the Pilot-PSI linear plasma generator. The essential parts of the diagnostic are a neodymium doped yttrium aluminum garnet laser operating at the second harmonic (532 nm), a laser beam line with a unique stray light suppression system and a detection branch consisting of a Littrow spectrometer equipped with an efficient detector based on a "Generation III" image intensifier combined with an intensified charged coupled device camera. The system is capable of measuring electron density and temperature profiles of a plasma column of 30 mm in diameter with a spatial resolution of 0.6 mm and an observational error of 3% in the electron density (n(e)) and 6% in the electron temperature (T(e)) at n(e) = 4 x 10(19) m(-3). This is achievable at an accumulated laser input energy of 11 J (from 30 laser pulses at 10 Hz repetition frequency). The stray light contribution is below 9 x 10(17) m(-3) in electron density equivalents by the application of a unique stray light suppression system. The amount of laser energy that is required for a n(e) and T(e) measurement is 7 x 10(20)n(e) J, which means that single shot measurements are possible for n(e)>2 x 10(21) m(-3).

Immediate Pain Improvement Is a Useful Predictor of Long-Term Favorable Outcome after Percutaneous Laser Disc Decompression for Cervical Disc Herniation

The purpose of this study was to evaluate the long-term clinical outcome of percutaneous laser disc decompression (PLDD) for cervical disc herniation and to identify factors affecting long-term favorable outcome. PLDD using the Ho:YAG laser has been regarded as an effective alternative for soft disc herniation. However, little is known about long-term favorable outcome parameters. We retrospectively reviewed the clinical and radiological data of 60 patients who underwent PLDD with laser-assisted spinal endoscopy (LASE) for contained cervical soft disc herniation from January 1998 to January 2000. The clinical outcome was measured using the Macnab criteria. Statistical analysis was performed using Fisher's exact test. Sex, age, operated level and location of disc herniation, amount of laser energy, and time for symptom improvement were selected as parameters. The mean follow-up period was 71.0 months (range, 59-83 months). The mean age was 45.7 years (range, 26-68 years), and the mean symptom duration was 13.0 months (range, 2-60 months). The Visual Analogue Scale (VAS) score was significantly improved from 7.9 preoperatively to 2.6 at the final follow-up (p < 0.001). At the final follow-up, 51 (85.0%) patients achieved a favorable outcome. Immediate (within 24 h) pain relief was achieved in 19 patients, and it was strongly related to long-term success (p = 0.006). The long-term clinical outcome of PLDD with LASE was fairly good, with a success rate of 85%. Immediate pain relief is a useful prognostic factor predicting favorable outcome following the procedure.

Laser-tattoo removal--a study of the mechanism and the optimal treatment strategy via computer simulations.

The physical mechanisms for laser-tattoo interactions and the tattoo particle breakup process are not well understood. This study investigates whether the mechanism of the breakup process can be identified via computer simulations and proposes a treatment strategy that can potentially minimize the collateral damage to the surrounding tissues. Note that the "removal" of tattoo particles is defined here as breakup of particles into smaller ones with sizes approaching or smaller than the visible wavelength of light so that they become less visible. The radiation-hydrodynamics code LATIS is used for the modeling. We first identify the magnitude of the tensile stress generated inside graphite tattoo particles as functions of laser pulse length and particle size. We then calculate the relationship between the surface laser fluence (defined as the time integrated energy flux) and the tensile strength of the tattoo particle at a given depth. If the laser pulse length is sufficiently short, strong acoustic waves with tensile strengths exceeding the fracture thresholds for graphite are generated. The strength of the wave decreases with particle size and increases as the laser pulse length decreases. Simulation results are in general agreement with clinical studies. Although temperatures of the tattoo particles never reach the melting point, a cavitation bubble around the particle can be formed. The steam generated can get into the cracked particles and induce steam-carbon reactions. Laser energy density decreases rapidly with the skin depth. Therefore, the minimum surface laser fluence, for a given pulse length, required for breaking up tattoo particles at a given skin depth, increases with particle depth. Computer simulations confirm that the breakup of tattoo particles is photoacoustic. For the same amount of laser energy, a shorter pulse is more efficient. The optimal pulse length is approximately 10-100 picosecond to minimize the laser fluence and the collateral damage. It is more difficult to break up the smallest tattoo particles that have diameters smaller than 10 nm; however, smaller particles are less important because they are less visible. Tissue surrounding the tattoo particles can be damaged by cavitation bubbles. These bubbles could be the cause of the empty vacuoles in the ash-white lesions throughout the dermis seen after treatment. Steam-carbon reactions can be induced. Particles then become grossly transparent because of this reaction. Different laser intensity should be used for pigments at different depths in order to minimize the collateral damage to the dermis.

Avaliação comparativa do efeito dos colírios de apraclonidina e latanoprost na profilaxia da hipertensão ocular pós capsulotomia com YAG Laser em pacientes não glaucomatosos

Objetivo: Comparar a eficácia do latanoprost 0,005% e da apraclonidina 1% na prevenção da hipertensão ocular pós-capsulotomia posterior com YAG laser, em pacientes não- glaucomatosos. Método: Trinta e seis pacientes (36 olhos) incluídos foram divididos em três grupos que usaram latanoprost 0,005%, apraclonidina 1% ou placebo. Foram realizadas medidas da pressão ocular antes da instilação de qualquer colírio, 30 minutos após a dilatação, 1 hora e 4 horas após o YAG laser. Resultados: Não houve diferença significativa entre os 3 grupos em relação à idade, pressão ocular inicial e pós-dilatação, assim como em quantidade de energia utilizada. Na primeira hora, tanto para a diferença absoluta quanto para o percentual de alteração da pressão intra-ocular, o grupo da apraclonidina apresentou redução estatisticamente maior em relação ao grupo controle (p < 0,05). O grupo do latanoprost não diferiu estatisticamente dos dois outros grupos(p > 0,05). Na 4a. hora não houve diferença significativa entre os grupos (p > 0,05). As medidas de pressão nos 4 intervalos não apresentaram variação estatisticamente significativa (p > 0,05). A quantidade de energia utilizada não mostrou correlação significativa com o aumento da Po (p > 0,05). Conclusão: A apraclonidina 1% apresentou maior eficácia na profilaxia da hipertensão após capsulotomia posterior com YAG laser quando comparada com latanoprost 0,005%.

鉄のエキシマレーザ加工時に誘起されるプラズマの解析 エキシマレーザによるアブレーション加工の基礎的研究 （第１報）

Emission spectra in KrF excimer laser induced plasma were measured with time resolution of the order of tens ns in laser materials processing of iron target; excitation temperature of the laser-induced plasma was determined by a Boltzmann plot of Fe (I), and electron density was determined from an intensity ratio of Fe(I) and Fe(II) lines. At a power density of 8×102 W/m2, the temperature and electron density were approximately 17000-18000 K and 5×1026 m-3 at the end of laser pulse of 30 ns, respectively. The absorption of KrF excimer laser was also measured in the laser induced plasma by using the probe laser beam travelling parallel to the target surface, which is split from the main KrF excimer laser. The absorption coefficient in the plasma thus obtained reached as high as approximetely 4×103 m-1 at the end of laser pulse duration. This value agreed well with the value calculated from the inverse-Bremsstrahlung theory when the excitation temperature and electron density obtained by the spectral method are used. This indicates that considerable amount of laser energy can be absorbed in the laser induced plasma without reaching the target via the absorption in the plasma at the later part of the laser pulse.