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PubMed1982

Clinical studies on high and low power laser radiation upon some structures of the anterior and posterior segments of the eye. Experiences in the treatment of some pathological conditions of the anterior and posterior segments of the human eye by means of a Nd:YAG laser, driven at various power levels.

A Q-switched Nd:YAG laser apparatus has been used in the treatment of a number of pathological conditions of the anterior and posterior segments of the human eye. This laser system may be driven in a free running mode, thereby allowing variation of pulse duration over a range of 12 ns to 10 ms. With increasing pulse duration, non-linear mechanical damage patterns characteristic of the biological effects at the lower exposure duration range become unimportant when compared to the so-called thermal effects met at the upper pulse duration range. The thermal damage mechanisms may be useful when applied together with the mechanical damage mechanism, for instance when iris perforations are intended. Because the Wise-Witter irradiation method for the treatment of open angle glaucoma depends on low power, thermal mechanisms, this instrument may also be useful for the treatment of this disease entity. This same irradiation mode may also be applied to at least some irradiation tasks of the retina and choroid.

Choroid↗
PubMed1990

Laser-induced shock wave lithotripsy. Influence of laser pulse energy and irrigation solutions on stone disintegration.

With a high intensity Q-switched Nd-YAG laser shock waves can be generated in a liquid close to the calculus. Up to 80 mJ single pulse energy with 8 nsec pulse duration can be transmitted through flexible quartz fibers. Energy conversion and enhancement can be accomplished at the fiber tip with optical focussing of the light at the quartz tip, with irrigation solutions and with high pulse energies. Iron-III-dextran solutions (1 mg Fe3+/1) and magnesium chloride (50 mmol/l) increased the pressure in the laser induced breakdown up to ten times (8,000-10,000 bar). Smaller stone particles and higher efficacy in stone fragmentation could be achieved.

Humans↗
PubMed2005

Epithelial healing and clinical outcomes in excimer laser photorefractive surgery following three epithelial removal techniques: mechanical, alcohol, and excimer laser.

PURPOSE: To evaluate epithelial healing, postoperative pain, and visual and refractive outcomes after photorefractive keratectomy (PRK) using three epithelial removal techniques. DESIGN: Prospective, nonrandomized, comparative trial. METHODS SETTING: Department of Ophthalmology, Yonsei University College of Medicine and Balgensesang Ophthalmology Clinic, Seoul, Korea. INTERVENTIONS: For the PRK procedure, the corneal epithelium was removed in one of three ways: mechanically (conventional PRK [PRK]) in 88 eyes of 44 patients; using excimer laser (transepithelial PRK [tPRK]) in 106 eyes of 53 patients; or using 20% diluted alcohol, laser-assisted subepithelial keratomileusis (LASEK) in 106 eyes of 53 patients. MAIN OUTCOME MEASURES: Epithelial healing, postoperative pain, uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), and remaining refractive error. RESULTS: The mean postoperative pain scores were 4.84 +/- 1.45 for PRK, 4.71 +/- 1.62 for tPRK, and 4.63 +/- 1.52 for LASEK (P = .125). The mean epithelial healing rates were 12.3 +/- 4.6 for PRK, 15.2 +/- 4.9 for tPRK, and 18.1 +/- 5.2 mm2/day for LASEK (P < .001). The postoperative 6-month remaining mean spherical equivalents (diopters) were -0.46 +/- 1.01 for PRK, 0.18 +/- 0.91 for tPRK, and -0.82 +/- 1.18 for LASEK (P = .01). The LASEK group showed less favorable UCVA than other groups. There was no significant difference in BSCVA between the groups. CONCLUSIONS: Postoperative pain, subepithelial opacity and BSCVA were similar regardless of the epithelial removal procedure. A faster epithelial healing rate did not result in better visual or refractive outcomes. Using the same nomogram, tPRK resulted in a slight overcorrection, and LASEK resulted in a slight undercorrection.

Adult↗
PubMed2006

Activation processes and polyethylene formation on a phillips model catalyst studied by laser ablation, laser desorption, and static secondary ion mass spectrometry.

Since the discovery of the Phillips catalysts, there still is much uncertainty concerning their activation, their molecular structure, the nature of the active chromium sites, and the polymerization mechanisms. Surface techniques are not easy to be used for such study according to the nonconductive behavior of the support. Therefore, model Phillips catalyst is elaborated by spin coating a trivalent chromium precursor on a silicon wafer. The surface characterization of this model catalyst is conducted by laser ablation mass spectrometry (LA-MS), laser desorption/ionization mass spectrometry (LDI-MS), and static secondary ion mass spectrometry (s-SIMS), at different steps of its preparation. To validate our approach, a comparison is also made between the model and the real Philips catalyst. Moreover, the model catalyst efficiency for polyethylene synthesis is evaluated and allows us to discuss the validity of the mechanisms previously proposed to explain the catalytic process. The characterization of Phillips model catalyst by mass spectrometry allows us to better understand the activation processes of such catalyst. Depending on the activation temperature, chromium oxide species are formed and anchored at the support surface. They consist mainly in mono-chromium sites at high temperature. The chromium valence is hexavalent. This model catalyst is active for the polymerization of ethylene. A pseudo-oligomer molecular weight distribution is observed by LA-MS, whereas s-SIMS allows us to elucidate the anchorage of the polymer at activate chromium surface sites.

Catalysis↗
PubMed2005

Assessment of nerve fiber layer thickness before and after laser in situ keratomileusis using scanning laser polarimetry with variable corneal compensation.

PURPOSE: To determine the effect of laser in situ keratomileusis (LASIK) on retinal nerve fiber layer (RNFL) thickness measurements obtained by scanning laser polarimetry with variable corneal compensation (SLP-VCC). SETTING: Gimbel Eye Centre, Calgary, Alberta. METHODS: Retinal nerve fiber layer thickness measurements were performed in both eyes of 25 consecutive healthy patients the day of LASIK surgery and 1 month after by trained examiners using the GDx-VCC nerve fiber analyzer. Thickness measurements and all other parameters provided by the software of the machine before and after LASIK were analyzed using the paired Student t test. RESULTS: Mean age of the patients was 39 years +/- 9.6 (SD) (range 24 to 57 years). The mean preoperative spherical equivalent was -4.15 +/- 1.76 diopters (D) (range -1.0 to -7.50 D) and the mean postoperative spherical equivalent, 0.12 +/- 0.39 D (range -0.75 to +1.00 D). Mean ablation depth was 62 +/- 23 mum. No statistically significant difference was found in SLP parameters after LASIK (P<.05). No clinically significant difference in RNFL thickness measurements was noted in any eye. CONCLUSION: These data suggest that SLP-VCC mean thickness measurements are not influenced by LASIK-induced alterations in corneal architecture. Measurements obtained with SLP-VCC before surgery may be used for future comparisons.

Adult↗
PubMed2006

Comparison of higher-order aberrations after wavefront-guided laser in situ keratomileusis and laser-assisted subepithelial keratectomy.

PURPOSE: To compare the higher-order aberrations (HOAs) in 70 eyes (38 patients) that had wavefront-guided laser in situ keratomileusis (LASIK) with those in 70 eyes (40 patients) that had wavefront-guided laser-assisted subepithelial keratectomy (LASEK) for the treatment of myopia. SETTING: Department of Ophthalmology, Yonsei University College of Medicine, Myongdong Bal-geun sesang Eye Clinic, and Seran Eye Center, Seoul, Korea. METHODS: In a prospective study, 140 consecutive eyes of 78 patients were treated with wavefront-guided LASIK or LASEK according to the patient's choice after each procedure had been thoroughly explained. The patients were followed for 6 months. Best corrected visual acuity (BCVA), uncorrected visual acuity (UCVA), manifest refraction, and wavefront aberrations were measured at baseline and 1, 3, and 6 months after surgery. RESULTS: There were no significant differences in postoperative BCVA, UCVA, and manifest refraction between groups. The mean root-mean-square wavefront error of HOAs for a scotopic pupil in the wavefront-guided LASIK group was significantly smaller than that in the wavefront-guided LASEK group at 1 month. Analyzing individual Zernike coefficients, the spherical aberration and second coma were significantly smaller in the wavefront-guided LASIK group than in the wavefront-guided LASEK group at 1 month. This difference in HOAs between groups disappeared at 3 and 6 months. CONCLUSIONS: The HOAs in the scotopic condition were not different between the wavefront-guided LASIK and LASEK groups beginning 3 months after surgery. However, the HOAs in the LASIK and LASEK groups had a different time course, especially in the case of spherical aberration. This finding suggests that postoperative changes in aberration contribute to the final outcome of wavefront-guided ablation.

Cornea↗
PubMed2006

Technique for measuring laser in situ keratomileusis flap thickness using the IntraLase laser.

Measurement of laser in situ keratomileusis flap thickness is required to estimate residual bed thickness. Historically, flap thickness has been assumed, estimated based on microkeratome head labeling, guessed based on flap handling characteristics, or calculated by subtraction pachymetry. We describe a method for measuring flap thickness before actual flap elevation using the IntraLase laser.

Corneal Stroma↗
PubMed2007

Laser in situ keratomileusis for astigmatism following laser thermal keratoplasty.

We describe 2 cases in which a staged laser in situ keratomileusis procedure was used to treat residual hyperopia and astigmatism after laser thermal keratoplasty. The procedure successfully reduced the spherical equivalent refractive error and residual astigmatism. All eyes maintained their best spectacle-corrected visual acuity and had an uncorrected visual acuity of at least 20/25 at the end of follow-up.

Adult↗
PubMed1997

Topographical analysis of ablation centration after excimer laser photorefractive keratectomy and laser in situ keratomileusis for high myopia.

PURPOSE: To evaluate the ablation centration after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) for high myopia and to assess the association between decentration and best corrected visual acuity (BCVA), glare, monocular diplopia, and halo phenomenon. SETTING: Mater Private Hospital, Dublin, Ireland. METHODS: Corneal topography was used to analyze centration in two groups of patients with myopia of more than 6.0 diopters: 18 had PRK and 18, LASIK. A standardized questionnaire assessed the preoperative and postoperative prevalence of glare, monocular diplopia, and halo phenomenon. RESULTS: "Significant" ablation decentration (0.5 mm) in the LASIK group (1.33 mm) was almost twice that in the PRK group (0.75 mm). Glare increased from 27% preoperatively to 42% in the PRK group; monocular diplopia increased in the LASIK group. Halo phenomenon decreased after both procedures. CONCLUSION: Laser in situ keratomileusis represents a step forward in the surgical correction of high myopia, but the accuracy of the corneal ablation location must be improved. Suction ring fixation of the globe or real time tracking systems may help improve centration.

Adult↗
PubMed1986

Laser lithotripsy of gallstone by means of a pulsed neodymium-YAG laser--in vitro and animal experiments.

Using a flashlamp pulsed Nd: YAG laser it is possible to destroy gallstones within a few seconds (median: 4 sec for stones less than 1.5 cc; 9.5 sec greater than 1.5 cc). In in vitro and animal studies it was shown that the median energy needed for stone destruction varies between 32 Joule for stones less than 1.5 cc and 80 Joules for stones greater than 1.5 cc. A 0.2 mm thick, flexible glass fibre makes possible retrograde laser lithotripsy by conventional endoscopes. Using a suitable technique the danger of thermal damage to tissue is small.

Animals↗
PubMed2000

Randomised prospective trial of contact laser prostatectomy (CLAP) versus visual laser coagulation of the prostate (VLAP) for the treatment of benign prostatic hyperplasia. 2-year follow-up.

OBJECTIVE: To determine the long-term efficacy and complications of visual laser coagulation/ ablation, VLAP (side-firing fibre) and direct contact laser ablation, CLAP (sapphire-tipped fibre) of the prostate in the treatment of benign prostatic hyperplasia (BPH). PATIENTS AND METHODS: Patients with clinical BPH, obstructed at voiding cystometry, were recruited and randomised to undergo either CLAP (21 patients) or VLAP (17 patients). At baseline, 1, 6, 12 and 24 months, patients underwent clinical evaluation, International Prostate Symptom Score (IPSS), uroflowmetry, post-void residual urine volume, and pressure/flow urodynamics. RESULTS: The mean operating time for CLAP was 37.7 min and 24.5 min for VLAP. There was minimal morbidity with only 5 men requiring bladder irrigation after CLAP, 1 of whom had a blood transfusion. No patient required irrigation after VLAP. The mean catheterisation time after CLAP was 4.5 days (range 1-31 days) and 13.2 days (range 7-70 days) after VLAP. IPSS and Qmax improved significantly and maintained at 2 years. After CLAP, the IPSS decreased from 20.9 to 13.5 at 2 years while Qmax rose from 10 to 15.5 ml/s at 2 years. After VLAP, the IPSS decreased from 21.8 to 13.3 at 2 years while Qmax rose from 10 to 15. 9 ml/s. There was no difference between CLAP and VLAP. Pressure/flow urodynamics at 6 months showed reduced bladder outflow obstruction. CONCLUSIONS: CLAP and VLAP offer the same improvement in flow rates and symptoms at 2years. Both procedures lead to minimal morbidity, but the excellent haemostasis that is achieved at VLAP makes it of more use in treating patients at high risk of haemorrhage after surgery.

Aged↗
PubMed2005

An overview of the use of lasers in general dental practice: 2. Laser wavelengths, soft and hard tissue clinical applications.

UNLABELLED: The profession now benefits from many different laser wavelengths that enable their use in nearly every dental specialty. This article will cover these wavelengths and their uses for soft and hard tissue procedures. CLINICAL RELEVANCE: There are many laser wavelengths available but their use within dentistry is quite tissue specific. It is hoped the reader will be able to decide which wavelength is best for a particular procedure.

Carbon Dioxide↗
PubMed2007

Laser-fiber system for ablation of intraocular tissue using the fourth harmonic of a pulsed Nd:YAG laser.

We report on a method for delivering high fluence pulsed 266 nm laser radiation to the target tissue via an optical fiber. The fourth harmonic of a Nd:YAG laser was concentrated using a hollow glass taper and launched into an optical fiber. Fluences of up to 2 J/cm(2) were routinely output at the tapered optical fiber tip. The maximum fluence generated before failure of the optical fiber was between 3.5 and 8 J/cm(2). Ablation of ocular tissue was demonstrated using fluences of 1.0 and 0.4 J/cm(2). The delivery system has the potential for use in intraocular surgical procedures.

Animals↗
PubMedDate not supplied

Comparison of laser in situ keratomileusis and photorefractive keratectomy for the correction of myopia of -6.00 diopters or less. Melbourne Excimer Laser Group.

PURPOSE: To evaluate the safety and efficacy of laser in situ keratomileusis (LASIK) compared to photorefractive keratectomy (PRK) for the correction of low or moderate myopia (-0.50 to -6.00 D) at 6 months after surgery. METHODS: The study population comprised a non-randomized consecutive series of 622 eyes of 392 patients who were treated with the Nidek EC-5000 excimer laser. LASIK was performed using the ACS Chiron microkeratome on 314 eyes and surface PRK on 308 eyes. All patients were treated using a standard protocol, then assessed at 1, 3, and 6 months postoperatively. RESULTS: Forty-four percent of the LASIK group and 67% of the PRK group attended their 6-month examination. Eighty percent of patients (111 eyes) after LASIK and 65% (136 eyes) after PRK had an uncorrected visual acuity of 20/20 or better. Spherical equivalent refraction was within +/-0.50 D of intended refraction in 78% (109 eyes) for LASIK and 82% (170 eyes) for PRK. Loss of two more lines of best spectacle-corrected visual acuity at 6 months occurred in 1.4% (2 eyes) of the LASIK group and 1.0% (2 eyes) of the PRK group. CONCLUSION: At 1 month follow-up, the percentage of eyes that achieved 20/20 uncorrected visual acuity was greater in the LASIK group than in the PRK group. At 6 months, visual and refractive outcomes of LASIK and PRK were similar. Although flap related complications occurred only after LASIK, the overall risk of loss of best spectacle-corrected visual acuity was not significantly greater than for PRK.

Adult↗
PubMedDate not supplied

Optic nerve head blood flow using scanning laser Doppler flowmetry after laser in situ keratomileusis.

PURPOSE: To investigate ocular blood flow changes following laser in situ keratomileusis (LASIK) in myopic eyes. METHODS: Seventeen eyes of ten myopic patients were included in the study. Mean age of the seven men and three women was 29.1+/-2.5 years. Mean spherical equivalent refraction was -7.70+/-2.52 D. LASIK was performed with the Hansatome microkeratome and Summit SVS Apex excimer laser. Optic nerve head blood flow was measured by using the Heidelberg Retinal Flowmeter preoperatively and postoperatively at 1 day, 1 week, and 1 month. Preoperative ocular blood flow data (blood flow, volume, velocity) were compared with postoperative data using variance analysis. Correlation analysis was performed for age of patients, suction time, and ocular blood flow data. RESULTS: Mean suction time was 19+/-7 seconds. There was no significant correlation between suction time, age, and ocular blood flow. We found an increase in blood flow at the lamina cribrosa taken 1 day postoperatively (P=.04). Blood flow returned to preoperative values at the 1-week and 1-month measurements in the lamina cribrosa region. There was no significant change in ocular blood flow data in the neuroretinal rim except an increase in velocity at the lower nasal quadrant on postoperative day 1 (P=.03). CONCLUSIONS: LASIK caused a temporary increase in blood flow at the lamina cribrosa region of the optical nerve head in healthy myopic eyes. The increase in blood flow may suggest a compensatory change for maintaining blood flow in the ocular nerve head following LASIK-induced ischemia.

Adult↗
PubMedDate not supplied

Prospective, paired comparison of laser in situ keratomileusis and laser epithelial keratomileusis for myopia less than -6.00 diopters.

PURPOSE: To compare visual and refractive results, contrast sensitivity, and tear stability after laser in situ keratomileusis (LASIK) in one eye and laser epithelial keratomileusis (LASEK) in the fellow eye for low myopia. METHODS: Patients diagnosed with low myopia, with a maximum difference of 1 D between their two eyes, were randomly assigned to receive LASEK on one eye and LASIK on the other eye. A total of 64 eyes of 32 patients with a mean age of 26.83 +/- 5.33 years were included in the study. Preoperative myopia ranged from -1.00 to -6.00 D. Follow-up was 6 to 12 months. Uncorrected (UCVA) and best spectacle-corrected visual acuity (BSCVA), Schirmer test results, tear break-up time, corneal asphericity, corneal uniformity index, predicted corneal acuity, and contrast sensitivity values were compared with preoperative values. A Wilcoxon test was used for statistical comparisons and a P-value less than .05 was considered significant. RESULTS: At 6 months after surgery, there was no statistically significant difference in UCVA, BSCVA, spherical and cylindrical refractive error, Schirmer test, or tear break-up time between groups. Contrast sensitivity values in the LASIK eyes were lower in comparison to preoperative values, but there was no change in the LASEK group. CONCLUSIONS: Based on 6-month results, LASEK for low myopia was safe and effective with predictable results, offered early refractive stability, and may be considered an alternative for LASIK.

Adult↗
PubMedDate not supplied

Holmium laser thermal keratoplasty for hyperopia in eyes overcorrected with laser in situ keratomileusis for myopia.

PURPOSE: To assess the efficacy and safety of holmium laser thermal keratoplasty (Ho:LTK) for hyperopia in eyes overcorrected after laser in situ keratomileusis (LASIK) for myopia. METHODS: We performed a prospective evaluation of Ho:LTK in eyes with secondary hyperopia from +1.00 to +5.50 D after LASIK. Thirty-seven eyes of 23 patients received one concentric 8-spot application at the 6-mm-diameter zone. Mean patient age was 41.3 +/- 13.0 years (range 20 to 68 yr). Mean corneal thickness was 455.86 +/- 31.20 microm (range 373 to 506 microm). RESULTS: Mean spherical equivalent refraction changed from +2.30 +/- 1.08 D to +0.45 +/- 1.00 D at 12 months after Ho:LTK. Thirty-one eyes (84%) were within +/- 1.00 D of emmetropia and 25 eyes (68%) were within +/- 0.50 D at 1 year. Mean change in refraction was 1.84 +/- 0.92 D. No eye lost 2 lines of best spectacle-corrected visual acuity. CONCLUSIONS: Ho:LTK is a suitable alternative for correcting secondary hyperopia resulting from LASIK for myopia. Parameter adjustments may be necessary for improving the results.

Adult↗