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At least 73 records · Page 4Linked to original sources

PubMedDate not supplied

[Quantitative analysis of corneal excisions using argon fluoride excimer laser (193 nanometers)].

Excimer lasers represent a new and distinctive class of laser-tissue interaction termed photoablation. They can ablate materials with a high degree of precision and minimal damage to surrounding structures. The argon Fluoride excimer laser, which offers the possibility of non-contact corneal cutting, has a potential for clinical application of keratorefractive surgery. Since each pulse of excimer laser etches some amounts of tissue from the cornea, the repetitive pulses focused to a narrow line can create linear excisions. In this study, a quantitative analysis of both depth and width of corneal excisions was made on cadaver eyes at a given fluence (600 mj/cm2) and a constant repetitive rate (20Hz). The amount of ablation per pulse was not constant and the excisional depth did not show a linear correlation with pulse numbers. Both the depth and width of transversal excisions were more homogenous than those of radial excisions along the entire length of ablation.

Cornea↗

PubMed1994

Electron microscopic findings in a cornea with recurrence of herpes simplex keratitis after excimer laser phototherapeutic keratectomy.

Excimer laser phototherapeutic keratectomy is emerging as an alternative therapy to corneal transplantation for the treatment of multiple corneal diseases. We report three cases of recurrence of herpes simplex keratitis after treatment of herpetic corneal scars with the excimer laser. In two cases, the patients underwent subsequent corneal transplantation. One corneal button examined with transmission electron microscopy (TEM) demonstrated a well-differentiated epithelium over the area of ablation, a linear, continuous basal lamina, and no viral particles. Anterior stromal scarring may have resulted from the laser treatment itself or may represent incomplete ablation of previous scars. Whether reactivation of the virus was stimulated by the laser or occurred as part of the natural history of the disease is uncertain. We recommend that patients who undergo excimer laser treatment for herpes simplex scarring receive careful follow-up including antiviral coverage.

Adult↗

PubMed1994

Excimer laser coronary angioplasty.

Excimer laser angioplasty has evolved from a difficult experimental procedure to a more refined intervention with flexible catheters, well-defined indications, and consistent results for certain lesion types such as aortoostial stenosis, total occlusions, and certain saphenous vein graft lesions. This article reviews the current clinical results with excimer laser angioplasty, discusses the procedural technique and indications, and emphasizes the need for rigorous comparison of excimer laser angioplasty with alternative approaches for patients with coronary artery disease.

Angioplasty, Balloon, Coronary↗

PubMedDate not supplied

Rapidly polymerized collagen gel as a smoothing agent in excimer laser photoablation.

BACKGROUND: Excimer laser photoablation effectively and precisely removes corneal tissue but may not smooth irregularities on the anterior corneal surface. An even surface might be obtained by applying a smoothing substance that fills in irregularities and ablates at the same rate as corneal tissue. Evaluation of collagen gel as a smoothing agent is reported. METHODS: Pure, type I collagen solutions were prepared to remain soluble at physiological pH and to spontaneously gel when exposed to cationic buffers. Collagen gels were formed on the surface of enucleated porcine corneas and on human donor corneas and exposed to varying pulses of 193-nanometer excimer laser energy. Effects of collagen gel on ablation depth, corneal surface smoothness, and smoothing of roughened cornea were evaluated by examining scanning electron micrographs of control and treated specimens. RESULTS: Collagen gels formed from 5 mg/ml collagen solutions dramatically altered the depth of photoablation. Photoablation of roughened cornea with collagen gels produced smooth corneal surfaces, whereas control eyes remained roughened and irregular. The smoothness of photoablated cornea surfaces improved when collagen gels were applied prior to photoablation. CONCLUSIONS: The rapidly gelling collagen solution appears to exhibit the functional properties required for an effective smoothing agent for excimer laser photoablation. The substance has low viscosity when applied to the corneal surface and forms a rigid gel when exposed to cationic buffer solution. In addition, the concentration of the collagen gel can be adjusted to provide different ablation rates.

Animals↗

PubMed1993

Infrared laser soft tissue ablation versus ultraviolet excimer laser. Experimental introduction of the Hol:YAG-laser in oral surgery.

The in vivo tissue ablation characteristics of a pulsed infrared laser (Hol:YAG, lambda = 2120 nm) and a pulsed excimer laser (XeCl, lambda = 308 nm) were studied in an animal model. Laser energy was delivered via nylon fibers for the Hol:YAG laser and via quartz fibers for the excimer laser. Laser incisions were made under precise reproducible conditions on the sublingual side of the tongue and the gingiva of white rats. Laser surgery was done at two different energy output settings for the Hol:YAG laser and at one setting for the excimer laser. Histologic studies revealed tissue defects with clean contours for both laser types with small zones of necrosis of the adjacent tissue (Hol:YAG: 180 microns to 640 microns; excimer: 40 microns to 160 microns) and without carbonization. Both laser types function on the principal of photoablation and permit excellent control of tissue ablation. Wound healing was studied over a 10-day period and showed complete wound closure by re-epithelialization. The in vivo tissue ablation characteristics and the surgical reliability of the two lasers are compared and discussed with respect to oral and periodontal surgery.

Animals↗

PubMed1996

[Phototherapeutic use of excimer laser].

The photorefractive excimer laser is not only able to alter the refractive power of the corneas but also suitable to treat superficial corneal pathologies. Authors performed phototherapeutic keratectomies (PTK) in 80 eyes of 77 patients. The age was on average (+/- S.D.) 49.4 +/- 22.03 years. The follow-up time varied between 3-24 months. All treatments were performed with the Aesculap Meditec MEL 60 ArF excimer laser, working in the 193 nm extreme ultraviolet-C range. Authors conclude that the best postoperative results can be achieved with PTK in cases of recurrent corneal erosions and superficial corneal opacities. Favourable outcome could be expected in treatment of infectious corneal ulcers. In cases of bullous keratopathy the subjective complaints decreased and it was successful to postpone the time of perforating keratoplasty. The PTK is not recommended in case of corneal Bowen disease and recurrent pterygia. A hyperopic shifts was observed in 2 eyes. Besides, the traditional surgical methods the phototherapeutic keratectomy is an important progress in treatment of superficial corneal pathologies. Applying the method, the recurrent erosions healed quicker, in most of the cases the transparency of the cornea could be reestablished in the pupillary area and the need for perforating keratoplasty could be postponed or avoided.

Corneal Diseases↗

PubMed2006

[Laser surgery for glaucoma: excimer-laser trabeculotomy].

BACKGROUND: Excimer-laser trabeculotomy (ELT) is a new, minimally invasive surgical procedure for the treatment of open-angle glaucoma that can easily be combined with cataract surgery. We herein report our experience with ELT as a stand-alone procedure and ELT plus cataract surgery. METHODS: A total of 135 patients with open-angle glaucoma (n = 128) or ocular hypertension (n = 7) (M : F = 49 : 86, mean age 69.7 +/- 1.2 years) were included in this study. Patients were divided into 2 groups: a) ELT as a stand-alone procedure (n = 75), b) combined cataract and ELT procedure (n = 60). Both groups were further divided into 2 subgroups: 1) Preoperative IOP > 22 mmHg, 2) Preoperative IOP < or = 22 mmHg. Kaplan-Meier survival curves were calculated. Success criterion was 20 % decrease of IOP and IOP < or = 21 mmHg and postoperative IOP-lowering medication < or = preoperative IOP-lowering medication. Follow-up time was 1 year. RESULTS: Group a) ELT, 1) preoperative IOP > 22 mmHg, 2) preoperative IOP < or = 22 mmHg: Kaplan-Meier survival curves showed a success rate of 57 % in subgroup 1 and of 41 % in subgroup 2. Group b) Combined cataract and ELT procedure, 1) preoperative IOP > 22 mmHg, 2) Preoperative IOP < or = 22 mmHg: success rate was 91 % in subgroup 1 and 52 % in subgroup 2. CONCLUSION: ELT is a promising IOP-lowering technique both as a stand-alone procedure and in combination with cataract surgery. It is especially suitable for patients with high preoperative IOP levels.

Aged↗

PubMed1989

[Coronary endarterectomy using an excimer laser. Preliminary peroperative results].

From experimental and clinical experience, safe coronary angioplasty cannot be performed with CW lasers. The excimer laser does present a number of advantages in vitro: non-thermal ablation of plaques and a linear relationship between the number of pulses and the depth of the crater, so that tissue ablation is quantitatively predictable. A 308 nm, 20 ns pulse duration, 1 to 5 repetition rate laser was specifically designed for clinical application. During cardiopulmonary bypass prior to bypass grafting in 10 symptomatic patients, a 1 mm diameter core UV-tipped fiberoptic was introduced via the coronary arteriotomy and directed in contact with the coronary stenosis. Laser power was progressively increased until the stenosis or occlusion was recanalized. The quality of this angioplasty was controlled by calibration of he neo-lumen, cardioplegia solution flow through the lased segment, and 8th day coronary angiography. The laser treated coronary segments of the first 4 patients showed clearly parallel-lined patent neo-lumen despite competitive bypass graft flow. The main limitation of the method is that laser coronary recanalization is confined to the fiber core diameter. The authors conclude that: 1) excimer laser angioplasty is a safe and efficient intra-operative procedure; 2) the most critical problem for percutaneous laser angioplasty remains flexibility of the apparatus as the fiber diameter must be large enough to provide an adequate arterial neo-lumen.

Aged↗

PubMed2005

[The mechanism and application of the correction for spherical myopia using small beam excimer laser].

In the laser ablation refractive surgeries, the corneal ablation model and its realization by laser are difficult to design. They greatly affect the results of those surgeries. This paper firstly presents a mathematical model for corneal ablation to correct the refractive error of spherical myopia, and then gives a technique of planning laser focus positions on cornea to realize the ablation model. Based on the principle of the correction for spherical myopia using small beam laser, our excimer laser corneal surgery system has been able to perform such refractive surgery. Now the corneal surgery system has been applied to clinical practice. Thirty-nine eyes with spherical myopia underwent LASIK using this kind of system. Their refractive states have been greatly improved. Preoperatively, the mean sphere was -5.57+/-2.95 D and the mean uncorrected visual acuity 0.12+/-0.07. One day after surgery, the mean sphere was -0.03+/-0.57 D and the mean uncorrected visual acuity 0.90+/-0.29. One month after surgery, the mean sphere was -0.68+/-0.98 D, and the mean uncorrected visual acuity 1.0+/-0.26.

Humans↗

PubMed1989

Laser dentistry: a new application of excimer laser in root canal therapy.

We report the first study of the application of excimer lasers in dentistry for the treatment of dental root canals. High-energy ultraviolet (UV) radiation emitted by an XeCl excimer laser (308 nm) and delivered through suitable optical fibers can be used to remove residual organic tissue from the canals. To this aim, UV ablation thresholds of dental tissues have been measured, showing a preferential etching of infiltrated dentin in respect to healthy dentin, at laser fluences of 0.5-1.5 J/cm2. This technique has been tested on extracted tooth samples, simulating a clinical procedure. Fibers of decreasing core diameters have been used to treat different sections of the root canal down to its apical portion, resulting in an effective, easy, and fast cleaning action. Possible advantages of excimer laser clinical applications in respect to usual procedures are also discussed.

Fiber Optic Technology↗

PubMed2001

Current multicentre studies with the excimer laser: design and aims.

Excimer laser ablation to remove atherosclerotic plaque has been used for over a decade as a methodology to treat cardiovascular disease. Improvements in the technique and technology of excimer laser angioplasty, coupled with the recognition of new clinical opportunities for this treatment modality, have resulted in a resurgence of interest in the laser. Three clinical trials are now being conducted to explore potential applications, including the LARS trial of excimer laser versus balloon angioplasty to treat in-stent restenosis, the PELA trial of excimer laser angioplasty in occluded superficial femoral artery disease, and the LACI trial of excimer laser angioplasty in limb-threatening ischaemia. This article describes the rationale and objectives of these new approaches to some of the more challenging problems in cardiovascular disease.

Angioplasty, Laser↗

PubMed1999

Recurrence of corneal dystrophy after excimer laser phototherapeutic keratectomy.

BACKGROUND: Excimer laser phototherapeutic keratectomy (PTK) can be useful to treat anterior corneal dystrophies both before and after penetrating keratoplasty. OBJECTIVE: To evaluate the recurrence of corneal dystrophies after excimer laser PTK. DESIGN: Retrospective case series. PARTICIPANTS: Fifty excimer laser PTK procedures were performed in 43 eyes of 33 patients with corneal dystrophies. Preoperative diagnoses included Reis-Bücklers dystrophy (13 eyes), granular dystrophy (11 eyes), anterior basement membrane (ABM) dystrophy (11 eyes), lattice dystrophy (7 eyes), and Schnyder crystalline dystrophy (1 eye). INTERVENTION: Two excimer lasers (VISX 20/20 model B and VISX Star) were used to perform all PTKs. MAIN OUTCOME MEASURES: After PTK, patients were followed on a regular basis with measurement of best-corrected visual acuity and biomicroscopic examination. Evidence of recurrent dystrophy was noted according to specific criteria. RESULTS: Follow-up range was from 1.1 to 71.2 months (mean, 19.5 months). Clinically significant recurrent dystrophy occurred in 17 eyes. The ABM dystrophy recurred in the form of recurrent corneal erosions in 5 (42%) of the 12 eyes within 6 to 9 months of PTK. Four of these five eyes had mild erosions, which were treated successfully with topical medications while one eye required an additional PTK for an erosion outside the initial treatment area. Eight (47%) of 17 eyes with Reis-Bücklers dystrophy developed clinically significant recurrence an average of 21.6 months after PTK. Three (23%) of 13 eyes with granular dystrophy were found to have a significant recurrence a mean of 40.3 months after PTK. Only one (14%) of seven eyes with lattice dystrophy developed a significant recurrence at 6 months after PTK. Six eyes with significant recurrence after PTK were retreated successfully with additional PTK. Three eyes later developed recurrence of granular and Reis-Bücklers dystrophy after the second PTK. The probability of recurrence of these dystrophies after PTK was calculated using the Kaplan-Meier survival analysis. CONCLUSION: Phototherapeutic keratectomy can restore and preserve useful visual function for a significant period of time in patients with anterior corneal dystrophies. Even though corneal dystrophies are likely to recur eventually after PTK, successful retreatment with PTK is possible.

Adolescent↗

PubMedDate not supplied

Histological comparison of corneal ablation with Er:YAG laser, Nd:YAG optical parametric oscillator, and excimer laser.

PURPOSE: To use histological techniques to assess and compare the ablation depth, local damage, and surface quality of corneal ablations by a Q-switched Er:YAG laser, an optical parametric oscillator laser at 2.94 microm, a long pulse Er:YAG laser, and a 193-nm excimer laser. METHODS: Human cadaver eyes and in vivo cat eyes were treated with a 6.0-mm diameter, 30-microm-deep phototherapeutic keratectomy ablation and a 6.0-mm diameter, -5.00-D photorefractive keratectomy ablation. Human cadaver eyes were also treated with a 5.0-mm diameter, -5.00-D laser in situ keratomileusis (LASIK) ablation. Fluences and pulse widths used were 200 mJ/cm2 and 70 ns for the Q-switched Er:YAG, 150 mJ/cm2 and 7 ns for the optical parametric oscillator laser (OPO), 500 mJ/cm2 and 50 microseconds for the long pulse Er:YAG, and 160 mj/cm2 and 20 ns for the excimer laser. In the ablation rate study, 12 porcine eyes were ablated by the OPO laser with a range of layers and at different fluences ranging from 60 to 150 mJ/cm2, all using a 1.5-mm spot on the eye. The ablation depth of these acute ablations was evaluated by light microscopy examination. RESULTS: In the acute damage study, light microscopy showed a thin surface layer in all samples with minimal thermal damage except on the long pulse Er:YAG corneas. Transmission electron microscopy revealed less than 0.3-microm surface damage for all specimens of both the optical parametric oscillator and the excimer laser samples with no evidence of collagen shrinkage. Transmission electron microscopy showed damage layers of 0.5 to 3 microm for Q-switched Er:YAG and 3 to 10 microm for long pulse Er:YAG. Scanning electron microscopy showed smooth surfaces in all eyes, although the excimer was the roughest. In the porcine eye study, ablations were produced in both PTK and PRK modes with the ablation rate per layer increasing with the fluence. At 120 mJ/cm2, the average ablation rate was 1.9 microm per layer. CONCLUSIONS: The histology from the short pulse mid-infrared optical parametric oscillator laser at 2.94 microm was comparable to the 193-nm excimer with a smooth, damage-free, ablation zone when performing PRK and LASIK.

Algorithms↗

PubMed2001

Excimer laser phototherapeutic keratectomy.

Excimer laser phototherapeutic keratectomy (PTK) is an important tool in the management of superficial corneal pathology. It works well in the treatment of anterior corneal dystrophies and degenerations, but we are learning that it may have a role in the treatment of certain patients with deeper corneal pathology. Indications also are being expanded to treat much less common conditions and also to treat children. Irregular astigmatism, which is not treated very well with current PTK techniques, may be addressed better with newer approaches, such as selective zonal ablation and the use of BioMask. As current PTK techniques are improved and newer methods are developed, this procedure will continue to be an excellent option for certain patients with superficial corneal problems.

Cornea↗

PubMedDate not supplied

Increasing the number of photorefractive keratectomy procedures from a single excimer laser gas fill.

Excimer laser ablative procedures are an expensive proposition for both the patient and the user. The high capital expenditure and the cost of consumables, notably the argon-fluoride gas, makes it imperative to achieve maximum utilization in terms of number of cases treated per fill of gas. This is particularly true in countries like India. The maximum number of cases can be treated by understanding not only the limitations of each fill of gas, but by proper patient scheduling and modifications to the treatment protocol. This paper outlines our modified protocol and the patient scheduling software that we developed to meet these criteria.

Cornea↗

PubMed1998

Analysis of corneal topography after excimer laser photorefractive keratectomy.

Excimer laser photorefractive keratectomy (PRK) is an effective treatment for myopia. We investigated the magnitude of optical zone decentration and qualitative patterns of corneal topography after this treatment. We performed computer-assisted videokeratography on 44 myopic eyes (29 patients) that had undergone PRK before and 1, 6, and 12 months after the procedure. Associations of clinical outcomes with decentration and topographic patterns were assessed. The normalized scale of the topography 1 month postoperatively showed a mean decentration of 0.33 +/- 0.23 mm (range 0-0.9). Thirty-four eyes had decentration of less than 0.50 mm; 10 had an ablation zone decentered from 0.5 to 0.9 mm. Analysis of geometric mean visual acuities between eyes with less than 0.5 mm decentration and those with 0.5 to 0.9 mm decentration demonstrated minimal differences. No eye was decentered more than 1 mm. Four main ablation patterns were noted on subtraction analysis: homogeneous, semicircular, keyhole, and central island. Over time, the number of eyes with a homogeneous pattern increased. Eyes with a homogeneous ablation pattern had significantly better uncorrected visual acuity than those with other patterns. The mean visual acuity was 20/29.1 in the homogeneous group and 20/38.5 in the pooled irregular group 1 month postoperatively (p < 0.05). There was no significant difference among the four ablation patterns at 6 or 12 months after PRK. Topographic patterns were not significantly associated with best-corrected vision.

Cornea↗

PubMed1992

Clinical follow-up of 193-nm ArF excimer laser photokeratectomy.

The excimer laser has been undergoing rapid development for clinical use since the early 1980s. The authors report 2-year follow-up results from studies in 31 eyes (15 women and 14 men) to evaluate the excimer laser in performing photokeratectomy. Patients were divided into two groups: 27 eyes (group 1) underwent phototherapeutic keratectomy, and 4 eyes (group 2) underwent photorefractive keratectomy. Visual function improved in 21 of 27 eyes in group 1 and in 2 of 4 eyes in group 2. Complications were minimal and manageable. The authors describe a procedure to minimize induced hyperopia in phototherapeutic keratectomy patients, and, although not statistically significant, less induced hyperopia was noted in these patients. Photokeratectomy may be an alternative to penetrating or lamellar keratoplasty and more invasive refractive procedures, but the long-term effects must be carefully observed.

Adult↗

PubMedDate not supplied

Excimer laser photorefractive keratectomy.

Excimer laser photorefractive keratectomy has been used for the correction of myopia, hyperopia and astigmatism. This laser removes tissue through a process termed photoablative decomposition, in which incident photon energy is sufficient to break molecular bonds. Selective removal of tissue across the anterior corneal surface results in a change in anterior corneal curvature. The surgical outcome may be influenced also by interindividual variability in wound healing and pharmacologic interventions. The nature of the excimer laser-tissue interaction, and clinical outcomes of predictability, stability and complications of surgery for myopia are discussed in detail.

Animals↗