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PubMedDate not supplied

One-year results of excimer laser photorefractive keratectomy for myopia.

BACKGROUND: Excimer laser photorefractive keratectomy for the correction of myopia is presently under investigation in the United States by the Food and Drug Administration (FDA). The Phase II-B FDA study is being conducted on 75 normally sighted myopic eyes utilizing three currently available excimer lasers. This report presents the 1-year results on 12 myopic eyes treated with the VISX excimer laser system at the Ellis Eye Center at Cedars-Sinai Medical Center in Los Angeles under the Phase II-B FDA protocol. METHODS: Twelve eyes of 12 patients with myopia between -1.75 and -5.00 diopters underwent 193 nm argon/fluoride excimer laser photorefractive keratectomy. The epithelium was mechanically removed, and fixation was accomplished with a suction ring which provided nitrogen flow across the corneal surface. The computer controlled corneal ablations were 5.00 mm in diameter and were accomplished with an iris diaphragm closing from large to small. RESULTS: The preoperative spherical equivalent myopia was -3.50 D (SD = 1.02) and the postoperative myopia was -0.25 (SD = 0.48). Eleven of the 12 patients achieved an uncorrected visual acuity of 20/30 or better and were corrected to within +/- 0.50 D of emmetropia. All corneas demonstrated a mild reticular subepithelial haze which was barely visible at 1 year. There were no vision-threatening complications and none of the eyes experienced a loss of best corrected visual acuity. CONCLUSIONS: In this small trial, the excimer laser appears to be capable of accurately changing the refractive power of the cornea for the correction of myopia with minimal side effects. Only when larger numbers of patients undergo the procedure will we be able to determine the safety and efficacy of photorefractive keratectomy as a refractive surgical procedure.

Adult↗
PubMed2004

[Laser in situ keratomileusis with a flying-spot excimer laser and a carriazo-barraquer microkeratome - outcomes after 6 months].

PURPOSE: To evaluate safety, efficacy, predictability and refractive stability of LASIK, using a flying-spot excimer laser, 91 eyes were examined during a 6-months follow-up. PATIENTS AND METHODS: Consecutively, 91 eyes were enrolled in the study, each eye previously underwent LASIK with the ESIRIS excimer laser (ESIRIS, supplier: eye-tech-solutions Schwind, Kleinostheim, Germany). 91 myopic eyes (mean preoperative refraction: - 5.4 D, range: - 3 to - 13.3 D, astigmatism: - 1 D, range: 1.3 to 3.5 D) were included. A full ophthalmological examination was performed during the first week, 1, 3 and 6 months postoperatively. RESULTS: 26 % of all eyes achieved an uncorrected visual acuity of 0.8, 35 % of 1.0 and 5 % 1.2 6 months postoperatively. 23 % of the eyes lost 1 line of best spectacle-corrected visual acuity (BSCVA), 25 % gained one or more lines of BSCVA. Refraction of 90 eyes were within +/- 1 D of emmetropia 6 months postoperatively. There was no change in spherical equivalent within the interval of 6 months, all eyes were within +/- 0.5 D. CONCLUSION: LASIK with the ESIRIS excimer laser was an effective and safe option with good stability and predictability within the specified interval.

Adult↗
PubMedDate not supplied

Excimer laser photorefractive keratectomy for hyperopia.

OBJECTIVE: Excimer laser photorefractive keratectomy (PRK) has been shown to be an effective method in the treatment of refractive errors, especially myopia. We evaluated prospectively the efficacy, predictability, stability, and safety of excimer laser PRK in the treatment of hyperopia. METHODS: Thirty-four hyperopic eyes were treated with an Aesculap-Meditec (MEL 60) excimer laser. The patients were divided into two groups. In the low-moderate hyperopia group, baseline spherical equivalent refraction was between +1.50 and +6.00 diopters (D) (mean, +4.20 +/- 1.30 D) and in the high hyperopia group between +6.25 and +9.75 D (mean, +7.70 +/- 1.30 D). Follow-up visits occurred 1, 3, 6, and 12 months after surgery. RESULTS: One-year results were available for a total 27 eyes (79%): 15 eyes with low to moderate hyperopia and 12 eyes with high hyperopia. One year after PRK in the low-moderate group, six eyes (40%) had a refractive error within +/- 1.00 D of emmetropia, but in the high hyperopia group only two eyes (17%) were within +/- 1.00 D of emmetropia; three eyes (20%) and one eye (8%) were within +/- 0.50 D, respectively. The stability of the refractive change was better in the low to moderate hyperopia group; in the high hyperopia group there was still some regression after 6 months. At 12 months, 10 eyes (67%) in the low-moderate and one eye (8%) in the high hyperopia group had postoperative uncorrected visual acuity of 20/40 or better. One eye in the low-moderate hyperopia group saw 20/20 without correction. Only one eye lost two lines of spectacle-corrected visual acuity. Haze was more intense in the high hyperopia group, but it did not reduce visual acuity. No vision-threatening complications were observed. CONCLUSIONS: When low to moderate hyperopia up to +6.00 D is treated, excimer laser PRK with the Aesculap Meditec MEL60 laser is safe and moderately effective, and refraction stabilizes after 3 months in most eyes. However, PRK is not sufficient to treat high hyperopia in an effective and predictable way.

Adolescent↗
PubMed1992

[The Excimer laser. I. The Lucerne evaluation procedure for Excimer therapy].

The Excimer laser has been available for clinical applications in the Lucerne Eye Hospital since September 1990. Excimer laser keratectomy as a refractive therapy option is meeting with widespread interest among patients. As this is an invasive method whose complications cannot be neglected and for which long-term experience is so far lacking, this interest has to be balanced by extremely strict and responsible diagnosis by those offering the therapy. The authors present their evaluation concept here. The figures below document the reticence exercised in diagnosis: 1100 information leaflets dispatched are contrasted in the final analysis with only 34 laser treatments in a period of 10 months. 50 of the 200 patients admitted (referred by specialists) for preliminary examinations were definitively excluded from treatment in Lucerne as early as the administrative stage, and 61 during the clinical evaluation proper.

Cornea↗
PubMed1997

Epithelial wound healing of the rat cornea after excimer laser ablation.

Rats with excimer corneal ablations (ArF 193 nm, 228 pulses, diameter 3,5 mm, 17.3 mJ per pulse, depth about 1/2 of corneal thickness) in one eye were killed 1, 2, 4, 6 and 13 days after treatment. The other eye served as control. The cell number per microscopic vision field, the labelling index (LI) and the mitotic rate (MR) were calculated for the peripheral, midperipheral and central areas of the corneal epithelium. The cell number showed a uniform depression in the remaining corneal epithelium at Day 1, normalizing from the centre to the periphery. The LI was only significantly increased at Day 1, while the MR was statistically significantly increased peripherally at Day 2 and in all areas at Day 6. However, when the corneal epithelium was evaluated as a whole, the MR was significantly increased at days 1, 2 and 6. The proliferative response of the epithelium was very homogenous irregardless of the distance to the original lesion. Both the migratory and the proliferative phases of the healing process seemed to be delayed when compared to the healing of pure epithelial wounds. However, the initiation of an increase in DNA synthesis seems not to be delayed, indicating that it is primarily the G2 phase that has been prolonged with this ablation procedure. The stromal thickness was increased from about one half of the normal values immediately after the treatment to above normal values at Day 4, thereafter decreasing to normal values at Day 13. Thus, the regenerative ability of the stroma is more pronounced in rats than in humans, but also in humans regeneration of the stroma can possibly explain the regression of the myopic shift seen some time after excimer laser treatment.

Animals↗
PubMed1995

[Current evaluation of myopia correction with the excimer laser].

Keratectomies with the excimer laser demonstrate extraordinarily smooth edges. Thermal and actinic side effects are negligible. Currently two techniques are in clinical use: the wide-field approach and the scanning-slit approach. A third one, the flying-spot approach is being tested in clinical studies. Postoperative refraction is mainly determined by the amount of correction. For corrections up to 6.0 D we found success rates of more than 90% and the refraction stabilizes during the first year after surgery. If the correction is higher, the success rate is decreased to 50% or less and the regression takes years. The complication rate is also dependent on the amount of correction: with corrections of more than 6.0 D it exceeds 1% and in corrections of 9.0 D and more, manifest corneal scars occur in more than 10% of the cases. Other complications are: eccentric ablation, IOP elevation due to steroid medication, and ptosis. Rheumatic diseases are absolutely contraindicated because of potential corneal melting ulcers, and subretinal neovascularization. In addition, corrections of more than 6.0 D are relatively contraindicated. More recent techniques like astigmatic PRK, LASIK, and hyperopic PRK are discussed.

Follow-Up Studies↗
PubMed1997

Computer simulation of centration effects on corneal-topography analysis of excimer laser photorefractive keratectomy ablations.

Excimer laser photorefractive keratectomy (PRK) procedures photoablate the central optical zone, potentially altering the corneal vertex normal and thus the corneal topography (CT) system reference axis. Anterior corneal surface coordinates (x, y, and z) were computer generated to simulate spherical and PRK-ablated corneal surfaces. Power maps were reconstructed by using surface tangents relative to various assumed CT reference axes, the original and displaced vertex normals. The simulation process eliminated focus, alignment, and surface-reconstruction errors. A simulated 5.00-D myopic PRK decentered 1 mm from the vertex produced a new corneal vertex 0.13 mm from the original position. Axial power-map generation by using this new reference axis produced a spherical keratectomy with astigmatic untreated periphery. This computer simulation demonstrates that reference axis changes are significant for even modest PRK decentration and can explain apparent steepening in untreated corneal areas. CT users should be aware that pre- and postoperative CT power maps may not be directly comparable.

Computer Simulation↗
PubMedDate not supplied

Laser in situ keratomileusis with the Nidek EC-5000 excimer laser for astigmatism greater than 4.00 D.

PURPOSE: To evaluate laser in situ keratomileusis (LASIK) performed with the Nidek EC-5000 excimer laser in 66 astigmatic eyes with cylinder from 4.00 to 8.00 D. METHODS: LASIK was performed with the Nidek EC-5000 excimer laser in 66 astigmatic eyes with cylinder from 4.00 to 8.00 D. Based on Chayet's nomogram, ablation zone diameters were 5.5 mm (steep meridian ablation) to 7.5 mm (flat meridian ablation). In eyes with simple myopic astigmatism, mixed astigmatism, and compound myopic astigmatism (low sphere), ablation was performed in both meridians. In eyes with simple hyperopic astigmatism, ablation was performed in the flat meridian alone. In eyes with compound hyperopic astigmatism, ablation zone diameter was 5.5 mm and the transition zone was 7.5 mm. RESULTS: Uncorrected visual acuity was 20/40 or better in 89% of eyes and was equal to preoperative best spectacle-corrected visual acuity in 62% of eyes. No eyes lost lines of best spectacle-corrected visual acuity. CONCLUSIONS: Using the Nidek EC-5000 excimer laser, we had satisfactory results in the treatment of astigmatic eyes with cylinder from 4.00 to 8.00 D, based on Chayet's nomogram.

Astigmatism↗
PubMed1993

In vitro evaluation of ablation parameters of normal and fibrous aorta using smooth excimer laser coronary angioplasty.

A modified excimer laser energy delivery system was used to irradiate 100 segments of normal and fibrous aorta in vitro. The laser beam was scanned into 8 fiber bundles consisting of 50 fibers each resulting in a reduction of the applied pulse energy. The total repetition rate was increased to 150 Hz in order to keep the repetition rate per fiber bundle close to 20 Hz and to minimize thermal injury. The results demonstrate that effective ablation (etch rate per 8 pulses > 2.0 microns) occurred at an energy fluency of 50 mJ/mm2 in both normal and fibrous aorta. Tissue damage (carbonization, tissue separation, fissures, cracks, and vacuolization) was in a range of 100 +/- 28 to 152 +/- 30 microns for normal aorta and in a range of 57 +/- 35 to 110 +/- 39 microns for fibrous aorta. We conclude that effective ablation of normal and fibrous human aorta can be achieved by the application of smooth excimer laser coronary angioplasty. This improvement of excimer laser technology may result in a reduction of shock wave- and cavitation-induced damage leading to a reduction of tissue injury. However, this awaits further in vitro and in vivo confirmation.

Angioplasty, Laser↗
PubMed2006

Aspirin reduces platelet aggregation during high-energy excimer laser.

BACKGROUND AND OBJECTIVES: Excimer laser is used clinically in arterial revascularization procedures. This study evaluated the efficacy of aspirin in reducing platelet aggregation during high-energy excimer lasing. STUDY DESIGN/MATERIALS AND METHODS: Platelet rich plasma (PRP) from seven rabbits was circulated in a dual organ chamber with aspirin added to one and the other was control. PRP was irradiated using an excimer laser (308 nm; 45 mJ/mm(2); 25 Hz; 5 minutes) via a 2.0 mm laser catheter. Platelet aggregation (particle volume) was measured by laser-light scattering. Morphology was evaluated by phase contrast and electron microscopy. RESULTS: Baseline platelet volume was 3.4 microm(3) for both control and aspirin groups. Following lasing, platelet volume peaked at 102.2 +/- 18.5 microm(3) for control compared to 43.1 +/- 49.2 microm(3) for aspirin-treated PRP (P < 0.0001). CONCLUSION: Aspirin reduces large platelet aggregates but not small aggregates by 58% during lasing of PRP.

Analysis of Variance↗
PubMed1992

Multifocal corneal topographic changes with excimer laser photorefractive keratectomy.

Excimer laser photorefractive keratectomy can flatten the central cornea, thereby eliminating myopic refractive errors; in older patients, however, presbyopia limits satisfaction. Computer-assisted topographic analysis of corneas after refractive surgery indicates that a minority of patients achieve a multifocal lens effect, such that they maintain reasonable acuity over a range of defocus. We have purposefully attempted to create a multifocal refractive effect and have analyzed the subsequent topographies quantitatively to determine if multifocality was achieved. In corneas not operated on and plastic hemispheres, a fairly small range of corneal powers is observed; the range of powers is increased after a monofocal ablation. After multifocal ablations, a greater spread of surface powers is observed, often with a bimodal distribution, indicative of an apparent multifocal effect. These observations suggest that in some patients undergoing photorefractive keratectomy for myopia, it may be possible to reduce symptoms of presbyopia, although a decrease in image contrast or monocular diplopia may complicate this approach.

Animals↗
PubMed2001

Dissociation between improvement in angina pectoris and myocardial perfusion after transmyocardial revascularization with an excimer laser.

Xenon chloride excimer laser transmyocardial revascularization significantly reduced angina in all patients and increased regional myocardial perfusion in most patients; however, there was no correlation between symptomatic improvement and flow improvement. Patients' symptomatic improvement preceded improved perfusion by several months.

Angina Pectoris↗
PubMed1988

Long-term healing of the central cornea after photorefractive keratectomy using an excimer laser.

Using an excimer laser at 193 nm, 3-mm diameter discs were ablated from the optical zone of monkey corneas at a variety of depths up to 130 micron. Tissue was examined by light and electron microscopy 4 and 5 weeks and 6 and 8 months postoperatively. With the exception of the deepest ablation, all corneas were clear immediately postoperatively. At 1 month, ablations of 40 micron remained clear, whereas all others showed some degree of haze. By 3 months, discs at 60 micron depth were clear, and there was less haze in others. Haze was progressively lost over 6 months, but in the deepest discs it could still be discerned on slit-lamp examination. Microscopic observation showed that reepithelialization had occurred within 24 to 48 hours. Over subsequent months, a normal morphology was maintained in this layer with the exception that basal cells were slightly more elevated particularly at the disc margins where the epithelium contained more cell layers. Stromal reorganization was accompanied by an initial phase of vacuolation and invasion by keratocytes, but by 6 months postoperatively almost all vacuolation had disappeared and keratocyte numbers had almost returned to normal. By 8 months, the morphology was near normal with the exception that Bowman's membrane was absent and there was still a degree of disorder in the immediate subepithelial stromal fibers. The basement membrane of epithelial cells was reestablished but slightly more undulant than in nonirradiated areas. This undulation was retained in the 8-month postoperative specimens and at this time a normal thickness of 60 nm was displayed.

Animals↗
PubMed1991

DNA damage in cultured human skin fibroblasts exposed to excimer laser radiation.

Ultraviolet excimer lasers are being considered for use in a variety of refractive and therapeutic procedures, the long-term biologic consequences of which are unknown. The effect of sublethal doses of 193-nm laser radiation on cellular DNA was examined in cultured human skin fibroblasts. In contrast to 248 nm, treatments with the 193-nm laser radiation below 70 J/m2 did not cause significant pyrimidine dimer formation in the skin cells. This was indicated by the lack of excision repair activities (unscheduled DNA synthesis assay), and further demonstrated by direct analysis of pyrimidine dimers in DNA from irradiated cells. However, a low level of unscheduled DNA synthesis could be detected following irradiation at 193 nm with 70 J/m2. Both the 193-nm and 248-nm radiation were able to induce chromosomal aberrations, as indicated by a micronucleus assay. A dose-dependent increase in micronuclei frequency was observed 48 and 72 h after laser irradiation. These results indicate that exposure of actively replicating human skin fibroblasts to sublethal doses of either 193- or 248-nm laser radiation can result in genotoxicity.

Cell Survival↗
PubMed1998

Patient-Related and Angiographic Predictors of Restenosis After Excimer Laser Coronary Angioplasty.

Excimer laser coronary angioplasty (ELCA) is a useful technique for the treatment of selected complex coronary lesions. However, this technology has been limited by significant restenosis and, to date, predictors of restenosis after use of this device are not clearly defined. In order to determine predictors of restenosis after ELCA, 43 lesions presenting with restenosis (> 50% diameter stenosis) at angiographic follow-up were compared to 46 lesions without restenosis, based on patient-related, qualitative and quantitative angiographic parameters. Univariate analysis revealed 9 variables with at least a borderline (p < 0.15) significant relation to restenosis: (1) age (p = 0.0759), (2) proximal left anterior descending site (p = 0.074), (3) presence of a restenotic lesion (p = 0.104), (4) lesion length (p = 0.0034), (5) reference diameter of the treated vessel (p = 0.0076), (6) post laser minimal luminal diameter (MLD) (p = 0.1160), (7) post-procedural MLD (p = 0.0001), (8) post-procedural stenosis (p = 0.0250) and (9) total procedural gain (p = 0.0051). After entering stepwise logistic regression analysis, only 3 variables emerged as independent predictors of restenosis: treatment of a restenotic lesion (p = 0.0255), lesion length (p = 0.0291) and post-procedural MLD (p = 0.0007). Based on these data, we conclude that post-procedural MLD is the most important predictor of restenosis after ELCA. Lesion length and the treatment of restenotic lesions are also independently associated with an increased risk of restenosis after ELCA. Therefore, achieving the best possible luminal result at the time of the first intervention should be the goal of the procedure, especially when treating high restenosis risk lesions.

Journal Article↗
PubMedDate not supplied

Bovine corneal stroma ablation rate with 193-nm excimer laser radiation: quantitative measurement.

Excimer lasers operating at 193 nm may become important surgical instruments in ophthalmology because of their ability to ablate tissue with excellent precision and minimal damage to adjacent tissue. However, the precision is limited by the accuracy of the measurement of the amount of tissue ablated per pulse at the fluence used. A measurement of the ablation rate of bovine corneal stroma over the range of fluences most likely to be useful for corneal surgery (50-400 mJ/cm2) is presented. The technique used produced reproducible results, the data from 47 animal eyes being averaged to further increase the precision. For this range of fluences, these results show a more precise measurement than previously published tissue ablation rate data. These results should be useful in accurately predicting the result of corneal surgery using the excimer laser if species differences are not major.

Animals↗
PubMed1993

[Excimer laser correction of myopia].

Excimer laser photorefractive keratectomy was performed on 100 myopic eyes. The preoperative spherical equivalent of myopia ranged from -2.00 to -9.99 diopters (D), mean -4.80 +/- 2.20 D. The procedure was performed under local anesthesia using 0.4% topical benoxinate HCl; corticosteroid eye drops were then used for up to 3 months. All patients achieved corrected visual acuity within 1 line of corrected preoperative visual acuity. The only complication was subepithelial reticular haze seen in all patients, which peaked at 4 weeks after the procedure and gradually diminished within 3 months. After follow-up of from 6-11 months, 93% of patients had achieved uncorrected visual acuity of 6/12 or better. Mean postoperative refraction was -0.20 +/- 0.97 D. 69% achieved a correction within +/- 0.50 diopter of emmetropia, 85% within +/- 1.00 D and 96% achieved corrected visual acuity of within 1 line of preoperative corrected visual acuity. This study and those in the literature show excimer laser to be a promising surgical treatment for myopia.

Follow-Up Studies↗
PubMedDate not supplied

Smoothness of ablation on acrylic by four different excimer lasers.

PURPOSE: There are many different excimer laser devices available for photoablative refractive surgery. Smoothness of ablation may vary with different excimer lasers systems. METHODS: Ablations were performed on polymethylmethacrylate (PMMA) plates of 8 x 4 x 0.5 cm, with four different excimer lasers: VISX-Star, Coherent Schwind Keratom I/II, Chiron Technolas Keracor 117C (Plano Scan), and the Nidek EC-5000, to determine and compare the homogeneity and smoothness of the surface. Ten -3.00 D samples, ten -6.00 D samples, and ten -9.00 D samples were ablated with each laser. The PMMA discs were examined with optical microscopy, documented by photographs, and each sample was measured quantitatively using a Hommel-Werkel rugosimeter. We used the same PMMA material throughout. RESULTS: Statistically significant differences in smoothness were found between the Chiron Technolas 117C and the VISX-Star, Nidek and VISX-Star, and Coherent Schwind and VISX-Star in the homogeneities achieved by ablating -3.00 D. Ablations of -6.00 D resulted in homogeneities that were statistically significantly different: Chiron Technolas 117C with the other three devices, the Nidek EC-5000 with the VISX-Star, and the Coherent-Schwind with the VISX-Star. In the ablations for -9.00 D, statistically significant differences in homogeneity were found between the Chiron Technolas 117C and Nidek, between the Chiron and VISX-Star, between the Coherent Schwind and VISX-Star, and between the Nidek and VISX-Star. The laser with the scanning spot system was smoother. CONCLUSION: Scanning spot technology produced smooth ablations even up to -9.00 D.

Lasers, Excimer↗