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PubMed1990

An introduction to excimer laser photorefractive keratectomy.

Laser research has rapidly expanded in the area of corneal sculpting in the past few years. Lasers with specific wavelengths in the ultraviolet and infrared ranges are best suited for ablating corneal tissue without disturbing clarity of the surrounding matrix. This is essential in laser refractive procedures. The excimer laser is an ultraviolet dimer laser with a wavelength of 193 nm. Excimer laser research has progressed rapidly and FDA-approved clinical trials are presently underway. This paper covers various aspects of the excimer's history, qualities of excimer laser ablation, mechanisms of damage, various laser delivery systems, and FDA-approved clinical trial results.

Cornea↗
PubMed1995

Usefulness of a prototype directional catheter for excimer laser coronary angioplasty in narrowings unfavorable for conventional excimer or balloon angioplasty.

We report clinical and angiographic results in 53 patients with 57 significant coronary or saphenous vein graft narrowings treated with directional excimer laser angioplasty. The target vessels were the left main (1%), anterior descending (32%), circumflex (19%), right coronary artery (39%), and vein grafts (9%). Lesions were morphologic class B1 (18%), B2 (79%), or C (3%), with 40 de novo and 17 restenotic lesions. Adjunctive balloon angioplasty was used in 53 lesions (93%). Mean pre- and postprocedural minimal lumen diameters were 0.6 +/- 0.3 and 1.9 +/- 0.7 mm (p < 0.001), corresponding to a mean diameter stenosis of 72 +/- 20% and 27 +/- 16%. Procedural success rate was 91%. Cumulative risk of death, Q-wave myocardial infarction, or emergency bypass operation was 9% (5 patients). Of patients who had a successful laser procedure, 28 (60%) with 30 lesions underwent angiographic follow-up at 6 +/- 3 months after the procedure. Restenosis rates (> 50% diameter restenosis or acute gain loss) were 37% and 23%, respectively. Four patients underwent bypass, 3 angioplasty, and 1 patient died from cancer. This study demonstrates the feasibility of directional application of laser energy to selected unfavorable narrowings for conventional excimer laser or balloon angioplasty. Further evaluation of this device using the now standard saline infusion technique is necessary to establish its ultimate role as a primary interventional device.

Aged↗
PubMed1996

[Corneal astigmatism after pterygium excision and subsequent phototherapeutic keratectomy with the excimer laser (193 rm)].

BACKGROUND: Phototherapeutic keratectomy with the excimer laser is a suitable procedure for corneal smoothing after pterygium excision. In this study the effect of postoperative excimer laser smoothing on induced and absolute astigmatism after pterygium surgery was investigated. MATERIALS AND METHODS: 60 of 53 eyes underwent pterygium surgery using a bare sclera technique. In addition 30 of the treated eyes underwent postoperative phototherapeutic keratectomy of the wound region with the excimer laser. Astigmatism was measured preoperatively and postoperatively after 6 months up to four years. RESULTS: Absolute astigmatism of patients treated with excimer laser decreased significantly from 1.38 +/- 0.83 D preoperative to 0.35 +/- 0.32 D postoperative (p < 0.0001). In this group mean induced astigmatism was 1.37 +/- 0.93 D. There was no correlation between the induced astigmatism and the number of excimer pulses applied (r = 0.0287; p = 0.905). Absolute astigmatism of the control group decreased from 1.10 +/- 0.85 D to 0.72 +/- 0.56 D (p < 0.05). There were no significant differences between the excimer- and the control group concerning preoperative astigmatism. Postoperative absolute astigmatism of the excimer group was significantly lower than absolute astigmatism of the control group (p < 0.0001). Mean induced astigmatism of the control group was 1.15 +/- 0.95 D and not significantly different from the excimer treated group (p = 0.2654). CONCLUSION: Phototherapeutic keratectomy with an excimer laser for corneal smoothing after pterygium excision reduces astigmatism significantly.

Adult↗
PubMed1997

[Effect of various ablation levels on endothelial density in the enucleated pig eye. Experimental study with the 193 nm Excimer laser].

UNLABELLED: The effects of deep excimer laser ablations on the corneal endothelial cell count are still unknown. MATERIALS AND METHODS: In an in-vitro study the endothelial cell counts of 125 pig corneas were examined after excimer laser ablation. Five groups of 25 eyes reach, one control group and four groups with 3, 10, 20, and 35 D of ablation were examined. After the laser treatment, a corneoscleral disc was prepared and stored for up 5 days in an organ culture medium. The endothelial cell density of 5 corneas in each group was measured in a period of 5 days with a phase contrast microscope. RESULTS: Significant cell loss, 13-25%, was measured in each group after 5 days. There were no significant differences between the ablated corneas and the control group. CONCLUSION: Deep excimer laser ablations do not significantly reduce the endothelial cell count.

Animals↗
PubMed1993

[Comparison between argon and excimer laser angioplasty in patients with lesions of the femoral and popliteal arteries: clinical and angiography results after 1 year].

The aim of this study was to compare acute and long term results of thermic argon laser versus athermic XeCl-excimer laser for recanalization of femoropopliteal lesions in 43 patients with peripheral vascular disease stage IIb to IV according to Fontaine. The argon laser system was applied in 29 lesions (9 stenoses, 20 occlusions up to 31 cm length) and an excimer laser was used in 28 lesions (10 stenoses, 18 occlusions up to 30 cm length). In all cases balloon dilatation followed laser recanalization to achieve a sufficient primary result (< 25% stenosis rate). Primary success was obtained in 86% with both laser systems. After 1 year 62.5 of the recanalized vessels with excimer laser and 56% with argon laser were still patent. Neither acute nor long term results showed significant differences between both laser systems. Compared to the argon laser, the procedure with the excimer laser was of shorter duration which may be advantageous under routine conditions. After one year, combining the results of both systems, the reocclusion rates of stenoses amounted to 22%, the reocclusion rates of short distance occlusions to 35% and that of long occlusions more than 10 cm length to 71%. With regard to the high reocclusion rate after reopening of long occlusions the laser systems seem to be of advantage, compared to balloon angioplasty mainly in critical stenosis and short occlusions which cannot be passed with the guide-wire.

Angiography↗
PubMedDate not supplied

Use of the 308-nm excimer laser for psoriasis and vitiligo.

The 308-nm excimer laser represents the latest advance in the concept of selective phototherapy. It emits a wavelength in the UV-B spectrum and thus shares the same indications as conventional phototherapy. Like other laser devices, the 308-nm excimer laser emits a monochromatic and coherent beam of light, can selectively treat a lesion while sparing surrounding healthy skin, and can deliver high fluencies. Clinicians have taken advantage of these properties to treat dermatologic disorders since 1997, with psoriasis and vitiligo attracting most attention. Initially, high fluencies (minimal erythemal dose, 8-16) were used, with excellent clinical results, to treat psoriasis vulgaris. The significance of side effects and the potential long-term carcinogenic risk associated with such fluencies have resulted in medium doses (about 3 minimal erythemal dose) being recommended, however. Interestingly, taking advantage of the selectivity of the laser, newer treatment protocols adapt the dose to the lesion and not to the minimal erythemal dose, as is the case for conventional phototherapies. Many prospective study series have also shown the efficacy and the good tolerance of the 308-nm excimer laser in the treatment of localized vitiligo. Induced rates of repigmentation seem to be higher than with narrowband UV-B. Moreover, the selectivity of the treatment prevents irradiation of healthy skin and limits unsightly tanning of surrounding skin. Aesthetically pleasing results are usually not achieved in extremities and bony prominences, which are not good indications for this technique. Combining the 308-nm excimer laser with 0.1% tacrolimus ointment has provided very interesting results, which need to be confirmed in larger series. The absence of actual data concerning the long-term risk for skin cancer after this treatment means that it should be considered with caution. Combination with topical steroids appears to be synergistic and potentially reduces long-term side effects; again, prospective data are lacking.

Humans↗
PubMed2004

[Repigmentation of persistent laser-induced hypopigmentation after tattoo ablation with the excimer laser].

Hypopigmented skin developed following tattoo removal with the Q-switched Nd:YAG laser. The hypopigmented area remained unchanged for over 4 years, until the use of the 308-nm xenon-chloride excimer laser induced a significant repigmentation in 40 sessions over 14 months. The excimer laser has the potential to influence the reduced activity of the melanocytes, as demonstrated with electron microscopy.

Adult↗
PubMed1994

Excimer laser ablation rate and corneal hydration.

During excimer laser photorefractive keratectomy, dehydration of the cornea begins as soon as the epithelium is removed. Corneal hydration might affect the excimer laser ablation rate, which could affect the accuracy of correction. We studied the effect of corneal hydration on the excimer laser ablation rate in bovine eyes. To control hydration, bovine corneoscleral rims were equilibrated in dextran solutions of varying concentrations. One button trephined from each rim underwent laser ablation. Hydrated tissue ablation rates (amount of collagen, ground substance, and water removed per pulse) and dry component ablation rates (amount of collagen and ground substance removed per pulse) were calculated from mass removed. The hydrated tissue ablation rate at physiologic hydration was 0.40 micron/pulse. As corneal hydration increased, the hydrated tissue ablation rate increased by 5.6 micrograms/cm2/pulse per increase in unit corneal hydration (simple linear regression analysis, P = .0001). The dry component ablation rate decreased linearly by 0.82 microgram/cm2/pulse per unit increase in corneal hydration (simple linear regression analysis, P = .0001). Both clinical data and theoretical arguments imply that dry component ablation rate determines refractive outcome after photorefractive keratectomy. Since the dry component ablation rate increases as the cornea dries, significant dehydration of the cornea before ablation might lead to relative overcorrections of myopia. Surgeons should use a technique that minimizes changes in hydration to maximize the predictability of excimer laser photorefractive keratectomy.

Animals↗
PubMedDate not supplied

[Treatment of bullous keratopathy with excimer laser].

PURPOSE: To evaluate the usefulness of excimer laser photokeratectomy in bullous keratopathy. MATERIAL AND METHODS: Treatment with excimer laser photokeratectomy was performed in 22 eyes with bullous keratopathy which developed after cataract extraction with IOL implantation. RESULTS: During 1 month follow-up a slight improvement of visual acuity, local state improvement and subjective symptoms regression were noted. This state was stable in 14 eyes for 6-12 months, in 8 eyes the recurrence of the disease occurred, but without pain symptoms. CONCLUSION: Excimer laser photokeratectomy does not restore corneal transparency but its benefit in bullous keratopathy is to decrease pain while awaiting for keratoplasty.

Aged↗
PubMedDate not supplied

Excimer laser photorefractive keratectomy for hyperopia.

BACKGROUND: Excimer laser photorefractive keratectomy has generated considerable interest as a technique for correcting myopia. In this study, the excimer laser was used to correct hyperopia. METHODS: A prospective clinical study based on the results of photorefractive keratectomy in 23 consecutive hyperopic eyes (one eye per patient) is presented. The excimer laser used in this study was a MEL 60 (Aesculap-Meditec); this laser emits 193-nanometer laser light. A 1-year follow-up study of two groups of eyes was performed. All patients were followed for 12 months. The first group comprised 15 hyperopic eyes with preoperative refraction between +2.0 and +7.5 diopters (mean spherical equivalent +4.7 +/- 1.6 D). The second group comprised eight aphakic eyes with preoperative refraction between +11.0 and +16.0 D (mean spherical equivalent +13.1 +/- 2.0 D). RESULTS: In group 1, 12 eyes (80%) were within +/- 1.0 D of the intended correction (baseline, +2.0 to +7.5 D) after 1 year. In group II, only three of the eight aphakic eyes (37%) were within +/- 1.0 D of the intended final refraction (baseline, +11.0 to +16.0 D). The stability of refraction in group I was better than in group II. At 12 months, best corrected visual acuity was unchanged in 14 eyes of group I. One eye had lost two lines. In group II, best corrected visual acuity was unchanged in six eyes after 12 months. In two eyes, best spectacle-corrected visual acuity was lower than the preoperative value, because of decentration of the ablation zone. After 1 year, 80% of the eyes in group I and 25% of those in group II had a visual acuity of 20/40 or better. CONCLUSION: Photorefractive keratectomy is an efficient and relatively safe procedure for correcting hyperopia up to +7.5 D. The predictability is good. Results of photorefractive keratectomy to correct highly hyperopic (aphakic) eyes are not as encouraging. Three patients in this study lost one to three lines of best spectacle-corrected visual acuity due to decentration of the clear zone. Two of the patients belonged to group II. Therefore, we do not recommend photorefractive keratectomy in highly hyperopic eyes, especially if they are aphakic, because even slight decentration may lead to loss of best corrected visual acuity. As in other refractive surgical procedures, great care must be taken to improve the centration of the clear zone.

Adult↗
PubMed1990

Fragmentation of biliary stones with a 308 nm excimer laser.

The use of a XeCl excimer laser (308 nm) for biliary stone fragmentation is reported. Laser energy is delivered via UV grade fused silica fibers to the target stones immersed in normal saline solution. Sixty biliary calculi--pigment (n = 40), and cholesterol (n = 20)--were fragmented in vitro. The total energy delivered per unit mass of the stone is kept constant. Two energy fluences (80 and 110 mJ/mm2) at two repetition rates (5 and 20 Hz) delivered through fibers of two core sizes (300 and 600 microns) are utilized to study the effect of different laser parameters on the fragmentation process. Although both pigment and cholesterol stones are susceptible to excimer laser fragmentation, higher fragmentation efficiency is obtained for the pigment stones than for the cholesterol stones. Our study suggests that higher energy fluence and larger fiber core size result in higher fragmentation efficiency for pigment stones. Fragmentation thresholds at stone surface for a variety of biliary calculi of known composition were measured. The threshold energy fluence is approximately 3 mJ/mm2 and 17 mJ/mm2 for pigment and cholesterol stones, respectively. Our study indicates that the 308 nm excimer laser may be effective as a laser lithotriptor with low threshold and good efficiency for biliary stone fragmentation.

Cholelithiasis↗
PubMed1994

Vasoreactivity and structure of human coronary arteries irradiated by excimer laser.

In this study the effects of excimer laser (308 nm) angioplasty on arteries have been studied. We report histology and vasoreactivity properties of human atherosclerotic and normal coronary arteries and bovine coronary arteries after exposure to pulsed excimer laser irradiation. Segments of isolated and pharmacologically active human coronary arteries were obtained within 5-8 hr postmortem. Segments of bovine arteries were obtained from fresh hearts. Side branches were ligated and vessels perfused with Krebs-Ringer's-bicarbonate solution in a perfusion apparatus to maintain their viability. Excimer laser irradiation was performed using a fused silica fiber advanced through the artery within a polyethylene cannula to assist with steerability and to protect against perforation. The fiber delivered a total of 40-60 J at its tip at 100 mJ/pulse at 15 pulses/sec. A total of 5 human atherosclerotic, 2 human normal, and 8 bovine arteries were used. Ablation of plaque was accomplished with remarkable ease and little resistance. Histologic studies showed clear-cut wedges inscribed by the catheter along the arterial wall without charring or thermal effects of coagulation necrosis. Vasoreactivity was assessed by measuring flow changes during perfusion before and after excimer angioplasty using a transient challenge with the vasoconstrictor serotonin. All excimer-irradiated arteries showed no increase in vasoreactivity during the challenge and showed preservation of relaxation properties following the challenge. In conclusion, coronary artery angioplasty by excimer laser appears to allow for effective plaque ablation with simultaneous preservation of structure and pharmacological properties of arteries.

Angioplasty, Laser↗
PubMed1995

[Effects of blowing or aspiration on ablation rate by excimer laser].

Accurate calibration of ablation rate by excimer laser prerequisite for precise photorefractive keratectomy (PRK). When a polymethylmethacrylate (PMMA) plate is ablated by excimer laser, debris is generated, which may affect homogeneity of the laser beam and energy density, and change the ablation rate. In order to clarify the effects of the debris on the ablation rate, we studied the changes in the ablation rate when the debris was removed by blowing or aspirating over the ablation area during PRK.PMMA plates were ablated using a scanning excimer laser system (EC-5000, NIDEK, Japan) in PRK mode under the following conditions: (1) with air blowing over the ablation area, (2) with aspiration of the debris, and (3) without treatment. The ablation rates were determined by measuring the refractive power of PMMA plates with a lens meter. The ablated surface was observed by scanning electron microscope (SEM). The ablation rate with blowing was the highest among the three conditions, that with aspiration was the second, and that without treatment was the lowest. The ablation rates with blowing showed no significant change when the ablation rates were changed. However, the ablation rates with aspiration or without treatment decreased as the pulse rate increased. The surface ablated during blowing was the smoothest in SEM photographs. We concluded that calibration of the ablation rate using PMMA plates must be done with appropriate air blowing.

Calibration↗
PubMed1993

Cell vitality in cartilage tissue culture following excimer laser radiation: an in vitro examination.

Excimer laser is used for cartilage debridement, although the resulting cell damage is yet unclear. For examination of cartilage survival after treatment, we used short-term tissue cultures of human joint cartilage. Specimens were treated with a XeCl-Excimer laser using different laser parameters, pulse energies, and repetition rates. Following treatment, discs were cultured for 8 days prior to examination. In contrast to the 20 microns damage zone as instant visible effect in histomorphologic examinations, we found a 0.3 mm zone in which approximately 50% of cartilage cells had morphological signs of damage on light microscopic examinations. Autoradiography revealed that cartilage cells in an 0.5-0.7 mm area surrounding the laser craters had no collagen synthesis. This examination indicates that cell damage of excimer laser is higher than expected from prior studies.

Adult↗
PubMed1996

High-precision, high-speed measurement of excimer laser keratectomies with a new optical pachymeter.

In excimer-laser photorefractive keratectomy (PRK) the depth of the stromal tissue ablation is calculated from calibration and empirical data but is not actually measured, since a noncontact high-precision instrument for the measurement of the actual ablation has not been available. With a newly developed method for optical pachymetry we studied the depth of corneal ablations performed with an excimer laser. The excimer laser (Schwind Keratom) was calibrated according to the manufacturers' instructions. On freshly enucleated pig eyes, planokeratectomies with a diameter of 5 mm and a planned depth of 20, 40, 80, 160, and 320 microns were performed. With a newly developed high-precision, high-speed reflectometer the corneal thickness was measured immediately before and after the keratectomy. All ablations were deeper than expected. For a planned keratectomy of 20 microns we found a mean ablation depth of 29 microns; for 40 microns, a mean depth of 51 microns; for 80 microns, a mean depth of 100 microns; for 160 microns, a mean depth of 200 microns; and for 320 microns, a mean depth of 396 microns. The differences between mean and maximal ablation values were 58.6% at the 20-micron setting, 40.9% at the 40-micron setting, 20.1% at the 80-micron setting, 11.5% at the 160-micron and 9.8% at the 320-micron setting. Ablation rates showed the highest degree of variation in the 20-micron ablation group. Absolute variations in the ablation depth increased with ablation depth. In photorefractive procedures the volume of the tissue ablated is calculated from the instrument calibration but is not actually measured. Although the greater than expected ablation depths may in part be explained by differences between human and porcine tissue, the high degree of variability in the laser ablations may have other causes. We suggest that variations in the postoperative refractive results of PRK, which are currently attributed to variations in corneal would healing, may in part be due to variations in ablation depth.

Animals↗
PubMed2004

Topical tacrolimus and the 308-nm excimer laser: a synergistic combination for the treatment of vitiligo.

OBJECTIVE: To compare the efficacy of combined tacrolimus and 308-nm excimer laser therapy vs 308-nm excimer laser monotherapy in treating vitiligo. DESIGN: Comparative, prospective, randomized, intraindividual study. PATIENTS: Fourteen patients, aged 12 to 63 years, with Fitzpatrick skin types II to IV. INTERVENTION: For each patient, 4 to 10 target lesions were chosen. The treatment applied to each target lesion was randomized by drawing lots. Each lesion was treated twice a week by the 308-nm excimer laser, for a total of 24 sessions. Initial fluences were 12 mcal/cm(2) (50 mJ/cm(2)) less than the minimal erythemal dose in vitiliginous skin. Then, fluences were increased by 12 mcal/cm(2) every second session. Moreover, topical 0.1% tacrolimus ointment was applied twice daily on target lesions receiving the combined tacrolimus and excimer laser treatment (group A). Group B target lesions received only excimer laser monotherapy. For each treated lesion, the untreated lesion on the opposite side served as the control. Tolerance was evaluated by a visual analog scale, and secondary events were recorded at each session. MAIN OUTCOME MEASURE: Treatment efficacy, which was blindly evaluated by 2 independent physicians by direct and polarized light photographs taken before and after treatment. RESULTS: Forty-three lesions were treated (23 in group A and 20 in group B). All patients completed the study. Repigmentation was observed in all group A lesions (100%) and in 17 (85%) of the 20 group B lesions. Repigmentation was not observed in the untreated lesions (control group). A repigmentation rate of 75% or more was obtained in 16 (70%) of the 23 group A lesions and in 4 (20%) of the 20 group B lesions. In UV-sensitive areas (the face, neck, trunk, and limbs, with the exception of bony prominences and extremities), 10 (77%) of 13 group A lesions had a repigmentation rate of 75% or more vs 4 (57%) of 7 group B lesions. In classically UV-resistant areas, 6 (60%) of 10 group A lesions had a repigmentation rate of 75% or more vs 0 of the 13 group B lesions. The mean number of sessions necessary for an improvement of repigmentation was 10 in group A and 12 in group B. Adverse effects have been limited, and tolerance was excellent. CONCLUSIONS: The combination treatment of 0.1% tacrolimus ointment plus the 308-nm excimer laser is superior to 308-nm excimer laser monotherapy for the treatment of UV-resistant vitiliginous lesions (P<.002). The efficacy and the good tolerance of the 308-nm excimer laser in monotherapy for treating localized vitiligo were also confirmed, but this treatment regimen should be proposed only for UV-sensitive areas.

Administration, Topical↗
PubMed1997

[Histological and ultrastructural study of corneal endothelium after excimer laser ablation in rabbit].

To investigate the effect of excimer laser ablation on the corneal endothelium in the early period, an excimer laser ablation was performed on rabbit cornea. Electron microscopy revealed an irregular space in the endothelial membrane facing Descemet's membrane 48 hours after the laser ablation. At 60 hours, electron-dense material was observed between the endothelial cells and Descemet's membrane. At 72 hours, electron-dense material was observed in Descemet's membrane, but no morphologic change was observed in the endothelium. These results suggest that excimer laser ablation may affect reversible corneal endothelium and it is important to perform a long-term follow-up of the corneal endothelium after excimer laser ablation in humans.

Animals↗
PubMedDate not supplied

The use of confocal microscopy in evaluating corneal wound healing after excimer laser keratectomy.

Corneal wound healing following excimer laser keratectomy is the major cause of regression of treatment results. The amount of anterior stromal haze that develops may be influenced by topical medications. Over a period of 6 months, we followed 15 New Zealand white rabbit eyes that underwent excimer laser keratectomy with the VISX 193-nm ArF laser at a fluence of 150 mJ/cm2 for a depth of 130 microns. Eyes were randomized to treatment with prednisolone acetate, diclofenac sodium (Voltaren), a combination of both, and a control group. Drops were administered four times a day for 1 week, two times a day for 3 weeks, and the drops were then tapered. All eyes were reepithelialized by 5 to 7 days. The tandem scanning confocal microscope (TSCM) was used to evaluate the corneal wound in vivo weekly for a month and monthly for 6 months. During the early postoperative period, the TSCM revealed significant anterior stromal keratocyte activation with cell elongation and the spindle-shaped appearance of fibroblasts in all groups. Collagenous stromal scarring was evident initially, then slowly decreased in all treatment groups. This study shows that TSCM is clinically useful for successive in vivo examinations of corneal wounds after excimer laser keratectomy and for comparing the effects of various topical medications.

Animals↗