YAG Laser Thermal Keratoplasty Research Articles

Non-contact Holmium:YAG Laser Thermal Keratoplasty for Hyperopia: Two-year Follow-up

We evaluated the safety and efficacy of the non-contact holmium:YAG laser thermal keratoplasty (LTK) for the treatment of mild to moderate hyperopia without astigmatism. A prospective, non-comparative case series included 50 eyes of 28 patients (aged > or =40 years) who had stable refraction and an astigmatic component < +0.50 diopters (D). We applied the non-contact pulsed holmium:YAG laser to treat the hyperopic spherical component using the Hyperion LTK System. All patients had minimum 12-month follow-up and 64% (18 patients) had 24-month follow-up. The mean age of patients was 48.4 +/- 8.23 years (range: 40 to 62 years). The preoperative hyperopic mean spherical equivalent refraction was +2.32 +/- 0.975 D (range: +1.00 to +4.75 D). Postoperatively, the subjective manifest refraction decreased from the preoperative mean value of +2.32 D to a mean -0.09 D at 1 month after surgery and regressed to +0.315 D at the last follow-up examination, resulting in a mean correction of +2.005 +/- 0.81 D at 24 months after surgery. Preoperatively, mean uncorrected visual acuity in LogMAR units was 0.798 +/- 0.353 and at 12 months after surgery, it was a mean 0.108 +/- 0.136. Keratometric power increased from 42.595 +/- 1.949 D before surgery to 44.605 +/- 1.626 D at 24 months after surgery. Holmium:YAG LTK was an acceptable alternative for the correction of mild to moderate hyperopia in this middle-aged population.

Cataract surgery after holmium:YAG laser thermal keratoplasty

A 64-year old man had noncontact holmium:YAG (Ho:YAG) laser thermal keratoplasty (LTK) performed in the left eye on March 10, 1998, and in the right eye on January 11, 1999. The patient achieved 1.3 diopters (D) and 1.4 D of corneal steepening in the right and left eye, respectively, which was the desired amount as his refractive error before Ho:YAG LTK was low. At the 3-month postoperative examination of the left eye, cortical cataracts were observed in both eyes. Approximately 1 year later, bilateral cataract extraction was recommended because of patient-reported decreased vision at distance and near and difficulty with vision in the presence of glare. Cataract surgery and intraocular lens (IOL) implantation was performed in both eyes in August 1999 using the keratotomy readings taken after noncontact Ho:YAG LTK to calculate IOL power. Although slight flattening of the cornea occurred after cataract extraction, the refractive outcomes achieved by noncontact Ho:YAG LTK were generally preserved.

Noncontact holmium:YAG laser thermal keratoplasty for hyperopia

Purpose: To describe our experience with noncontact holmium:YAG laser thermal keratoplasty (Ho:YAG LTK).Setting: Refractive Surgery and Cornea Department, Clinica de Ojos Dr. Nano, Buenos Aires, Argentina.Methods: In this retrospective study, 182 hyperopic eyes from 116 patients were treated with noncontact Ho:YAG LTK. Mean age was 50 years ± 7 (SD), and the spherical equivalent (SE) of the subjective mean refraction (SMR) was +2.50 ± 0.87 diopters (D). Eyes with corneal power of more than 45 D, corneal pachymetry thicker than 550 µm, and previous corneal surgery or disease were excluded. Holmium:YAG laser parameters include one to three rings of eight spots arranged in a radial and symmetrical array. Pulse energy was 240 mJ, with five pulses per spot. Patients were followed for 12 months.Results: The mean uncorrected visual acuity from 3 to 12 months was 20/40 (20/200 to 20/25), improving an average of three Snellen lines. Mean best spectaclecorrected visual acuity was 20/25 at all postoperative examinations, the same as preoperatively. Mean SE of the SMR was + 1.50 ± 0.98 D (range −0.75 to +4.50 D) at 6 months and +1.25 ± 0.96 D (+0.25 to +3.25 D) at 1 year. After 9 months, 17% of operated eyes were retreated.Conclusion: In this study, Ho:YAG LTK was safe and effective, provided satisfactory correction of low hyperopia, and had a low complication rate. Good patient selection is the key to obtaining good results.

Laser thermal keratoplasty for the treatment of photorefractive keratectomy overcorrections: A 1-year follow-up

Objective To evaluate the results of holmium:YAG laser thermal keratoplasty (LTK) treatment for overcorrection of myopia after a photorefractive keratectomy (PRK) treatment. Participants Thirty-six eyes (33 patients) were treated with a nontouch holmium:YAG laser (Sunrise Technologies, Model LTK, Freemont, CA) because of hyperopia (mean ± standard deviation of +2.06 diopter [D] ± 0.75, ranging from +1.0 to +3.5 D) following a PRK treatment. A control LTK group treated for primary hyperopia, who had preoperative refraction values not statistically different from the PRK + LTK group, was used for comparison. Intervention The number of spots applied varied from 8 to 24, and the energy used was 200 to 240 mJ. A maximum of three rings of four to eight spots were placed between 6 and 8 mm from the visual axis. Results Twelve months after the LTK retreatment for PRK patients, mean refraction was +1.14 D ± 1.09. Regression from 1 to 12 months was 0.5 D ± 1.1. At 12 months, 50% of eyes were within 1 D of emmetropia; 93% of eyes had uncorrected visual acuity (UCVA) of 20/40 or better; and 24% of eyes had UCVA of 20/20 or better. Refraction was not stable for 11 eyes (34%) that regained original sphere values or higher. Best-corrected visual acuity was not affected, and haze was not increased nor decreased by the procedure. Conclusions Twelve months after an LTK retreatment for an initial PRK, two thirds of the retreated eyes did not need further retreatments. However, clinical data showed that LTK should be kept for +1 to +2 D of hyperopia for PRK overcorrection retreatments.

Radial and staggered treatment patterns to correct hyperopia using noncontact holmium:YAG laser thermal keratoplasty

Purpose: To compare the effects of two treatment patterns in the correction of hyperopia by noncontact holmium:YAG laser thermal keratoplasty (LTK).Setting: Divisione Oculistica, Ospedale S. Gerardo, Monza, Italy.Methods: Using two treatment patterns, we performed noncontact LTK in one session in 16 eyes of 8 patients with isometropic hyperopic refractive errors; mean preoperative subjective cycloplegic refraction was +4.90 diopters (D) ± 1.17 (SD). The treatment consisted of 24 spots in three concentric rings of eight spots each; ring diameters were 6.0, 7.0, and 8.0 mm, respectively. Each spot received seven pulses of laser energy at 30 mJ/pulse. We treated one eye of each patient with a radial pattern (the spots of the three rings aligned on the eight semimeridians) and the fellow eye with a staggered pattern (the spots of the contiguous rings at 22.5 degrees from each other). Follow-up at 1, 15, 30, 90, 180, and 360 days included subjective cycloplegic refraction, uncorrected (UCVA) and spectaclecorrected visual acuity (SCVA), computerized videokeratography (CVK), and Scheimpflug camera examination.Results: One year postoperatively, the mean subjective cycloplegic refraction was +2.75 ± 1.6 D in the eyes treated with the radial pattern and +3.40 ± 1.6 D in those treated with the staggered pattern; the mean change in subjective cycloplegic refraction was 2.15 and 1.50 D, respectively. Mean UCVA improved by five lines in the radial group and by four lines in the staggered group. Mean SCVA returned to preoperative levels by day 15 in the radial group and at 1 year in the staggered group; at 1 year, SCVA improved by one line in the radial group and remained unchanged in the staggered group. No eye lost one or more lines of SCVA. Refractive astigmatism was essentially unchanged in both groups. Scheimpflug photography and CVK indicated larger and more uniform corrected zones in the radial group.Conclusions: Radial and staggered patterns effectively corrected low hyperopia, although both were subject to a certain amount of regression. The radial pattern produced faster postoperative recovery of SCVA and demonstrated greater refractive stability.

Hyperopia correction by noncontact holmium: YAG laser thermal keratoplasty: five-pulse treatments with 1-year follow-up.

Previous noncontact holmium (Ho): YAG laser thermal keratoplasty (LTK) studies on correction of low to moderate hyperopia have used treatment algorithms based on ten-pulse, variable-pulse-energy treatment parameters. The purpose of this study was to evaluate the safety, effectiveness, and stability of new five-pulse, constant-pulse-energy treatment parameters for noncontact Ho:YAG LTK. Thirty-nine hyperopic patient eyes [up to +4.75 diopters (D) refractive error] were treated using simultaneous noncontact delivery of Ho:YAG laser energy (Sunrise) with two symmetrical octagonal rings of eight spots per ring and radial spot patterns on centerline diameters of 5 and 6 mm (group A), 6 and 7 mm (group B), or 6.5 and 7.5 mm (group C). Each ring of spots received five pulses of laser light at 5 Hz pulse repetition frequency and a fixed pulse energy of 240 mJ. Thirty of the 39 patient eyes (77%) had 1-year follow-up exams. At 1 year, the mean Snellen uncorrected distance visual acuity lines gained was 3.7 +/- 0.5/6.8 +/- 2.7/5.3 +/- 3.3 for groups A, B, and C. The mean changes in subjective manifest refraction (spherical equivalent) were -2.08 +/- 1.13 D, -1.83 +/- 0.88 D, -1.22 +/- 0.88 D for groups A, B, and C respectively. None of the eyes lost two or more lines of spectacle-corrected distance visual acuity. There were no clinically significant complications in any patient. This clinical study indicates that five-pulse noncontact LTK treatments of low hyperopia are safe and effective. The stability has to be confirmed with longer follow-up.

Hyperopia Correction by Noncontact Holmium: YAG Laser Thermal Keratoplasty: U.S. Phase IIA Clinical Study with 2-year Follow-up

Purpose: This study was performed to determine the long-term efficacy, safety, and stability of noncontact holmium:yttrium aluminum garnet (Ho:YAG) laser thermal keratoplasty (LTK) for correction of low-to-moderate hyperopia.Methods: The authors treated 1 eye each of 28 patients for correction of low-tomoderate hyperopia (up to +3.88 diopters [D] refractive error) using the Sun 1000 Corneal Shaping System (Sunrise Technologies, Inc., Fremont, CA). Treatments were performed with one or two rings of eight spots per ring with centerline diameters of 6 mm (one ring) or 6 and 7 mm (two rings), ten pulses of laser light at 5-Hz pulse repetition frequency, and pulse energies ranging from 208 to 242 mJ. Follow-up was 2 years.Results: At 2 years after surgery, uncorrected distance visual acuity was improved by 1 or more lines of Snellen visual acuity in 19 (73%) of 26 of the treated eyes. The mean lines gained was 2.5 ± 2.2/3.3 ± 2.7 for one- and two-ring treatment groups, respectively. The mean change in spherical equivalent of the subjective manifest refraction was −0.53 ± 0.33 D/−1.48 ± 0.58 D for one- and two-ring treatment groups. Regression between 1 and 2 years was 0.01 D and 0.16 D, respectively. In the onering treatment group (18 eyes), 13 eyes (72%) had refractive corrections (range, −0.38 to −1.13 D), and 5 eyes (29%) were unchanged (within ±0.25 D) relative to their preoperative measurements. In the two-ring treatment group, all eight eyes (100%) had reductions in their hyperopia (range of corrections, −0.38 to −2.25 D). None of the eyes lost two or more lines of spectacle-corrected distance visual acuity. There were no sight-threatening complications.Conclusions: This initial U.S. clinical study indicates that noncontact laser thermal keratoplasty treatment of low hyperopia is safe and produces modest but persistent corrections with 2-year follow-up. Expanded studies of this treatment method are warranted.

Histological changes and wound healing response following noncontact holmium: YAG laser thermal keratoplasty

To evaluate acute histological changes and the induced wound healing response in corneal tissue following noncontact holmium:YAG laser thermal keratoplasty (LTK).LTK using 10 pulses and a range of radiant energies was performed on 3 human corneas one day prior ro their removal at penetrating keratoplasty. Rabbit corneas were treated with 10-pulse and 5-pulse LTK and followed for up to 3 months. Tissues were studies with light and transmission electron microscopy and immunohistochemistry.The amount of acute tissue injury increased with increasing pulse radiant energy. In human corneas, changes in the irradiated zones included epithelial cell injury and death loss of fine filamentous structure in Bowman's layer, disruption of stromal lamallae, and keratocyte injury and death. In the rabbit corneas, similar acute changes were noted. By 3 weeks, epithelial hyperplasia and stromal contraction were present. Wound healing in the rabbit corneas included repair of the epithelial attachment complex, keratocyte activation, synthesis of type I collagen, partial restoration of stromal keratan sulfate and type VI collagen, and retrocorneal membrane formation. Compared to 10-pulse treatments, 5-pulse treatments produced less acute tissue injury and had more rapid restoration of normal stromal architecture.Noncontact LTK produces acute epithelial and stromal tissue changes and in rabbit corneas stimulates a brisk wound healing response. These changes could contribute to postoperative regression of induced refractive correction. Further work is required to determine if reductions in the magnitude of acute tissue injury and induced wound healing response will enhance the efficacy and stability of LTK.

Correction of hyperopia induced by photorefractive keratectomy using non-contact Ho:YAG laser thermal keratoplasty.

To evaluate the safety and effectiveness of non-contact holmium:YAG laser thermal keratoplasty in correcting hyperopia induced by photorefractive keratectomy (PRK). Non-contact holmium:YAG laser thermal keratoplasty was applied to 14 eyes with significant hyperopia induced by PRK. The mean spherical equivalent refraction before holmium:YAG laser thermal keratoplasty was +4.20 +/- 1.80 diopters (D) (range, +1.75 to +6.25 D). The results were evaluated 12 months after holmium:YAG laser thermal keratoplasty. No sight-threatening complications occurred. Recovery of spectacle-corrected visual acuity took from 2 to 6 weeks. The immediate significant myopic shift that developed in all eyes gradually receded over 6 to 8 weeks. All eyes were relatively stable after 9 months. At 12 months, there was no statistically significant difference (p < .005) between the mean preoperative spectacle-corrected visual acuity (0.71 +/- 0.12) and the mean postoperative uncorrected visual acuity (0.65 +/- 0.28). At 12 months there was a mean increase of 4.60 +/- 1.20 D in central keratometric power. Total regression did not occur in any eye. Non-contact holmium:YAG laser thermal keratoplasty offers a safe and effective alternative to correct PRK-induced hyperopia.

Correction of hyperopia with non-contact Ho:YAG laser thermal keratoplasty.

To assess the potential of non-contact holmium:YAG laser thermal keratoplasty to safely and effectively correct hyperopia up to +5.00 diopters (D). Non-contact laser thermal keratoplasty with a holmium:YAG laser using energies ranging from 215 to 255 mJ with 6, 7, and 8-min ablation zone diameters, was applied to 57 sighted eyes of 42 hyperopic patients in a controlled study. All patients were followed for 15 months after surgery. Preoperative spectacle-corrected visual acuity returned to baseline levels from 2 to 6 weeks after treatment. Regression of effect was evident in all eyes, and after 15 months was total in 18 eyes (31.5%). The mean cycloplegic refraction before surgery was +3.80 +/- 0.22 D (range, +1.50 to +5.00 D); after surgery, it was +1.40 +/- 0.12 at 3 months, +1.69 +/- 0.19 D at 6 to 8 months, and +1.73 +/- 0.16 D at 15 months. At the end of the study, 41 eyes (71.9%) had an uncorrected visual acuity of 20/40 or better. Thirty-two eyes (58.8%) were within +/- 1.00 D of the intended refraction. Patient age and central pachymetric values were significantly correlated with regression (ANOVA, (p less than .005). Regression of initial effect can be large with non-contact holmium:YAG laser thermal keratoplasty. We think the technique works best up to +3.00 D in older individuals with central corneal thickness less than 525 microns. Algorithms to improve the final results should include an initial calculated overcorrection adjusted on variables that influence regression such as patient age and corneal thickness.

Hyperopia Correction by Noncontact Holmium:YAG Laser Thermal Keratoplasty: United States Phase IIA Clinical Study with a 1-year Follow-up

This study was performed to evaluate the safety and effectiveness of noncontact holmium: YAG (Ho:YAG) laser thermal keratoplasty (LTK) for correcting low to moderate hyperopia. Twenty-eight patients were treated unilaterally to correct low to moderate hyperopia (up to +3.88 diopters [D] refractive error) using simultaneous noncontact delivery of Ho:YAG laser energy. Treatment parameters included one or two symmetric octagonal rings of eight spots per ring with centerline diameters of 6 mm (1 ring) or 6 and 7 mm (2 rings), ten pulses of laser light at 5-Hz pulse repetition frequency, and variable pulse energy, ranging from 208 to 242 mJ. Follow-up was 1 year in 26 (93%) of the 28 patients. At 1 year postoperatively, uncorrected distance visual acuity was improved in all patients. The mean change in subjective manifest refraction (+/- spherical equivalent [SE]) was -0.55 +/- 0.33 D and -1.64 +/- 0.61 D for one and two-ring treatment groups, respectively, with good stability in the refractive change after approximately 6 months. In the one-ring treatment group (17 eyes), refractive corrections of -0.50 to -1.13 D were achieved in ten eyes (59%), and seven eyes (41%) were unchanged (within +/- 0.25 D) relative to their preoperative measurements. In the two-ring treatment group, all eight eyes (100%) had substantial refractive corrections (range, -0.75 to -2.50 D). Mean induced refractive astigmatism was 0.25 +/- 0.29 D and 0.47 +/- 0.53 D for one- and two-ring treatments, respectively. None of the eyes lost two or more lines of spectacle-corrected distance visual acuity. These was no clinically significant change in endothelial cell density with respect to preoperative values. Glare and contrast sensitivity testing indicate that peripheral corneal opacities produced by LTK do not degrade vision. The amount of refractive change in each group was correlated with the amount of laser pulse energy. This initial United States clinical study with 1-year follow-up indicates that noncontact LTK treatment of low hyperopia is safe and effective, providing persistent, though modest, refractive corrections in 59% of the one-ring group and larger, persistent, refractive corrections in 100% of the two-ring group.

Histologic changes and wound healing response following 10-pulse noncontact holmium:YAG laser thermal keratoplasty.

Noncontact holmium:YAG laser thermal keratoplasty (Ho:YAG LTK) is a promising new technology for correction of hyperopia and astigmatism. We studied the acute histologic changes and wound healing response following Ho:YAG LTK performed with treatment parameters encompassing those used in clinical studies. We performed 10-pulse noncontact Ho:YAG LTK on three human corneas 1 day before their removal at penetrating keratoplasty and on six New Zealand white rabbit corneas followed for up to 3 months. Tissues were studied with light and transmission electron microscopy and immunohistochemistry. The amount of acute tissue injury increased according to the pulse radiant energy. In human corneas, changes in the irradiated zones included epithelial cell injury and death, loss of fine filamentous structure in Bowman's layer, disruption of stromal lamellae, and keratocyte injury and death. In the rabbit corneas, similar acute changes were noted. By 3 weeks, epithelial hyperplasia and stromal contraction were present. Wound healing in the rabbits included repair of the epithelial attachment complex, keratocyte activation, synthesis of type I collagen, partial restoration of stromal keratan sulfate and type VI collagen, and retrocorneal membrane formation. Noncontact Ho:YAG LTK produces acute epithelial and stromal tissue changes and in rabbit corneas stimulates a brisk wound healing response.

Hyperopia Correction by Noncontact Holmium.YAG Laser Thermal Keratoplasty: Clinical Study with Two-year Follow-up

Background: Thermal keratoplasty to correct hyperopia has been attempted with nonlaser and laser devices. Problems have included long-term regression and irregular induced astigmatism. The present clinical study was performed to investigate the safety, efficacy, and stability of a noncontact mode of holmium:YAG laser energy delivery and a modified laser thermal keratoplasty treatment procedure for correction of low hyperopia.Methods: Seventeen patients underwent noncontact holmium:YAG laser thermal keratoplasty in their nondominant eyes for correction of hyperopia of up to 3.00 diopters. Treatment parameters included simultaneous delivery of eight holmium:YAG laser spots in a symmetrical octagonal array with a centerline diameter of 6 mm, 10 pulses of laser light at 5-Hz pulse repetition frequency, and pulse energies of 159 to 199 mJ. Follow-up was 2 years in 15 of 17 patients.Results: In the 15 eyes examined at 2 years after surgery, mean uncorrected distance Snellen visual acuity improved from 20/125-1 to 20/50-2. The mean change in spherical equivalent of subjective manifest refraction was -0.79 diopter. Eleven of these 15 eyes (73%) had a mean refractive correction of -1 .1 diopters (range, -0.38 to -2.63 diopters); regression between 14 days and 2 years was 0.2 diopter. Four eyes (27%) had no persistent refractive correction (within ± 0.25 diopter). Mean induced refractive astigmatism was 0.18 diopter. None of the eyes lost two or more lines of spectacle-corrected distance vision. The amount of refractive correction at 2 years after surgery was correlated to the treatment pulse energy and the volume of the opacified corneal tissue observed immediately after treatment.Conclusions: This technique of noncontact laser thermal keratoplasty produced safe, effective, and persistent corrections of low hyperopia in the majority of treated eyes.

Corneal topographic changes after noncontact holmium:YAG laser thermal keratoplasty to correct hyperopia

Purpose: To analyze the changes in corneal curvature induced by laser thermal keratoplasty (LTK) to correct hyperopia.Setting: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas.Methods: We performed LTK on nine hyperopic eyes using a noncontact holmium: YAG (Ho:YAG) laser. Five eyes received a single ring of eight spots at the 6 mm zone (Group A); four received a second ring of eight at the 7 mm zone (Group B). Computerized videokeratography (CVK) was obtained preoperatively and 1, 30, 90, 180, and 360 days postoperatively. We calculated the net dioptric changes in the following CVK values: corneal curvature at the 1, 3, 5, and 7 mm zones; effective corneal refractive power (Eff RP); and spherical equivalent of subjective manifest refraction (SE SMR). We classified difference maps according to the pattern of induced change.Results: At 1 year, steepening at the 1, 3, 5, and 7 mm CVK zones was 0.5 diopter (D), 0.6 D, 0.1 D, and −0.42 D, respectively, in Group A and 1.5 D, 1.5 D, 1.1 D, and 0.54 D, respectively, in Group B. Effective corneal refractive power increased 0.6 D in Group A and 1.5 D in Group B. Mean change in SE SMR was -0.6 D in Group A and −1.4 D in Group B. Most regression occurred during the first 90 days. Difference maps showed five bow-tie, two irregularly irregular, one semicircular, and one homogeneous patterns.Conclusions: Noncontact Ho:YAG LTK produced peripheral corneal flattening and central corneal steepening. A greater change in curvature was produced using a two-ring treatment.

Holmium laser thermal keratoplasty of 10 poorly sighted eyes.

ABSTRACT BACKGROUND: The holmium:YAG laser shrinks stromal collagen and changes corneal refractive power, reportedly without recurrent or persistent epithelial defects, stromal necrosis, or damage to the epithelium and endothelium observed with some other thermokeratoplasty techniques. METHODS: We studied the safety of the holmium:YAG laser using various patterns and energy densities after treating 12 poorly sighted eyes, two immediately prior to corneal transplantation and 10 followed for a mean period of 90 days (range, 60 to 180 days). Visual acuity, intraocular pressure and inflammation, central corneal endothelial cell density and thickness, and intraocular structures of the eye were indices evaluated regularly. Patients were also assessed for specific symptoms during the post-operative period. RESULTS: There were no problems with epithelial healing and no stromal necrosis or evidence of endothelial damage; no significant differences were noted in any of the endothelial cell indices examined. A mean change in corneal curvature of 1.10 diopter (D) was achieved, but varying amounts of regression of this effect was noted. CONCLUSIONS: Holmium:YAG laser thermal keratoplasty appears to be safe over a follow up of up to 180 days. Corneal refractive changes on the order of 1.05 D can be achieved using the parameters employed in this study. Whether or not larger, persistent corneal refractive change can be achieved with a holmium:YAG laser remains to be determined. [J Refract Surg. 1995,11:358-365.]