Richard F. Menefee

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-to-moderate 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 one-ring 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.

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 6mm, 10 pulses of laser light at 5-Hz pulse repetition frequency, and pulse energies of 159 to 199mJ. 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.

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

PURPOSE 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. METHODS 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. RESULTS 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. CONCLUSIONS 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

BACKGROUND 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. METHODS 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. RESULTS 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 Bowmans 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. CONCLUSIONS Noncontact Ho:YAG LTK produces acute epithelial and stromal tissue changes and in rabbit corneas stimulates a brisk wound healing response.

Noncontact Holmium: YAG Laser Thermal Keratoplasty to Correct Hyperopia: 18-Month Follow-Up

PURPOSE To assess the safety and efficacy of noncontact holmium:yttrium aluminium garnet laser thermal keratoplasty (Ho:YAG LTK) for correction of low to moderate hyperopia. METHODS We performed noncontact Ho:YAG LTK on 1 eye each of 28 patients for correction of hyperopia up to +3.88 dpt. Treatments were conducted with 1 or 2 symmetrical octagonal rings of 8 spots/ring with centerline diameters of 6 mm (1 ring) or 6 and 7 mm (2 rings), 10 pulses of laser light at 5 Hz pulse repetition frequency, variable pulse energy in the range of 208-242 mJ and a nominal spot diameter between 615 and 623 microns. RESULTS At 18 months after surgery, 20 of 22 (91%) treated patient eyes had improved uncorrected distance visual acuity. The mean change in subjective manifest refraction (spherical equivalent) was -0.52 +/- 0.35 dpt and -1.41 +/- 0.53 dpt for 1- and 2-ring treatment groups, respectively, with good stability in the refractive change after 6 months. The mean induced refractive astigmatism was small (0.30 +/- 0.37 dpt/0.25 +/- 0.29 dpt for 1-/2-ring treatments). None of the eyes lost 2 or more lines of spectacle-corrected distance visual acuity. There were no clinically significant changes in glare and contrast sensitivity. CONCLUSIONS Noncontact LTK treatment of low hyperopia is safe and effective, and it is more stable and less prone to induce astigmatism than previously reported contact mode LTK treatments.

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

Abstract• Background: 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. • Methods: 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 followup exams. • Results: At 1 year, the mean Suellen 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. • Conclusion: 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.

Chemical laser interactions with human cardiovascular tissue

Repetitively pulsed (rp) hydrogen fluoride (HF) chemical laser interactions with human cardiovascular tissue (normal aorta) have been studied to understand tissue ablation phenomenology, effects, and mechanisms under well characterized laser irradiation conditions. RP HF chemical laser experiments have been performed at two wavelengths (A = 2.78 ,m and 2.91 pm) over a fluence range of 0.5 to 1 1 J/cm2 to determine ablation efficiencies and effective enthalpies of ablation (Q) as a function of wavelength and fluence. The experimental results are analyzed to consider the physical and chemical processes associated with thermochemical ablation of human cardiovascular tissue by pulsed infrared lasers.

Chemical Laser Interactions With Human Corneal Tissue

Repetitively pulsed (rp) hydrogen fluoride (HF) chemical laser interactions with human corneal tissue have been studied to understand tissue ablation phenomenology, effects, and mechanisms under well characterized laser irradiation conditions. RP HF chemical laser experiments have been performed at two wavelengths (? = 2.78 pm and 2.91 μm) over a fluence range of 0.6 to 10 J/cm2 to determine ablation efficiencies and effective enthalpies of ablation (Q*) as a function of wavelength and fluence. The experimental results are analyzed to consider the physical and chemical processes associated with thermochemical ablation of human corneal tissue by pulsed mid-infrared lasers.

Chemical Laser Interactions With Human Cardiovascular Tissues

Continuous wave (cw) and repetitively pulsed (rp) hydrogen fluoride (HF) and deuterium fluoride (DF) chemical laser interactions with human cardiovascular tissues have been studied in order to understand ablation phenomenology, effects, and mechanisms under well characterized laser irradiation conditions. CW HF/DF experiments were performed on normal and atherosclerotic tissues over a broad irradiance range (3-20 kW/cm2) to determine thermal coupling coefficients and effective enthalpies of ablation as a function of laser wavelength and tissue type. Similar experiments were completed using a rp HF chemical laser with a submicrosecond pulse duration. Plume probing experiments were also performed to characterize particle formation (i.e., spallation) generated by rp laser ablation. All of the data are used to consider the physical and chemical processes associated with thermal coupling phenomenology and thermochemical pyrolysis and ablation of cardiovascular tissues irradiated by infrared lasers.

Small‐scale laser effects experiments on graphite: Coupling coefficient, lateral loss, and effective heat of ablation

This work concerns laser‐interaction experiments performed on a fine‐grained, nearly isotropic graphite grade known as GraphNOL. They were carried out with a cw/DF laser of 100‐W output power, at peak irradiances varying from 10 to 50 kW/cm2 on targets of, typically, 1.5‐mm diameter. One of the major objectives was to accept the difficulties associated with such small sizes and rely on analytical techniques for estimating the lateral heat loss, developing a scaling law, and formulating an improved, parametric representation of the effective heat of ablation (Q*). The procedure rests on Breaux’s formula (Ballistic Research Laboratories report no. 1834) heuristically extended to accommodate the concept of a lateral loss parameter, which relates linearly to a scaling parameter that combines target thickness, target diameter, and spot size, thus specifying how geometrical factors correlate in terms of their impact on radial losses. Our investigation demonstrates that a small‐scale, low‐cost laser ablation exp...