First clinical results of epithelial laser in situ keratomileusis with a 1000 Hz excimer laser

Thermal Load During Corneal Excimer Laser Ablation: Impact of Different Ablation Parameters

PURPOSE

To characterize the impact of different ablation parameters on the change in peak corneal temperature during corneal excimer laser ablation.

METHODS

Forty-two ablations were performed (21 on polymethylmethacrylate [PMMA] and 21 on porcine eyes) simulating photorefractive keratectomy (PRK), transepithelial PRK, and laser in situ keratomileusis (LASIK) treatments. Each ablation was recorded using infrared thermography. The change in peak corneal temperature was analyzed with respect to varying ablation parameters.

RESULTS

Excellent correlation between the temperature rise in PMMA and porcine eyes was found. The change in peak corneal temperature was significantly higher in myopic than in hyperopic corrections, ranging from 6 °C for hyperopic corrections to 16 °C for a -18.00 diopters (D) correction. The change decreased with larger optical zones. Of all analyzed metrics, the refractive correction together with the maximum slope of the treatment showed the best coefficient of determination. Transepithelial ablations led to a higher change in peak corneal temperature than pure stromal ablations. Isothermal lines as a function of the refractive correction and optical zone diameter were calculated with a hypersurface model. If keeping the change in peak corneal temperature below 8 °C is the limit, only 3.00 to 4.00 D can be treated (6.5 mm or larger optical zone); for 10 °C, a maximum of 7.00 D (7 mm or larger optical zone) can be treated and for 12 °C, 10.00 D can be treated (6 mm or larger optical zone).

CONCLUSIONS

The effect of different parameters on change in peak corneal temperature during corneal laser ablation could be quantitatively evaluated. Cooling the cornea may aid in avoiding thermal denaturation. This is particularly important for transepithelial ablations, which further increase the thermal load due to the extra ablation of the epithelium. [J Refract Surg. 2020;36(10):667-676.].

Safety, efficacy, and predictability of laser in situ keratomileusis to correct myopia or myopic astigmatism with a 750 Hz scanning-spot laser system

PURPOSE

To evaluate the clinical outcomes of laser in situ keratomileusis (LASIK) to correct myopia or myopic astigmatism using the Amaris 750S 750 Hz excimer laser.

SETTING

Private LASIK center, Tokyo, Japan.

DESIGN

Case series.

METHODS

Patients with myopia or myopic astigmatism (spherical equivalent -0.50 to -11.63 diopters [D]), a corrected distance visual acuity (CDVA) of 20/20 or better, and an estimated residual bed thickness of 300 μm or more had LASIK using the aspheric aberration-free ablation profile of the 750 Hz scanning-spot laser and the Femto LDV Crystal Line femtosecond laser for flap creation. Study parameters included uncorrected distance visual acuity (UDVA), CDVA, manifest refraction, astigmatism, and higher-order aberrations (HOAs).

RESULTS

The study included 1280 eyes (685 patients). At 3 months, 96.6% of eyes had a UDVA of 20/20 or better and 99.1% had 20/32 or better; 94.1% of eyes were within ± 0.50 D of the intended correction and 98.9% were within ± 1.00 D; 89.7% of eyes had no residual cylinder and 96.0% had a postoperative astigmatism of less than 0.50 D. All eyes had a postoperative CDVA of 20/20 or better. The HOAs increased postoperatively (P<.001), with mean total postoperative corneal and ocular HOAs of 0.66 μm ± 0.20 (SD) and 0.56 ± 0.23 μm, respectively. The efficacy index and safety index were 1.02 and 1.06, respectively.

CONCLUSION

Laser in situ keratomileusis with the 750 Hz scanning-spot laser was safe, effective, and predictable. No specific clinical side effects that might be associated with a high repetition rate occurred.

FINANCIAL DISCLOSURE

Mr. Magnago is an employee of Schwind eye-tech-solutions GmbH. No other author has a financial or proprietary interest in any material or method mentioned.

Clinical results of using a high-repetition-rate excimer laser with an optimized ablation profile for myopic correction in 10 235 eyes

PURPOSE

To evaluate the visual outcomes, safety, stability, efficacy, and predictability of laser in situ keratomileusis (LASIK) to correct myopia using a high-repetition-rate excimer laser with an optimized ablation profile.

SETTING

Private clinic, Tokyo, Japan.

DESIGN

Retrospective noncomparative study.

METHODS

In this study, patients had LASIK using the Schwind Amaris excimer laser for myopic correction.

RESULTS

The study comprised 10  235 eyes of 5191 patients. The patients' mean age was 33.9 years ± 7.84 (SD) (range 18 to 56 years). The mean preoperative manifest refraction spherical equivalent (MRSE) was -5.02 ± 2.17 diopters (D) (range -2.75 to -11.50 D). Three months postoperatively, 82.0% of patients achieved an uncorrected distance visual acuity of -0.18 logMAR or better and 96.9% achieved 0.00 logMAR or better. The MRSE was within ±0.50 D of the intended refractive target in 88.4% of eyes and within ±1.00 D in 98.8%. Despite using the profile designed to minimize postoperative aberrations, the postoperative corneal and ocular higher-order aberrations increased.

CONCLUSION

Laser in situ keratomileusis using a high-repetition-rate excimer laser was a safe and effective procedure, yielding predictable results for a wide range of myopic patients.

FINANCIAL DISCLOSURE

Mr. Magnago is an employee of Schwind Eye-Tech Solutions GmbH & Co. KG. No other author has a financial or proprietary interest in any material or method mentioned.

One-step transepithelial topography-guided ablation in the treatment of myopic astigmatism

PURPOSE

To evaluate one-step topography-guided transepithelial ablation in the treatment of low to moderate myopic astigmatism using a 1KHz excimer laser.

METHODS

Retrospective study of 117 consecutive eyes available for evaluation 12 months after surgery. Pre- and post-operative visual and refractive data as well as post-operative pain and haze were analyzed. A novel technique integrating custom refractive- and epithelial- ablation in a single uninterrupted procedure was used.

RESULTS

The mean pre-operative spherical equivalent (SE) and the mean cylinder were: -3.22 diopters (D) ±1.54 (SD) (range -0.63 to -7.25 D) and -0.77 D ±0.65 (range 0 to -4.50 D), respectively. At 12 months after surgery: no eyes lost ≥2 lines of corrected distant visual acuity (CDVA). Safety and efficacy indexes were 1.27 and 1.09, respectively. Uncorrected distant visual acuity (UDVA) was ≥20/20 in 96.6% of the eyes. Manifest refraction spherical equivalent was within ±0.5 D of the desired refraction in 93.2% of the eyes. Average root mean square (RMS) wavefront error measured at central 6 mm, increased from 0.38 pre-operatively to 0.47 µm post-operatively. Refractive stability was achieved and sustained 1 month after surgery. No visually significant haze was registered during the observation period. Post-operative pain was reported in 4.5% of patients.

CONCLUSIONS

One-step transepithelial topography-guided treatment for low to moderate myopia and astigmatism performed with a 1 KHz laser, provided safe, effective, predictable and stable results with low pain and no visually significant haze.

Corneal stromal ablation with femtosecond ultraviolet pulses in rabbits

PURPOSE

To determine the effectiveness of femtosecond ultraviolet (UV) pulses in ablating corneal stroma in a rabbit model and to compare the healing response between eyes treated with femtosecond UV pulses and eyes treated with standard excimer photorefractive keratectomy.

SETTING

Laser Research Center, Vilnius University, Vilnius, Lithuania.

DESIGN

Experimental study.

METHODS

Myopic photoablation using a femtosecond UV solid-state laser system was applied to corneas of pigmented rabbits. Experiments in 16 eyes were performed for optimization of the laser system parameters (fluence, spot size, pulse repetition rate) and calibration of ablation rate. In 7 rabbits, deep femtosecond UV ablation (∼130 μm) in 1 eye and shallow ablation (∼30 μm) in the contralateral eye were performed. Nine rabbits received an approximately 30 μm ablation with femtosecond UV pulses in 1 eye and with a conventional excimer system in the contralateral eye. Two eyes were used as controls. The ablation process and surface-temperature dynamics were monitored and recorded. Surface quality and haze development were evaluated. Rabbits were humanely killed 0 to 6 months after surgery, and eyes were enucleated for histological examination.

RESULTS

Rabbit corneas ablated with femtosecond UV pulses or excimer laser radiation were similar in terms of the corneal wound-healing process, surface quality, and histology.

CONCLUSIONS

The experiments indicate the feasibility of clinical application of femtosecond UV lasers for stromal ablation. The ability to switch between laser harmonics allows fast changeover from infrared to the UV mode, implying that a wide range of ophthalmic procedures can be performed using a single solid-state laser device.

FINANCIAL DISCLOSURE

Ms. Gabryte and Mr. Danielius are paid employees of Light Conversion Ltd. Mr. Danielius is a shareholder of Light Conversion Ltd. No other author has a financial or proprietary interest in any material or method mentioned.

Safety, efficacy, predictability and stability of laser in situ keratomileusis (LASIK) with a 1000-Hz scanning spot excimer laser

PURPOSE

To evaluate the safety, efficacy, predictability and stability of laser in situ keratomileusis (LASIK) with a 1000-Hz scanning spot excimer laser (Concept System 1000; WaveLight GmbH, Erlangen, Germany).

METHODS

LASIK was performed on twenty eyes with myopia or myopic astigmatism (mean spherical equivalent refraction: -3.97±1.72 dioptres (D); mean cylinder: -0.84±0.77 D) using a microkeratome for flap creation and the Concept System 1000 for photoablation. Patients were examined preoperatively as well as 1, 3 and 6 months after the treatment. Manifest sphere and cylinder, uncorrected (UCDVA) and best corrected (BCDVA) distance visual acuity, corneal topography and pachymetry were analysed.

RESULTS

We observed no adverse events that might have been associated with the use of a repetition rate of 1000 Hz. All eyes maintained or had improved BCDVA at 6 months after treatment when compared to preoperative values. Six months after LASIK, UCDVA was 20/20 or better in 85% and 20/25 or better in 100% of the eyes. The spherical equivalent refraction was within ±0.50 D in 95% of the eyes at 6 months after surgery. The refraction stayed stable over time; 95% of the eyes changed<0.5 D postoperatively.

CONCLUSION

LASIK with the prototype 1000-Hz excimer laser was safe, efficient and predictable. The postoperative refraction was stable over time. There were no specific clinical side-effects that might be associated with the use of such a high repetition rate.