Excimer laser treatment of corneal surface pathology: a laboratory and clinical study (original) (raw)
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Acute light and electron microscopic study of ultraviolet 193-nm excimer laser corneal incisions
1988
The 193-nm ultraviolet beam from an argon fluoride excimer laser was focused on the corneas of rabbits to produce incisions of the type necessary for radial keratotomy. The energy densities used were in two ranges, 1.0 to 2.1 J/cm 2 per pulse and 200 to 700 mJ/cm 2 per pulse. The eyes were enucleated and fixed for histologic and electron microscopic examination immediately after exposure. Structural analysis of the higher energy density exposures showed ridging on the surface of the cornea, micro-pitting on the stromal surface inside the cut, and denudation of the endothelium under the ablation zone. The lower energy density incisions did not exhibit significant surface ridging or endothelial cell loss but did exhibit significant stromal swelling during the laser exposure thus making it difficult to produce incisions of a precisely controlled depth. Beam profile measurements and infrared thermal measurements of the cornea surface during laser exposure were made.
Superficial keratectomy with the 193 nm excimer laser
Acta Ophthalmologica, 2009
Rough corneal surfaces may be smoothed by performing a superficial keratectomy with the 193 nm excimer laser. In order to smooth an irregular surface, a substance must be used during ablation to protect low corneal areas so that high spots are ablated preferentially. A simple, accurate, and reproducible method for modelling various corneal surface irregularities was developed. The technique uses the excimer laser to imprint the patterns of various metallic grids onto the stromal surface. The model was used to facilitate a comparison of three potential smoothing agents: 0.5% tetracaine, 2% hydroxypropylmethylcellulose, and a fluorescein-containing hyaluronate preparation. Preliminary results indicate that tetracaine may be the most efficacious smoothing agent.
Corneal surface ablation by 193 nm excimer laser and wound healing in rabbits
Investigative ophthalmology & visual science, 1989
The 193 nm argon fluoride excimer laser was used to ablate a 6 mm diameter area of the central rabbit cornea under various conditions of power, beam configuration and exposure time. High repetition rates or prolonged exposures produced charring and prevented rapid epithelial wound closure. Endothelial vacuolization, reduction in density, and displacement of cell material into Descemet's layer resulted in these experiments. A beam of low and uniform power intensity (40 pulses per second, 100 seconds at 23 mJ/cm2) reduced stromal damage, cellular infiltration, and epithelial irregularities including punctate staining and cell exfoliation. Epithelial rehealing occurred within two days. Basal lamina and hemidesmosomes were reformed by one week. Endothelial damage was not detected. Excimer laser ablation may allow removal of superficial dystrophies or scars, followed by rapid healing from normal corneal reparative processes.
Treatment of corneal dystrophies with excimer laser
Acta Ophthalmologica, 2009
Thirty-three eyes with different corneal dystrophies underwent phototherapeutic keratectomy to ablate corneal opacities, surface irregularities and corneal wounds. For most patients the treatment goal was to improve vision but also corneal woundhealiig, glare problems and unstable refraction were indications for treatment. In 27 eyes with the treatment goal to improve vision, 23 improved 2 lines or more on the visual chart used. In none of the patients has the treatment led to a worsening of the condition. The mean follow-up time was 9 months. Excimer laser ablation of corneal dystrophies seems to be a good treatment, which can improve visual functions considerably, heal corneal wounds and in this way postpone corneal grafting in many cases.
Excimer laser ablation of a corneal protuberance
Journal of Cataract and Refractive Surgery, 1992
The ablation of a post-traumatic superficial corneal nodule with an argon fluoride excimer laser is reported. Three months postoperatively the area had a smooth surface with no distortion of adjacent cornea.
Ophthalmology, 2004
To demonstrate the efficacy and safety of topographically guided excimer laser photorefractive keratectomy (PRK) in treating superficial corneal opacities. Design: Prospective, noncomparative interventional case series. Methods: Twenty-six eyes of 24 patients with postinfectious (n ϭ 6), post-traumatic (n ϭ 18), and post-PRK (n ϭ 2) scars were treated with an excimer laser linked to a computerized videokeratography unit with a topographically supported customized ablation workstation. Main Outcome Measures: Manifest spectacle refraction, best spectacle-corrected visual acuity (BSCVA), uncorrected visual acuity (UCVA), change of corneal clarity, and topographic indexes of surface regularity. Results: The mean follow-up period was 7.7Ϯ2.1 months (Ϯ standard deviation) (range ϭ 6-12). Corneal clarity and corneal topography patterns improved in all eyes. Uncorrected visual acuity improved from 0.7Ϯ0.8 logarithm of the minimum angle of resolution (logMAR) to 0.4Ϯ0.5 logMAR (P ϭ 0.008), and BSCVA improved from 0.3Ϯ0.6 logMAR to 0.1Ϯ0.6 logMAR (PϽ0.001). The BSCVA increased in all eyes (Ն2 lines in 76.9% of eyes and 1 line in 23.1%). The mean spherical equivalent refraction changed from Ϫ0.125Ϯ2.77 diopters (D) to ϩ1.33Ϯ1.28 D (P ϭ 0.019). Conclusions: The use of topographically guided PRK with the topographically supported customized ablation method resulted in significant increases of UCVA and BSCVA and improved corneal clarity in all patients. The technique seems to be safe and effective for treating various superficial corneal diseases, including postinfectious, post-traumatic, and post-PRK scars.
Seminars in Ophthalmology, 2016
Purpose: To investigate and compare the long-term safety, efficacy, and accuracy of PRK (photorefractive keratectomy) and LASEK (laser epithelial keratomileusis) in myopic corneas having residual corneal thickness less than 400 micron meters (µm). Methods: The medical reports of the patients who had undergone excimer laser surface ablation between 2007-2011 and had a residual corneal thickness less than 400 µm were retrospectively reviewed. Results: Forty-two eyes of 42 patients with a mean age of 28.79±7.76 years were enrolled into the study. Twenty-two PRK and 20 LASEK procedures were performed. The mean follow-up time was 45.00±11.80 months. At the end of follow-up, no ectasia was detected. Nineteen percent of eyes had trace haze. No eyes lost any lines in corrected distance visual acuity. Eighty-one percent of the patients had an uncorrected distance visual acuity better than 20/40. The regression rate was 16.7%. Sixty-two percent of eyes were within ±1.00 D. The safety and efficacy indexes were 1.19±0.42 and 1.00±0.40, respectively. There was not any difference between LASEK and PRK regarding achieved spherical equivalent refraction, haze ratio, visual acuity, safety, efficacy, and regression. Conclusions: Both PRK and LASEK are safe and effective in myopic corneas having thin residual thickness.
Human corneal ablation threshold using the 193-nm ArF excimer laser
Investigative ophthalmology & visual science, 1999
To determine the human corneal threshold ablation energy density for the 193-nm ArF excimer laser, approximating clinical conditions. The VISX Star (Santa Clara, CA) 193-nm argon fluoride excimer laser was used to ablate the cornea in human eye bank eyes under clinical conditions. Corneas were exposed to energy densities of 10, 20, 30, 35, 40, 45, and 140 to 160 mJ/cm2. Corneas were fixed for light and transmission electron microscopy immediately after laser exposure. Different ablation thresholds for various corneal structural elements were observed. The ablation threshold for the collagen in the corneal stroma was determined to be 30 mJ/cm2. Keratocytes had ablation thresholds of 40 mJ/cm2. These different ablation thresholds accounted for the production of stromal peaks and valleys, with the keratocytes atop the peaks. Different corneal structural elements have different ablation threshold energy densities.
Laser interactions with the cornea
Survey of Ophthalmology, 1986
Principles of laser-tissue interactions in the eye are reviewed. Cornea1 structure and function are summarized, with particular regard for features related to laser treatment. h summary of argon and carbon dioxide laser techniques in the cornea is presented, followed by a review of studies on cornea1 response to ultraviolet radiation. A detailed description is then given of the characteristics of excimer laser tissue ablation. Potential applications of this process in cornea1 and keratorefractive surgery are reviewed. (Surv Ophthalmol 31:37-53, 1986)