Comparison of the Levels of Transforming Growth Factor-ß1 in Tear Fluid in Patients with High Myopia after Transepithelial Photorefractive Keratectomy and Laser Subepithelial Keratomileusis (LASEK).

We compared the level of transforming growth factor-ß1 (TGF-ß1) in the tear fluid of 20 patients with high myopia who underwent transepithelial photorefractive keratectomy (T-PRK) in one eye and laser subepithelial keratomileusis (LASEK) in the contralateral eye. Tear fluid samples were collected with scaled microcapillary tubes before (day 0) and on days 1, 3, and 5 after surgery. The release of TGF-ß1 was determined by multiplying the concentration of TGF-ß1 by capillary tear fluid flow. Corneal haze was also evaluated in 1, 3, and 6 months after surgeries. The median TGF-ß1 release after T-PRK and LASEK differed significantly on days 1 and 3 (p<0.005) and on day 5 (p<0.05). The mean corneal haze score after T-PRK and LASEK also significantly differed in 1 month (p<0.005), but no significant differences in this parameter were revealed at later terms. Thus, the level of TGF-ß1 in the tear fluid after T-PRK was lower than after LASEK, which can be the cause of less pronounced corneal haze in 1 month after surgery.

Epi-Bowman Blunt Keratectomy Versus Diluted EtOH Epithelial Removal in Myopic Photorefractive Keratectomy: A Prospective Contralateral Eye Study.

PURPOSE: To compare the outcomes and complications of Epi-Bowman blunt keratectomy (EBK) using a blunt epikeratome (Epi-Clear, Orca Surgical, Israel), with alcohol delamination of the corneal epithelium during photorefractive keratectomy (PRK) in contralateral eyes. METHODS: This prospective, randomized contralateral eye study included 44 eyes of 22 patients undergoing PRK for bilateral myopia or myopic astigmatism. In each patient, epithelial delimitation was performed using an Epi-Clear epikeratome EBK (EBK group) on 1 eye and diluted ethanol (EtOH) on the fellow eye (EtOH group). Postoperative pain, epithelial healing, epithelial profile, and visual outcome were compared between the 2 groups. RESULTS: The mean postoperative pain scores were 0.37 ± 0.25 for the EBK group and 0.82 ± 0.22 for the EtOH group (P = 0.043). The mean epithelial defect size at day 3 postoperatively was 1.61 ± 1.46 and 2.25 ± 1.69 mm, respectively (P = 0.034). The postoperative 3-month remaining mean spherical equivalent was 0.04 ± 0.49 diopters for the EBK group and 0.21 ± 0.26 D for the EtOH group (P = 0.520). There was no significant difference in UCVA and BCVA between the groups. CONCLUSIONS: Our data suggest that this novel EBK device and technique may minimize postoperative pain, accelerate re-epithelialization, and offer earlier visual recovery, compared with EtOH when used for myopic PRK.

Retrospective Analysis of the Post-Operative Changes in Higher-Order Aberrations: A Comparison of the WaveLight EX500 to the VISX S4 Laser in Refractive Surgery.

INTRODUCTION: In an attempt to maximize treatment outcomes, refractive surgery techniques are being directed toward customized ablations to correct not only lower-order aberrations but also higher-order aberrations specific to the individual eye. Measurement of the entirety of ocular aberrations is the most definitive means to establish the true effect of refractive surgery on image quality and visual performance. Whether or not there is a statistically significant difference in induced higher-order corneal aberrations between the VISX Star S4 (Abbott Medical Optics, Santa Ana, California) and the WaveLight EX500 (Alcon, Fort Worth, Texas) lasers was examined. METHODS: A retrospective analysis was performed to investigate the difference in root-mean-square (RMS) value of the higher-order corneal aberrations postoperatively between two currently available laser platforms, the VISX Star S4 and the WaveLight EX500 lasers. The RMS is a compilation of higher-order corneal aberrations. Data from 240 total eyes of active duty military or Department of Defense beneficiaries who completed photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK) refractive surgery at the Wilford Hall Ambulatory Surgical Center Joint Warfighter Refractive Surgery Center were examined. Using SPSS statistics software (IBM Corp., Armonk, New York), the mean changes in RMS values between the two lasers and refractive surgery procedures were determined. A Student t test was performed to compare the RMS of the higher-order aberrations of the subjects' corneas from the lasers being studied. A regression analysis was performed to adjust for preoperative spherical equivalent. The study and a waiver of informed consent have been approved by the Clinical Research Division of the 59th Medical Wing Institutional Review Board (Protocol Number: 20150093H). RESULTS: The mean change in RMS value for PRK using the VISX laser was 0.00122, with a standard deviation of 0.02583. The mean change in RMS value for PRK using the WaveLight EX500 laser was 0.004323, with a standard deviation of 0.02916. The mean change in RMS value for LASIK using the VISX laser was 0.00841, with a standard deviation of 0.03011. The mean change in RMS value for LASIK using the WaveLight EX500 laser was 0.0174, with a standard deviation of 0.02417. When comparing the two lasers for PRK and LASIK procedures, the p values were 0.431 and 0.295, respectively. CONCLUSION: The results of this study suggest no statistically significant difference concerning induced higher-order aberrations between the two laser platforms for either LASIK or PRK. Overall, the VISX laser did have consistently lower induced higher-order aberrations postoperatively, but this did not reach statistical significance. It is likely the statistical significance of this study was hindered by the power, given the relatively small sample size. Additional limitations of the study include its design, being a retrospective analysis, and the generalizability of the study, as the Department of Defense population may be significantly different from the typical refractive surgery population in terms of overall health and preoperative refractive error. Further investigation of visual outcomes between the two laser platforms should be investigated before determining superiority in terms of visual image and quality postoperatively.

Advanced Surface Ablation With a New Software for the Reduction of Ablation Irregularities.

PURPOSE: To compare visual outcomes and postoperative aberrations after surface ablation performed with a 750-Hz versus a 1,050-Hz excimer laser coupled with an ablation software designed to reduce corneal surface irregularity. METHODS: Retrospective comparative trial of myopic eyes that had refractive surgery consecutively treated with transepithelial advanced surface ablation with a 750-Hz excimer laser (750 group) versus a 1,050-Hz excimer laser coupled with the Smart Pulse Technology ablation software (SPT group). The SPT algorithm is a laser pulse technology software aimed at reducing surface irregularity of the stromal bed at the end of treatment. The authors evaluated the effect of this smoothing on final visual acuity. Patients were observed for 6 months. RESULTS: A total of 139 eyes in the 750 group and 40 eyes in the SPT group were evaluated. Epidemiological and preoperative refractive data of the two groups were comparable. Uncorrected distance visual acuity improved with time and was significantly better in the SPT group (-0.04 ± 0.61 logMAR for the SPT group vs 0.02 ± 0.78 logMAR for the 750 group) (P < .001). At 6 months, 55% versus 21% achieved 20/16 or better (P = .005) and 90% versus 65% achieved 20/20 or better (P = .019) visual acuity in the SPT and 750 groups, respectively. Corrected distance visual acuity improved with time and appeared to be influenced by group (P = .054), with better results in the SPT group. Coma and trefoil improved significantly with time in a similar manner in both groups. CONCLUSIONS: Surface ablation with the 1,050-Hz excimer laser and SPT software, aimed at reducing the final superficial stromal irregularity, led to improvement of 6-month uncorrected visual acuity. [J Refract Surg. 2017;33(2):89-95.].

[Influence of Different Ablation Frequencies on the Clinical Results of Photorefractive Keratectomy Using the Same Excimer Laser Platform: A Contralateral Eye Study]. / Einfluss unterschiedlicher Ablationsfrequenzen auf die klinischen Ergebnisse bei photorefraktiver Keratektomie unter Verwendung derselben Excimer-Laser-Plattform: Ein kontralateraler Vergleich.

Background The objective of this study was to evaluate postoperative clinical outcomes of photorefractive keratectomy (PRK) using different ablation frequencies. Patients and Methods In this prospective, contralateral eye study, 56 eyes of 28 patients with myopia or myopic astigmatism were included. PRK was performed using the MEL90 excimer laser system (Carl Zeiss Meditec, Germany). One eye of each patient was treated with a repetition rate of 250 Hz, while the other one was treated with a repetition rate of 500 Hz. The treatment pattern in the 250 Hz and 500 Hz group only differed in terms of ablation frequency; there was no difference in laser pulse energy, spot size or ablation profile. Postoperative follow-ups were at 3 and 7 days and 1, 3 and 6 months. The following parameters were assessed: Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), higher-order aberrations (HOAs), corneal re-epithelisation time and corneal haze. Results Ablation depth was proportional to laser pulse counts at both frequencies. At 6 months, 100.0% of the eyes in the 250 Hz group and 96.4% in the 500 Hz group had a UDVA of 0.00 logMAR or better; 100% of the eyes in both groups were within ± 1.00D of the attempted correction. All eyes had a postoperative CDVA of 0.00 logMAR or better. There was no difference between the groups in postoperative HOAs, corneal re-epithelisation time or corneal haze. Conclusions Photorefractive keratectomy with a repetition rate of 250 Hz and 500 Hz showed comparable efficacy, safety and predictability in the correction of myopia. There were no significant complications due to the high repetition rate, such as postsurgical corneal haze.

[Riboflavin photoprotection with cross-linking effect in photorefractive ablation of the cornea]. / Fotoprotektsiya riboflavinom s effektom krosslinkinga pri fotorefraktsionnoi ablyatsii rogovitsy.

UNLABELLED: Photorefractive ablation is inevitably accompanied by oxidative stress of the cornea and weakening of its biomechanical and photoprotective properties. AIM: To validate the expediency of riboflavin use in photorefractive ablation for photoprotection of the cornea and cross-linking. MATERIAL AND METHODS: The effects of riboflavin use in photorefractive ablation was first studied in a series of in vitro and in vivo experiments performed on 56 eyes of 28 rabbits, and then on 232 eyes of 142 patients with different degrees of myopia. Biomechanical testing of corneal samples was performed with Zwick/RoellВZ 2.5/TN1S tensile-testing machine. Transepithelial photorefractive keratectomy (TransPRK) and femtosecond laser-assisted in situ keratomileusis (Femto-LASIK) were performed on Wavelight-Allegretto200, MEL-80, and WaveLight-EX500 excimer laser systems and also VisuMax and WaveLight-FS200 femtosecond lasers. For preliminary examinations, an appropriate set of diagnostic tools was used. RESULTS: In vivo experiments have proved that, in the absence of conservative therapy, riboflavin is able to produce both photoprotective and cross-linking effects to the cornea. Corneal syndrome was thus reduced and re-epithelialization after TransPRK accelerated. Biomechanical testing of corneal samples revealed an increase in tolerated load from 12.9±1.4 N to 18.3±1.2 N (p=0.0002) and tensile strength from 8.6±1.7 MPa to 12.4±1.7 MPa (p=0.007). Clinical studies conducted in a group of patients with mild to moderate myopia have also confirmed the photoprotective effect of riboflavin at months 1-12 after TransPRK. There were no significant differences in uncorrected visual acuity (ranged from 0.80±0.16 to 0.85±0.15) and corrected visual acuity at baseline (0.83±0.14). Evaluation of the optical and refractive effect achieved after Femto-LASIK with riboflavin photoprotection in the fellow eye has shown that this technique is not inferior to the traditional one as to its refractive accuracy, but provides better maintenance of biomechanical and photoprotective properties of the cornea. CONCLUSION: Photorefractive ablation of the cornea with preliminary saturation of the stroma with riboflavin solution ensures its photoprotection and provides an additional cross-linking effect.

Retrospective Analysis Comparing the Preoperative and Postoperative "Q" Values for 2 Different Lasers in Refractive Surgery.

PURPOSE: To compare the presurgical and postsurgical corneal asphericity, or "Q value," between VISX Wavefront-guided treatment and Allegretto Wave Wavefront-optimized treatment in photorefractive keratectomy for the correction of myopia. METHODS: This is a retrospective database analysis performed at the Joint Warfighter Refractive Surgery Center, Lackland Air Force Base, TX. All data were accessed through the Institutional Review Board-approved Joint Warfighter Refractive Surgery Center database. Fifty-one patient records (102 eyes) were reviewed to determine the change in the Q value after photorefractive keratectomy for the correction of myopia. RESULTS: The average change in the Q value per diopter of treatment sphere over the entire study population was 0.12 (±0.04) for Allegretto and 0.14 (±0.04) for VISX (P = 0.004). There was no statistical difference among the preoperative and postoperative best-corrected visual acuities (BCVAs), low-contrast BCVA (BCVA 5%), or quality of vision complaints between both platforms. CONCLUSIONS: Low to moderate myopic correction with the Allegretto laser was associated with a smaller change in the Q value per diopter of treatment and therefore more closely maintained the original prolate shape of the cornea when compared with VISX. No difference in the postoperative visual outcome between both groups was detected.

High-speed photorefractive keratectomy with femtosecond ultraviolet pulses.

Femtosecond near-infrared lasers are widely used for a number of ophthalmic procedures, with flap cutting in the laser-assisted in situ keratomileusis (LASIK) surgery being the most frequent one. At the same time, lasers of this type, equipped with harmonic generators, have been shown to deliver enough ultraviolet (UV) power for the second stage of the LASIK procedure, the stromal ablation. However, the speed of the ablation reported so far was well below the currently accepted standards. Our purpose was to perform high-speed photorefractive keratectomy (PRK) with femtosecond UV pulses in rabbits and to evaluate its predictability, reproducibility and healing response. The laser source delivered femtosecond 206 nm pulses with a repetition rate of 50 kHz and an average power of 400 mW. Transepithelial PRK was performed using two different ablation protocols, to a total depth of 110 and 150 µm. The surface temperature was monitored during ablation; haze dynamics and histological samples were evaluated to assess outcomes of the PRK procedure. For comparison, analogous excimer ablation was performed. Increase of the ablation speed up to 1.6 s/diopter for a 6 mm optical zone using femtosecond UV pulses did not significantly impact the healing process.

New Scheimpflug camera device in measuring corneal power changes after myopic laser refractive surgery.

PURPOSE: To assess the accuracy of a combined Scheimpflug camera-Placido disk device (Sirius, CSO, Italy) in evaluating corneal power changes after myopic photorefractive keratectomy (PRK). METHODS: Two hundred and thirty-seven eyes of 237 patients that underwent myopic PRK with a refractive error, measured as spherical equivalent, ranging from -10.75 D to -0.5D (mean -4.63 ± 2.21D), were enrolled in this study. Corneal power evaluation using Sirius were performed before, 1, 3 and 6 months after myopic PRK. Mean simulated keratometry (SimK) and mean pupil power (MPP) were measured. Correlations between changes in corneal power, measured with SimK and MPP, and variations in subjective refraction, calculated at corneal plane, were evaluated using Pearson test at every follow up; differences between preoperative and postoperative data were evaluated with the Student paired t-test. RESULTS: A good correlation has been detected between the variations in subjective refraction measured at corneal plane 1, 3 and 6 months after myopic PRK and both SimK (R(2) = 0.8463; R(2) = 0.8643; R(2) = 0.7102, respectively) and MPP (R(2) = 0.6622; R(2) = 0.5561; R(2) = 0.5522, respectively) but corneal power changes are statistically undervalued for both parameters (p < 0.001). CONCLUSIONS: Even if our data should be confirmed in further studies, SimK and MPP provided by this new device do not seem to accurately reflect the changes in corneal power after myopic PRK.

Estudo comparativo entre a técnica manual e a escova rotatória na remoção do epitélio corneano na ceratectomia fotorrefrativa (PRK) / Comparative study between manual and brush de-epithelization in photorefractive keratectomy (PRK)

Objetivo: Comparar a influência de duas técnicas de remoção do epitélio da córnea quanto ao tempo de aplicação, ao conforto intraoperatório, à sintomatologia e à reepitelização no pós-operatório de ceratectomia fotorefrativa (PRK). Métodos: Este estudo prospectivo e randomizado incluíram 58 olhos de 29 pacientes que tiveram ambos os olhos submetidos sequencial e simultaneamente à PRK, sendo que em um dos olhos foi realizado a desepitelização manual com espátula e no outro, a técnica mecanizada com escova rotatória. Resultados: A técnica mais rápida, medida em segundos, foi a escova rotatória (16,4 ± 6,3) em comparação com a manual (35,7 ± 7,6). Não houve diferença entre os métodos quanto ao desconforto referido pelo paciente durante a cirurgia e quanto ao tipo de sintoma referido no pós-operatório (p>0,05). A análise de variância (ANOVA) mostrou que o método da escova estava relacionado a uma maior intensidade de sintomas [F(8,104)=1,5; p<0,05], e o teste post hoc indicou que essa diferença só foi significante (p<0,05) no 2º dia de pós-operatório. Todos os olhos dos 2 grupos apresentaram epitelização corneana completa no 5º dia de pós-operatório. Conclusão: Neste estudo, observou-se que a desepitelização com escova rotatória foi superior à técnica manual unicamente pelo seu menor tempo de aplicação. Comparativamente esteve relacionada a um mesmo nível de desconforto intraoperatório e uma intensidade maior nos sintomas pós-operatórios. .

Objective: To compare the influence of two techniques for corneal epithelial removal in photorefractive keratectomy (PRK) - blunt scrape versus rotary brush - regarding duration of technique application, intraoperative comfort, and reepithelization. Methods: This prospective randomized study included 58 eyes of 29 patients that underwent simultaneous and sequential PRK in both eyes - blunt scrape (scraped group) in one eye and rotary brush (brushed group) in the fellow eye. Results: The faster technique, measured in seconds, was the rotary brush (16.4 ± 6.3) compared to the blunt scrape (35.7 ± 7.6). There was no difference between the methods regarding discomfort reported by the patient during surgery and the type of symptom reported postoperatively (p>0.05). The analysis of variance (ANOVA) showed that the brushed group were related to a greater intensity of symptoms [F (8.104) = 1.5, p<0.05] and post hoc testing indicated that this difference was only significant (p<0.05) on day 2. All eyes of the 2 groups showed complete corneal epithelialization on day 5 postoperatively. Conclusion: In this study, it was found that epithelial removal with rotating brush was superior to manual only by its shorter application. It showed the same level of intraoperative discomfort and determined a greater intensity of symptoms postoperatively. .

Excimer laser surface ablation: a review of recent literature.

The aim was to review the recently published literature on excimer laser surface ablation procedures, including photorefractive keratectomy (PRK), laser sub-epithelial keratomileusis (LASEK), microkeratome-assisted PRK (epi-LASIK) and trans-epithelial (laser-assisted) PRK, to help elucidate where and how surface ablation may best fit into current refractive surgical practice. The emphasis was on publications within the last three years and included systemic reviews, meta-analyses and randomised controlled trials. Where such evidence did not exist, selective large series cohort studies, case-controlled studies and case series with follow-up preferably greater than six months were examined and included. Refractive and visual outcomes are excellent and comparable to those after LASIK even in complex cases after previous corneal surgery. Indeed, surface ablation combined with corneal collagen cross-linking may be used in selected eyes with biomechanical instability, where LASIK is contraindicated. In addition, there is evidence to suggest that there may be less induction of higher order aberrations with surface techniques. Long-term stability and safety appear to be extremely satisfactory. The literature supports the use of modern excimer laser surface treatments, with outcomes comparable to those after LASIK and evidence of less induction of higher-order aberrations. Follow-up studies at 10 to 20 years indicate excellent stability and safety.

Efficacy of two silicone-hydrogel contact lenses for bandage use after photorefractive keratectomy.

PURPOSE: To evaluate the efficacy of two silicone hydrogel (SiH) contact lenses, approved for continuous wear for one week, following photorefractive keratectomy (PRK). METHODS: Forty seven myopic patients (94 eyes) undergone bilateral PRK were enrolled in this prospective, double-masked, comparative study. One eye of each patient was fitted with a Lotrafilcon B lens (Ciba Vision, Duluth, US; 30-day recommended replacement) whereas the fellow eye was fitted with an Asmofilcon A lens (Menicon, Nagoya, Japan; 14-day recommended replacement). Epithelial defect size was assessed using slit lamp biomicroscopy on the day of surgery and at days 1-4 post-operatively. Uncorrected and best-corrected visual acuity and retinal straylight (C-Quant, Oculus Optigerate, Germany) were evaluated pre-operatively and one month post-operatively. RESULTS: Average epithelial defect size for Asmofilcon A and Lotrafilcon B was 25.5±11.0mm(2) vs. 27.1±9.9mm(2) at day 1 (p=0.007) and 6.3±7.0mm(2) vs. 9.2±9.5mm(2) at day 2 (p=0.012) post-operatively. Re-epithelialization at day 3 was completed in 87.2% of the eyes fitted with Asmofilcon A lenses, compared to 74.5% with Lotrafilcon B lenses (p=0.012). At the 3rd post-operative day 29.8% of re-epithelialized eyes showed irregular suture with Lotrafilcon B, compared to 12.8% eyes with Asmofilcon A lenses (p<0.001). Finally, no statistically significant differences were found post-operatively between the two lenses retinal straylight (p=0.98) and best-corrected visual acuity (p=0.68). CONCLUSIONS: SiH lenses can be used as an effective bandage after PRK due to the limited time requested for achieving complete corneal re-epithelialization. Faster and smoother epithelial healing is provided with Asmofilcon A over Lotrafilcon B lenses.

Long-term follow-up of photorefractive keratectomy for myopia: Comparative study of excimer lasers.

PURPOSE: To compare the long-term results of photorefractive keratectomy (PRK) for low to moderate myopia performed using a broad-beam laser system or a scanning-slit laser system. SETTING: Department of Ophthalmology, University of Helsinki, Helsinki, Finland. DESIGN: Case-control study. METHODS: This follow-up study comprised eyes with myopia (-1.25 to -7.00 diopters [D]) or myopic astigmatism (astigmatism lower than -2.50 D) corrected by PRK using a broad-beam (Visx) or scanning-slit (Nidek) laser. Follow-up included a visit at 3 months and at more than 8 years. The uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and manifest refraction were recorded. RESULTS: The broad-beam group comprised 27 eyes and the scanning-slit group, 34 eyes. At the last postoperative follow-up, the UDVA was 0.0 or better in 55% of eyes in the broad-beam group and 65% of eyes in the scanning-slit group. The CDVA was 0.0 or better in all eyes in the broad-beam group and 96% of eyes in the scanning-slit group. Regarding predictability, 48% and 73% of the eyes, respectively, were within ±0.50 D of the intended spherical equivalent refraction. There were no statistically significant differences between the 2 laser groups in any preoperative or postoperative parameter. CONCLUSION: There were no significant differences in UDVA, CDVA, or SE after PRK for low to moderate myopia between the broad-beam laser system and the scanning-slit laser system. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.

Scattered ultraviolet emissions during refractive surgery using a high-frequency, wavefront-optimized excimer laser platform.

PURPOSE: To evaluate occupational ultraviolet (UV) exposure during photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) with the Allegretto Wave Eye-Q 400 Hz excimer laser. SETTING: Walter Reed Center for Refractive Surgery, Washington, DC, USA. METHODS: Intraoperative UV measurements were performed during PRK with epithelial removal using an Amoils brush, PRK with epithelial removal using 20% ethanol, or femtosecond LASIK. A LaserStar power/energy meter with a silicone detector (model PD-10) was used for the measurements. The maximum pulse energy 25.4 cm from the corneal surface was recorded for each surgical procedure. Measurements were evaluated using a worst-case scenario for exposure of operating room personnel, and the results were compared with the occupational exposure limit set by the International Commission on Non-Ionizing Radiation Protection. RESULTS: Measurements were taken during 15 cases of each procedure. The mean maximum exposure was 129.38 nJ/pulse +/- 79.48 (SD) during brush PRK, 69.72 +/- 68.80 nJ/pulse during ethanol PRK, and 29.17 +/- 13.82 nJ/pulse during LASIK. The mean maximum exposure per eye was 0.085 mJ/cm(2), 0.046 mJ/cm(2), and 0.01 mJ/cm(2), respectively. The worst-case cumulative exposure during a heavy workday of 20 patients (40 eyes) was calculated at 3.92 mJ/cm(2), 1.51 mJ/cm(2), and 0.79 mJ/cm(2) for brush PRK, ethanol PRK, and LASIK, respectively. CONCLUSION: Results indicate that the excimer laser platform used in the study may yield greater UV exposure than previous systems; however, the levels did not exceed occupational exposure limits. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.

Excimer laser surface ablation - a review.

Corneal surface laser ablation procedures for the correction of refractive error have enjoyed a resurgence of interest, especially in patients with a possible increased risk of complications after lamellar surgery. Improvements in the understanding of corneal biomechanical changes, the modulation of wound healing, laser technology including ablation profiles and different methods for epithelial removal have widened the scope for surface ablation. This article discusses photorefractive keratectomy, trans-epithelial photorefractive keratectomy, laser-assisted sub-epithelial keratomileusis and epithelial-laser-assisted in situ keratomileusis.

[Excimer laser trabeculotomy: minimally invasive glaucoma surgery]. / Minimal-invasive Glaukomchirurgie: Excimer-Laser-Trabekulotomie.

Excimer laser trabeculotomy (ELT) is a minimally invasive method for reducing intraocular pressure. It can be performed as a stand-alone procedure or in combination with cataract surgery in just a few minutes. Laser spots are applied in the anterior chamber angle via an endoscopic camera or a gonio lens. In contrast to argon laser trabeculoplasty, shunts between the anterior chamber and Schlemm's canal are prepared by a photoablative laser, thus improving the outflow of aqueous humour. Best results can be expected in patients with moderately elevated intraocular pressure and cataract undergoing the combined procedure.

System performance evaluation of refractive surgical lasers: a mathematical approach.

A study was conducted for the purpose of improving the designs of the next generation of refractive surgical laser systems. Two common refractive laser systems, variable-spot scanning (type A) and small-spot scanning (type B), are discussed by identifying sources of error that could adversely affect the capability of these lasers to accurately produce complex, customized wavefront guided ablations. A mathematical model was used to construct a laser simulator that models the two common laser systems in terms of the root-mean-square error. Error sources from ablation profile fitting, ablation registration, eye tracking, and the laser delivery system are compared, and the relative contribution of each to the overall system error is analyzed. This system-level analysis can be helpful to the improvement of both laser systems.

Automated visual axis alignment for refractive excimer laser ablation.

PURPOSE: To describe the use of new laser alignment and delivery software in the NIDEK Advanced Vision Excimer laser platform (NAVEX) that allows centration based on surgeon specification. METHODS: Descriptive article with a case report. RESULTS: The software allows specification via numeric entry of the exact placement of the laser tapered to the position of the visual axis or the line of sight. CONCLUSIONS: The ability to specify the exact location of the laser ablation based on pupil position is fundamental in patients undergoing custom ablation and those with eccentric fixation. A conservative treatment strategy is recommended for initial experience with this alignment software.