Ablation Profile Research Articles

Laser in situ keratomileusis for different degrees of myopia

To determine the efficacy, predictability, stability and safety of laser in situ keratomileusis (LASIK) in treating patients with different degrees of myopia. We enrolled 386 eyes of 200 consecutive patients who underwent LASIK and divided them into four groups according to their degree of preoperative spherical equivalent (SE). Group 1 eyes ranged between - 1.00 and - 3.99 dioptres (D) (low myopia). Group 2 eyes ranged between - 4.00 and - 5.99 D (moderate myopia). Group 3 eyes ranged between - 6.00 and - 9.99 D (high myopia). Group 4 eyes were over - 9.99 D (extreme myopia). Follow-up was at 1 day, 1 week and 1, 3, 6, 12 and 18 months postoperatively. Our study included 386 eyes of 200 patients with SE ranging from - 3.00 to - 16.00 D (mean - 7.14 +/- 2.87 D). All eyes were seen at 1 day postoperatively. A total of 360 eyes (93%) were examined at 1 week, 330 eyes (85%) at 1 month, 281 eyes (73%) at 3 months, 247 eyes (64%) at 6 months, 199 eyes (52%) at 12 months and 142 eyes (37%) at 18 months. The postoperative data from 1 day to 12 months were used because of the low follow-up rate at 18 months postoperatively. Group 1 consisted of 30 eyes. The mean SE was - 3.52 +/- 0.43 D preoperatively and - 0.40 +/- 0.58 D at 1 month, - 0.46 +/- 0.60 D at 6 months and - 0.42 +/- 0.50 D at 12 months postoperatively. Uncorrected visual acuity (UCVA) was 20/40 or better in 95% of eyes at 1 day and in 100% of eyes at 6 and 12 months postoperatively. Group 2 consisted of 151 eyes. The mean SE was - 5.36 +/- 0.67 D preoperatively and - 0.54 +/- 0.78 D at 1 month, - 0.56 +/- 0.90 D at 6 months and - 0.55 +/- 0.82 D at 12 months postoperatively. Uncorrected VA was 20/40 or better in 95% of eyes at 1 day and in 100% of eyes at 6 and 12 months postoperatively. Group 3 consisted of 167 eyes. The mean SE was - 8.15 +/- 0.94 D preoperatively and - 0.58 +/- 0.90 D at 1 month, - 0.67 +/- 1.00 D at 6 months and - 0.64 +/- 0.95 D at 12 months postoperatively. Uncorrected VA was 20/40 or better in 90% of eyes at 1 day and in 98% of eyes at 6 and 12 months postoperatively. Group 4 consisted of 38 eyes. The mean SE was - 11.09 +/- 1.10 D preoperatively and - 1.25 +/- 1.20 D at 1 month, - 1.13 +/- 1.30 D at 6 months and - 1.20 +/- 1.25 D at 12 months postoperatively. Uncorrected VA was 20/40 or better in 78% of eyes at 1 day, in 94% at 6 months and in 90% at 12 months postoperatively. Intraoperative complications (free cap) occurred in two eyes and postoperative complications were observed in three eyes, making the total complications rate 1.29% (5/386). Seven eyes lost one Snellen line of BCVA, five lost two lines and two lost more than two lines (total: 3.64%, 14/386). In conclusion, LASIK is effective, predictable and safe for correcting myopia but is more accurate for correcting myopia up to -10.00 D. With more improvement in algorithms and ablation profile, we believe that LASIK can offer better results for higher myopia.

Modelling of pellet ablation in additionally heated plasmas

A neutral gas and plasma shielding model is presented that describes the interaction of a pellet with the high energy ions and electrons generated during heating or current drive experiments. The main improvements are the self-consistent calculations of the electrostatic sheath at the cloud–plasma interface and of the extra ablation due to the fast tail of the electron and ion distributions, including heating in the volume of the pellet. With regard to the comparison between the code predictions and the experimental results, realistic three-dimensional (space, energy, pitch angle) distributions have been used for both the ions and electrons. For ohmic discharges, the code has been tested on more than 40 well-documented pellets selected in the International Pellet Ablation DataBASE. For additionally heated plasmas (ion cyclotron resonance heating—minority regime—and lower hybrid current drive, 2–4 MW of injected power), Tore Supra data have been used. In these different cases, the calculations are in good agreement with the experimental penetrations and ablation profiles. A parametric study is also presented, which enlightens the control parameter that governs the pellet penetration. In what concerns the capability of pellet injection to fuel reactor grade plasmas, it is shown that no strong extra ablation due to the α-particles is expected.

Experimental and clinical investigation of efficiency and ablation profiles of new solid-state deep-ultraviolet laser for vision correction

To investigate the efficiency and ablation profiles of a newly developed, all-solid-state laser platform. Experimental investigations performed at Katana Technologies GmbH, Kleinmachnow, Germany, and clinical study, at the Ophthalmology Clinic, University of Messina, Messina, Italy. Experimental studies were performed on poly(methyl methacrylate) (PMMA) and in porcine eyes using an all-solid-state, Q-switched, frequency-shifted laser (LaserSoft, Katana Technologies GmbH) with a Gaussian spot with a diameter of 0.2 mm in the target plane, a peak fluence of 350 mJ/cm2, and a repetition rate of 1 kHz. The ablation profiles were determined using a profile meter (MicroProf, Fries Research and Technology GmbH), corneal topography was analyzed with a TMS 2N (Tomey Inc.), and corneal thickness was measured with an ultrasound pachymeter (DGH Technology). In the clinical study, 9 human eyes were treated with photorefractive keratectomy. The mean outcome measures were uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), corneal topography, and corneal transparency. The follow-up was 1 month for all eyes and 3 months for 4 eyes. Safety, efficacy, and predictability were evaluated. Smooth profiles were found in the PMMA and the porcine eyes. The topographic maps showed central steepening after the hyperopic ablation and slight central flattening of the surface after the myopic treatment. No eye lost lines of BSCVA; the UCVA improved in all eyes. All eyes were within +/-1.00 diopter (D) of emmetropia, and 89% were within +/-0.50 D. The efficacy of the ablation was good, with the profile meter results confirmed by the topographic measurements.

Clinical Photoablation With a 500-Hz Scanning Spot Excimer Laser

The aim of this study was to use a 500-Hz scanning spot laser (Concept500, WaveLight Laser Technologie AG, Erlangen, Germany) to investigate potential side effects that might be associated with the use of a high repetition rate laser platform. Seven eyes were treated using a 500-Hz scanning spot laser for laser in situ keratomileusis (LASIK). The local frequency of the ablation was kept below 40 Hz to avoid local heating of corneal tissue. With the exception of the high repetition rate (500 Hz), all other laser parameters such as fluence, algorithm, ablation profile, and spot diameter were identical to a standard WaveLight Allegretto laser system. Patients were examined at 1 month and 1 year after initial treatment. Preoperative and postoperative examination included manifest sphere and cylinder, uncorrected and best spectacle-corrected visual acuity (BSCVA). All eyes were treated for myopia or myopic astigmatism. Five eyes received spherocylindrical and two eyes spherical ablation only. No adverse events correlated with the use of a high repetition rate laser system were observed during surgery or at any point during follow-up. All eyes maintained or had improved BSCVA at 12 months after treatment when compared to preoperative values. The use of an excimer laser with a maximal repetition rate of 500 Hz and a local repetition rate of less than 40 Hz was free of any specific side effect that might be associated with the use of such a high repetition rate.

Comparison of Cross Cylinder Ablation Using the Optimized Ablation Transition Zone and the Torsion Error Detector for Correction of Astigmatism

To compare the safety and efficacy of laser in situ keratomileusis (LASIK) in correcting high myopic astigmatism using two different ablation profiles using the Nidek EC-5000 CX II laser). Fifteen patients (25 eyes) had LASIK for compound myopic astigmatism, using the Optimized Ablation Transition Zone (OATz) ablation profile and activated torsion error detection (TED). Results were compared with those obtained with a cross cylinder ablation profile for myopic astigmatism. For eyes treated with TED, on postoperative day 7, 76% had visual acuity equal to or better than baseline best spectacle-corrected visual acuity (BSCVA) and 56% of eyes had overcorrected astigmatism. On postoperative day 20, none of the eyes had residual astigmatism more than 1.00 D and 72% eyes were within +/-0.50 D cylinder; 92% of eyes had residual astigmatism within 30 degrees of the preoperative axis and 12% remained astigmatically overcorrected at 20 days. Eighty-eight percent of eyes were either fully corrected or had mild myopic astigmatism. Comparison of results with cross cylinder ablation showed that 24% had overcorrection and 60% of patients with high astigmatism were overcorrected up to 1.75 D and developed hyperopic astigmatism in the opposite axis. Results with the cross cylinder ablation profile were good up to 2.00 D of myopic astigmatism. Correction of astigmatism using the OATz profile and TED with the Nidek EC-5000 CX II laser produced good results in high as well as pure astigmatism treatments, compared to the cross cylinder ablation profile. Ablation depth was greater in OATz with TED-based corrections. Overcorrections were less with OATz with TED, and residual astigmatism was at the same baseline axis, thereby increasing patient satisfaction.

Comparison of Conventional and OATz Ablation Profiles for Laser in situ Keratomileusis to Correct Myopia up to -10.00 Diopters

To compare results of laser in situ keratomileusis (LASIK) using two different ablation profiles for correction of myopia between -0.50 and -10.00 D with the Nidek NAVEX system. In a prospective nonrandomized study, 249 myopic eyes (151 patients) had LASIK for correction of myopia. The Nidek MK-2000 micro-keratome and the Nidek NAVEX excimer laser system were used in all eyes. Conventional LASIK was performed in 112 eyes of 64 patients with a 6.0-mm ablation zone and 7.5-mm transition zone (conventional group). LASIK with the Nidek OATz ablation profile was performed in 137 eyes of 87 patients, with variable ablation and transition zones (OATz group). Mean baseline manifest refraction was -4.11 +/- 1.83 D in the conventional group and -5.45 +/- 2.27 D in the OATz group. Baseline best spectacle- corrected visual acuity was 20/20 or better in 83.9% of eyes in the conventional group and 81.0% of eyes in the OATz group. Mean follow-up was 3.6 months (range 3 to 8 mo). At last follow-up, manifest refraction was within +/-0.50 D of emmetropia in 86% of eyes (within +/-1.00 D in 99.1%) in the conventional group and 94.2% of eyes (within +/-1.00 D in 100%) in the OATz group. Uncorrected visual acuity was 20/40 or better in all eyes. No eyes in either group lost 2 or more lines of BSCVA. The Nidek NAVEX system was safe and predictable in correcting myopia up to -10.00 D with the OATz ablation profile. OATz LASIK was similar to conventional LASIK in both refractive and visual outcomes.

Pseudo-accommodative Cornea: A New Concept for Correction of Presbyopia

Efficacy, predictability, stability, and safety of multifocal ablation with a peripheral near zone for correction of myopia, hyperopia, and presbyopia was assessed. We performed a retrospective study of 83 hyperopic eyes and 77 myopic eyes. Baseline mean spherical equivalent refraction in the hyperopia group was +1.54 +/- 0.90 D (range 0 to +4.00 D) and in the myopia group, -4.31 +/- 2.62 D (range -12.00 to -0.25 D). Mean near addition was 2.40 D in the hyperopia group and 1.75 D in the myopia group. All eyes had multifocal laser in situ keratomileusis (LASIK) with a peripheral near zone, using a Nidek EC-5000 excimer laser. Pseudoaccommodative cornea (PAC) software version 6T was used to calculate the multistep ablation profile. Three months after surgery, 80 eyes (96.4%) of the hyperopia group and 75 eyes (97.4%) of the myopia group were examined. Postoperative mean spherical equivalent refraction was -0.19 +/- 0.58 D (range -1.75 to +1.00 D) in the hyperopia group and -0.50 +/- 0.75 D (range -2.50 to -0.75 D) in the myopia group. Fifty-eight eyes (72.5%) of the hyperopia group and 50 eyes (66.7%) of the myopia group were within +/-0.50 D of emmetropia. One percent of eyes in the hyperopia group and no eyes in the myopia group lost 2 or more lines of BSCVA; 5% of eyes in the hyperopia group and 12% eyes in the myopia group gained 2 or more lines of BSCVA. Mean near addition was 0.11 D in the hyperopia group and 0.07 in the myopia group. Binocular unaided near visual acuity was J3 or better in all eyes of both groups and J1 or better in 35% eyes in the hyperopia group and 41% of eyes in the myopia group. Multistep multifocal ablation with a peripheral near zone using the Nidek EC-5000 excimer laser and PAC software version 6T was effective, predictable, stable, and relatively safe over a period of 3 months.

One-year Results of Custom Laser Epithelial Keratomileusis With the Nidek System

To evaluate long-term results of custom laser epithelial keratomileusis (LASEK) for correction of myopia and hyperopia using the Custom Ablation Transition Zone (CATz) software and hyaluronic acid masking fluid (Laservis) for final corneal smoothing. We conducted a prospective study of 297 eyes of 167 patients. All eyes had LASEK for correction of myopia or hyperopia. The Nidek EC-5000 excimer laser, FinalFit software, and CATz ablation profile was used in all eyes. Laservis was used as masking fluid to remove corneal micro-irregularities during the final phase of the treatment. Mean preoperative spherical equivalent refraction was -5.46 +/- 2.57 D (range -14.13 to +3.50 D). At 1 year after LASEK, mean spherical equivalent refraction was -0.15 +/- 0.50 D (range -4.00 D to +1.00 D). LASEK with the Nidek EC-5000 excimer laser, FinalFit and Custom Ablation Transition Zone (CATz) software, with corneal smoothing, was safe and effective at 1 year after surgery.

Higher Order Aberrations With Aspheric Ablations Using the Nidek EC-5000 CX II Laser

To analyze the change in higher order aberrations in myopic and myopic astigmatic eyes following an aspheric ablation profile for laser in situ keratomileusis (LASIK) using a Nidek EC-5000 CX II excimer laser system. We performed a retrospective audit of 38 eyes (19 patients) with myopia and myopic astigmatism. A customized aspheric transition zone profile (CATz) was used in all eyes (profile 4) with an ablation zone of 5 mm and a transition zone of 9 mm using FinalFit software and a Nidek EC-5000 CX II excimer laser system. Mean higher order aberrations (RMS) increased from 0.42 microm at baseline to 0.57 microm at 6-month follow-up. Mean spherical aberrations (Z12) increased from 0.02 microm at baseline to 0.33 microm after LASIK. Mean spherical aberration defocus equivalent (DEQ) increased from 0.56 microm at baseline to 1.54 at 6 months after surgery. Mean trefoil (Z6) was -0.11 microm at baseline and -0.14 microm at the 3-month examination. Mean coma (Z7) was -0.09 microm at baseline and -0.10 microm after surgery. Mean coma (Z8) was -0.03 at baseline and 0 at the 3-month examination. Mean trefoil (Z9) was -0.03 at baseline and -0.12 at the 3-month examination. The amount of postoperative higher order aberrations in these myopic eyes was acceptable. However, the clinical significance of these numerical changes in aberrations is not known.

The Theoretical Effect of Measured Wavefront Diameter on Estimating Peripheral Wavefront Data

To compare the difference between wavefront data measured in the periphery and that calculated from estimations using a smaller measured region. A total of 32 eyes were measured using the Alcon LADARWave aberrometer (Alcon Laboratories Inc, Fort Worth, Tex). Aberrations were measured through a dilated pupil to the 6th order at a 6.5-mm diameter. Data were then "clipped" to 5.0, 5.5, and 6.0 mm, and each of these smaller diameter wavefronts was used to estimate the larger diameter wavefront coefficients. The measure of interest was the mean and range of error between the estimated and measured values, and how they varied for the different diameters of known data. The differences in both the mean and range of error were inversely correlated to the diameter of the region of known data. As this region grew smaller, the region estimated grew larger, with resultant larger mean errors. At 5 mm, the estimated zone was an annulus of 0.75-mm width; in this case the estimated higher order aberrations were 60% higher than those measured, with a range of 40% lower to 300% higher. At 5.5 mm and 6.0 mm, these differences were much smaller, but statistically significant. The differences were greatest when significant peripheral aberrations were measured, as can occur with post-laser in situ keratomileusis eyes. Basing a treatment on an estimation of the peripheral wavefront may lead to an inaccurate ablation profile. The inaccuracy increases as the size of the measured wavefront decreases relative to the planned ablation zone. The inaccuracy is also greatest when significant peripheral aberrations are present. Refractive surgery systems should only treat optical zones that are smaller than or equal to the diameter of the measured wavefront.

Entry system development for Mars Netlander mission

For a long time, EADS SPACE Transportation has been developing specific technologies and engineering capabilities in the field of re-entry. The first achievements were dedicated to ballistic missiles, but since recent years, these skills have found direct application into planetary exploration. Among these missions, EADS SPACE Transportation was involved in: • Huygens program, in charge of the system activities and of the Thermal Protection System. • Beagle 2, launched in June 2003 with ESA Mars Express orbiter, in charge of the Thermal Protection System. More recently, EADS SPACE Transportation was given the responsibility for the development of entry Thermal Protection System for the four NetLander probes, in the frame of the CNES Mars Premier program for which EADS SPACE Transportation has been selected by Alcatel Space for the development of the TPS. EADS SPACE Transportation has based its technical choices, on the Beagle 2 technologies well adapted to this application: • the Norcoat Liège, a lightweight ablative material, for the external thermal protection of both the Back Cover and the Front Shield. • A Nida/carbon layers sandwich for the Front Shield structure. For Programmatic point of view, the main objectives of this approach is to reduce the development risks and to increase the mission robustness in capitalizing on Beagle 2 experience and on a sound industrial basis, and to control the cost. For technical point of view, the major challenges of the Mars Netlander mission defined by the Prime is the mass saving and the design flexibility. Therefore, the materials have been optimised in line with these challenges: • At the beginning of the phase B, a refined mechanical concurrent engineering has been performed for the Front Shield structure to optimize every part which are governed both by global requirements (volume allocation, overall stiffness and deformations) and by local ones (reinforcement zones under the sufM brackets, I/F with the Back Cover). • Heat flux tests have been performed in the mission extreme conditions combining heat loads and aerodynamic shear stress to increase the material behaviour knowledge (ablation profiles, temperature prediction/results correlation) and at the end to reduce the sizing margins.

Clinical outcomes using the NAVEX platform

The NIDEK Advanced Vision Excimer Laser (NAVEX) platform has been used to treat primary eyes and in a wide variety of therapeutic applications. Use of an extremely robust scanning slit skiascopy aberrometer has enabled the treatment of eyes in the latter category. Primary outcomes using NAVEX have shown a reduced induction of higher order aberrations, a maintenance or gain of contrast sensitivity in most patients, and excellent refractive outcomes. By using an ablation profile that minimizes the amount of induced spherical aberrations, large effective optical zones are seen postoperatively.

Optimized and wavefront guided corneal refractive surgery using the Carl Zeiss Meditec platform: the WASCA aberrometer, CRS-Master, and MEL80 excimer laser.

The Carl Zeiss Meditec platform for custom ablation incorporates a suite of technology integrating high-resolution wavefront aberrometry (WASCA), corneal surface shape data (TOSCA), energy stabilized excimer laser delivery (MEL80), and surgeon-controlled individualization of the ablation profile (CRS-Master). Together, these components deliver increasingly higher accuracy and sophistication in treatment planning for corneal refractive surgery.

Alcon CustomCornea platform with LADARWave and LADARVision.

The Alcon CustomCornea platform is a basis of refractive surgery using a wavefront sensor (LADARWave) to provide the desired ablation profile, and an excimer laser(LADARVision) to administer it to the eye. These two systems are linked using identical software features to align the wavefront measurement and the ablation such that there fractive correction is delivered to the correct location on the eye. The technology behind these two systems and the clinical outcomes achieved using CustomCornea will be discussed.

Topographically supported customized ablation for the management of decentered laser in situ keratomileusis

Purpose To evaluate the efficacy, predictability, and safety of topographically supported customized ablations (TOSCAs) for decentered ablations following laser in situ keratomileusis (LASIK). Design Prospective nonrandomized clinical trial. Methods Nine patients (11 eyes) with LASIK-induced decentered ablations underwent TOSCA following flap lifting. Topographically supported customized ablation was performed using a corneal topographer to obtain a customized ablation profile, combined with a flying spot laser. Results Mean follow-up was 9.22 ± 2.82 months (range 6–12 months). No intra- or postoperative complications were observed. Manifest refraction (spherical equivalent) did not change significantly (pre-TOSCA: −0.14 ± 1.58 diopters [range, –1.75 to +3.00 diopters] to +0.46 ± 1.02 diopters [range, −1.00 to +1.75 diopters]; P = .76), whereas there was a statistically significant reduction in the refractive astigmatism (pre-TOSCA: –1.55 ± 0.60 diopters [range, −3.00 to −0.75 diopters] to –0.70 ± 0.56 diopters [range, −2.00 to −0.25 diopters]; P = .003). Mean uncorrected visual acuity improved significantly ( P < .001) from 0.45 ± 0.16 (range, 0.2–0.7) to 0.76 ± 0.29 (range, 0.2–1.2) at last follow-up. Mean best-corrected visual acuity improved from 0.74 ± 0.22 (range, 0.4–1.0) to 0.95 ± 0.20 (range, 0.6–1.2; P = .002). Eccentricity showed a statistically significant reduction after TOSCA treatment (pre-TOSCA: 1.59 ± 0.46 mm [range, 0.88–2.23 mm]; post-TOSCA: 0.29 ± 0.09 mm [range, 0.18–0.44 mm]; P < .001). Conclusion In our small sample, enhancement LASIK procedures with TOSCA appear to improve uncorrected and best-corrected visual acuity as well as eccentricity in patients with LASIK-induced decentered ablation.

Semiconductor Nanowires Prepared by Diffraction-Mask-Projection Excimer-Laser Patterning

Substrate-adhered semiconductor nanowires can be prepared by locally confined laser ablation of high-quality thin films. Wurtzitic GaN films with thicknesses of several tens of nanometers were deposited by ion-beam-assisted molecular beam epitaxy on 6H-SiC. Diffraction-mask-projection laser ablation (at a wavelength of 248 nm) was used to convert the thin film into a well-ordered arrangement of parallel, substrate-adhered nanowires. The ablation profile generated by the stripe-patterned phase mask was shown to sharpen upon multipulse application. Hence, structural widths of the remaining semiconductor banks below 200 nm can be achieved. Beyond substrate adherence, the introduced methodology makes the preparation of growth-direction-independent nanowire orientations feasible.

Watching meteors on Triton

The thin atmosphere of Neptune's moon Triton is dense enough to ablate micrometeoroids as they pass through. A combination of Triton's orbital velocity around Neptune and its orbital velocity around the Sun gives a maximum meteoroid impact velocity of approximately 19 km s −1, sufficient to heat the micrometeoroids to visibility as they enter. The ablation profiles of icy and stony micrometeoroids were calculated, along with the estimated brightness of the meteors. In contrast to the terrestrial case, visible meteors would extend very close to the surface of Triton. In addition, the variation in the meteoroid impact velocity as Triton orbits Neptune produces a large variation in the brightness of meteors with orbital phase, a unique Solar System phenomenon.

Wavefront-optimized ablation profiles: Theoretical background

Purpose: To describe a method for calculating wavefront-optimized ablation profiles to precompensate for the spherical aberration and higher-order astigmatism induced by myopic, hyperopic, and astigmatic corneal laser corrections. Setting: IROC–Institut für Refraktive und Ophthalmo-Chirurgie, and Institute for Biomedical Engineering, Swiss Federal Institute of Technology, Zürich, Switzerland. Methods: The basic ablation profile for myopic, hyperopic, and astigmatic correction is derived from the 2nd-order Zernike representation of wavefront aberrations. Including 4th-order spherical aberration and higher-order astigmatism in the theoretical calculation of the ablation profile allows precompensation for the expected amount of higher-order aberrations (HOAs). The shapes of wavefront-optimized ablation profiles are compared with the shapes of “classic” ablation profiles for myopic and astigmatic corrections. Results: The introduction of precompensating spherical aberration and higher-order astigmatism leads to a more aspheric ablation profile with a significant increase in ablation depth (up to 35%) in the midperiphery of the optical zone. The central ablation depth remains unchanged in the myopic correction but increases by 3% in cylinder correction. Conclusions: Wavefront-optimized ablation profiles provide a simple method to precompensate for the expected 4th-order spherical aberration and higher-order astigmatism in the average eye. Further clinical studies must be performed to prove the theoretical results; demonstrate the reduction in HOAs; and predict safety, predictability, and stability of wavefront-optimized ablation profiles.

Electron Microscopy of Surface Smoothness of Porcine Corneas and Acrylic Plates With Four Brands of Excimer Laser

This study compares ablation smoothness patterns produced on four different excimer laser devices available for photorefractive surgery. VISX calibration plastic and porcine cornea were ablated with standard -3.00-D, -6.00-D, and -9.00-D settings using four different excimer lasers: VISX S2 Smooth Scan, Nidek EC-5000, Autonomous Ladar Vision System, and Bausch and Lomb Technolas. Electron microscopy and laser interferometry were used for qualitative evaluation of the ablated surfaces. Corneal ablation surface smoothness was graded by ten independent observers. Calibration plastic ablated surfaces were evaluated quantitatively for smoothness by laser interferometry. The independent observer assessment of corneal ablation surface smoothness demonstrated that the Autonomous small spot Gaussian profile laser produced the smoothest ablation surfaces, followed by the other broad beam lasers. In comparing ablation smoothness among various refractive powers (-9.00 D, -6.00 D, and -3.00 D), a trend was observed that indicated a correlation of higher refractive settings with decreasing surface smoothness. However, this trend was not statistically significant. The quantitative laser interferometry measurements supported the independent observer ranking of the Autonomous flying small spot ablation profile as the smoothest. However, there were differences between the laser interferometry smoothness rankings and independent observer smoothness rankings. There were significant differences in ablation surface smoothness among the four excimer lasers tested.

Laser in situ keratomileusis correction of mixed astigmatism by bitoric ablation

Purpose To evaluate the effect of bitoric ablation (cross cylinder) in 1 eye and ordinary monotoric treatment in the contralateral eye of patients with mixed astigmatism. Setting Instituto Oftalmológico de Alicante and University of Miguel Hernández, Alicante, Spain. Methods A comparative consecutive study was initiated in 30 eyes of 15 patients with mixed astigmatism. In each patient, 1 eye was treated with bitoric ablation (Group 1) and the other eye was treated with monotoric ablation (Group 2). The decision to treat with bitoric or monotoric ablation was randomized. All patients were operated on by the same surgeon (J.L.A.) and examined by the same investigators (M.J.A., M.A.H.). All completed a 6-month follow-up. Visual acuity was estimated by transforming the Snellen chart readings into logMAR equivalents. In Group 1, theoretical ablation was also performed on glass slides by making 3 ablation profiles (positive, negative, and bitoric). Results There was a statistically significant improvement in the mean uncorrected visual acuity (UCVA), the mean spherical equivalent (SE), and the mean refractive cylinder in Group 1 ( P<.0001, P = .04, P<.0001, respectively) and in the mean refractive cylinder in Group 2 ( P = .01). Better results were obtained in the mean incremental change in UCVA, best corrected visual acuity, SE, and refractive cylinder in Group 1. Conclusions Treatments to correct mixed astigmatism vary in ablation profiles and depth. Bitoric ablation appears to be safer, more effective, and more tissue sparing than the standard treatment.