VISX Laser Research Articles

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.

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. 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). 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. 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.

The effect of silicone hydrogel bandage soft contact lens base curvature on comfort and outcomes after photorefractive keratectomy.

To evaluate the relative pain and the relative amount of contact lens loss experienced using two different base curvatures (BCs) of the Acuvue Oasys bandage soft contact lens (BSCL) after photorefractive keratectomy (PRK). One hundred forty patients undergoing PRK on either the Allegretto or the VISX laser at the Joint Warfighter Refractive Surgery Center in Lackland AFB, TX, were randomized to one of the two different BCs of the Acuvue Oasys BSCL: 8.4 or 8.8 mm. Patients were evaluated on postoperative days 1 and 4 during which they completed a survey rating absolute pain in each eye on a visual analog pain scale. Lens loss was recorded throughout the study. Patients treated on the Allegretto laser preferred the 8.4-mm BC lens, whereas comfort after treatment on the VISX depended on corneal shape. For VISX, patients with very flat corneas (steep K ≤42 preoperative or ≤38 postoperatively) preferred an 8.8-mm BC lens while patients with very steep corneas (steep K >45 preoperative or >42 postoperative) preferred an 8.4-mm BC lens, though these results were largely not statistically significant. Patients who lost their lenses prematurely tended to be those whose corneal curvature did not match their contact lens BC. Individuals treated with the Allegretto laser or individuals with more prolate corneas should likely be fit with an 8.4-mm BC Acuvue Oasys BSCL while individuals with more oblate corneas should likely be fit with an 8.8-mm BC lens to minimize postoperative pain and premature BSCL loss.

Predicting transepithelial phototherapeutic keratectomy outcomes using Fourier domain optical coherence tomography.

The aim of this study was to use Fourier domain optical coherence tomography to predict transepithelial phototherapeutic keratectomy outcomes. This is a prospective case series. Subjects with anterior stromal corneal opacities underwent an excimer laser phototherapeutic keratectomy (PTK) combined with a photorefractive keratectomy using the VISX S4 excimer laser (AMO, Inc, Santa Ana, CA). Preoperative and postoperative Fourier domain optical coherence tomography images were used to develop a simulation algorithm to predict treatment outcomes. Main outcome measures included preoperative and postoperative uncorrected distance visual acuities and corrected distance visual acuity. Nine eyes of 8 patients were treated. The nominal ablation depth was 75 to 177 μm centrally and 62 to 185 μm peripherally. Measured PTK ablation depths were 20% higher centrally and 26% higher peripherally, compared with those for laser settings. Postoperatively, the mean uncorrected distance visual acuity was 20/41 (range, 20/25-20/80) compared with 20/103 (range, 20/60-20/400) preoperatively. The mean corrected distance visual acuity was 20/29 (range, 20/15-20/60) compared with 20/45 (range, 20/30-20/80) preoperatively. The MRSE was +1.38 ± 2.37 diopters (D) compared with -2.59 ± 2.83 D (mean ± SD). The mean astigmatism magnitude was 1.14 ± 0.83 D compared with 1.40 ± 1.18 D preoperatively. Postoperative MRSE correlated strongly with ablation settings, central and peripheral epithelial thickness (r = 0.99, P < 0.00001). Central islands remained difficult to predict and limited visual outcomes in some cases. Optical coherence tomography measurements of opacity depth and 3-dimensional ablation simulation provide valuable guidance in PTK planning. Post-PTK refraction may be predicted with a regression formula that uses epithelial thickness measurements obtained by optical coherence tomography. The laser ablation rates described in this study apply only to the VISX laser.

Outcomes of custom laser in situ keratomileusis: Dilated wavescans versus undilated wavescans

To evaluate refractive outcomes of custom laser in situ keratomileusis (LASIK) based on undilated and pharmacologically dilated wavefront aberrometry with the Visx laser system. Clinical refractive practice, St. Louis, Missouri, USA. Comparative case series. Eyes that had LASIK using dilated wavescans (study group) were evaluated for the reason for use of dilated scans; age; preoperative refractive error; preoperative root mean square (RMS), coma, trefoil, and spherical aberration values; postoperative uncorrected distance visual acuity (UDVA); postoperative refractive error; percentage of iris-registration capture; and enhancement rate. The study group was compared with a control group that had LASIK using undilated wavescans. The study group comprised 52 eyes (31 patients) and the control group, 104 eyes (55 patients). At 1 month, the mean postoperative UDVA was 20/21 in the study group and 20/22 in the control group and at 3 months, 20/22 and 20/20, respectively. At 1 month, the mean postoperative spherical equivalent (SE) was +0.07 diopter (D) ± 0.49 (SD) in the study group and +0.14 ± 0.30 D in the control group and at 3 months, -0.01 ± 0.44 D and +0.02 ± 0.23 D, respectively; there was no statistically significant difference between groups at either timepoint. There was no statistically significant difference in preoperative RMS or postoperative coma, trefoil, or spherical aberration between the groups. Although the study group had a slightly higher enhancement rate, the difference was not statistically significant. Compared with custom LASIK based on undilated wavescans, use of dilated wavescans for custom LASIK resulted in comparable postoperative outcomes. No author has a financial or proprietary interest in any material or method mentioned.

Role of flap thickness in laser in situ keratomileusis enhancement for refractive undercorrection

To determine which preoperative and/or perioperative factors determine the need for an enhancement for refractive undercorrection in laser in situ keratomileusis (LASIK) for spherical or spherocylindrical myopia. Clinical refractive surgery outpatient facility. In this nested case-control study within a retrospective cohort, 3850 of the 9777 eyes operated on between January 1996 and August 2005 who met the selection criteria were studied. Only patients whose refractive goal was plano were included. Control eyes were those whose latest spherical equivalent (SE) refraction was within +/-0.37 diopters (D) of emmetropia. Cases were defined as enhancements for undercorrection with an SE refraction worse than or equal to -0.50 D performed less than 6 months following the primary surgery. Factors associated with enhancement included increasing patient age (odds ratio [OR] = 1.048, P<.001), decreasing follow-up time (OR = 0.994, P<.001), increasing minus laser sphere (OR = 0.700, P<.001) and cylinder settings (OR = 0.718, P<.001), female sex (OR = 1.112, P = .046), and corneal toricity (OR = 1.237, P = .012). The Summit laser had a significant risk for enhancement (OR = 1.726, P<.001) compared with the Visx laser, whereas the Wavelight Allegretto had a lowered risk (OR = 0.630, P = .049). Enhancement risk with the Autonomous was no different from that with the Visx (OR = 1.120, P = .342). Increasing flap thickness (OR = 1.009, P<.001) was more strongly associated with enhancement risk than residual stromal bed thickness. After controlling for patient age, time to follow-up or surgery, corneal cylinder, sphere and cylinder laser settings, laser manufacturer, patient sex, and corneal thickness, increasing flap thickness was found to be a more important predictor of enhancement for refractive undercorrection than residual stromal thickness.

US Trends in Refractive Surgery: 2003 ISRS/AAO Survey

ABSTRACT PURPOSE: To determine the latest trends in refractive surgery in the United States. METHODS: All US members of the International Society of Refractive Surgery of the American Academy of Ophthalmology were mailed the 2003 refractive surgery survey dealing with volumes, types, preferences of refractive surgery performed, and use of new emerging technology. Questions regarding radial keratotomy (RK), astigmatic keratotomy (AK), limbal relaxing incisions (LRI), photorefractive keratectomy (PRK), laser in situ keratomileusis (LASIK), laser subepithelial keratomileusis (LASEK), intracorneal ring segments (ICRS), laser thermokeratoplasty (LTK), conductive keratoplasty (CK), phakic intraocular lenses (PIOL), clear lens extractions (CLE), and scleral expansion (SE) procedures were examined in the survey. Use of lasers, microkeratomes, pupillometry instruments, postoperative medications, wavefront analyzers, topographers, etc were examined. RESULTS: In 2003, LASIK continued to dominate for refractive errors between -8.00 to +3 diopters. Surgeons are waiting on the PIOL for high myopes and are performing CLE for high hype ropes. Photorefractive keratectomy, LASIK, LASEK, CLE, PIOL, and CK appeared to have bright futures; whereas, RK, ICR, LTK and SE were on the decline. Bilateral LASIK at the same surgical session is offered by 98% of surgeons. VISX lasers are used 2:1 over all other lasers in the United States. Zeiss- Humph rey still dominates topographers at 37%. The Bausch &amp; Lomb Hansatome (48%) leads microkeratomes. Surgeons are charging, on average, $300-$500 more per eye for custom ablations and these ablations have already been accepted and integrated into refractive practices. Comanaging of refractive surgery patients is significantly down from previous years. Fourth -gene ration fluoroquinolones overtook the postoperative antibiotic prescriptions, with prednisolone and fluoromethalone dominating as anti-inflammatories. CONCLUSIONS: Trends and changes as refractive surgery grows in the mainstream of ophthalmology in the United States continue to be elucidated by this professional organization survey. [J Refract Surg. 2005;21:87-91.]

The Theoretical vs. Measured Laser Resection for Laser in situ Keratomileusis

To measure the excimer laser resection during and after laser in situ keratomileusis (LASIK) and to determine the rate of stromal ablation and factors predicting its measurement. A retrospective, comparative, interventional case study of 6010 eyes undergoing LASIK surgery was performed. In vivo ultrasonic pachymetry was performed as a measure of the laser resection (1'MLR). The theoretical laser resection generated by one of three separate excimer lasers (Summit Apex Plus, Alcon LadarVision, VISX) was recorded. The change in central comeal thickness measured at enhancement surgery (2'MLR) and the change in the residual stromal thickness prior to the laser ablation at the primary and enhancement procedure (3'MLR) were recorded as separate measures of the laser resection. Paired sample t test and regression analysis was performed to determine the relationships and to develop a model predictive of laser resection for each laser. For all lasers, 1'MLR produced the highest estimate compared to 3'MLR. Laser-induced stromal desiccation, microkeratome effects, and change in measured flap thickness were the most likely causes for the differences. Laser resection was overestimated in the Alcon theoretical laser resection group, but underestimated in the Summit and VISX groups. The difference between 2'MLR and 3'MLR was due to epithelial hyperplasia, which measured 8.3, 17.8, and 10.8 microm in the Alcon, Summit, and VISX enhancement groups, respectively. Stromal ablation rates were 11.79, 8.26, and 12.71 microm per spherical equivalent diopter laser setting for the Alcon, Summit, and VISX lasers, respectively, when measured with 3'MLR. Multiple pre- and perioperative factors were associated with laser resection. To accurately predict residual corneal thickness, the expected laser resection for an attempted refractive change must be known. As the laser resection can be laser-specific, the surgeon needs to establish the mean and range of tissue removal for a given attempted correction.

Understanding Pre-market Approval and Labeling Differences of Two Leading Customized Ablation Platforms: A Call for Reform at the FDA

To analyze the Food and Drug Administration (FDA) pre-market approval reported data for two currently available wavefront-guided excimer laser systems. VISX and Alcon myopic wavefront laser in situ keratomileusis (LASIK) trials were analyzed based on public information available in the pre-market approval documents. Clinical tests and outcomes reporting varied between pre-market approvals. One pre-market approval reported contrast sensitivity whereas the other did not, although data was collected in both studies. Based on the FDA definition of "accountability," one pre-market approval reported 12-month accountability of 97.7% although only 24.5% of patients were analyzed at that interval. One pre-market approval reported 6-month results whereas the other reported 6- and 12-month results. One pre-market approval reported grouped pre- and postoperative subjective survey results; the other reported individual changes in pre- to postoperative subjective symptoms. We recommend an FDA revision to the definition of "accountability" and also recommend future FDA refractive surgery trials be guided by standardized criteria.

Topographic changes in corneal asphericity and effective optical zone after laser in situ keratomileusis

Purpose: To determine the relationship between the spherical refractive change after myopic excimer laser surgery and the effective optical zone (EOZ) and corneal asphericity determined by corneal topography. Setting: Baylor College of Medicine, Houston, Texas, USA. Methods: Preoperative and postoperative topographies along with refractions were evaluated in all patients who had had laser in situ keratomileusis since January 1999 and had at least 6 months of follow-up. The VISX Smoothscan S2 excimer laser and the Hansatome® microkeratome (Bausch & Lomb) were used in all cases. Because optical zones are oval with astigmatic treatments with the VISX laser, only patients with spherical refractions and treatments were included. Thirty-nine cases met the criteria; their treatments ranged from −1.50 to −18.00 diopters (D). The preoperative and postoperative corneal asphericities (Q-values) were taken directly from the Holladay Diagnostic Summary Report on the EyeSys 2000, version 4.0. The mean diameter of the optical zone was measured on the local radius of curvature map using the outer edge of the yellow zone, which corresponds to 2 color changes or approximately 0.50 D steepening from the mean central radius (green). Results: The EOZ decreased as the amount of treatment increased. The decrease was slightly nonlinear, decreasing slightly more rapidly at higher treatments. For an “intended” 6.0 mm optical zone, the nominal EOZs from the least-squares second-order polynomial regression were 6.0 mm for −1.5 D, 5.4 mm for −5.0 D, 4.6 mm for −10.0 D, 3.8 mm for −15.0 D, and 3.2 mm for −18.0 D. The least-squares second-order polynomial regression yielded a standard error of the estimate (SEE) of ± 0.22 mm ( R 2 = 0.90). The asphericity increased nonlinearly in a positive direction (oblate) with the amount of treatment, indicating greater amounts of correction produced progressively more oblate corneal surfaces. The least-squares second-order polynomial regression yielded an SEE of ± 0.42 ( R 2 = 0.55). Conclusions: The EOZ decreased and the Q-value increased with the amount of myopic excimer laser treatment. The optical zone was approximately 4.3 mm with a spherical treatment of −12.0 D. These findings may explain the clinical studies that indicate high myopic treatments (above −12.0 D) are associated with poor visual outcomes.

Photorefractive keratectomy for moderate myopia with the VISX and Summit excimer lasers: a retrospective study

Purpose: To present photorefractive keratectomy (PRK) results for myopia ranging from -4,00 to - 6,00 diopters performed with the VISX and Summit excimer lasers. Methods: To be eligible for this study, patients had to be 20 to 45 years of age, have -4.00 to -6.00 diopters of myopia and have no more than 1 D of astigmatism. The Summit group was composed of 51 eyes. The baseline preoperative spherical equivalent of myopia was -5.22 ± 0.17 and surgeries were performed with the Excimed UV 200 LA Excimer Laser. In the VISX group, there were 53 eyes and the baseline refractive error was -4.85 ± 0.16 and surgeries were performed with the Twenty/Twenty Excimer Laser. Results: At six-month examination, haze ranged from 0 to 1 (M:0.56 ± 0.07) in the VISX group and from 0 to 3 (M:0.58 ± 0.08) in the Summit group. Uncorrected vision at six months was 20/20 or better in 22% of eyes and 20/40 or better in 83% of eyes in the VISX group. In the Summit group, 25% of eyes were 20/20 or better and 71% were 20/40 or better at the six-month examination. Conclusion: It is reassuring that PRK of patients with -4.00 to -6.00 D of myopia results in acceptable results.

Predictability of radial keratotomy after excimer laser photorefractive keratectomy

Purpose: To evaluate the results of radial keratotomy (RK) after photorefractive keratectomy (PRK).Setting: London Centre for Refractive Surgery.Methods: This study comprised six eyes having RK enhancement after PRK. Outcome measures were the effect of the incisions on post-PRK haze and best corrected visual acuity (BCVA), predictability of the result on already flattened corneas, and the validity of standard radial keratotomy (RK) nomograms. All PRKs were done when refraction was stable with one of two VISX lasers: the TwentyTwenty or Star. Mean follow-up was 14 months.Results: All eyes had further corneal flattening. The standard RK nomograms were deemed appropriate. There was no loss of BCVA because of aggravated haze or irregular astigmatism.Conclusion: Radial keratotomy after PRK proved safe, economical, and effective after PRK in six eyes.

Outcomes of Spherocylinder Treatments in the Comprehensive Refractive Surgery LASIK Study

The CRS LASIK Study is a surgeon-sponsored collaborative project to evaluate LASIK outcomes with the Summit and VISX lasers. The current report includes 3-month outcomes in the first group of patients who underwent spherocylindrical corrections of 1 to 10 diopters of myopia and 1 to 4 diopters of astigmatism with the Summit Apex Plus and VISX Star lasers. Cohort selection criteria were applied to select 911 eyes that underwent surgery between April 1, 1996 and October 1, 1997 in the range of study. Eyes with preoperative best spectacle-corrected visual acuity of worse than 20/40 (0.5) were excluded. Outcomes were stratified according to myopic treatment range. One day uncorrected visual acuity was 20/40 or better in 83% of eyes with both lasers. At 3 months, 20/40 uncorrected acuity was found in 93% of Summit and 90% of VISX eyes in the -1.00 to -4.00 D group, in 88% of Summit and 84% of VISX eyes in the -4.01 to -7.00 D group, and in 67% of Summit and 70% of VISX eyes in the -7.01 to -10 D group. Three-month manifest refractive outcomes in the -1.00 to -4.00 D group were within +/- 1 D of target in 91% of the Summit eyes, and 89% of the VISX Eyes. In the -4.01 to -7.00 D range, 72% of the Summit eyes and 74% of the VISX eyes fell within +/- 1 D, and in the -7.01 to -10 D range, the rates were 53% for Summit and 56% for VISX. No eyes lost two lines or more acuity with either laser. Three-month visual and refractive outcomes in LASIK are comparable with the Summit Apex Plus and VISX Star lasers. Loss of BSCVA of two lines or more was not seen. CRS LASIK Study protocols are ongoing to provide longer follow-up and to study other refractive indications.

Clinical results of excimer laser photorefractive keratectomy: A multicenter study of 265 eyes

Efficacy, predictability, and safety of excimer laser photorefractive keratectomy were evaluated at centers in Paris and Brest, France. Photoablation was performed with the VISX laser on 265 eyes (151 at the Paris center and 114 at the Brest center). The eyes were clinically and statistically evaluated over a six month follow-up. Initial myopia ranged from −0.7 to −19.4 diopters (D) (mean spherical equivalent [SE] −5.9 D) in the Paris center and from −0.9 to −14.5 D (SE −4.5 D) in the Brest center. At both centers, the mean uncorrected visual acuity was worse than 20/200; over 90% of cases in each center had a best uncorrected visual acuity of 20/100 or worse. Results are reported globally and for subgroups of myopia: Group A, SE better than or equal to −3.0 D; Group B, SE worse than −3.0 D and better than or equal to −7.0 D; Group C, SE worse than −7.0 D. Uncorrected visual acuity was significantly improved in the patients followed for six months; 64% of Paris cases and 62% of Brest cases obtained an uncorrected visual acuity of 20/40 or better. Predictability of the treatment was good; 67% of Paris eyes and 74% of Brest eyes were less than 1.0 D from the intended correction after six months. The data suggest that the initial myopia affected the efficacy and predictability of the treatment; results in the mild to moderate myopia eyes were significantly better than results in the severe myopia eyes. One case of visual acuity regression (less than one line) was observed in the two groups. This was associated with corneal haze of moderate intensity.

Epithelial alterations following photorefractive keratectomy for myopia.

A retrospective observational study was conducted to test the hypothesis that there is clinically measurable epithelial hyperplasia after photorefractive keratectomy (PRK), and to determine its effect on the epithelial oxygen uptake rate. One hundred myopic eyes who had been previously treated unilaterally with PRK were examined. Fifty eyes were treated with the Summit excimer laser (Summit Technology, Waltham, Mass) 27 +/- 7 months previously with ablation zone diameters of 4.1, 4.3, 4.5, or 5.0 mm. Fifty eyes were treated with the VISX excimer laser (VISX Inc, Sunnyvale, Calif) 5 +/- 4 months previously with one ablation zone diameter of 6.0 mm. The untreated eyes served as controls. Epithelial thickness was measured at a standardized central area within the ablation zone with a modified optical pachometer. Oxygen uptake rate was measured in a subgroup of 30 eyes (20 Summit and 10 VISX). The epithelium after PRK was 24% thicker than in the control eye in the Summit group (mean difference 13 +/- 10 microns; p < .01) and 7% thinner in the VISX group (mean difference -4 +/- 10 microns; p < .01). A higher oxygen uptake rate correlated with a thicker epithelium (r = 0.42; p < .05). The epithelium was significantly thicker after PRK between 13 and 37 months after treatment with the Summit excimer laser using ablation zone diameters of 4.1 to 5.0 mm. The epithelium was thinner between 1 and 15 months after treatment with the VISX laser using an ablation zone diameter of 6.0 mm. An increase in oxygen uptake rate reflected the metabolic rate of a greater number of cells in the hyperplastic layer.

Effect of Nitrogen Flow on Recovery of Vision After Excimer Laser Photorefractive Keratectomy Without Nitrogen Flow

Excimer laser (VISX) photorefractive keratectomy was performed using nitrogen flowing through the ocular fixation ring. It was felt that eliminating nitrogen flow may provide faster early visual rehabilitation. Two groups of 50 consecutive eyes underwent photorefractive keratectomy with (N2 flow) and without (no N2 flow) nitrogen flow, and were evaluated at 1 month postoperatively. There were more under- or overcorrections exceeding 1.00 diopter (D) in the N2 flow than in the no N2 flow groups. Eighteen eyes in the N2 flow and 11 in no N2 flow groups saw 20/50 or less, without correction. Fourteen eyes in the N2 flow and nine eyes in the no N2 flow groups lost two or more lines of best spectacle-corrected visual acuity. Four eyes in the N2 flow and none in the no N2 flow groups increased more than 1.00 D of astigmatism. The elimination of nitrogen flow in photorefractive keratectomy performed with the VISX laser appears to improve visual results in the early postoperative period.