Guy M. Kezirian

PURPOSE: To compare laser in situ keratomileusis (LASIK) results obtained with the femtosecond laser (IntraLase Corp.) to those obtained using 2 popular mechanical microkeratomes. SETTING: Private practice, Greensboro, North Carolina, USA. METHODS: This retrospective analysis compared LASIK outcomes with the femtosecond laser to those with the Carriazo-Barraquer (CB) microkeratome (Moria, Inc.) and the Hansatome microkeratome (Bausch & Lomb, Inc.). The 3 groups were matched for enrollment criteria and were operated on under similar conditions by the same surgeon. RESULTS: There were 106 eyes in the IntraLase group, 126 eyes in the CB group, and 143 eyes in the Hansatome group. One day postoperatively, the uncorrected visual acuity (UCVA) results in the 3 groups were similar; at 3 months, the UCVA and the best spectacle-corrected visual acuity results were not significantly different. A manifest spheroequivalent of +/-0.50 diopter (D) was achieved in 91% of eyes in the IntraLase group, 73% of eyes in the CB group, and 74% of eyes in the Hansatome group (P<.01). IntraLase flaps were significantly thinner (P<.01) and varied less in thickness (P<.01) than flaps created with the other devices. The mean flap thickness was 114 microm +/- 14 (SD) with the IntraLase programmed for a 130 microm depth, 153 +/- 26 microm with the CB using a 130 microm plate, and 156 +/- 29 microm with the Hansatome using a 180 microm plate. Loose epithelium was encountered in 9.6% of eyes in the CB group and 7.7% of eyes in the Hansatome group but in no eye in the IntraLase group (P =.001). Surgically induced astigmatism in sphere corrections was significantly less with the IntraLase than with the other devices (P<.01). CONCLUSIONS: The IntraLase demonstrated more predictable flap thickness, better astigmatic neutrality, and decreased epithelial injury than 2 popular mechanical microkeratomes.

Purpose: To demonstrate analytical methods for evaluating the results of keratorefractive surgical procedures and emphasize the importance of intraocular astigmatism. Setting: University of Texas Medical School, Houston, Texas, USA. Methods: A standard data set, provided by an editor of this journal, comprising the preoperative and postoperative keratometric and refractive measurements of 100 eyes that had keratorefractive surgery was evaluated by 2 methods, vector and spheroequivalent (SEQ) analysis. The individual and aggregate surgically induced refractive changes (SIRCs) and prediction errors were determined from the refractive and keratometric measurements using both methods and then compared. The refraction vertex distance, keratometric index of refraction, and corneal asphericity were used to make the results calculated from refractive data directly comparable to those derived from keratometric data. Doubled-angle and equivalency plots as well as frequency and cumulative histograms were used to display the data. Standard descriptive statistics were used to determine the mean and standard deviation of the aggregate induced astigmatism after converting the polar values (cylinder and axis) to Cartesian (x and y) values. Results: The preoperative SEQ refractive errors were undercorrected by at least 0.25 diopter (D) in most cases (78%). Six percent were corrected within ± 0.24 D, and 16% were overcorrected by at least 0.25 D SEQ. The mean SEQ was −6.68 D ± 2.49 (SD) before and −0.61 ± 0.82 D after surgery, reflecting a SIRC SEQ of −6.07 ± 2.40 D. The defocus equivalent (DEQ) was 7.41 ± 2.53 D before and 0.96 ± 0.74 D after surgery; for a nominal 3.0 mm pupil, this corresponded to an estimated improvement in uncorrected visual acuity (UCVA) from worse than 20/200 to better than 20/25, respectively. The predictability of the treatment decreased as the attempted refractive correction increased. The average magnitude of the refractive astigmatism was 1.46 ± 0.61 D before and 0.40 ± 0.38 D after surgery. The centroid of the refractive astigmatism was +0.96 × 87.9 ± 0.85 D, ρ = 0.43 before and +0.11 × 83.1 ± 0.37, ρ = 0.49 after surgery. The decrease in the square root of the centroid standard deviation shape factor (ρ1/2) indicated an 8% increase in the amount of oblique astigmatism in the population. The prevalence of preoperative keratometric irregular astigmatism in excess of 0.5 D in this group of patients was 13%. The correlation between keratometric and refractive astigmatism was extremely poor before (r2 = 0.26) and especially after surgery (r2 = 0.02), demonstrating the presence of intraocular astigmatism and the limitations of manual keratometry. The centroid of intraocular astigmatism at the corneal plane was +0.48 × 178 ± 0.49 D, ρ = 0.59, and was compensatory. Conclusions: The 2 analytical methods are complimentary and permit thorough and quantitative evaluation of SIRCs and allow valid statistical comparisons within and between data sets. The DEQ allows comparison of refractive and visual results. The decrease in refractive predictability with higher corrections is well demonstrated by the SEQ and doubled-angle plots of the SIRC. Doubled-angle plots were particularly useful in interpreting errors of cylinder treatment amount and errors in alignment. The correlation between refractive and keratometric astigmatism was poor for preoperative, postoperative, and SIRC data, indicating the presence of astigmatic elements beyond the corneal surface (ie, intraocular astigmatism). Sources of error in refractive outcome statistics include the use of multiple lens systems in the phoropter, errors in vertex calculations, difficulty in accurately defining the axis of astigmatism, and failure to consider measurement errors when working with keratometric data. The analysis of this particular data set demonstrates the significant clinical benefits of refractive surgery: an 8-fold increase in UCVA, an 11-fold decrease in SEQ refractive error, as well as a 9-fold and nearly a 2 1/2-fold decrease in the magnitude and distribution of astigmatism, respectively.

PURPOSE: To compare the outcomes of wavefront-guided laser in situ keratomileusis (LASIK) performed using the IntraLase femtosecond laser with the outcomes using the Hansatome mechanical microkeratome. SETTING: Private clinic, Overland Park, Kansas, USA. METHODS: In a prospective contralateral-eye study performed under institutional review board supervision, 51 consecutive patients (102 eyes) had bilateral wavefront-guided LASIK for myopia using the Alcon LADARVision laser. One eye of each patient was randomized to have the flap created with the IntraLase femtosecond laser and the other flap using a standard compression head Hansatome microkeratome. All other treatment parameters were the same. RESULTS: The IntraLase group had significantly better mean uncorrected visual acuity (UCVA) at all intervals from 1 day to 3 months postoperatively. The mean spheroequivalent at 3 months was more myopic with the Hansatome (-0.34 diopter [D] +/- 0.28 [SD]) than with the IntraLase (-0.19 +/- 0.24 D) (P<.01). The mean residual astigmatism at 3 months was also significantly higher in the Hansatome group than in the IntraLase group (0.32 +/- 0.25 D and 0.17 +/- 0.20 D, respectively) (P<.01). The differences in UCVA persisted after spheroequivalent outcomes were controlled for but equilibrated when the analysis was modified to control for manifest postoperative astigmatism. Aberrometry showed significantly higher astigmatism and trefoil in the Hansatome group. Recovery of corneal sensation and epithelial integrity was similar between groups. CONCLUSIONS: The statistically better UCVA and manifest refractive outcomes after LASIK with the IntraLase femtosecond laser may be the result of differences in postoperative astigmatism and trefoil. These findings are consistent with previous findings of better astigmatic outcomes with the IntraLase laser and may have clinical significance for wavefront-guided treatments.

PURPOSE: To compare visual outcomes using the WaveLight ALLEGRETTO WAVE to administer either wavefront-optimized (standard LASIK) or wavefront-guided (custom LASIK) treatments in myopic eyes. METHODS: In this prospective, open-label, multicenter study conducted in the United States, 374 eyes were randomized by alternating enrollment to receive either wavefront-optimized or wavefront-guided LASIK treatments with this laser platform. Bilateral treatments were administered, with both eyes of each patient receiving the same treatment. Corneal flaps were created using the IntraLase femtosecond laser. RESULTS: In this FDA clinical trial, results at 3 months postoperatively revealed that 93% of eyes in both cohorts receiving either wavefront-optimized or wavefront-guided treatments attained an uncorrected visual acuity (UCVA) of 20/20 or better. Seventy-six percent of eyes with the wavefront-optimized treatment and 64% of eyes with the wavefront-guided treatment achieved UCVA of 20/16 or better. None of the eyes that received either treatment lost two lines or more of best spectacle-corrected visual acuity (BSCVA). In addition, 58% of eyes with wavefront-optimized treatment and 62% of eyes with wavefront-guided treatment gained one line or more of BSCVA. None of the eyes in either treatment group underwent retreatment. CONCLUSIONS: In the majority of eyes, no statistically significant differences were found between either treatment group in regard to visual acuity and refractive outcomes. Wavefront-guided treatments are not required in most cases with this laser, but may be considered if the magnitude of preoperative root-mean-square (RMS) higher order aberrations is >0.35 microm. In this study population, 83% of eyes had preoperative RMS higher order aberrations of <0.3 microm.

PURPOSE: To develop a minimum set of analyses and a format for presentation of outcomes of astigmatism correction by laser systems that reshape the cornea. METHODS: An Astigmatism Project group was created under the auspices of the American National Standards Institute (ANSI) Z80.11 Working Group on Laser Systems for Corneal Reshaping. The Astigmatism Project Group was made up of experts in astigmatism analyses from academia, government, and industry. An extensive literature review was conducted to identify all currently available methodologies for the evaluation of astigmatic outcomes. Project Group members discussed the utility of each method and its specific parameters for evaluating the effectiveness of astigmatism-correcting devices. They gave consideration to unique terminology and analyses required for evaluation of correction of astigmatism by laser systems that reshape the comea. RESULTS: The Project Group defined a comprehensive list of analysis variables needed for the evaluation of astigmatism-correcting devices and generated a mathematical definition for each term. They developed a minimum set of analyses needed for evaluation of astigmatism treatments by laser systems that reshape the cornea. They established methods for calculating the refractive error analysis variables and constructed recommended table and graph formats for data presentation. CONCLUSIONS: This article contains the recommendations of the Astigmatism Project Group of the American National Standards Institute. We propose it as a standard reference for astigmatic refractive error analyses for the evaluation of safety and effectiveness of laser systems that reshape the cornea.