Customized LASIK Treatment for Myopia: Relationship Between Preoperative Higher Order Aberrations and Refractive Outcome

Precision of a commercial hartmann-shack aberrometer: limits of total wavefront laser vision correction

PURPOSE

To assess the intrasession and intersession precision of higher-order aberrations (HOAs) measured using a commercial Hartmann-Shack wavefront sensor (Zywave; Bausch & Lomb) in refractive surgery candidates.

DESIGN

Prospective, experimental study of a device.

METHODS

To analyze intrasession repeatability, 1 experienced examiner measured 30 healthy eyes 5 times successively. To study intersession reproducibility, the same clinician obtained measurements from another 30 eyes in 2 consecutive sessions at the same time of day 1 week apart.

RESULTS

For intrasession repeatability, excellent intraclass correlation coefficients (ICCs) were obtained for total ocular aberrations, total HOAs, and second-order terms (ICC, > 0.94). The ICCs for third-order terms also were high (ICCs, > 0.87); however, fourth-order ICCs varied from 0.71 to 0.90 (Z(4)(0) = 0.90); and fifth-order ICCs were less than 0.85. For intersession reproducibility, only total ocular aberrations, total ocular HOAs, second-order terms, Z(4)(0), Z(3)(1), and Z(3-)(3) had ICCs of 0.90 or more. Bland-Altman analysis showed that the limits of agreement (were clinically too wide for most higher-order Zernike terms, especially for the third-order terms (> 0.21 μm).

CONCLUSIONS

Total ocular aberrations, total HOAs, and second-order terms can be measured reliably by Zywave aberrometry without anatomic recognition. Third-order terms and Z(4)(0) are repeatable, but not as reproducible between visits. Fourth-order terms, except for Z(4)(0), and fifth-order terms are not sufficiently reliable for clinical decision making or treatment. Because the variability of Zywave can be a major limitation of a truly successful wavefront-guided excimer laser procedure, surgeons should consider treating HOA magnitudes that are more than the intrasession repeatability values (2.77 × S(w)) as those presented in this study.

Prospective contralateral eye study to compare conventional and wavefront-guided laser in situ keratomileusis

PURPOSE

To compare outcomes of customized/wavefront guided with conventional ablation in myopic patients with or without astigmatism undergoing laser in situ keratomileusis.

METHODS

A prospective, comparative, contralateral eye study was performed. Sixty-eight eyes of 34 myopic patients with similar refractive error in both eyes were included. One eye was randomly selected to undergo conventional and the fellow eye customized ablation. Surgery was performed using the Technolas 217z laser (Bausch & Lomb, Surrey, UK). Uncorrected visual acuity, manifest refractive spherical equivalent (MRSE), astigmatism, aberrometry and contrast sensitivity were recorded pre and 3 months postoperatively.

RESULTS

Mean MRSE treated in the conventional and customized groups were 3.77 ± 1.61 dioptres and -3.83 ± 1.59 dioptres respectively. Three months postoperatively there was no significant difference between the groups in mean MRSE (p = 0.99) or cylinder (p = 0.56). The factor increase in postoperative total higher order aberrations (HOAs) was less in the customized (1.32) compared with the conventional (1.54) treatment group but did not reach statistical significance (p = 0.08). Scotopic contrast sensitivity decreased significantly postoperatively in the conventional but not in the customized treatment group.

CONCLUSION

Visual acuity and refractive error outcomes were similar in both treatment group and no patient preference was observed. Customized ablation was associated with a smaller but not statistically significant postoperative increase in HOAs, better preservation of scotopic contrast sensitivity, quicker treatment time and removal of less corneal tissue.

Advanced corneal surface ablation efficacy in myopia: changes in higher order aberrations

OBJECTIVE

To evaluate the change of ocular and corneal higher order aberrations (HOAs) after wavefront-guided advanced surface ablation (WF-ASA) for myopia using 4 different epithelial management techniques (AA-PRK, LASEK, Epi-PRK, and Epi-LASIK).

DESIGN

Retrospective single centre excimer database analysis.

PARTICIPANTS

Two hundred and forty eyes equally divided between the 4 WF-ASA techniques, matched for mean and range of required spherical correction.

METHODS

Ocular wavefront aberrations were measured using the wavescan aberrometer and corneal aberrations were obtained from corneal topography elevation maps and calculated by ray-tracing. All data were collected preoperatively and 3 months following treatment. The aberrations were described as Zernike polynomials, and analysis focused on total HOAs and spherical aberration (SA).

RESULTS

Three months postoperatively, there was a statistically significant surgically induced increase in total HOAs and SA both for ocular and corneal analysis (p < 0.001). There was no statistically significant difference in the induced ocular SA and HOAs between the groups, but the differences in induced corneal SA and HOAs were significant (p < 0.010). Ocular changes in SA were weakly correlated to preoperative SA (20.30, p < 0.001) but strongly correlated to applied spherical correction (20.68, p < 0.001). Surgically induced corneal SA was weakly correlated to preoperative corneal SA (20.34, p < 0.001) and applied spherical correction (20.46, p < 0.001).

CONCLUSIONS

Three months postoperatively, all procedures resulted in an increase in ocular and cornealHOAs and SA. Induced aberrations were most strongly correlated to the applied spherical power correction. Modifying the existing ablation pattern to compensate for induced HOAs might improve the outcome.

Development of an advanced nomogram for myopic astigmatic wavefront-guided laser in situ keratomileusis (LASIK)

BACKGROUND AND OBJECTIVE

To identify the relationship between preoperative parameters and postoperative overcorrection or undercorrection in eyes with myopic astigmatism treated with wavefront-guided laser in situ keratomileusis (LASIK), and to develop an advanced surgical nomogram.

PATIENTS AND METHODS

A retrospective chart review of 468 eyes that underwent wavefront-guided LASIK for myopia with astigmatism with the Alcon LADARVision 4000 (Alcon Laboratories, Fort Worth, TX), of which 235 had flaps created by microkeratome (OneUse; Moria Surgical, Doylestown, PA) and 233 by femtosecond laser (Intralase; AMO, Santa Ana, CA). Manifest sphere, cylinder, and spherical equivalent were recorded preoperatively and 3 months postoperatively. Various parameters from patient records were analyzed to identify which had greatest influence on outcomes.

RESULTS

Manifest spherical equivalent was the most important predictor of surgical overcorrection, with the second being spherical aberration. In both groups, there was a statistically significant (P < .0001) correlation of spherical aberration with the amount of overcorrection. Using these two parameters, compensatory nomograms were derived.

CONCLUSION

Surgical overcorrection in wavefront-guided LASIK for myopic astigmatism correlates positively with the amount of spherical equivalent treated and preoperative spherical aberration. Nomograms incorporating spherical aberration may improve accuracy of outcomes.

Effect of laser in situ keratomileusis on vision analyzed using preoperative optical quality

PURPOSE

To evaluate the effect on vision of laser in situ keratomileusis (LASIK) based on preoperative optical quality.

SETTING

Universitat Politècnica de Catalunya, Terrassa, and Barcelona Institute of Ocular Microsurgery, Barcelona, Spain.

DESIGN

Comparative case series.

METHODS

The relative change in optical quality and visual acuity were evaluated in eyes that had LASIK for myopia. The optical quality was assessed before and 3 months after surgery using parameters provided by a double-pass system. Patients were classified into 4 groups by preoperative optical quality: low (Group 1), moderate (Group 2), high (Group 3), and very high (Group 4).

RESULTS

The study evaluated 25 patients (50 eyes). The optical quality parameters improved postoperatively in Group 1 and Group 2, with the improvement ranging from 15% to 21% and from 13% to 17%, respectively. The preoperative and postoperative optical quality in Group 3 was similar. The optical quality in Group 4 worsened significantly by percentages ranging from -20% to -26%. Although visual acuity had the same trend, there were no statistically significant changes.

CONCLUSION

The changes in optical quality after LASIK surgery depended on the patient's preoperative optical quality; visual acuity showed the same trend, although no change was significant.

Comparison of LASIK with the OPDCAT or OATz algorithm using the NIDEK EC-5000CXII excimer laser

PURPOSE

To compare refractive outcomes, higher order aberrations, visual quality, and patient satisfaction between aspheric and whole-eye wavefront aspheric LASIK algorithms.

METHODS

Two hundred seventy-four eyes of 152 patients undergoing LASIK for myopia and myopic astigmatism were divided into two groups: eyes that underwent treatment using either the OPD-guided customized aspheric treatment (OPDCAT) or optimized aspheric treatment zone (OATz). Both groups were subdivided into two groups based on preoperative manifest refraction spherical equivalent (MRSE) <or= 6.00 diopters (D) and eyes with MRSE >or = - 6.00 D. Both groups were additionally subdivided into eyes with preoperative ocular higher order aberrations <0.40 microm and eyes with higher order aberrations >or = 0.40 microm. A P value <.05 was considered statistically significant.

RESULTS

At 3 months postoperatively, 88.3% (242/274) of eyes were available for follow-up. Postoperatively, 91.4% of eyes in the OPDCAT group and 90.6% of eyes in the OATz group were within 0.50 D. No difference in refractive outcomes and patient satisfaction among groups or subgroups was noted (P>.05). A significantly less change in asphericity (less oblate) was noted for the OPDCAT group (0.31 +/- 0.30) compared with the OATz group (0.51 +/- 0.35) (P<.05). A lower induction of aberrations in the OPDCAT group compared with the OATz group was noted ( P<.05). Mesopic contrast sensitivity was significantly higher for the OPDCAT groups and subgroups (P<.05).

CONCLUSIONS

Refractive outcomes between groups or subgroups were equivalent. A significantly lower induction of higher order aberrations and less change in asphericity in the OPDCAT group was noted. The OPDCAT algorithm was more likely to maintain mesopic contrast sensitivity.

Femtosecond laser in laser in situ keratomileusis

Flap creation is a critical step in laser in situ keratomileusis (LASIK). Efforts to improve the safety and predictability of the lamellar incision have fostered the development of femtosecond lasers. Several advantages of the femtosecond laser over mechanical microkeratomes have been reported in LASIK surgery. In this article, we review common considerations in management and complications of this step in femtosecond laser-LASIK and concentrate primarily on the IntraLase laser because most published studies relate to this instrument.

Analysis of optimized profiles for 'aberration-free' refractive surgery

PURPOSE

To provide a model of an aberration-free profile and to clinically evaluate the impact of treatments based upon these theoretical profiles in the post-operative cornea.

METHODS

Aberration-free profiles were deduced from the Zernike expansion of the difference between two corneal cartesian-ovals. Compensation for the focus-shift effects of removing corneal tissue were incorporated by preserving the location of the optical focus of the anterior corneal surface. Simulation of the surgical performance of the profile was performed by means of simulated ray-tracing through a cornea described by its anterior surface and pachymetry. Clinical evaluation was retrospectively analysed in terms of visual outcomes, corneal wavefront aberration and asphericity changes at 3-month follow-up compared to the baseline on 100 eyes treated for compound myopic astigmatism.

RESULTS

The proposed 'aberration-free' profiles theoretically preserve aberrations, becoming more oblate asphericity after myopic treatments, and more prolate after hyperopic ones. In the clinical evaluation, 94% of eyes were within +/-0.50 D of emmetropia. BSCVA improved significantly (p < 0.001). Induced corneal aberrations at 6-mm were below clinically relevant levels: 0.123 +/- 0.129 microm for HO-RMS (p < 0.001), 0.065 +/- 0.128 microm for spherical aberration (p < 0.001) and 0.058 +/- 0.128 microm for coma (p < 0.01), whereas the rate of induced aberrations per achieved D of correction were -0.042, -0.031, and -0.030 microm D(-1) for HO-RMS, SphAb, and coma (all p < 0.001). Induction of positive asphericity correlated to achieved correction (p < 0.001) at a rate 3x theoretical prediction.

CONCLUSIONS

'Aberration-free' patterns for refractive surgery as defined here together with consideration of other sources of aberrations such as blending zones, eye-tracking, and corneal biomechanics yielded results comparable to those of customisation approaches. Having close-to-ideal profiles should improve clinical outcomes decreasing the need for nomograms, and diminishing induced aberrations after surgery.

Efficacy of an aspheric treatment algorithm in decreasing induced spherical aberration after laser in situ keratomileusis

PURPOSE

To determine the effectiveness of an aspheric laser in situ keratomileusis (LASIK) algorithm for myopia with and without astigmatism in minimizing postoperative induction of spherical aberration.

SETTING

Four sites in Asia.

METHODS

Patients with -1.00 to -10.00 diopters (D) of spherical myopia with -4.00 D or less of astigmatism were recruited. Patients randomly had bilateral Zyoptix aspheric algorithm (aspheric group) or bilateral conventional Zyoptix Tissue Saving algorithm (control group). A Technolas 217z100 excimer system was used for LASIK ablation. Visual effectiveness, safety, higher-order aberrations, and corneal asphericity (Q value) were evaluated postoperatively.

RESULTS

The aspheric group comprised 86 eyes and the control group, 84 eyes. At 3 months, the high-contrast uncorrected distance visual acuity was 20/20 or better in 78% of eyes in the aspheric group and 83% of eyes in the control group. The control treatment induced 0.22 microm of spherical aberration, which was significantly higher than the 0.04 microm induced with the aspheric treatment (6.0 mm pupil) (P<.0001). The aspheric treatment induced significantly less vertical coma and trefoil (P = .02). Eyes in the aspheric group had significantly lower Q values (P<.0001). There was no statistically significant difference in the manifest refraction spherical equivalent between the 2 groups (P >.05). Although high- and low-contrast corrected distance visual acuity (CDVA) was similar between the groups, the aspheric group gained more lines of low-contrast CDVA.

CONCLUSION

The aspheric algorithm was more effective than the conventional algorithm in reducing induced spherical aberration and maintaining corneal asphericity after myopic LASIK.

Controlled induction of spherical aberration with custom soft contact lenses

BACKGROUND

This study investigated the non-invasive induction of spherical aberration (SA) levels consistent with complication-free wavefront-guided (WFG) refractive surgery using custom WFG soft contact lenses and quantified the resulting impact on visual performance.

METHODS

Twelve healthy individuals of typical military age (mean of 26.08 +/- 1.92 years) meeting the inclusion criteria of emmetropia (less than +/- 0.50 DS and less than +/- 0.50 DC) as measured by subjective refraction served as subjects. Five plano lenses were manufactured to induce a range of SA typical of those encountered after refractive surgery. The measured SA values over a 6 mm artificial pupil in these five lenses were -0.224 microm, 0.074 microm, 0.214 microm, 0.495 microm and 0.621 microm. For each subject, the level of total ocular aberrations through 10 Zernike radial orders over a 6 mm pupil was measured with a custom Shack-Hartmann wavefront sensor, while wearing each lens. Visual performance was evaluated using high contrast visual acuity (HCVA) measured through a 6 mm artificial pupil.

RESULTS

Custom WFG soft contact lenses can be manufactured to include the range of SA that occurs with complication-free refractive surgery (-0.20 microm to +0.60 microm) and produces a change in SA within a similar range when worn on the eye. High contrast visual performance with these lenses varied, depending on the amount of SA in each lens. Visual performance worsened with greater amounts of positive or negative SA and a quadratic fit to the data peaked at +0.209 microm.

CONCLUSIONS

Defined levels of SA can be manufactured and induced (non-invasively) with WFG soft contact lenses and their effect on logMAR high contrast visual performance can be measured. Results show that subjects' best logMAR HCVA occurs with the presence of positive residual SA. When designing the actual test lens, the targeted change in aberrations for each subject will likely be better achieved by first measuring the aberrations of a template lens on the eye and then compensating for unique subject dependent eye-lens interactions.

Use of adaptive optics to determine the optimal ocular spherical aberration

PURPOSE

To explore the impact of spherical aberration (SA) on contrast sensitivity using an adaptive optics vision simulator to determine the optimal amount of SA to include in customized corrections of wavefront aberrations.

SETTING

Laboratorio de Optica, Universidad de Murcia, Murcia, Spain, and AMO Groningen BV, Groningen, The Netherlands.

METHODS

An adaptive optics vision simulator consisting of a wavefront sensor, a 97-segmented deformable mirror to induce and correct aberrations of the eye, and a visual testing path was constructed for this study. The deformable mirror allows the effective ocular wavefront aberration to be manipulated and the resulting visual performance to be measured simultaneously. Subjective measurements of contrast sensitivity at 15 cycles per degree were performed with a 4.8 mm pupil in 5 subjects with different levels of naturally occurring SA. Contrast sensitivity was measured when SA values of -0.09 microm, 0.0 microm, 0.09 microm, and 0.182 microm were induced when the other natural aberrations of the eye were present, when the aberrations were corrected, and at defocus values of +/-0.25 diopter (D) and +/-0.50 D.

RESULTS

Subjects experienced peak contrast sensitivity performance with varying levels of SA when their natural aberrations were present; however, average contrast performance peaked at 0 mum of SA. When all higher-order aberrations were corrected, all 5 subjects' peak performance occurred at 0 microm of SA.

CONCLUSIONS

The adaptive optics vision simulator reduced the root-mean-square wavefront aberration of the eye by up to a factor of 4 and allowed noninvasive testing of the visual performance resulting from any ocular wavefront aberration introduced by customized correction procedures. This study showed that, on average, contrast performance peaked when SA was completely corrected.

Customized LASIK Treatment for Myopia Based on Preoperative Manifest Refraction and Higher Order Aberrometry: The Rochester Nomogram

PURPOSE

To develop and test the efficacy of myopic treatment, based on preoperative manifest refraction and higher order aberrations, in enhancing the postoperative refractive error following customized LASIK treatment and compare results with the manufacturer-recommended sphere offset Zyoptix treatment nomogram, which does not account for the preoperative higher order aberrations.

METHODS

One hundred seventy-five myopic eyes (89 patients) were treated based on the Rochester nomogram, which specified the amount of myopia to be treated based on preoperative manifest refraction and higher order aberrations, including third order aberrations and spherical aberration. Postoperative refractive error was measured at 1 month and compared to that theoretically estimated with the Zyoptix nomogram.

RESULTS

The mean preoperative sphere and cylinder were -4.52 +/- 2.05 diopters (D) and -0.81 +/- 0.70 D, respectively. The mean postoperative spheres were +0.04 +/- 0.33 D and +0.31 +/- 0.54 D, using the Rochester and Zyoptix nomograms, respectively. The mean postoperative spherical equivalent refractions were -0.11 +/- 0.34 D and +0.15 +/- 0.53 D using the Rochester and Zyoptix nomograms, respectively. The Rochester nomogram reduced the range of postoperative spherical equivalent to +/- 1.00 D, which was significantly better than that using the Zyoptix nomogram (t = 5.46, P < .0001), which would have resulted in 8% of eyes with a postoperative spherical equivalent refraction > +/- 1.00 D. Using the Rochester nomogram, 93.1% of eyes attained a postoperative UCVA > or = 20/20. The percentage of postoperative hyperopic overcorrection decreased to 2.8% in the Rochester nomogram group from 22.3% using the Zyoptix nomogram, which only adjusts spherical values based on preoperative sphere and does not account for preoperative aberrations.

CONCLUSIONS

The Rochester nomogram compensates for the effect of preoperative higher order aberrations on sphere and provided reduced range of postoperative spherical equivalent refraction.