Higher Order Aberrations and Relative Risk of Symptoms After LASIK

An update on intraocular lens power calculations in eyes with previous laser refractive surgery

PURPOSE OF REVIEW

There is an ever-growing body of research regarding intraocular lens (IOL) power calculations following photorefractive keratectomy (PRK), laser-assisted in-situ keratomileusis (LASIK), and small-incision lenticule extraction (SMILE). This review intends to summarize recent data and offer updated recommendations.

RECENT FINDINGS

Postmyopic LASIK/PRK eyes have the best refractive outcomes when multiple methods are averaged, or when Barrett True-K is used. Posthyperopic LASIK/PRK eyes also seem to do best when Barrett True-K is used, but with more variable results. With both aforementioned methods, using measured total corneal power incrementally improves results. For post-SMILE eyes, the first nontheoretical data favors raytracing.

SUMMARY

Refractive outcomes after cataract surgery in eyes with prior laser refractive surgery are less accurate and more variable compared to virgin eyes. Surgeons may simplify their approach to IOL power calculations in postmyopic and posthyperopic LASIK/PRK by using Barrett True-K, and employing measured total corneal power when available. For post-SMILE eyes, ray tracing seems to work well, but lack of accessibility may hamper its adoption.

Q-value customized versus wavefront-optimized ablation in femtosecond laser-assisted LASIK for myopia and myopic astigmatism: a prospective contralateral comparative study

Background

Corneal refractive surgery for myopia results in an oblate shift with increased postoperative aberrations inversely affecting the quality of vision. Aspheric ablation profiles have been introduced to minimize such a problem. The aim of this study was to compare changes in corneal asphericity, central and mid-peripheral pachymetry between the Q-value customized and the wavefront-optimized (WFO) ablation profiles.

Methods

A prospective, comparative non-randomized fellow eye study was conducted. Eighty eyes of 40 eligible patients underwent femtosecond laser-assisted laser in situ keratomileusis for myopia and myopic astigmatism. In each patient, the more myopic eye was included in the custom-Q ablation experimental group and the other less myopic eye was included in the WFO control group. For the custom-Q group, the target asphericity was set to the preoperative Q-value. Corneal asphericity, central and mid-peripheral pachymetric changes and the root mean square of corneal higher-order aberrations (RMSh) were assessed 6 months following surgery. Visual and refractive outcomes were also evaluated in both platforms 6 months postoperatively.

Results

The mean preoperative refractive spherical equivalent was significantly more myopic in the custom-Q group than in the WFO group (P = 0.001). The mean Q-value changed from − 0.2 ± 0.1 to 0.6 ± 0.7 and from − 0.2 ± 0.1 to 0.4 ± 0.5 in the custom-Q and WFO groups, respectively. The oblate shift in corneal asphericity was not significantly different between both treatment groups (P = 0.094). The mean ablation depth at the pupillary center was significantly greater in the custom-Q group (P = 0.011), while there was no significant difference at the mid-peripheral pachymetry (P = 0.256). The RMSh significantly increased in both treatment profiles (P < 0.001) with no significant difference between the two groups (P = 0.06). The uncorrected distance visual acuity (UDVA) and the manifest refraction spherical equivalents (MRSE) significantly improved in both treatment groups (P < 0.001).

Conclusions

The custom-Q treatment profile with target asphericity set at the preoperative Q-value achieved comparable outcomes vs. the WFO profile in terms of postoperative corneal asphericity and mid-peripheral pachymetry despite the greater amount of ablation, the smaller optical zone, and the resulting increase in postoperative corneal flattening in the custom-Q group.

Trial registration (Clinicaltrials.gov): NCT04738903, 4 February 2021- Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT04738903

Evaluation of Disk Halo Size and Identification of Correlated Factors in Myopic Adults

This study aimed to evaluate glare source-induced disk halo size and assess its correlation with higher-order aberrations (HOAs), pupillometry findings, and contrast sensitivity in myopic adults (aged 23.8 ± 4.4 years). In this cross-sectional study, 150 eyes of 150 patients were assessed. All patients underwent routine ophthalmic examinations, wavefront aberrometry, halo size measurement, dynamic pupillometry, and contrast sensitivity tests. Spearman's correlation analysis and independent sample t-tests were performed for data analysis. The mean halo radius was 82.5 ± 21.8 and 236.7 ± 52.2 arc min at 5 and 1 cd/m² luminance levels, respectively. The values were inversely correlated with internal spherical aberration (SA) (r = −0.175, p = 0.032 and r = −0.241, p = 0.003, respectively), but not correlated with spherical equivalent (SE, both p > 0.05). Positive correlations were observed between halo radius and pupil size, contraction amplitude, and dilation speed during pupillary light reflex. Halo radii at 5 and 1 cd/m² luminance levels were not significantly correlated with the area under the log contrast sensitivity function (r = −0.093, p = 0.258 and r = −0.149, p = 0.069, respectively). The mean halo radius was not clinically different between myopic and healthy eyes at 5 cd/m² luminance level and did not differ significantly between the high and low-to-moderate myopia at 5 and 1 cd/m² luminance levels (all p > 0.05). According to a stepwise linear regression model, the internal SA had a negative effect on the halo radius under low photpic condition; the average pupil diameter, internal SA and corneal HOAs played a large role in determining the halo radius under mesopic condition.

Simulations of Decentration and Tilt of a Supplementary Sulcus-Fixated Intraocular Lens in a Polypseudophakic Combination Using Ray-Tracing Software

This study aimed to assess image quality after the tilt and decentration of supplementary intraocular lenses (IOLs) in a two-lens configuration. One was designed for sulcus fixation with a nominal power range of 1D–10D and was combined with a capsular fixation 20D IOL. The optical performance of a ray-tracing model was tested under IOL misalignment through the area under the modulation transfer function (MTFa) and wave aberrations. Tilting by 10° resulted in a 4% reduction of the MTFa for a 10D IOL as compared to 9% for the 20D lens. The two models demonstrated good tolerance to a 1 mm decentration; as for the 10D sulcus-fixated lens, the MTFa loss was 2%, and 4% for the capsular fixation lens. Coma and astigmatism increased three- and four-fold, respectively, after a 10° tilt compared to the aberration level induced by the 1 mm decentration. Both analyses showed a trend towards a lower MTF impact and fewer optical errors with decreasing nominal power. In conclusion, when misaligned, low-power sulcus-fixated IOLs might retain their good optical quality. An extreme tilt of 10° has a more detrimental effect on the IOL performance than a 1 mm decentration. The proper alignment of a high-power capsular fixation lens is important in achieving a desirable postoperative outcome.

Laboratory evaluation of higher-order aberrations and light scattering in explanted opacified intraocular lenses

Background

Intraocular lens (IOL) calcification is a serious condition that can only be treated by removing the clouded lens. Since explantation bears the risk of complications, it is often deferred until the patient finds the symptoms intolerable. Usually, as the IOL opacifies, visual acuity is minimally affected early on. In this study, we assessed the impact of IOL opacification on optical quality.

Methods

We analyzed ten opacified explanted IOLs (Oculentis GmbH). Wavefront aberrations were obtained with a SHSOphthalmic device (Optocraft GmbH), which features a Hartmann-Shack sensor. The root mean square (RMS) of higher-order aberrations (HOAs) was compared. The effect of calcification on image quality was assessed through the Strehl ratio (SR). We detected light scattering with a C-Quant (Oculus GmbH) and expressed it as a straylight parameter.

Results

At 2 mm, 3 mm and 4 mm, the mean RMS (±standard deviation) was 0.033 μm (±0.026 μm), 0.044 μm (±0.027), and 0.087 μm (±0.049), respectively. The mean SR value was 0.81 ± 0.15 at 3 mm, with four IOLs showing a nearly diffraction-limited performance, but in two explants, opacification precluded reliable measurements. Increased straylight was found in all opacified IOLs with a mean value of 150.2 ± 56.3 deg²/sr at 3 mm.

Conclusions

We demonstrated that IOL opacification induces HOAs. However, the RMS remained low, which resulted only in a slight reduction of the SR-derived optical quality. On the other hand, we found a severe straylight elevation in the opacified lenses, which may result in dysphotopsia, such as glare, and subjective complaints, despite good visual acuity.

Comparison of objective and subjective visual quality early after implantable collamer lens V4c (ICL V4c) and small incision lenticule extraction (SMILE) for high myopia correction

PURPOSE

To investigate differences in the objective and subjective visual quality of patients with high myopia following implantable collamer lens V4c (ICL V4c) versus small incision lenticule extraction (SMILE) early postoperatively.

METHODS

This prospective analysis included 94 eyes of 57 patients (8 males) in the ICL V4c group (mean spherical equivalent (SE), -8.07 ± 1.03 dioptres (D)) and 103 eyes of 57 patients (13 males) in the SMILE group (mean SE, -7.85 ± 0.78 D). Refractive parameters and wavefront aberrations were recorded preoperatively and 6 months postoperatively. Subjective visual quality was scored with the Quality of Vision questionnaire, and operation satisfaction was evaluated 6 months postoperatively.

RESULTS

At 6 months postoperatively, the efficacy index was 1.17 ± 0.16 in the ICL and 1.09 ± 0.20 in the SMILE group; the safety index was 1.21 ± 0.18 in the ICL and 1.12 ± 0.16 in the SMILE group. A significant increase in total higher-order aberrations (HOAs) in both the ICL and SMILE groups was observed, but to a lesser degree in ICL (p < 0.05). In the ICL group, trefoil significantly increased (p < 0.05), whereas in the SMILE group, coma, trefoil and spherical aberration significantly increased (p < 0.05). Glare, haloes and blurred vision had the highest incidences after both types of surgery, and postoperative haloes were significantly more common following ICL; 96.1% of ICL-treated and 94.9% of SMILE-treated patients were satisfied with their visual outcomes.

CONCLUSION

ICL V4c caused lower HOAs induction than SMILE. Despite the postoperative visual disturbances, both ICL and SMILE provided good efficacy, safety, predictability and high satisfaction in correcting high myopia.

Theoretical Analysis of Wave-Front Aberrations Induced from Conventional Laser Refractive Surgery in a Biomechanical Finite Element Model

Purpose

To examine the biomechanical effects-induced wave-front aberrations after conventional laser refractive surgery.

Methods

A finite element model of the human eye was established to simulate conventional laser refractive surgery with corrected refraction from –1 to –15 diopters (D). The deformation of the anterior and posterior corneal surfaces was obtained under the intraocular pressure (IOP). Then, the surface displacement was converted to wave-front aberrations.

Results

Following conventional refractive surgery, significant deformation of the anterior and posterior corneal surfaces occurred because of the corneal biomechanical effects, resulting in increased residual wave-front aberrations. Deformation of the anterior surface resulted in a hyperopic shift, which was significantly increased with the increasing refractive correction. The residual high-order aberrations consisted of spherical aberration, vertical coma, and y-trefoil. Spherical aberration was significantly positively correlated to enhanced refraction correction. The effect of posterior corneal surface on induced wave-front aberration was less than the anterior corneal surface. The IOP slightly affects the postoperative defocus, coma, and spherical aberration. When treatment decentration occurred during the procedure, the hyperopic shift decreased as the eccentricity increased. Treatment decentration had a significant impact on the spherical aberration and the coma. In addition, the ocular tissue elasticity played a key role in hyperopic shift, whereas it had little effect on the other aberrations.

Conclusions

Among the many factors that affect high-order aberrations after conventional laser refractive surgery, the alterations in corneal morphology caused by biomechanical effects must be considered, as they can lead to an increase in postoperative residual wave-front aberrations.

Higher-order aberration measurements: Comparison between Scheimpflug and dual Scheimpflug-Placido technology in normal eyes

PURPOSE

To compare higher order aberrations (HOAs) in normal eyes between a Scheimpflug imaging system (Pentacam HR) and dual Scheimpflug-Placido imaging system (Galilei G4).

SETTING

Emory University, Atlanta, Georgia, and the University of Southern California, Los Angeles, USA.

DESIGN

Retrospective case series.

METHODS

Eyes screened for refractive surgery were evaluated sequentially using a Scheimpflug device and a dual Scheimpflug-Placido device. Differences, correlations, and agreement between values for total root mean square (RMS), trefoil, coma, and spherical aberration were analyzed, and Bland-Altman plots were generated.

RESULTS

One hundred five eyes of 105 patients (44 men, 61 women) were evaluated. Total RMS, coma, and trefoil were significantly different between groups (all P < .001), while spherical aberration values were not. There was moderate correlation between devices for trefoil (r = 0.475 to 0.652), coma (r = 0.574 to 0.651), and spherical aberration (r = 0.483) and a strong correlation for total cornea RMS (r = 0.817). There was no directional bias between groups. The 95% limits of agreement for absolute values was 0.039 μm for trefoil at 30 degrees, 0.405 μm for trefoil at 0 degree, 0.553 μm for horizontal coma, 0.545 μm for vertical coma, 0.318 μm for spherical aberration, and 0.617 μm for RMS.

CONCLUSIONS

A Scheimpflug imaging device and dual Scheimpflug-Placido imaging device generated statistically different values for total cornea HOAs; however, the correlation between devices was moderate to strong and there was reasonable agreement in all measures for normal eyes. Based on these findings, the devices appear functionally equivalent for clinical use, although caution is warranted for outcomes-based research protocols that report HOAs.

Corneal aberrations after small-incision lenticule extraction versus Q value-guided laser-assisted in situ keratomileusis

Previous studies compared ocular aberration and visual quality after small-incision lenticule extraction (SMILE) and Q value-guided femtosecond laser-assisted in situ keratomileusis (Q-FS-LASIK), but anterior corneal surface aberration properties are poorly known. This study aimed to compare the changes in anterior corneal surface aberration after SMILE versus Q-FS-LASIK.This was a prospective, observational cohort study. Patients with myopia and myopic astigmatism underwent SMILE or Q-FS-LASIK at Hangzhou MSK Eye Hospital between January 2015 and November 2015. High order aberration (HOA), primary spherical aberration (PSA), primary coma aberration (PCA), primary vertical coma aberration (PVCA), and primary horizontal coma aberration (PHCA) were assessed using pre- and postoperative Sirius scanning.Both surgery were associated with significant increases in postoperative HOA, PSA, and PCA (both groups P < .01). In the SMILE group (n = 51), the variations in HOA, PSA, and PCA were no longer significant after postoperative week 2 (P > .05). In the Q-FS-LASIK group (n = 73), the variations in HOA and PCA were no longer significant after postoperative day 1 (P > .05). In the SMILE group, the 3-month changes in PCA were not correlated with spherical, spherical equivalent (SE), and spherical plus cylinder measurements. Cylinder measurements were not correlated with HOA, PSA, and PCA. In the Q-FS-LASIK group, the 3-month changes in PCA correlated with spherical, SE, and spherical plus cylinder measurements.Both SMILE and Q-FS-LASIK resulted in an increase in HOA, PSA, and PCA at postoperative day 1, but Q-FS-LASIK introduced lower HOA and showed better stability. Spherical measurement was related to PSA.

Comparing aspheric ablation profile with standard corneal ablation for correction of myopia and myopic astigmatism, a contralateral eye study

The purpose of this study is to compare visual outcomes of myopic refractive surgery, using tissue saving (TS), a standard ablation profile by a Technolas 217z100, and aberration smart ablation (ASA), an aspheric algorithm by a MEL 80 excimer laser in two eyes of one patient. In this prospective interventional paired-eye controlled study, a total of 100 eyes of 50 participants with myopia with or without astigmatism underwent thin-flap Femto-LASIK, using a Femto LDV femtosecond laser (Ziemer Ophthalmic Systems AG, Port, Switzerland). For each patient, one eye was randomly treated with tissue-saving algorithm (TS group) by the Technolas 217z100 excimer laser and the other eye was treated with optimized smart ablation profile (ASA group) by the MEL 80 excimer laser. Outcome measures were uncorrected distance visual acuities (UDVAs), corrected distance visual acuities (CDVAs), manifest refraction, higher-order aberrations (HOAs), contrast sensitivity, and patient satisfaction 12 months after surgery. At 12 months postoperative, "45 subjects returned with mean" UDVA was - 0.02 ± 0.08 Logarithm of mean angle of resolution (LogMAR) for TS group and - 0.02 ± 0.09 LogMAR for ASA group (P = 0.91). Of the TS eyes, 42/45 (93.3%) and 32/45 (71.1%) were within ± 0.5 D and ± 0.25 D of target refraction, respectively, and of the ASA eyes, 41/45 (91.1%) and 30/45 (66.6%) were within ± 0.5 D and ± 0.25 D of target refraction, respectively. No statistically significant differences were observed between groups in HOAs changes and contrast sensitivity function. Aspheric and non-aspheric LASIKs using the two different excimer lasers provide similar results in myopic and myopic astigmatism patients.

Quality of Vision After Wavefront-Guided or Wavefront-Optimized LASIK: A Prospective Randomized Contralateral Eye Study

PURPOSE

To compare the effect of wavefront-guided and wavefront-optimized LASIK using different laser platforms on subjective quality of vision.

METHODS

The dominant eyes of 55 participants with myopia were randomized to receive either wavefront-guided LASIK treatment by the VISX Star S4 IR Custom-Vue excimer laser system (Abbott Medical Optics, Inc., Santa Clara, CA) or wavefront-optimized treatment by the WaveLight Allegretto Wave Eye-Q 400-Hz excimer laser system (Alcon Laboratories, Inc., Fort Worth, TX), whereas the fellow eye had the alternate laser treatment. Patients completed a questionnaire assessing quality of vision and visual symptoms (daytime and nighttime glare, daytime and nighttime clarity, halos, haze, fluctuating vision, and double vision) preoperatively and at postoperative months 1, 3, 6, and 12.

RESULTS

At 3, 6, and 12 months postoperatively, there was no significant difference in any individual symptom between the wavefront-guided and wavefront-optimized groups, although at 12 months wavefront-guided eyes trended toward having more excellent vision (wavefront-guided vs wavefront-optimized; 2.26 vs 2.43; P = .039). In the subgroup of patients with preoperative root mean square (RMS) higher order aberrations (HOAs) less than 0.3 µm in both eyes, the wavefront-optimized group demonstrated a trend toward worsened nighttime clarity (P = .009), daytime clarity (P = .015), and fluctuating vision (P = .046), and less excellent vision (P = .009) at 12 months.

CONCLUSIONS

Twelve months after surgery, most patients' self-reported visual symptoms were similar in eyes receiving wavefront-guided or wavefront-optimized LASIK. In general, 36% of patients preferred wavefront-guided LASIK, 19% preferred wavefront-optimized LASIK, and 45% had no preference at 12 months. The wavefront-guided preference was more pronounced in patients with lower baseline HOAs (RMS < 0.3 µm).

Comparison of Measurements and Clinical Outcomes After Wavefront-Guided LASEK Between iDesign and WaveScan

PURPOSE

To compare the measurements of refractive errors and ocular aberrations obtained using iDesign and WaveScan (Abbott Medical Optics, Inc., Santa Ana, CA), and to compare surgical outcomes of wavefront-guided LASEK using ablation profiles based on both aberrometers.

METHODS

Ninety myopic eyes of 45 normal patients were evaluated using both the iDesign and WaveScan to measure spherical and cylindrical errors, spherical equivalents, and Zernike coefficients of ocular aberrations. Wavefront-guided LASEK was performed in a different group of 59 eyes of 30 patients divided into two groups, the iDesign and Wavescan groups. The clinical outcomes between the two groups including uncorrected visual acuity, refractive errors, contrast sensitivity, and ocular aberration were compared at 1, 3, and 6 months postoperatively.

RESULTS

The iDesign produced significantly higher myopic values for refractive errors than the WaveScan, as well as significantly lower levels of total higher order, third, fourth, and fifth order root mean square values and Zernike coefficients of vertical coma and spherical aberration. At postoperative 1, 3, and 6 months, there were no statistically significant differences between the two groups in terms of uncorrected visual acuity and remaining refractive errors. The percentages of patients with spherical equivalents within ±1.00 and ±0.50 diopters of emmetropia were 100% (29 eyes) and 75.9% (22 eyes), respectively, in the iDesign group and 96.7% (29 eyes) and 70.0% (21 eyes), respectively, in the WaveScan group. Mesopic contrast sensitivity values were significantly higher, and the change in root mean square values for spherical aberration was significantly lower in the iDesign group.

CONCLUSIONS

There were significant differences between the iDesign and the WaveScan in the measurements of refraction and ocular aberrations. Wavefront-guided LASEK based on an ablation profile from the iDesign demonstrated comparable refractive predictability with the WaveScan group, resulting in minimal physician adjustment and superior postoperative visual quality.

Higher Order Aberrations and Visual Outcomes in Wavefront-Optimized Sub-Bowman Keratomileusis: Flap Creation Using Femtosecond Laser Versus Mechanical Microkeratome

PURPOSE

The aim of this study was to compare the outcomes of wavefront-optimized sub-Bowman keratomileusis (SBK) performed using the 150 KHz IntraLase femtosecond (IFS) laser (Abbot Medical Optics) with those using the Moria Evo 3 One Use-Plus SBK mechanical microkeratome (Moria SA).

DESIGN

A prospective comparative clinical trial.

METHODS

Fifty patients had bilateral wavefront-optimized SBK performed for myopia or myopic astigmatism. In 25 patients, the flap was created with the 150 KHz IFS laser (group 1) and in the other 25 with the Moria One Use-Plus SBK mechanical microkeratome (group 2). All other treatment parameters were the same. Results were reported for 1 eye per patient in each group (ie, 25 eyes in each group).

RESULTS

Efficacy, refractive stability, predictability, and safety profiles were comparable between the 2 groups. Although higher order aberrations (HOAs) increased significantly in both groups after laser in situ keratomileusis, intergroup comparison revealed that group 1 was associated with a significantly higher induction of both total HOAs [mean root mean square (RMS), 0.63 ± 0.20 in group 1 vs 0.52 ± 0.14 in group 2; P = 0.031] and spherical aberrations (RMS, 0.37 ± 0.17 in group 1 vs 0.22 ± 0.09 in group 2; P < 0.001) as compared with group 2.

CONCLUSIONS

Flaps created using the Moria Evo 3 One Use-Plus SBK mechanical microkeratome were associated with significantly lower induction of total HOAs and spherical aberrations as compared with 150 KHz IFS flaps at the end of 3 months follow-up.

A limitation of Hartmann-Shack system in measuring wavefront aberrations for patients received laser refractive surgery

Purpose

To explore the relationship between ablation parameters of myopic laser surgery and measurement area of wavefront aberration (WA) with Hartmann-Shack wavefront sensor.

Methods

58 subjects undergone myopic laser surgeries and 74 uncorrected myopic subjects were enrolled in this experiment. The laser ablation parameters were obtained from surgical records, which included spherical error (Rx), depth, and optical zone (OZ) of ablation. The measured area of WA was tested by the WASCA, and the real pupil size was tested by Pentacam. The corneal eccentricity (E value) and curvature was also measured with the Pentacam. All the measurements were performed under mydriatic condition.

Results

For uncorrected myopic eyes, the measured area of WA was similar with the real pupil size. But for the corrected eyes, the measured area of WA was smaller than the real pupil size with a mean difference of 0.66 ± 0.54 mm for moderate myopia (t = 6.45, p < 0.0001) and 1.76 ± 0.55 mm for high myopia (t = 18.92, p < 0.0001), but not for mild myopia. The Rx (t = -3.20, p = 0.0017), OZ (t = 64.4, p < 0.0001) and postoperative corneal E value (t = 2.52, p = 0.017) were the independent factors of measured area of WA. Measured area of WA = -0.81*Rx + 1.13*OZ + 0.49*postoperative corneal E value (r² = 0.997).

Conclusions

The WASCA has a limitation in measuring wavefront aberration over the whole pupil area when it’s used for patients received myopic laser surgery. The measured area is smaller than the real pupil size and depends linearly on ablation depth, optical zone and corneal eccentricity.

Refractive outcome of wavefront guided laser in situ keratomileusis and wavefront guided photorefractive keratectomy in high pre-existing higher order aberration

PURPOSE

To compare visual outcome and higher order aberrations (HOA) between wavefront-guided LASIK (WF-LASIK) and wavefront guided PRK (WF-PRK) in patients with high preoperative HOA.

METHODS

Randomized prospective interventional study. Conducted at Guru Nanak Eye Centre, Maulana Azad Medical College, Delhi, India. Eighty myopic eyes of forty patients were included.

INCLUSION CRITERIA

age more than 21 years, best corrected visual acuity of 20/20 or better, a stable refraction, to be off soft contact lens for minimum 14 days prior to preoperative examination, preoperative RMS HOA more than 0.35 μ, preoperative central corneal thickness at least 500 μm, estimated residual stromal bed thickness of at least 275 μm in patients undergoing WF-LASIK and 350 μm in patients undergoing WF-PRK. Exclusion criteria were severe dry eye, blepharitis, corneal disease and warpage, uveitis, posterior segment abnormalities involving the macula or optic nerve and systemic diseases. Patients were randomly divided into two groups. They underwent either WF-LASIK (group A) or WF-PRK (group B) over 2 years (40 eyes each). Patients were followed up for 6 months. Main outcome measures were efficacy, safety, stability, predictability and HOA.

RESULTS

At 6 months mean uncorrected visual acuity (logMAR) in group A was -0.01 ± 0.04 and group B was 0.00 ± 0.07 (P = 0.23). HOA RMS (6mm pupil) in group A was 0.61 ± 0.24 μm and group B was 0.55 ± 0.25 μm. The increase was statistically significant in both the groups (P < 0.05). Both the groups showed similar efficacy, predictability and safety.

CONCLUSION

WF-LASIK and WF-PRK have similar efficacy, safety and predictability, though WF-PRK induces less HOA.

Comparison of optical quality parameters and ocular aberrations after wavefront-guided laser in-situ keratomileusis versus wavefront-guided laser epithelial keratomileusis for myopia

BACKGROUND

To compare optical quality, ocular scattering, and higher-order aberrations (HOAs) after laser in-situ keratomileusis (LASIK) versus laser epithelial keratomileusis (LASEK).

METHODS

A total of 47 eyes from 47 participants who had undergone LASIK (group I) or LASEK (group II) procedure at least 6 months prior were enrolled. Ocular aberrations and modulation transfer function (MTF) values measured using iTrace, a ray-tracing type aberrometer, were compared to MTF (modulation transfer function) cut-off values, Strehl ratio, and objective indices of scattering obtained using the Objective Quality Analysis System II (OQAS II).

RESULTS

There was no significant correlation between the postoperative optical quality parameters and the HOAs between both groups. In group I, the MTF cut-off value was significantly correlated with cylinder refraction (p = 0.037), and the objective scattering index (OSI) was positively correlated with spherical equivalent (p = 0.023). In group II, there was a statistically significant correlation between the OSI and achieved refractive correction (p = 0.001). Regression analysis showed that the OSI was the most significant predictor of MTF cut-off values after refractive surgery. Additionally, MTF values measured by OQAS were significantly lower than those measured by iTrace without correlation.

CONCLUSION

Optical quality after refractive surgery may be influenced by not only ocular aberrations but also by scattering. Even though the accuracies of the machines used in this study to measure optical quality have yet to be proven, this study showed limited correlation among the values measured using the two different machines after refractive surgery. Therefore, for more generalized evaluation of visual function after refractive surgery, more advanced optical devices still need to be developed.

Retrospective analysis of changes in the anterior corneal surface after Q value guided LASIK and LASEK in high myopic astigmatism for 3 years

Background

To compare the corneal high-order aberrations (HOAs), asphericity and regularity after Q-value guided laser in situ keratomileusis (LASIK) and laser epithelial keratomileusis (LASEK) in high myopic astigmatism.

Methods

In this retrospectively comparative study, we measured the corneal HOAs, asphericity indices (Q values) and corneal regularity indices preoperatively and 36 months postoperatively in 70 eyes (35 patients) with Q-value guided surgeries. All the patients with high myopic astigmatism were divided into two groups which included 34 eyes underwent LASIK and 36 eyes underwent LASEK procedures. The main impact factors of the high-order aberrations were also analyzed.

Results

In the two groups, the efficacy index was more than 1.00 and safety index approached 1.00 at year 3 postoperatively. Statistically significant (P < 0.05) increased in Q values and main corneal HOAs (spherical aberrations and coma) following Q-value guided LASIK and LASEK procedures. Spherical aberrations increased more in the LASEK group and there was statistically difference compared to the LASIK group (P < 0.05). LASEK had better effects in correcting corneal astigmatism (P < 0.05). All the corneal regularity indices after surgeries increased and there was no significant difference (P = 0.707, P = 0.8 and P = 0.224, respectively) between the two groups. The main impact factors of spherical aberration included the optic zone size, changes of Q value, surgical procedure and the corrected refraction.

Conclusions

In high myopic astigmatism, Q-value guided ablation showed good safety, efficacy and predictability. Q value, regularity indices, spherical aberration and coma increased in both LASIK and LASEK procedures. Astigmatism could be corrected more effectively by LASEK but greater spherical aberration could be created. The difference might be related to the different healing mechanisms. Optic zone size and the corrected refraction might be the main influence factors on the anterior corneal high order aberrations.

Meta-analysis of wavefront-guided vs. wavefront-optimized LASIK for myopia

PURPOSE

To detect possible differences in clinical outcomes between wavefront-guided laser in situ keratomileusis (LASIK) and wavefront-optimized LASIK for the treatment of myopia.

METHODS

A comprehensive literature search of Cochrane Library, MEDLINE, and EMBASE to identify relevant trials comparing LASIK with wavefront-guided and wavefront-optimized. A meta-analysis was performed on the results of the reports. Statistical analysis was performed using RevMan 5.0 software.

RESULTS

Seven articles describing a total of 930 eyes were identified. There were no statistically significant differences in the final proportion of eyes achieving uncorrected distance visual acuity of 20/20 or better [odds ratio, 1.04; 95% confidence interval (CI), 0.66 to 1.65; p = 0.86], manifest refractive spherical equivalent within ± 0.50 D of the target (odds ratio, 0.96; 95% CI, 0.53 to 1.75; p = 0.90). No patient lost ≥ 2 lines of distance-corrected visual acuity at posttreatment. The changes in higher order aberrations were not statistically significant different between the two groups with preoperative root-mean-square (RMS) higher order aberrations <0.3 μm (weighted mean difference, 0.01; 95% CI, -0.02 to 0.04; p = 0.57). However, wavefront-guided had a significant better postoperative aberration profile than wavefront-optimized with preoperative RMS higher order aberrations >0.3 μm (weighted mean difference, -0.10; 95% CI, -0.15 to -0.06; p < 0.00001).

CONCLUSIONS

Both wavefront-guided and wavefront-optimized LASIK have shown excellent efficacy, safety, and predictability. The wavefront-guided technology may be a more appropriate choice for patients who have preoperative RMS higher order aberrations >0.3 μm.

Method for expressing clinical and statistical significance of ocular and corneal wave front error aberrations

PURPOSE

The significance of ocular or corneal aberrations may be subject to misinterpretation whenever eyes with different pupil sizes or the application of different Zernike expansion orders are compared. A method is shown that uses simple mathematical interpolation techniques based on normal data to rapidly determine the clinical significance of aberrations, without concern for pupil and expansion order.

METHODS

Corneal topography maps (TOMEY, Inc, Nagoya, Japan) from 30 normal corneas were collected, and the corneal wave front error was analyzed by Zernike polynomial decomposition into specific aberration types for pupil diameters of 3, 5, 7, and 10 mm and Zernike expansion orders of 6, 8, 10, and 12. Using this 4 × 4 matrix of pupil sizes and fitting orders, the best-fitting 3-dimensional functions were determined for the mean and standard deviation of the root-mean-square error for specific aberrations. The functions were encoded into a software application to determine the significance of data acquired from nonnormal cases.

RESULTS

The best-fitting functions for 6 types of aberrations were determined: defocus, astigmatism, prism, coma, spherical aberration, and all higher-order aberrations. A clinical screening method of color coding the significance of aberrations in normal, postoperative laser in situ keratomileusis, and keratoconus cases having different pupil sizes and different expansion orders is demonstrated.

CONCLUSIONS

A method to calibrate wave front aberrometry devices using a standard sample of normal cases was devised. This method could be potentially useful in clinical studies involving patients with uncontrolled pupil sizes or in studies that compare data from aberrometers that use different Zernike fitting-order algorithms.

IntraLase femtosecond laser vs mechanical microkeratomes in LASIK for myopia: a systematic review and meta-analysis

PURPOSE

To evaluate the safety, efficacy, and predictability of IntraLase (Abbott Medical Optics) femtosecond laser-assisted compared to microkeratome-assisted myopic LASIK.

METHODS

A comprehensive literature search of Cochrane Library, PubMed, and EMBASE was conducted to identify relevant trials comparing LASIK with IntraLase femtosecond laser to LASIK with microkeratomes for the correction of myopia. Meta-analyses were performed on the primary outcomes (loss of ≥2 lines of corrected distance visual acuity [CDVA], uncorrected distance visual acuity [UDVA] 20/20 or better, manifest refraction spherical equivalent [MRSE] within ±0.50 diopters [D], final refractive SE, and astigmatism), and secondary outcomes (flap thickness predictability, changes in higher order aberrations [HOAs], and complications).

RESULTS

Fifteen articles describing a total of 3679 eyes were identified. No significant differences were identified between the two groups in regards to a loss of ≥2 lines of CDVA (P=.44), patients achieving UDVA 20/20 or better (P=.24), final UDVA (P=.12), final mean refractive SE (P=.74), final astigmatism (P=.27), or changes in HOAs. The IntraLase group had more patients who were within ±0.50 D of target refraction (P=.05) compared to the microkeratome group, and flap thickness was more predictable in the IntraLase group (P<.0001). The microkeratome group had more epithelial defects (P=.04), whereas the IntraLase group had more cases of diffuse lamellar keratitis (P=.01).

CONCLUSIONS

According to the available data, LASIK with the IntraLase femtosecond laser offers no significant benefits over LASIK with microkeratomes in regards to safety and efficacy, but has potential advantages in predictability.

Effects of advanced surface ablations and intralase femtosecond LASIK on higher order aberrations and visual acuity outcome

BACKGROUND/AIMS

To study the changes in wavefront (ocular) and corneal higher order aberrations (HOAs) and visual acuity (VA) outcome following wavefront-guided advanced surface ablation (ASA) techniques and intralase femtosecond LASIK (iLASIK) in myopia treatment.

METHODS

Ocular aberration and corneal topography of 240 eyes in the ASA techniques (this was equally divided into a flap-on group where the epithelial flap was preserved and reapplied to the photoablated stromal bed and a flap-off group when the epithelial flap was discarded during the procedure), and 138 eyes in the iLASIK group were obtained before and 3 months following treatment. The correlation of aberrations with best spectacle-corrected visual acuity was analyzed.

RESULTS

At 3 months, there was statistically significant (P < 0.001) surgically induced increase in spherical aberration (SA) in each of the techniques for both ocular and corneal analysis. iLASIK induced significantly less ocular and corneal HOAs (P < 0.001). The mean manifest refractive spherical equivalent was closer to attempted correction compared to other groups (P < 0.001). Eighty-three eyes (70%) of flap-on, 80 (67%) flap-off and 94 eyes (68%) in the iLASIK group achieved 20/20 uncorrected VA. Fifteen eyes (11%) accomplished 20/12.5 or better in iLASIK compared to 4 (3%) for flap-on and 7 (6%) for flap-off ASA group. Only the flap-off treatment showed a consistent correlation between the corrected aberrations and visual performance.

CONCLUSION

At 3 months, all procedures resulted in a significant increase in HOAs and SA. All had comparable 20/20 VA and 11% of iLASIK patients achieved 20/12.5 or better level.

Lasers in refractive surgery: history, present, and future

The history of laser refractive surgery is reviewed, followed by an overview of the current state of the field as well as a look at promising future developments.

Visual acuity and higher-order aberrations with wavefront-guided and wavefront-optimized laser in situ keratomileusis

PURPOSE

To compare visual acuity and higher-order aberrations (HOAs) after wavefront-guided and wavefront-optimized laser in situ keratomileusis (LASIK).

METHODS

This retrospective study comprised refraction-matched myopic eyes that had wavefront-guided (Visx Star S4 laser) or wavefront-optimized (WaveLight Allegretto Wave laser) LASIK targeted for emmetropia. Preoperative and postoperative manifest refraction spherical equivalent (MRSE), uncorrected (UDVA) and corrected (CDVA) distance visual acuities, and preoperative and postoperative HOAs were compared.

RESULTS

Preoperatively, there were no significant differences between the wavefront-guided and wavefront-optimized groups in age, sex, corneal thickness, MRSE, or HOAs (all P>.05). The mean MRSE was -2.88 diopters (D) +/- 2.6 (SD) and -2.96 +/- 2.6 D, respectively, preoperatively and -0.01 +/- 0.25 D and -0.02 +/- 0.33 D, respectively, postoperatively; 96% of all eyes were within +/-0.50 D of emmetropia postoperatively. There were no differences in UDVA, CDVA, MRSE, or HOAs between groups (all P>.05). The UDVA was 20/20 or better in 85% of eyes in the wavefront-guided group and 86% of eyes in the wavefront-optimized group. All eyes had 20/25 or better CDVA postoperatively; no eye lost 2 lines of CDVA. Fourteen eyes were converted from wavefront-guided to wavefront-optimized treatment because of poor limbal ring alignment (8 eyes), a wave scan not consistent with the manifest refraction (5 eyes), and no iris registration (1 eye).

CONCLUSIONS

Wavefront-guided LASIK and wavefront-optimized LASIK produced equivalent visual outcomes and no differences in HOAs. Wavefront-guided treatment could not be performed in many eyes because of difficulties during wavefront measurement.

Comparison of higher order aberrations after LASIK and LASEK for myopia

PURPOSE

To compare the change in higher order aberrations (HOAs) after LASIK and laser epithelial keratomileusis (LASEK).

METHODS

This prospective comparative study measured HOAs preoperatively and 3 months postoperatively in 65 eyes (41 patients) that underwent LASIK and 65 eyes (50 patients) that underwent LASEK. Preoperative refraction was limited to myopia up to -5.00 diopters (D) and astigmatism <or=-0.75 D. Patients were matched for age, manifest refraction, and HOAs. All procedures were wavefront-guided using the VISX S4 Star excimer laser (Abbott Medical Optics). Laser in situ keratomileusis flap creation was performed with a Moria ONE Use-Plus disposable microkeratome creating a nasal hinge. Laser epithelial keratomileusis flap creation was performed with 18% v/v unpreserved ethanol instilled for 40 seconds. The epithelium was displaced with an epi-peeler, creating a 6- to 8-mm superior hinge. Higher order aberrations were measured with the NIDEK OPD-Scan II.

RESULTS

Statistically significant (P<.05) changes in five Zernike polynomial terms following LASIK ( Z4-4, Z40, Z44, Z5-3, Z60) were noted. There was a decrease in Zernike term Z5-3 and increases in the remaining four Zernike terms. Statistically significant changes in five Zernike polynomial terms following LASEK ( Z3-1, Z40, Z5-5, Z5-1, Z60) were noted. There was a decrease in Zernike term Z3-1 and increases in the remaining four Zernike terms.

CONCLUSIONS

Wavefront-guided LASIK and LASEK caused increases in spherical aberration, with LASIK additionally causing increases in two fourth order HOAs and LASEK additionally causing increases to two fifth order HOAs. As the same laser treatment was applied, it is presumed that the differences relate to the method of flap creation.

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.

Customized aspheric treatment zone ablation to treat irregular corneas after corneal refractive surgery

PURPOSE

To describe the retreatment of highly aberrated corneas due to previous keratorefractive surgery using topography-guided aspheric treatments.

METHODS

Eight eyes (five patients) with reduced mesopic visual quality due to previous keratomileusis, excimer laser surgery, or radial keratotomy underwent retreatment with the customized aspheric treatment zone (CATz) algorithm with the CXIII excimer laser (NIDEK Co Ltd) to correct corneal wavefront aberrations. Before CATz treatments, all patients were satisfied with their preoperative photopic vision (all 20/30 or better uncorrected) yet were dissatisfied with their vision at night. All eyes had >20 microm (range: 20 to 33 microm) of corneal irregularity before CATz retreatment. All eyes had a flap cut or flap lift procedure for CATz retreatment.

RESULTS

One year after treatment with CATz, no eyes lost best spectacle-corrected visual acuity (BSCVA); all eyes had BSCVA of 20/30 or better. Mean modulation transfer function increased by 13% by the end of the first postoperative year. A 0.45-microm decrease was noted in coma 1 year postoperatively.

CONCLUSIONS

The CATz algorithm is effective in the treatment of severe corneal irregularities due to previous corneal surgery.

Higher-order aberrations after wavefront-optimized photorefractive keratectomy and laser in situ keratomileusis

PURPOSE

To analyze the changes in higher-order aberrations (HOAs) that occur after wavefront-optimized photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK).

SETTING

Emory Eye Center and Emory Vision, Atlanta, Georgia, USA.

METHODS

This retrospective analysis comprised eyes that had PRK or LASIK from June 2004 through October 2005. Postoperative outcome measures included 3-month uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest refraction spherical equivalent (MRSE), changes in the root mean square (RMS) and grouped coefficient HOAs (microns) measured with a corneal analyzer, and subjective assessment of visual aberrations.

RESULTS

One hundred consecutive eyes of 54 patients had PRK, and 100 contemporaneous consecutive eyes of 71 patients had LASIK. The PRK and LASIK populations were similar in general demographics, preoperative HOAs, and postoperative UCVA and BSCVA. The mean MRSE was slightly hyperopic after PRK (mean +0.11 diopters [D]) and slightly myopic after LASIK (mean -0.19 D) (P< .0001). There were no statistically significant changes in RMS or grouped coefficient HOA values after PRK or LASIK, nor were there significant differences in postoperative RMS or grouped coefficient HOA values between PRK and LASIK. One percent of PRK and LASIK patients reported a subjective increase in postoperative visual aberrations; 5% reported a subjective improvement postoperatively.

CONCLUSIONS

Wavefront-optimized excimer laser surgery did not induce significant HOAs after PRK or LASIK. The 2 techniques were equally efficacious and had equivalent postoperative HOA profiles.

Comparative study of higher-order aberrations after conventional laser in situ keratomileusis and laser epithelial keratomileusis for myopia using the technolas 217z laser platform

PURPOSE

To examine changes in higher-order aberrations (HOAs) after PlanoScan laser in situ keratomileusis and (LASIK) and laser epithelial keratomileusis (LASEK).

DESIGN

Prospective, comparative study.

METHODS

Myopic patients undergoing LASIK (65 eyes of 36 patients) and LASEK (50 eyes of 28 patients) at a private practice were selected randomly. Surgery was performed using the Technolas 217z laser (Bausch & Lomb, Surrey, United Kingdom). Main outcome measures included uncorrected visual acuity (UCVA), manifest refractive spherical equivalent (MRSE), and aberrometry (Zywave; Bausch & Lomb, Rochester, New York, USA) and were recorded before surgery and at three and 12 months after surgery.

RESULTS

There was no statistical difference between both groups in terms of MRSE (P = .91), ablation depth (P = .47), scotopic pupil size (P = .38), or optical zone (P = .07). Before surgery, there was no statistical difference in root mean square (RMS) of total (P = .70), third- (P = .79), fourth- (P = .23), and fifth- (P = .33) order aberrations and individual terms. Three months after surgery, RMS of total HOA was raised significantly more (P = .03) after LASIK (1.46-factor increase) than LASEK (1.25-factor increase). One year after surgery, a reduction in total HOAs was observed in 13.8% of LASIK- and 48.5% of LASEK-treated eyes compared with preoperative levels.

CONCLUSIONS

Postoperative increases in total HOA and vertical coma were significantly greater in LASIK- than in LASEK-treated eyes. Postoperative reduction in total HOAs was observed in a number of eyes with high preoperative levels and occurred more frequently in LASEK-treated eyes.

Wavefront-guided LASIK for the correction of primary myopia and astigmatism a report by the American Academy of Ophthalmology

OBJECTIVE

To describe wavefront-guided (WFG) LASIK for the primary treatment of low to moderate levels of myopia and astigmatism and to examine the evidence on the safety and effectiveness of the procedure in comparison with conventional LASIK.

METHODS

Literature searches conducted in 2004, 2005, 2006, and 2007 retrieved 209 unique references from the PubMed and Cochrane Library databases. The panel selected 65 articles to review, and of these, chose 45 articles that they considered to be of sufficient clinical relevance to submit to the panel methodologist for review. During the review and preparation of this assessment, an additional 2 articles were included. A level I rating was assigned to properly conducted, well-designed, randomized clinical trials; a level II rating was assigned to well-designed cohort and case-controlled studies; and a level III rating was assigned to case series, case reports, and poorly designed prospective and retrospective studies. In addition, studies that were conducted by laser manufacturers before device approval (premarket approval) were reviewed as a separate category of evidence.

RESULTS

The assessment describes studies reporting results of WFG LASIK clinical trials, comparative trials, or both of WFG and conventional LASIK that were rated level II and level III. There were no studies rated as level I evidence. Four premarket approval studies conducted by 4 laser manufacturers were included in the assessment. The assessment did not compare study results or laser platforms because there were many variables, including the amount of follow-up, the use of different microkeratomes, and the level of preoperative myopia and astigmatism.

CONCLUSIONS

There is substantial level II and level III evidence that WFG LASIK is safe and effective for the correction of primary myopia or primary myopia and astigmatism and that there is a high level of patient satisfaction. Microkeratome and flap-related complications are not common but can occur with WFG LASIK, just as with conventional LASIK. The WFG procedure seems to have similar or better refractive accuracy and uncorrected visual acuity outcomes compared with conventional LASIK. Likewise, there is evidence of improved contrast sensitivity and fewer visual symptoms, such as glare and halos at night, compared with conventional LASIK. Even though the procedure is designed to measure and treat both lower- and higher-order aberrations (HOAs), the latter are generally increased after WFG LASIK. The reasons for the increase in HOA are likely multifactorial, but the increase typically is less than that induced by conventional LASIK. No long-term assessment of WFG LASIK was possible because of the relatively short follow-up (12 months or fewer) of most of the studies reviewed.

[Application of wavefront analysis in clinical and scientific settings. From irregular astigmatism to aberrations of a higher order--Part II: examples]

In recent years, wavefront analysis has ceased to be purely a laboratory application and emerged as a method used in ophthalmological diagnosis. This development has been promoted mainly by the widespread use of wavefront-guided LASIK (laser in situ keratomileusis). However, aberrometry is still not a common diagnostic technique, and for many ophthalmologists interpretation of the results is difficult. The second part of this serial paper reviews findings that are relevant for the ophthalmological community and highlights current scientific applications in this area.

Higher-order aberrations and visual acuity after LASEK

BACKGROUND

To determine ocular higher-order aberrations (HOAs) in eyes with supernormal vision after myopic astigmatic laser subepithelial keratomileusis (LASEK) and to compare the findings with those in eyes with natural supernormal vision.

METHODS

Ocular HOAs were measured after LASEK in 20 eyes of 12 myopic astigmatic patients with postoperative uncorrected visual acuity (UCVA) of >20/16 (group 1). Patients who were included in the study had no visual symptoms like glare, halo or double vision. The measurements were taken 8.3 +/- 3 months after LASEK surgery. In group 2 ocular HOAs were examined in 20 eyes of 10 subjects with natural UCVA of >20/16 as a control. Measurements were taken across a pupil with a diameter of 4.0 mm and 6.0 mm. Root-mean-square (RMS) values of HOAs, Z(3)-1, Z(3)1, Z(4)0, Z(5)-1, Z(5)1 and Z(6)0 were analyzed.

RESULTS

The mean RMS values for each order were higher in group 1 when compared with group 2 at 4.0 mm and 6.0 mm pupil diameters. There was no statistically significant difference between groups in spherical and coma aberrations (P > 0.05). Mean RMS values for total HOAs were 0.187 +/- 0.09 microm at 4.0 mm and 0.438 +/- 0.178 microm at 6.0 mm pupil in group 1 and 0.120 +/- 0.049 microm at 4.0 mm and 0.344 +/- 0.083 microm at 6.0 mm pupil in group 2. The difference between groups in total HOAs was statistically significant at 4.0 mm and 6.0 mm pupil diameters (P < 0.05).

CONCLUSION

Ocular HOAs exist in eyes with supernormal vision. After LASEK, the amount of HOAs of the eye increases under both mesopic and photopic conditions. However the amount of HOA increase does not seem to be consistent with visual symptoms.