Wavefront-guided ablation: evidence for efficacy compared to traditional ablation

Topography-guided treatment in regular and irregular corneas

Over the last decade, refractive surgery has been revolutionized by advancements in ablation profiles, available for the treatment of both regular and irregular corneas. Advances in corneal imaging have helped highlight the presence of higher-order aberrations, the correction of which could result in a better quality of vision. Topographic measurements being static are more repeatable and pupil independent and therefore provide the ideal platform for correction of both lower and higher-order aberrations and could result in improved visual quality even in patients with seemingly regular corneas. The combination of topography-guided treatment with collagen cross-linking has further increased the scope of treating irregular corneas like keratoconus, post-laser in-situ keratomileusis ectasia, and pellucid marginal degeneration. This review delves into the current literature and guidelines available for the topographic treatment of regular and irregular corneas.

Anatomical and Visual Outcomes after LASIK Performed in Myopic Eyes with the WaveLight® Refractive Suite (Alcon® Laboratories Inc., USA)

Purpose

To evaluate changes in corneal anatomy and quality of vision following LASIK refractive surgery for mild to high myopia using the WaveLight® Refractive Suite (Alcon® Laboratories Inc., USA). Setting. Rothschild Foundation, Paris, France.

Design

Prospective interventional case series.

Methods

We examined 60 myopic eyes (average SE −4.5 D, from −9.3 to −0.75 D) of 30 patients from 21.3 to 38.7 years old. Pachymetry, keratometry, Q factor, corneal aberrations, visual acuity (VA), contrast sensitivity, dry eye assessment, and quality of vision were measured preoperatively, one day (D1), and 1, 3, and 6 months postoperatively.

Results

6 months postoperatively, keratometry became flatter, and the Q factor became more oblate (from −0.18 ± 0.08 to +0.19 ± 0.06). Pachymetry decreased by 117.9 ± 62.2 µm at D1 and increased by 37.87 ± 32.6 µm between D1 and M6. Refraction was emmetropic at D1 and remained stable thereafter. Six months after surgery, VA was slightly but nonsignificantly improved (<0.05 log MAR), whereas contrast sensitivity remained unchanged. Quality of vision was not affected by surgery and was more related to dry eye symptoms than to corneal HOAs (r² = 0.49; p < 0.001 vs. r² = 0.03; p < 0.001).

Conclusions

LASIK surgery for moderate to high myopia, performed with the WaveLight® Refractive Suite, showed good postoperative outcomes, with demonstrated safety, predictability, efficiency, and stability. This is probably due to well-controlled spherical aberration and the use of large optical zones. Besides, we can assume that the patients' quality of vision depends more on the postoperative dry eye disease generated by the laser than on the induced HOAs.

Topography-guided versus wavefront-optimized laser in situ keratomileusis for myopia: Surgical outcomes

PURPOSE

To compare the outcomes of topography-guided and wavefront-optimized surgery in patients having laser in situ keratomileusis (LASIK) for myopia.

SETTING

Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, and BALGEUN-EYE21 Operation Center, Gwangju, South Korea.

DESIGN

Prospective case study.

METHODS

Patients had topography-guided LASIK in 1 eye and wavefront-optimized LASIK in the contralateral eye using Contoura Vision software and the WaveLight EX500 excimer laser. Refractive and visual outcomes were analyzed 3 months postoperatively.

RESULTS

The study comprised 43 patients. In both groups, the postoperative uncorrected distance visual acuity (UDVA) was 0.0 logarithm of the minimum angle of resolution or better in 90.7% of eyes and the residual spherical equivalent (SE) refractive error was ±0.75 diopter (D) in 81.4% of eyes. The UDVA, residual SE refractive error, and astigmatism did not differ significantly between the 2 groups. There was significant induction of higher-order aberrations (HOAs) in both groups, although corneal coma and trefoil did not increase and ocular trefoil decreased significantly in the topography-guided group (P = .038). However, in the wavefront-optimized group, corneal coma and trefoil increased significantly (P < .001 and P = .046, respectively) and ocular trefoil did not change significantly. In addition, topography-guided LASIK induced significantly fewer corneal total HOAs (P < .001), coma (P < .001), and trefoil (P = .020) than wavefront-optimized LASIK.

CONCLUSION

Although both topography-guided LASIK and wavefront-optimized LASIK safely and effectively achieved the predicted refractive and visual outcomes, topography-guided LASIK induced fewer HOAs and significantly decreased ocular trefoil, corneal total HOAs, and coma.

Effect of Iris registration on visual outcome in wavefront-guided LASEK for myopic astigmatism

PURPOSE

This study aimed to investigate the effect of iris registration (IR) on visual outcomes in wavefront-guided LASEK for myopic astigmatism.

METHODS

The retrospective chart review was performed for wavefront-guided LASEK using VISX Star S4 in patients with myopic astigmatism (cylinder ≥ 1.00 diopter[D]). Eyes were divided into IR group (LASEK with IR at the time of surgery) and Non-IR group (LASEK without IR system + failed-IR engagement during LASEK). Visual acuity (VA), astigmatism, higher-order aberration (HOA), and contrast sensitivity were assessed preoperatively and 3 months postoperatively. The IR and Non-IR groups were subcategorized depending on the spherical equivalent (lower myopia ≤-5.00 D vs. higher myopia >-5.00 D) for the comparison of HOA changes.

RESULTS

Postoperative uncorrected VAs showed no differences between IR (n = 30) and Non-IR (n = 46). In astigmatic vector analyses, no differences were noted in the mean magnitude of error and the mean angle of error between two groups. There were no differences in postoperative total HOA, spherical aberration (SA), coma, and trefoil between the groups, either. The total HOA and SA increased in both groups, while coma increased only in Non-IR. In higher myopia, ΔRMS of coma was smaller in IR. Preoperative and postoperative total HOA were linearly correlated in Non-IR, but not for IR. Contrast sensitivity of 12 cycles per degree improved in both groups.

CONCLUSION

IR had similar outcomes to conventional trackers in wavefront-guided LASEK, with less tendency of inducing coma, especially in higher myopia.

The Characteristics of Excimer Laser Refractive Surgery Candidates

PURPOSE

To determine the demographic and refractive characteristics of excimer laser refractive surgery candidates in Iran.

METHODS

This was a cross-sectional study between 2010 and 2014. All information was collected from 28 centers randomly selected from 12 provinces. Then, for each season of the year, one week was chosen through simple random selection, and within each week, 3 days were again chosen randomly. All excimer laser surgical procedures performed during these 3 days were identified by training staff, and data were extracted from patient charts.

RESULTS

A total of 14,569 charts were reviewed; 67.5% of the subjects were female and the rest were male. Of the total surgeries, 18.6% had been done in 2010 which reached to 19.1% in 2014. The mean age of people receiving refractive surgery showed an upward trend (P<0.001) and female patients were significantly younger than male patients (P<0.001). The 25 to 39 years age group received the highest number of surgeries (31.9% of the total) and there was a significant association with gender (P<0.001). The most common refractive error was compound myopic astigmatism with a prevalence of 79.3%. In 2010, 33.3% of the performed surgeries were covered by insurance policies, and this decreased to 30.2% in 2014 (P<0.001).

CONCLUSION

Women with compound myopic astigmatism in the age range of 25 and 35 years are the most frequent users of excimer laser refractive surgery. Less than one-third of laser refractive surgeries are covered by insurance policies. Therefore, proper planning for improving services to this group must be given priority.

Wavefront-guided versus wavefront-optimized photorefractive keratectomy: Clinical outcomes and patient satisfaction

PURPOSE

To compare visual outcomes following Visx Star S4 Customvue wavefront-guided and Allegretto Wave Eye-Q 400 Hz wavefront-optimized photorefractive keratectomy (PRK).

SETTING

Warfighter Refractive Eye Surgery Program and Research Center, Fort Belvoir, Virginia, and Walter Reed National Military Medical Center, Bethesda, Maryland, USA.

DESIGN

Prospective randomized clinical trial.

METHODS

Active-duty United States military soldiers were randomized to have wavefront-guided (Visx Star S4 Customvue) or wavefront-optimized PRK. Participants were followed up to 12 months postoperatively. Primary outcome measures were uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and manifest spherical equivalent (SE). Secondary outcome measures included refractive astigmatism, higher-order aberrations (HOAs), contrast sensitivity, subjective visual complaints, and patient satisfaction.

RESULTS

The study evaluated 108 soldiers (mean age 30.3 years ± 6.3 [SD]; mean manifest SE -3.51 ± 1.63 D). At 12 months postoperatively, achieved UDVA, CDVA, manifest SE, and refractive astigmatism were comparable between wavefront-guided and wavefront-optimized groups (P > .213). Spherical aberration and total HOAs significantly increased from baseline in both groups (P < .006). The change in coma, trefoil, spherical aberration, and total HOAs (P > .254) were comparable between groups. There were fewer losses of photopic low-contrast visual acuity (LCVA) at 5% contrast after wavefront-guided compared to wavefront-optimized treatment (P = .003). There was no significant difference between treatment groups in visual symptoms, overall vision expectation, and satisfaction (P > .075).

CONCLUSION

Wavefront-guided treatment offered a small advantage in photopic LCVA. Refractive outcomes, HOAs, self-reported visual difficulties, overall vision expectation, and satisfaction were otherwise comparable between wavefront-guided and wavefront-optimized treatments.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Efficacy of Wavefront-guided Photorefractive Keratectomy with Iris Registration for Management of Moderate to High Astigmatism by Advanced Personalized Treatment Nomogram

Purpose:

To evaluate the efficacy of photorefractive keratectomy (PRK) using the advanced personalized treatment (APT) nomogram for correction of moderate to high astigmatism.

Methods:

This prospective interventional case series included 60 consecutive eyes of 30 patients undergoing wavefront-guided PRK (Zyoptix 217 Z100 excimer laser, Bausch & Lomb, Munich, Germany) using the APT nomogram and iris registration for myopic astigmatism. Mitomycin-C was applied intraoperatively in all eyes. Ophthalmic examination was performed preoperatively and 1, 3 and 6 months postoperatively.

Results:

Preoperatively, mean sphere was -1.68 ± 2.08 diopters (D), mean refractive astigmatism was -3.04 ± 1.05 D and mean spherical equivalent (SE) was -3.12 ± 1.77 D. Six months postoperatively, mean sphere was + 0.60 ± 0.64 D (P < 0.005), mean cylinder was -0.43 ± 0.46 D (P < 0.005) and mean SE was + 0.28 ± 0.48 D (P < 0.005). Hyperopic overcorrection (≥ +1.0 D) occurred in 3 (5%) eyes. Postoperatively, root mean square (RMS) of higher order aberrations (HOAs) was significantly increased (P = 0.041). RMS of spherical aberration (Z [4, 0]) showed no significant change after surgery (P = 0.972).

Conclusion:

Considering the acceptable residual refractive error, low rate of hyperopic overcorrection, acceptable uncorrected visual acuity, and low risk of postoperative corneal haze, PRK using the APT nomogram with iris registration and mitomycin-C use is a safe and effective modality for treatment of moderate to high astigmatism.

Comparison of corneal shape changes and aberrations induced By FS-LASIK and SMILE for myopia

PURPOSE

To compare corneal curvatures, corneal power calculations, and higher-order aberrations (HOAs) of femtosecond laser-assisted LASIK (FS-LASIK) with small incision lenticule extraction (SMILE) following surgery for moderate to high myopia.

METHODS

A retrospective study of 736 eyes of 368 patients treated with SMILE and 148 eyes of 74 patients treated with FS-LASIK. Preoperative mean spherical equivalent was -7.3 ± 1.5 diopters in the SMILE group and -7.6 ± 1.3 diopters in the FS-LASIK group. Corneal curvatures, corneal power calculations performed by ray tracing, and HOAs measured with Scheimpflug technology before and 3 months after surgery were analyzed.

RESULTS

Corneal curvatures changed significantly in the anterior corneal surface, but not in the posterior corneal surface, in both groups; after SMILE, the sagittal curvature was constant for the central 4-mm diameter, in contrast to FS-LASIK where the curvature showed a gradual steepening with increasing diameter. Corneal power calculations were different across the cornea depending on the measurement diameter between the two groups postoperatively. Measured over a 5-mm zone on the total cornea, FS-LASIK induced 0.11 µm more coma (P < .001) and 0.13 µm higher spherical aberration (P < .001) as compared to SMILE; similar results in other HOAs were seen for the anterior corneal surface. Negligible differences in HOAs were induced on the posterior corneal surface.

CONCLUSIONS

SMILE and FS-LASIK produced distinct changes in anterior corneal shape evident in different postoperative corneal curvatures and power measurements between the two groups. Postoperative HOAs were much lower after SMILE as compared to FS-LASIK.

Wavefront-guided versus non-wavefront-guided photorefractive keratectomy for myopia: meta-analysis of randomized controlled trials

Purpose

To compare the efficacy, predictability, safety, and induced higher-order aberrations (HOAs) between wavefront-guided and non-wavefront-guided photorefractive keratectomy (PRK).

Methods

The Cochrane Central Register of Controlled Trials, PubMED, and EMBASE were searched for randomized controlled trials. Trials meeting the selection criteria were quality appraised, and data was extracted by 2 independent authors. Measures of association were pooled quantitatively using meta-analytical methods. Comparisons between wavefront-guided and non-wavefront-guided ablations were made as pooled odds ratios (ORs) or weighted mean differences. The pooled ORs and 95% confidence intervals (CIs) were computed for efficacy, safety, and predictability. The weighted mean differences and 95% CIs were used to compare induced HOAs.

Results

The study covered five trials involving 298 eyes. After wavefront-guided PRK, the pooled OR of achieving an uncorrected distance visual acuity of 20/20 (efficacy) was 1.18 (95% CI, 0.53–2.60; p = 0.69), the pooled OR of achieving a result within ±0.50 diopter of the intended target (predictability) was 0.86 (95% CI, 0.40–1.84; p = 0.70). No study reported a loss of 2 or more lines of Snellen acuity (safety) with either modality. In eyes with wavefront-guided PRK, the postoperative trefoil aberrations (mean difference −0.02; 95% CI, −0.03 to −0.00; p = 0.03) were significantly lower. There were no significant differences between the two groups in the postoperative total HOAs (mean difference −0.04; 95% CI, −0.23 to 0.14; p = 0.63), spherical (mean difference 0.00; 95% CI, −0.08 to 0.09; p = 0.93), and coma (mean difference −0.06; 95% CI, −0.14 to 0.03; p = 0.20) aberrations.

Conclusions

According to the meta-analysis, wavefront-guided PRK offered no advantage in efficacy, predictability, or safety measures over non-wavefront-guided PRK, although it may have induced fewer trefoil aberrations.

Accounting for the phase, spatial frequency and orientation demands of the task improves metrics based on the visual Strehl ratio

Advances in ophthalmic instrumentation have allowed high order aberrations to be measured in vivo. These measurements describe the distortions to a plane wavefront entering the eye, but not the effect they have on visual performance. One metric for predicting visual performance from a wavefront measurement uses the visual Strehl ratio, calculated in the optical transfer function (OTF) domain (VSOTF) (Thibos et al., 2004). We considered how well such a metric captures empirical measurements of the effects of defocus, coma and secondary astigmatism on letter identification and on reading. We show that predictions using the visual Strehl ratio can be significantly improved by weighting the OTF by the spatial frequency band that mediates letter identification and further improved by considering the orientation of phase and contrast changes imposed by the aberration. We additionally showed that these altered metrics compare well to a cross-correlation-based metric. We suggest a version of the visual Strehl ratio, VScombined, that incorporates primarily those phase disruptions and contrast changes that have been shown independently to affect object recognition processes. This metric compared well to VSOTF for letter identification and was the best predictor of reading performance, having a higher correlation with the data than either the VSOTF or cross-correlation-based metric.

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.

Custom vs conventional PRK: a prospective, randomized, contralateral eye comparison of postoperative visual function

PURPOSE

To determine whether VISX S4 (VISX Inc) custom photorefractive keratectomy (PRK) results in better visual outcomes than VISX S4 conventional PRK.

METHODS

Photorefractive keratectomy was performed on 80 eyes from 40 patients in this randomized, prospective, contralateral eye study. Dominant eyes were randomized to one group with the fellow eye receiving the alternate treatment. Primary outcome measures included uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), contrast sensitivity, and root-mean-square (RMS) higher order aberrations.

RESULTS

Mean UDVA was -0.023±0.099 (20/19) in the custom group and -0.044±0.080 (20/18) in the conventional group 6 months after surgery (P=.293). Mean CDVA was -0.073±0.067 (20/17) in the custom group and -0.079±0.071 (20/17) in the conventional group 6 months after surgery (P=.659). Total higher order aberration RMS and spherical aberration increased in both groups compared to preoperative values (P<.05). Coma increased in the conventional group (P<.05) whereas it was similar to preoperative values in the custom group. No significant differences were noted in induction of trefoil.

CONCLUSIONS

Custom and conventional PRK were shown to be safe and effective with excellent visual acuity and contrast sensitivity performance at 6 and 12 months. Conventional PRK induced more coma than custom PRK; however, this did not seem to correlate with clinical outcomes.

Wavefront analysis and Zernike polynomial decomposition for evaluation of corneal optical quality

Wavefront-guided excimer laser refractive surgery and new customized intraocular lens and contact lens designs are major clinical applications of corneal wavefront analysis. Other therapeutic applications include corneal disorders, conventional excimer laser refractive surgery, incisional techniques and cataract surgery, corneal transplantation, intrastromal corneal ring segment implantation, and crosslinking therapy. Basic data regarding corneal wavefront aberrations, such as distribution in the population and changes with aging, are essential for understanding the nature of each aberration and correcting it. Corneal aberrometry also improved our comprehension of the optical effects of the aforementioned topics while helping us assess the success of the procedures. Zernike polynomials are representations of the higher- and lower-order aberrations of the cornea, allowing a mathematical approach to their determination. Polynomials are used to model individual components of the wavefront in familiar terms. This article reviews the current knowledge of the wavefront aberrations of the human cornea and analyzes studies in the fields of anterior segment surgery and/or therapy, diseases, and optical quality in the context of this knowledge.

Validity of scaling zernike coefficients to a larger diameter for refractive surgery

PURPOSE

To investigate the validity of a Zernike rescaling algorithm to a larger wavefront diameter.

METHODS

Using 4256 preoperative wavefront examinations, the variability of inter-examination wavefront root-mean-square (RMS) was compared to the error induced due to scaling Zernike coefficients to a larger diameter. The validity of scaling Zernike coefficients was set when the error due to the scaling was the same as the variability of the inter-examination wavefronts. The inter-examination variability was calculated from eyes having at least 3 same-day, preoperative examinations over the same diameters. Error from scaling Zernike coefficients to a larger diameter was calculated by comparing the wavefront for a (scaled-up) set of Zernike coefficients to the wavefront of the average of Zernike coefficient sets at a larger diameter for the same eye. Wavefront diameters of 5, 5.5, 6, 6.5, and 7 mm were considered.

RESULTS

No significant difference was found for the variability for different pupil sizes. The error due to scaling Zernike coefficients to a larger pupil size was generally smaller than the inter-examination variability when the new diameter was 0.25 mm larger than the original diameter. The error was comparable to the inter-examination variability when the new diameter was 0.5 mm larger. The error became larger when the new diameter was >0.75 mm larger than the original diameter.

CONCLUSIONS

Rescaling Zernike coefficients from a smaller diameter to a larger one has practical applications in optical zone extension for wavefront-guided refractive surgery.

Efficacy, predictability, and safety of wavefront-guided refractive laser treatment: metaanalysis

PURPOSE

To compare the efficacy, predictability, safety, and induced higher-order aberrations (HOAs) between wavefront-guided and non-wavefront-guided ablations.

SETTING

Division of Ophthalmology and Visual Sciences, University of Nottingham, Nottingham, United Kingdom.

DESIGN

Metaanalysis.

METHODS

The Cochrane Central Register of Controlled Trials, PubMED, and EMBASE were searched for randomized controlled trails. Trials meeting the selection criteria were quality appraised and data extracted by 2 independent authors. Measures of association were pooled quantitatively using metaanalytical methods. Comparison between wavefront-guided and non-wavefront-guided ablations was measured as pooled odds ratios (ORs) or weighted mean differences. The pooled ORs and 95% confidence intervals (CIs) were computed for efficacy, safety, and predictability. The weighted mean difference and 95% CIs were used to compare induced HOAs.

RESULTS

Eight trials involving 955 eyes were included. After wavefront-guided LASIK, the pooled OR of achieving uncorrected distance visual acuity (UDVA) of 20/20 (efficacy) was 1.10 (95% CI, 0.66-1.83; P=.72), the pooled OR of achieving a result within ± 0.50 diopter of intended target (predictability) was 1.03 (95% CI, 0.60-1.75; P=.92), and the weighted mean difference in induced HOAs was -0.09 (95% CI, -0.17 to -0.01; P=.04). No study reported loss of 2 or more lines of Snellen acuity (safety) with either modality.

CONCLUSIONS

Metaanalysis showed no clear evidence of a benefit of wavefront-guided over non-wavefront-guided ablations. However, there was a lack of standardized reporting of UDVA better than 20/20, which might mask an advantage in wavefront-guided treatment. With high preexisting HOAs, wavefront-guided has advantages over non-wavefront-guided treatment.

In vivo measurements of thermal load during ablation in high-speed laser corneal refractive surgery

PURPOSE

To evaluate the thermal load of ablation in high-speed laser corneal refractive surgery with the AMARIS excimer laser (SCHWIND eye-tech-solutions).

METHODS

Thermal load from refractive corrections on human corneas using a 500-Hz laser system with a fluence of 500 mJ/cm(2) and aspheric ablation profiles was recorded with an infrared thermography camera. Each single in vivo measurement was analyzed and temperature values were evaluated.

RESULTS

Overall, the maximum temperature change of the ocular surface induced by the refractive ablations was ≤4°C. The increase in the peak temperature of the ocular surface never exceeded 35°C in any case. This low thermal load was independent of the amount of correction the eye achieved.

CONCLUSIONS

The thermal load of the ablation in high-speed laser corneal refractive surgery was minimized using a computer algorithm to control the peak temperature to avoid corneal collagen denaturation with minimal compromise on treatment duration.

Temporal evolution of ocular aberrations following laser in situ keratomileusis

PURPOSE

To study the temporal evolution of ocular aberrations after standard LASIK to correct myopia.

METHODS

The ocular, corneal and internal aberrations for a 6-mm pupil were measured in 22 young myopic eyes (n = 12 subjects; range -2.0 to-7.6 D) before and during a 9-month follow-up after standard myopic LASIK. Ocular aberrations were measured with a Hartmann-Shack wavefront sensor, while corneal aberrations were estimated from the elevation data obtained by corneal topography. For every patient and condition the eye's modulation transfer function (MTF) and Strehl ratio (SR) were calculated.

RESULTS

Compared to preoperative results, we found that standard myopic LASIK produced a significant increase of ocular high-order aberrations at 1 month after surgery. During the next 8 months, we found a small increase of ocular and corneal positive spherical aberration (SA), although with a large inter-subject variability. However, all eyes treated for myopia higher than -5 D showed a significant increase of positive SA during the first 6 months after surgery.

CONCLUSIONS

Standard myopic LASIK decreases ocular optical quality. For most subjects, the increase in aberrations induced by the surgery was stable during the next 9 months after LASIK. However, further changes of the ocular SA after myopic LASIK are possible in patients treated for higher amounts of myopia. The changes in aberrations mainly appeared between the first and the sixth month after surgery, which suggests the need to wait at least 6 months after myopic LASIK before comparing outcomes, especially for patients treated for higher myopias.

Higher-order aberration changes after Implantable Collamer Lens implantation for myopia

PURPOSE

To investigate the changes in higher-order aberrations (HOAs) induced by implantation of Implantable Collamer Lenses (STAAR Surgical) and to explain them in relation to the surgical incision and optical properties.

DESIGN

Prospective, observational case study.

METHODS

This study included 56 eyes undergoing Implantable Collamer Lens insertion for myopic correction. The corneal incision size was determined according to the amount of astigmatism. HOAs were measured before surgery and 3 months after surgery in 25 eyes having small superior incision (<3.2 mm) surgery and in 31 eyes with large superior incision (3.2 to 4.5 mm) surgery. Changes in spherical aberration, coma, trefoil, and total HOAs (third to sixth order) were analyzed. Laboratory measurements of aberration profiles of Implantable Collamer Lenses with different optical powers were performed to validate clinical measurements.

RESULTS

In the small-incision group, trefoil (Z(3)(-3)) and spherical aberration changed significantly (P=.004). In the large-incision group, in addition to trefoil and spherical aberration, total HOA changed significantly (mean change, 0.13 ± 0.17; P=.001). Significant correlations were observed among the incision size, the astigmatism induced, and the trefoil induced. Induced trefoil showed a predominant pattern at the orientation of the incision meridian. Optical measurement of aberrations of the Implantable Collamer Lenses confirmed the postoperative negative spherical aberration.

CONCLUSIONS

HOA changes after Implantable Collamer Lens insertion were increased trefoil and induced negative spherical aberration. These changes may be explained by the effect of the corneal incision and the negative spherical aberration in the Implantable Collamer Lens, respectively.

Patient-Specific Modeling of Corneal Refractive Surgery Outcomes and Inverse Estimation of Elastic Property Changes

The purpose of this study is to develop a 3D patient-specific finite element model (FEM) of the cornea and sclera to compare predicted and in vivo refractive outcomes and to estimate the corneal elastic property changes associated with each procedure. Both eyes of a patient who underwent laser-assisted in situ keratomileusis (LASIK) for myopic astigmatism were modeled. Pre- and postoperative Scheimpflug anterior and posterior corneal elevation maps were imported into a 3D corneo-scleral FEM with an unrestrained limbus. Preoperative corneal hyperelastic properties were chosen to account for meridional anisotropy. Inverse FEM was used to determine the undeformed corneal state that produced <0.1% error in anterior elevation between simulated and in vivo preoperative geometries. Case-specific 3D aspheric ablation profiles were simulated, and corneal topography and spherical aberration were compared at clinical intraocular pressure. The magnitude of elastic weakening of the residual corneal bed required to maximize the agreement with clinical axial power was calculated and compared with the changes in ocular response analyzer (ORA) measurements. The models produced curvature maps and spherical aberrations equivalent to in vivo measurements. For the preoperative property values used in this study, predicted elastic weakening with LASIK was as high as 55% for a radially uniform model of residual corneal weakening and 65% at the point of maximum ablation in a spatially varying model of weakening. Reductions in ORA variables were also observed. A patient-specific FEM of corneal refractive surgery is presented, which allows the estimation of surgically induced changes in corneal elastic properties. Significant elastic weakening after LASIK was required to replicate clinical topographic outcomes in this two-eye pilot study.

Changes in higher order wavefront aberrations after contact lens corneal refractive therapy and LASIK surgery

PURPOSE

To compare ocular higher order aberrations induced by corneal refractive therapy (CRT, Paragon Vision) to those produced by LASIK for patients with comparable levels of myopia.

METHODS

A retrospective chart review of 11 patients who used CRT lenses and 12 patients who underwent LASIK for correction of low to moderate myopia was performed. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest refraction, and optical higher order aberrations were recorded before and 1 month after treatment for each patient.

RESULTS

The CRT group consisted of 11 patients (4 men, 7 women) with a mean age of 29.1+/-5.2 years (range: 23 to 40 years), and the LASIK group consisted of 12 patients (3 men, 9 women) with a mean age of 39.2+/-12.0 years (range: 23 to 60 years). Manifest refraction decreased statistically significantly from -2.81+/-1.05 diopters (D) at baseline to -0.77+/-0.64 D following CRT treatment at 1 month (P<.0001) and from -3.11+/-1.21 D at baseline to -0.43+/-0.27 D at 1 month after LASIK (P<.0001). Both CRT and LASIK exhibited no significant changes in total higher order aberrations for 4-mm pupils but induced statistically significant increases in total higher order aberrations for 6-mm pupils. Corneal refractive therapy and LASIK both exhibited statistically similar factors of change for total higher order aberrations and coma-like higher order aberrations for 6-mm pupils. Corneal refractive therapy demonstrated a statistically significant greater factor of increase in spherical-like higher order aberrations for 6-mm pupils (P=.01).

CONCLUSIONS

Contact lens corneal refractive therapy and LASIK can effectively correct myopia, but both increase higher order aberrations for 6-mm pupils to a similar degree. However, spherical-like aberrations were statistically significantly greater after CRT than after LASIK.

Comparison of custom ablation and conventional laser in situ keratomileusis for myopia and myopic astigmatism using the Alcon excimer laser

PURPOSE

To compare the refractive outcomes, higher order aberrations, and contrast sensitivity after laser in situ keratomileusis (LASIK) using wavefront ablation and conventional ablation.

SETTING

Private practice in Córdoba, Spain and a free-standing outpatient surgery center.

METHODS

This was a prospective, nonrandomized, observational case series comparing outcomes of 239 eyes that underwent LASIK for myopia and myopic astigmatism with either wavefront or conventional ablation using the LADARVISION excimer laser. Manifest refractive sphere ranged from 0.50 D to -8.00 D with astigmatism up to -4.00 D. Eighty-nine eyes underwent conventional LASIK (conventional group), and 150 eyes underwent custom ablation (custom group). Refractive outcomes, ocular higher order root mean square (HOA-RMS), and contrast sensitivity were tested for statistically significant differences between groups. A P-value less than 0.05 was considered statistically significant. Six month postoperative data are reported here.

RESULTS

Postoperatively, the mean SE was -0.03 D +/- 0.19 D for the custom group, and -0.14 D +/- 0.35 D for the conventional group (P = 0.003). Ninety-nine percent of the eyes in the custom group, and 92% of the eyes in the conventional group were within 0.50 D of the intended correction (P > 0.05). The HOA-RMS was 0.16 mum lower in the custom group (P < 0.001). Contrast sensitivity was statistically significantly better at 3 cycles per degree (cpd) (P < 0.001) and 6 cpd (P = 0.009) in the custom group.

CONCLUSION

There was a statistically significant lower induction of HOA-RMS and better predictability and contrast sensitivity in eyes that underwent custom ablation with the LADARVISION excimer laser.

LASIK for myopia and astigmatism using the SCHWIND AMARIS excimer laser: an international multicenter trial

PURPOSE

To assess the efficacy, predictability, and safety of LASIK for the surgical correction of low to moderate myopia with astigmatism using the SCHWIND AMARIS excimer laser.

METHODS

Six international study sites enrolled 358 eyes with a manifest refraction spherical equivalent (MRSE) from -0.50 to -7.38 diopters (D) (mean sphere: -3.13+/-1.58 D) with up to -5.00 D of astigmatism (mean: -0.69+/-0.67 D). All eyes underwent treatment with the nonwavefront-guided aspheric algorithm of the SCHWIND AMARIS excimer laser. All eyes were targeted for emmetropia. Refractive outcomes and corneal higher order aberrations were analyzed pre- and postoperatively. Visual quality was assessed using photopic and mesopic contrast sensitivity. Six-month postoperative outcomes are reported.

RESULTS

At 6 months postoperative, the MRSE for all eyes was -0.21+/-0.20 D, and 96% (343/358) of eyes had MRSE within +/-0.50 D. Uncorrected visual acuity was 20/20 or better in 98% (351/358) of eyes, and no eyes lost 2 or more lines of best spectacle-corrected visual acuity. The total corneal higher order aberrations root-mean-square increased by 0.09 microm, spherical aberration increased by 0.08 microm, and coma increased by 0.04 microm postoperatively. Photopic and mesopic contrast sensitivity did not change 6 months postoperatively.

CONCLUSIONS

Treatment of myopia with astigmatism using the SCHWIND AMARIS excimer laser is safe, efficacious, predictable, and maintains visual quality.

The SCHWIND AMARIS Total-Tech Laser as An All-Rounder in Refractive Surgery

PURPOSE

To describe and argument an overview of the main features and unique technical points of AMARIS Total-Tech Laser, coupled with patient outcomes supporting the decision to perform LASIK treatments with maximised outcomes.

SETTINGS

Dr. M.C. Arbelaez, Muscat Eye Laser Center, Muscat, Sultanate of Oman.

METHODS

The findings collected during 18-month experience using SCHWIND AMARIS Total-Tech Laser have been reviewed to provide arguments for supporting the decision to perform LASIK treatments with maximised outcomes. For updated clinical outcomes, the last 100 myopic astigmatism treatments, the last 100 hyperopic astigmatism treatments, the last 30 ocular-wavefront-guided treatments, and the last 30 corneal-wavefront-guided treatments, all with 6-month follow-up, were included. For all those, LDV femtosecond system was used to prepare the flaps, and AMARIS flying spot system was used to perform ablations. Clinical outcomes were evaluated in terms of predictability, refractive outcome, safety, wavefront aberration, and contrast sensitivity.

RESULTS

6-month postoperatively, mean defocus was -0.14+/-0.31D and astigmatism 0.25+/-0.37D. 70+/- eyes were within +/-0.25D of emmetropia. 43+/- eyes gained lines of best spectacle-corrected visual acuity. For Aberration-Free treatments, none of the aberration metrics changed from pre- to postoperative values in a clinically relevant amount. For ocular-wavefront-guided treatments, the surgery did not change coma or spherical aberration, and reduced trefoil (p<0.005). For corneal-wavefront-guided treatments, the trefoil, coma, and spherical aberrations, as well as the total root-mean-square values of higher order aberration, were significantly reduced (p<.05) when the pre-existing aberrations were greater than the repeatability and the biological noise.

CONCLUSIONS

Although this review does not allow for evidence-based conclusions, following our strategy, LASIK results were excellent. LASIK surgery with AMARIS system yield excellent outcomes. Refractions were reduced to subclinical values with no induction of High-Order-Aberrations. Neither adverse events nor complications were observed.

Effects of monochromatic aberration on visual acuity using adaptive optics

PURPOSE

To investigate the effect on visual acuity of correcting specific Zernike aberrations.

METHODS

Visual acuity was tested for 12 young subjects using a Freiburg Acuity Test procedure under conditions with wavefront aberrations corrected by an adaptive optics system. The adaptive optics system consists of a Hartmann-Shack wavefront sensor, a deformable mirror, relevant optical channels and closed loop control system. Five aberration correction paradigms were used to correct different Zernike terms.

RESULTS

With the second order aberration fully corrected, a significant improvement in visual acuity was observed (0.056 logMAR, t = 2.79, p = 0.018). Further correction of third order Zernike aberrations resulted in an additional improvement of 0.041 logMAR (t = 2.63, p = 0.023). But an additional correction of spherical aberration did not produce a significant increase in visual acuity (t = 1.10, NS). Full correction of aberrations achieved the best visual acuity with an improvement of 0.022 logMAR (t = 2.46, p = 0.032). The visual acuity was found to increase with the root mean square values of the residual aberrations with a linear relationship (r = 0.63, p < 0.0001).

CONCLUSIONS

Correction of monochromatic wavefront aberrations improves visual acuity for normal eyes and the improvement of visual acuity is proportional to the change of root mean square of wavefront aberrations.

Experimental evaluation of optimized ablation patterns for laser refractive surgery

A new experimental model based on plastic (Filofocon A) artificial eyes was used to study the ablation profiles and the outcomes of three state-of-the-art refractive surgery excimer lasers provided with narrow-beam flying spot and optimized algorithms (Ladarvision 4000, Alcon; Technolas 217 Z100, Bausch and Lomb; Allegretto wave Eye-Q, Wavelight). The 3-D ablation patterns produced by myopic laser corrections (-9, -6 and -3 D) on flat and spherical surfaces of Filofocon A were measured using high resolution optical profilometry. We found significant differences across lasers in the shape and depth of the ablation patterns. A comparison of the ablation patterns on flat and on spherical surfaces provided a measurement of the laser efficiency losses from the center to the periphery at each point of the spherical plastic corneas. This effect also varied across lasers, depending on their fluence (120-400 mJ/cm(2)). Estimates of the post-operative corneal shapes were obtained from the measurement on Filofocon A and plastic-corneal tissue correction factors. The predicted post-operative corneal ablation shape, ablated volume, asphericity and spherical aberration varied across lasers, as well as the relative contribution of ablation pattern designs and efficiency losses to the increased asphericity. Although the results show that the algorithms have been optimized to reduce the induction of spherical aberration, they would still benefit from the application of correction factors for efficiency effects derived from a systematic approach using experimental plastic models. These models have proved useful (1) to assess the outcomes of different lasers or ablation algorithms, (2) for precise calibration and testing of the lasers, and (3) to calculate experimental correction factors for efficiency effects.

A comparison of corneal cellular responses after 213-nm compared with 193-nm laser photorefractive keratectomy in rabbits

PURPOSE

Corneal refractive surgery is typically performed using a 193-nm excimer laser. However, a recently developed 213-nm solid-state (5th harmonic) Nd:YAG laser presents some practical and user safety advantages, although the biological impact of using this wavelength remains poorly characterized. Here, we provide in vivo and in vitro comparisons of the corneal cellular outcomes after irradiation with 213 and 193 nm wavelengths.

METHODS

New Zealand White rabbits underwent photorefractive keratectomy with -5 diopters and a 6.5-mm optical zone and studied at time points up to 1 year. The development of haze was examined ophthalmologically and by detecting myofibroblasts immunohistochemically. Cell death was quantified using a terminal deoxynucleotidyl transferase-dUTP nick end labeling (TUNEL) assay, and the number of stromal keratocytes undergoing apoptosis estimated histologically. Superoxide dismutase activity was estimated in vitro by enzyme-linked immunosorbent assay in irradiated rabbit corneal keratocytes.

RESULTS

Our results demonstrate subtle differences in the cellular outcomes after irradiation with 213- and 193-nm lasers, despite similar degrees of corneal haze developing in both treatment groups. In vivo, the 213-nm laser results in more stable stromal cell numbers, implying a more predictable ablation outcome. In vitro, higher levels of superoxide dismutase in corneal keratocytes irradiated with 213 nm compared with 193 nm wavelengths suggest a better endogenous protection against free radicals induced by laser surgery.

CONCLUSIONS

The more favorable cellular responses after irradiation with 213 nm compared with 193 nm wavelengths are consistent with good clinical outcomes previously reported. Ablation with a 213 nm wavelength may result in better wound healing, leading to a more reliable correction of refractive errors.

Visual performance after reduced blinking in eyes with soft contact lenses or after LASIK

PURPOSE

To evaluate visual performance during concentrated visual work in patients wearing soft contact lenses or after LASIK.

METHODS

Thirty-one eyes of 17 patients who had worn soft contact lenses before LASIK were examined by the following tests immediately and 10 seconds after eye opening: 1) functional visual acuity, which is defined as visual acuity measured after prolonged eye opening without blinking; 2) surface regularity index (SRI) and surface asymmetry index (SAI) in corneal topography; and 3) higher order aberration measured with NIDEK OPD-Scan. Results were compared in the same patients before (with soft contact lenses and no eye surgery) and 1 month after LASIK (without soft contact lenses).

RESULTS

Functional visual acuity was significantly decreased 10 seconds after eye opening compared with immediately after eye opening, both with soft contact lenses and after LASIK, and decreased to a greater extent with soft contact lenses. The SRI and SAI were significantly increased 10 seconds after eye opening compared with immediately after eye opening, both with soft contact lenses and after LASIK, and increased to a greater extent with soft contact lenses. Higher order aberration was increased 10 seconds after eye opening with soft contact lenses, but not after LASIK.

CONCLUSIONS

Our results suggest that prolonged eye opening induces a decreased quality of vision in eyes of soft contact lens wearers and after LASIK. Under conditions in which blinking is restricted due to concentrated visual work, such as visual display terminal work, reading, and driving, visual performance may be more compromised with soft contact lens wear than after LASIK.

A retrospective comparison of LASIK outcomes for myopia and myopic astigmatism with conventional NIDEK versus wavefront-guided VISX and Alcon platforms

POSE: To compare visual, refractive, and safety outcomes among a non-wavefront scanning-slit laser (NIDEK EC-5000) and wavefront-driven lasers (Alcon CustomCornea and VISX CustomVue).

METHODS

A retrospective comparison of outcomes for 290 eyes that underwent LASIK for myopia and myopic astigmatism with either a conventional or custom ablation excimer laser system were compared. The preoperative refractive error and age of the patients were matched. Outcomes were tested for statistically significant differences among the conventional laser and each of the custom ablation lasers. A P value <.05 was considered statistically significant. Data with 3-month follow-up are reported.

RESULTS

Postoperatively, mean manifest refraction spherical equivalent was -0.12+/-0.31 diopters (D) (range: -1.50 to 0.75 D) for the NIDEK group, -0.13+/-0.39 D (range: -1.88 to 0.75 D) for the VISX group, and -0.06+/-0.26 D (range: -0.75 to 0.75 D) for the Alcon group. Eighty-nine percent of eyes in the NIDEK group, 88% of eyes in the VISX group, and 92% of eyes in the Alcon group were within a half-diopter of intended correction. None of the NIDEK and VISX eyes and 3% of Alcon eyes lost 2 or more lines of best spectacle-corrected visual acuity. No statistically significant differences in any of the outcomes studied between conventional and custom ablation treatments were noted (P>.05).

CONCLUSIONS

No statistically significant differences were observed in safety, efficacy, or predictability of eyes that underwent conventional ablation with the NIDEK EC-5000 scanning slit laser compared to custom ablation with the VISX CustomVue or Alcon CustomCornea laser systems.

Advanced personalized nomogram for myopic laser surgery: first 100 eyes

PURPOSE

To report the results in the first 100 eyes treated for myopia using a new advanced nomogram.

SETTING

Private refractive surgery clinic.

METHODS

This prospective interventional case series comprised 58 patients (100 eyes) consecutively treated for myopia with laser in situ keratomileusis (LASIK) or laser-assisted subepithelial keratectomy (LASEK) performed by the same surgeon. All treatments used a new nomogram for the Zyoptix 217 Z100 excimer laser. Postoperative mean sphere, cylinder, and spherical equivalent (SE) refraction were evaluated 3 months postoperatively. Safety, efficacy, and predictability were also evaluated.

RESULTS

In the LASIK group (34 eyes), the mean postoperative sphere was +0.18 diopters (D) +/- 0.47 (SD), the mean postoperative cylinder was -0.10 +/- 0.23 D, and the mean postoperative SE was 0.04 +/- 0.36 D. In the LASEK group (64 eyes), the respective means were 0.10 +/- 0.22 D, -0.05 +/- 0.13 D, and +0.03 +/- 0.16 D. Hyperopic overcorrection (> or = +1.00 D) occurred in 4.1% of patients. Ninety-five percent of eyes in the LASIK group and 97% of eyes in the LASIK group had an uncorrected visual acuity of 1.0 (20/20) or better. Patient satisfaction was slightly higher than that of other laser refractive surgery patients at the clinic.

CONCLUSIONS

The use of the advanced nomogram increased treatment accuracy in terms of UCVA and postoperative mean refraction and reduced the rate of hyperopic overcorrection over that in earlier studies. The need for enhancement procedures was reduced, and patient satisfaction was high.

Advances in technologies for laser-assisted in situ keratomileusis (LASIK) surgery

Laser-assisted in situ keratomileusis (LASIK) has become the most widely used form of refractive surgery today. The objective of this surgical technique is to modify the anterior corneal shape by ablating tissue from the stroma by means of the excimer laser after creating a hinged corneal flap. This way, we are able to change the refractive status of the patient, providing better unaided vision. Continuous improvements in the original technique have made the surgical procedure safer, more accurate and repeatable. These progressions are due to the development of novel technologies that are the responsible for new surgical instrumentation, which makes the surgical procedure easier for the surgeon, and better excimer laser ablation algorithms, which increase the optical quality of the ablation and thus the safety of the vision correction procedure. This article aims to describe the more relevant advances in LASIK that have played an important role in the spread and popularity of this technique.

[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.

Corneal wavefront-guided retreatments for significant night vision symptoms after myopic laser refractive surgery

PURPOSE

To evaluate the results of corneal wavefront (WF)-guided enhancements in patients with night vision symptoms and significantly high positive spherical aberration (SA) after myopic laser refractive surgery.

DESIGN

Noncomparative, interventional case series.

METHODS

Twenty-eight eyes of 20 patients with significant night vision symptoms and positive corneal SA (Z(4)(0)) higher than 0.5 microm after myopic laser refractive surgery were included in the study at Vissum-Instituto Oftalmologico de Alicante, Spain. Enhancement surgery was planned to remove residual refractive error and corneal SA (Z(4)(0)) in all cases. All patients underwent corneal WF-guided excimer laser retreatments using the ESIRIS/SCHWIND excimer laser system (Schwind Eye Tech Solutions, Kleinostham, Germany). The main outcome measures were visual symptoms, change in corneal SA (Z(4)(0)), and corneal asphericity (Q-value).

RESULTS

Subjective reports of night vision symptoms were improved in all patients. Mean corneal SA (Z(4)(0)) decreased from 0.75 +/- 0.19 microm before surgery to 0.43 +/- 0.42 microm after surgery (P < .001). Mean asphericity in the 4.5-mm zone significantly decreased from 1.02 +/- 1.07 before surgery to 0.52 +/- 0.88 after surgery (P = .008), and the mean asphericity in 8 mm did not change significantly (P = .362). The mean spherical equivalent significantly shifted to hyperopia from -0.22 +/- 1.14 diopters (D) before surgery to 0.33 +/- 0.54 D after surgery (P = .025).

CONCLUSIONS

Cornea wavefront-guided retreatment was effective in improving subjective night vision symptoms, reducing corneal SA, and decreasing asphericity in eyes that underwent myopic laser refractive surgery.

Higher Order Aberrations Comparison in Fellow Eyes Following IntraLase LASIK With WaveLight Allegretto and CustomCornea LADARVision4000 Systems

PURPOSE

To compare the differences in objective and subjective visual outcomes with wavefront-optimized versus wavefront-guided excimer laser ablations using two different excimer laser platforms.

METHODS

In this prospective, randomized, matched, contralateral eye study, one eye was treated with the Alcon CustomCornea system, and the fellow eye was treated with the WaveLight Allegretto Wavefront-Optimized system. The IntraLase FS30 femtosecond laser was used to create all flaps. Treatments were randomized to the dominant eye, and optical treatment zones were matched to 6.5 mm. Patients were observed for 3 months after surgery. Initial data analysis was available for the first 28 eyes of 14 patients.

RESULTS

The only statistically significant differences between the groups were seen in the amount of higher order aberrations-the 14 eyes in the WaveLight group had a mean preoperative root-mean-square (RMS) error of 0.37 microm compared to 0.36 microm for 14 eyes in the Alcon group. Of the 8 patients who had 3-month follow-up, 8 eyes in the WaveLight group had a mean RMS error of 0.58 microm at 3 months, compared to 0.41 microm in the 8 eyes in the Alcon group.

CONCLUSIONS

Early results from this study have shown that both laser platforms produce accurate refractive outcomes; however, the Alcon CustomCornea LADARVision4000 system induces statistically significantly fewer higher order aberrations than the WaveLight Allegretto system.