Photorefractive keratectomy with aspheric profile of ablation versus conventional photorefractive keratectomy for myopia correction

Typical localised element-specific finite element anterior eye model

Purpose

The study presents an averaged anterior eye geometry model combined with a localised material model that is straightforward, appropriate and amenable for implementation in finite element (FE) modelling.

Methods

Both right and left eye profile data of 118 subjects (63 females and 55 males) aged 22-67 years (38.5 ± 7.6) were used to build an averaged geometry model. Parametric representation of the averaged geometry model was achieved through two polynomials dividing the eye into three smoothly connected volumes. This study utilised the collagen microstructure x-ray data of 6 ex-vivo healthy human eyes, 3 right eyes and 3 left eyes in pairs from 3 donors, 1 male and 2 females aged between 60 and 80 years, to build a localised element-specific material model for the eye.

Results

Fitting the cornea and the posterior sclera sections to a 5th-order Zernike polynomial resulted in 21 coefficients. The averaged anterior eye geometry model recorded a limbus tangent angle of 37° at a radius of 6.6 mm from the corneal apex. In terms of material models, the difference between the stresses generated in the inflation simulation up to 15 mmHg in the ring-segmented material model and localised element-specific material model were significantly different (p < 0.001) with the ring-segmented material model recording average Von-Mises stress 0.0168 ± 0.0046 MPa and the localised element-specific material model recording average Von-Mises stress 0.0144 ± 0.0025 MPa.

Conclusions

The study illustrates an averaged geometry model of the anterior human eye that is easy to generate through two parametric equations. This model is combined with a localised material model that can be used either parametrically through a Zernike fitted polynomial or non-parametrically as a function of the azimuth angle and the elevation angle of the eye globe. Both averaged geometry and localised material models were built in a way that makes them easy to implement in FE analysis without additional computation cost compared to the limbal discontinuity so-called idealised eye geometry model or ring-segmented material model.

A comparison between wavefront-optimized and wavefront-guided photorefractive keratectomy in patients with moderate-to-high astigmatism: A randomized clinical trial

Purpose:

Methods:

Results:

Conclusion:

Contralateral Eye Study of Topography Guided versus Q Value Adjusted Photorefractive Keratectomy in Myopia and Myopic Astigmatism

Purpose of the Study

To compare visual outcome, higher order aberrations (HOAs) of topography guided and Q value adjusted ablation in the fellow eye of patients undergoing photorefractive keratectomy (PRK) for the correction of myopia and myopic astigmatism.

Methods

Prospective randomized controlled interventional clinical study. The eyes of 52 patients undergoing PRK for myopia and astigmatism were included, that is, 104 eyes in total. In each patient, eyes were randomly allocated to group I: one eye received topography guided PRK using Contoura ablation software, or group II: the other eye received Q value adjusted PRK using Custom Q ablation software.

Follow-Up

Six months.

Results

At the end of 6 months, LogMAR UDVA was -0.04 ± 0.12 and -0.05 ± 0.11 (p = 0.688), while LogMAR CDVA was -0.06 ± 0.09 and -0.06 ± 0.1 in group I and group II, respectively (p = 0.972). Both groups showed a progressive oblate shift with time. This oblate shift was insignificantly less in group I by Topolyzer at 6mm, 15° and 30° at 6 months (p = 0.102, p = 0.138, p = 0.245, respectively). Topolyzer identified a significant difference between the change in coma and trefoil in both groups at 6 months (p<0.001 and p = 0.001, respectively). This was caused by the significant worsening of coma in group II (p<0.001) and the significant improvement of trefoil in group I (p = 0.007). No significant difference was found between groups in the change of ISV or ABR (p = 0.955 and 0.982, respectively). Ablation depth is a significant predictor of ΔQ at 6mm, 15° and 30° (p = 0.009, 0.039 and 0, respectively). No significant difference was found in the Strehl ratio or contrast sensitivity, although they were insignificantly better in group I (p = 0.785 and p = 0.745, respectively).

Conclusion

TG PRK and CQ PRK yielded similar results regarding UDVA, CDVA, MRSE, safety, predictability and contrast sensitivity. Both groups showed a progressive oblate shift, which was less in the TG group but the difference was statistically insignificant. TG PRK showed significantly improved trefoil HOA as compared to CQ PRK.

Comparison of Wavefront-Guided Femtosecond LASIK and Optimized SMILE for Correction of Moderate-to-High Astigmatism

PURPOSE

To compare refractive outcomes, higher order aberrations (HOAs), and the changes in contrast sensitivity after wavefront-guided femtosecond laser-assisted in situ keratomileusis (WFG LASIK) and optimized small incision lenticule extraction (SMILE) for moderate-to-high astigmatism correction.

METHODS

This prospective, randomized study included 87 eyes: 40 eyes in the WFG LASIK group and 47 eyes in the SMILE group. Manual cyclotorsion compensation by marking the horizontal axis before SMILE surgery was used for optimized SMILE. Refractive diopter, aberrations, and contrast sensitivity were assessed 3 months postoperatively. The Alpins vector analysis method was used to analyze the astigmatic changes after surgery.

RESULTS

There were no significant differences in the corrected distance visual acuity and refraction between the two groups after surgery. The fitted curve of surgically induced astigmatism versus target induced astigmatism was described as y = 0.9905 x + 0.0009 in the WFG LASIK group and y = 0.9672 x + 0.0026 in the SMILE group. The percentage of corneal astigmatism axis change within 5 degrees was statistically significant (chi-square test: 10.632, P = .001). HOAs increased in both the WFG LASIK and SMILE groups after surgery (t = -3.655, P = .001, t = -3.784, P = .001, respectively). However, comparison of the changes of HOAs between both groups was not significant (t = -0.565, P = .575). The improvement in contrast sensitivity in the WFG LASIK group was significantly higher than that in the SMILE group.

CONCLUSIONS

WFG LASIK and optimized SMILE can achieve similar outcomes for astigmatism correction. Optimized SMILE with marking could achieve good astigmatism correction, even without an eye tracking system. [J Refract Surg. 2021;37(3):166-173.].

Limbus misrepresentation in parametric eye models

Purpose

To assess the axial, radial and tangential limbus position misrepresentation when parametric models are used to represent the cornea and the sclera.

Methods

This retrospective study included 135 subjects aged 22 to 65 years (36.5 mean ±9.8 STD), 71 females and 64 males. Topography measurements were taken using an Eye Surface Profiler topographer and processed by a custom-built MATLAB code. Eye surfaces were freed from edge-effect artefacts and fitted to spherical, conic and biconic models.

Results

When comparing the radial position of the limbus, average errors of -0.83±0.19mm, -0.76±0.20mm and -0.69±0.20mm were observed within the right eye population for the spherical, conic and biconic models fitted up to 5mm. For the same fitting radius, the average fitting errors were -0.86±0.23mm, -0.78±0.23mm and -0.73±0.23mm for the spherical, conic and biconic models respectively within the left eye population. For the whole cornea fit, the average errors were -0.27±0.12mm and -0.28±0.13mm for the spherical models, -0.02±0.29mm and -0.05±0.27mm for the conic models, and -0.22±0.16mm and 0.24±0.17mm for the biconic models in the right and left eye populations respectively.

Conclusions

Through the use of spherical, conic and biconic parametric modelling methods, the eye’s limbus is being mislocated. Additionally, it is evident that the magnitude of fitting error associated with the sclera may be propagating through the other components of the eye. This suggests that a corneal nonparametric model may be necessary to improve the representation of the limbus.

Comparison of clinical outcomes between wavefront-optimized versus corneal wavefront-guided transepithelial photorefractive keratectomy for myopic astigmatism

PURPOSE

To evaluate and compare the clinical outcomes, including visual acuity, refractive errors, and aberrations, between aberration-free transepithelial photorefractive keratectomy (PRK) and corneal wavefront-guided transepithelial PRK in eyes with myopic astigmatism.

SETTING

Yonsei University College of Medicine and Eyereum Eye Clinic, Seoul, South Korea.

DESIGN

Retrospective comparative case series.

METHODS

Patients with myopic astigmatism were treated with aberration-free transepithelial PRK or corneal wavefront-guided transepithelial PRK using a 1050 Hz high-repetition excimer laser. The safety, efficacy, predictability, and corneal aberrations were compared preoperatively and 1, 2, 3, and 6 months postoperatively.

RESULTS

The study comprised 188 patients (188 eyes); 91 eyes had aberration-free transepithelial PRK and 97 eyes corneal wavefront-guided transepithelial PRK. Six month after surgery, the mean uncorrected distance visual acuity was comparable (-0.06 logMAR ± 0.07 [SD] aberration-free group; -0.06 ± 0.06 logMAR wavefront-guided group). The safety, efficacy, and predictability of refractive and visual outcomes were also comparable between groups. Corneal total root-mean-square (RMS) higher-order aberrations (HOAs) increased after treatment in both groups, although fewer RMS HOAs were induced in the corneal wavefront-guided group than in the aberration-free group. Spherical aberration increased similarly after treatment in both groups. However, coma and trefoil increased only in the aberration-free group.

CONCLUSIONS

Aberration-free transepithelial PRK and corneal wavefront-guided transepithelial PRK were safe and effective for correction of myopic astigmatism without difference in visual acuity and refractive outcomes. However, the corneal wavefront-guided profile induced fewer corneal aberrations than the aberration-free profile.

Distribution and related factors of corneal regularity and posterior corneal astigmatism in cataract patients

Purpose

To study the distribution of posterior corneal astigmatism (PCA) and its influencing factors in Chinese patients before cataract surgery.

Patients and methods

A retrospective study was conducted in the First Affiliated Hospital of Soochow University, Suzhou, China. In all, this study enrolled 121 eligible eyes of 121 cataract patients. The astigmatism, aberrations and Q value of anterior, posterior and total cornea and anterior segment parameters (ACD, CCT, WTW, ATA) were measured by the Sirius System, and AL was measured by Lenstar LS 900. Cataract was diagnosed using slit-lamp examination.

Results

The mean age of patients was 67.44±10.66 years old. Mean PCA was 0.31±0.17 (range 0.05–1.09) D and 85.9% eyes had PCA values <0.5 D. With-the-rule (WTR) astigmatism predominated the anterior cornea astigmatism (ACA) (48.8%) and total corneal astigmatism (TCA) (61.2%), while against-the-rule (ATR) astigmatism predominated posterior (86.0%). Significant positive correlation was found between the astigmatic power vector (APV) of ACA and PCA (Pearson correlation=0.318, P<0.001); TCA and PCA (Pearson correlation=0.204, P=0.025); keratometric astigmatism and PCA (Pearson correlation=0.356, P<0.001); this study also found a positive correlation between primary spherical aberration (Z4°) of the total cornea and PCA (Pearson correlation=0.266, P=0.003); primary spherical aberration (Z4°) of the corneal front surface and PCA (Pearson correlation=0.260, P=0.004); total corneal aberrations (Total cornea root mean square [RMS]) and PCA (Pearson correlation=0.327, P<0.001); total corneal higher-order aberrations (Total HOA RMS) (Pearson correlation=0.232, P=0.011); total corneal lower-order aberrations (Total LOA RMS) (Pearson correlation=0.250, P=0.006). A positive linear correlation between Q value of corneal front surface and PCA, either 6 mm pupil diameter (Pearson correlation=0.264, P=0.003) or 8 mm pupil diameter (Pearson correlation=0.184, P=0.043) was found in this study.

Conclusion

Corneal aberration, Q value (front surface specifically) was essential that we need to take into consideration when we conduct PCA and intraocular lens measurement in clinics.

Comparison between Wavefront-optimized and corneal Wavefront-guided Transepithelial photorefractive keratectomy in moderate to high astigmatism

BACKGROUND

To compare the clinical outcomes of wavefront-optimized (WFO) transepithelial photorefractive keratectomy (trans-PRK) and corneal wavefront-guided (CWFG) trans-PRK for myopic eyes with moderate to high astigmatism.

METHODS

One hundred ninety-six eyes (196 patients) with moderate to high astigmatism (≥ 1.75 D) treated with WFO or CWFG trans-PRK (101 and 95 eyes, respectively) were retrospectively registered. Safety, efficacy, predictability, vector analysis, and corneal aberrations were compared between groups preoperatively and at 6 months postoperatively.

RESULTS

At postoperative 6 months, the mean logMAR uncorrected distance visual acuity was similar in the WFO (- 0.07 ± 0.08) and CWFG (- 0.07 ± 0.07) groups. Safety, efficacy, and predictability of refractive and visual outcomes were also similar. The correction indices were 1.02 ± 0.14 and 1.03 ± 0.13 in the WFO and CWFG groups, respectively, with no significant difference. The absolute values of the angle of error were significantly higher in the WFO group (2.28 ± 2.44 vs. 1.40 ± 1.40; P = 0.002). Corneal total root mean square higher-order aberrations and corneal spherical aberrations increased postoperatively in both groups; however, the change was smaller in the CWFG group. Corneal coma showed a significant increase postoperatively only in the WFO group.

CONCLUSIONS

WFO and CWFG trans-PRK are safe and effective for correcting moderate to high astigmatism. However, CWFG trans-PRK provides a more predictable astigmatism correction axis and fewer induced corneal aberrations.

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.

Visual performance after excimer laser photorefractive keratectomy for high myopia

PURPOSE:

To evaluate the efficacy, safety, predictability, and visual performance of excimer laser photorefractive keratectomy (PRK) for myopia greater than −8 diopters (D).

METHODS:

Fifty-four patients (104 eyes) with myopia from −8D to −13D and cylinder up to −4D received surface ablation technique with the Allegretto wave version 1009-1 excimer laser to correct their refractive error. The patients were examined on days 1, 3, 7, and 14 and 1, 3, 6, and 12 months postoperatively. Visual acuity, manifest refraction, corneal haze, topography, intraocular pressure, contrast sensitivity, and wavefront aberration were evaluated.

RESULTS:

Twelve months postoperatively, 95% of eyes were within 1D of the intended correction. In addition, 94% of eyes had attained uncorrected distance visual acuity of 20/25 or better, and 98% of eyes had improved or remained their corrected distance visual acuity. All eyes exhibited barely detectable corneal haze which peaked during the 1^st month with a gradual reduction in the 3^rd month. Ninety-five percent of patients had no or only mild degree of night glare.

CONCLUSIONS:

Excimer laser PRK is an effective and predictive treatment for high myopia greater than −8D with or without astigmatism up to −4D. The incidence of complication is low. All patients who are candidates for laser in situ keratomileusis can be candidates for surface ablation, especially those with preoperative thinner cornea or higher risk of corneal flap complications.

A pilot study: LASEK with the Triple-A profile of a MEL 90 for mild and moderate myopia

Background

To investigate the visual and refractive outcomes in patients with mild to moderate myopia after laser-assisted subepithelial keratectomy (LASEK) using the 500 Hz pulse rate of the Triple-A profile.

Methods

Thirty-six eyes of 20 patients (mean age, 27.5 ± 4.6 years) were included in this prospective, consecutive study. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), corneal topography, and corneal aberrations were measured preoperatively and 1 day, 1 week, 1, 3 and 6 months post-operation.

Results

At 1 week after surgery, UDVA was better than or equal to 20/25 in all eyes. At postoperative 6 months, the efficacy and safety index was 1.05 ± 0.13 and 1.12 ± 0.15, respectively; all eyes had a UDVA of 20/20 or better, and no eyes showed a loss in CDVA; 100% of the eyes were within ±1.00 D of the attempted spherical equivalent (SE) correction.

Conclusion

The postoperative results indicate that using the Triple-A ablation profile of the MEL 90 excimer laser with a 500 Hz pulse rate is a safe, efficient, and predictable method to correct mild to moderate myopia.

Comparison of clinical outcomes in PRK with a standard and aspherical optimized profile: a full case analysis of 100 eyes with 1-year follow-up

PURPOSE

One hundred eyes from 55 adult patients with myopia were retrospectively studied to determine the comparative safety, efficacy, and predictability of aberration smart ablation (ASA) and a new advanced ablation algorithm (Triple-A) using the MEL(®) 80 excimer laser.

METHODS

Fifty myopic eyes with a manifest refraction spherical equivalent (MRSE) between -1.0 diopters (D) and -9.75 D were consecutively treated with photorefractive keratec-tomy ASA, and 50 myopic eyes with an MRSE between -1.38 D and -11.0 D with photorefractive keratectomy Triple-A. Uncorrected distance visual acuity, MRSE, the absolute value of the cylinder, corrected distance visual acuity, and postoperative complications at 1 month, 3 months, 6 months, and 12 months (1 year) were descriptively analyzed and compared at 1 year.

RESULTS

After 12 months, the MRSE variance was statistically significantly better in patients triaged to receive Triple-A compared with patients receiving ASA (ASA, ±0.7 D; Triple-A, ±0.15 D; P<0.001). Furthermore, no patient in the Triple-A group had any cylinder postoperatively. Patients in the Triple-A treatment arm achieved a superior result. No statistically significant difference in the two treatment arms was noted for the analysis of the mean MRSE at 12 months (P=0.78).

CONCLUSION

Triple-A was more effective than standard aspherical surgical intervention in a number of treatment outcome parameters (eg, MRSE, astigmatism, efficacy index). The two surgical procedures were equivalent in terms of safety.

Topographic analysis of the centration of the treatment zone after SMILE for myopia and comparison to FS-LASIK: subjective versus objective alignment

PURPOSE

To evaluate the centration of the treatment zone after small incision lenticule extraction (SMILE) and compare it to femtosecond laser-assisted LASIK (FS-LASIK).

METHODS

Sixty-nine myopic eyes of 36 patients who underwent SMILE were compared to 69 myopic eyes of 36 patients treated with FS-LASIK. All procedures were performed by a single surgeon using the VisuMax platform (Carl Zeiss Meditec, Jena, Germany). The Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany) was used for preoperative and postoperative topography and pachymetry. The centration of the treatment zone was estimated pachymetrically by the distance of the thickest point on the corneal thickness differential map from the topographical center of the entrance pupil and the coaxial corneal light reflex.

RESULTS

In SMILE cases, the mean decentration of the lenticule from the center of the entrance pupil was 0.326 ± 0.196 mm (range: 0.014 to 1.062 mm), whereas the distribution of the lenticule centers demonstrated a nasalization pattern. In FS-LASIK cases, this value was 0.452 ± 0.224 mm (range: 0.02 to 1.040 mm), whereas the ablation centers were distributed randomly. In relation to the coaxial corneal light reflex, the decentration in SMILE was 0.315 ± 0.211 mm (range: 0.0 to 1.131 mm), whereas FS-LASIK eyes demonstrated a mean decentration of 0.516 ± 0.254 mm (range: 0.103 to 1.265 mm). The decentration from the reference point of its technique (coaxial corneal light reflex in SMILE, the entrance pupil center in FS-LASIK) was significantly more extended in the FS-LASIK group (P < .001).

CONCLUSIONS

The centration of the treatment zone as measured by the Pentacam was better for patient-controlled fixation during SMILE than active eye tracker-assisted 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.

Three different aspheric treatment algorithms of laser-assisted sub-epithelial keratectomy in patients with high myopia

PURPOSE

To compare visual outcomes and quality in high myopia patients treated using one of three aspheric treatment algorithms based on the NIDEK Advanced Vision Excimer Laser System.

METHODS

Sixty eyes of 60 high myopia patients (>-6 diopter) underwent topography-guided (CATz) (20 eyes), wavefront-guided (OPDCAT) (20 eyes), or topography and wavefront-guided (OPA) (20 eyes) laser-assisted sub-epithelial keratectomy. Visual acuity, manifest refraction spherical equivalent (MRSE), ocular and corneal higher order aberrations, corneal asphericity, point spread function (Strehl ratio) and modulation transfer function (MTF) were compared preoperatively and 1, 3 and 6 months postoperatively.

RESULTS

Six months after surgery, logMAR uncorrected visual acuity was 0.02 ± 0.09 in the CATz group, 0.02 ± 0.07 in the OPDCAT group and 0.02 ± 0.08 in the OPA group, and there were no statistically significant differences (P = 0.5355). No statistical differences were found among the three groups in MRSE (P = 0.3541). Induced spherical aberrations and the change of corneal asphericity were less in the OPA group than in the others (P < 0.0001). The MTF was slightly better in the OPA group than in the others. The Strehl ratio showed no statistically significant differences among the three groups.

CONCLUSIONS

All three aspheric treatment algorithms were safe and effective in correcting high myopia. Among them, the OPA algorithm maintained optical quality and physiologic cornea longer than the others.

A contralateral, randomized comparison of optimized prolate ablation and conventional LASIK for myopia with the NIDEK excimer laser platform

PURPOSE

To compare the refractive, visual acuity, topographic, and spherical aberration outcomes of LASIK using the Quest excimer laser platform with the optimized prolate ablation (OPA) profile (NIDEK Co Ltd) in one eye and conventional ablation profile in the fellow eye of the same patient.

METHODS

Thirty-seven myopic patients underwent LASIK bilaterally, with one eye randomized to receive OPA ablation (-3.88±1.42 diopters [D], range: -1.53 to -7.50 D) and the fellow eye to receive conventional ablation (-3.89±1.37 D, range: -1.75 to -7.00 D). Independent and paired t tests were used for testing differences between groups at last postoperative follow-up (6 or 12 months).

RESULTS

Postoperatively, 97% (32/33) of OPA eyes and 94% (31/33) of conventional eyes saw 20/20 or better without correction (P>.05). No eyes lost 2 or more lines of distance corrected visual acuity. Manifest refraction spherical equivalent was -0.16 D in the OPA group and -0.05 D in the conventional group (P>.05). Ocular spherical aberration was -0.003 μm in the OPA group and +0.102 μm in the conventional group (P<.05). Corneal asphericity was statistically lower after OPA (0.07±0.26) compared to conventional ablation (0.30±0.26) (P<.001). The mean programmed optical zone and achieved postoperative horizontal diameter of the effective optical zone were statistically significantly larger in the OPA group (P<.05).

CONCLUSIONS

Postoperative visual acuity and refractive outcomes were similar between groups. Laser in situ keratomileusis using the OPA profile for the correction of myopia induced significantly less corneal and ocular spherical aberration, resulted in normal postoperative asphericity in 94% of eyes, and larger horizontal diameter of the effective optical zone compared to the conventional profile.

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.

Wavefront-guided and aspheric ablation for myopia -- one-year results of the zyoptix personalized treatment advanced algorithm

PURPOSE

To evaluate the visual outcome and change in higher-order aberrations (HOAs) 1 year post simultaneous wavefront-guided and aspheric photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK).

DESIGN

Prospective interventional case series.

METHODS

Consecutive myopic patients undergoing PRK (38 eyes of 23 patients) and LASIK (42 eyes of 25 patients) using the Technolas 217z100 excimer laser (Technolas Perfect Vision) in a private laser clinic were included. Main outcome measures were uncorrected distance visual acuity (UDVA), manifest refraction (MRSE), HOAs, and spherical aberration (Z(4)(0)).

RESULTS

At 1 year, 87% (32/37) of PRK eyes and 81% (30/37) of LASIK eyes had UDVA of 20/20 or better (P = .75). Mean ± SD MRSE was -0.26 ± 0.31 diopters (D) in the PRK and -0.16 ± 0.34 D in the LASIK group (P = .222). There was no significant increase in total HOA root mean square (RMS) in the PRK group. Mean ± SD total HOA RMS increased from 0.402 ± 0.14 μm to 0.496 ± 0.17 μm (P = .013) in the LASIK group at 1 year. Z(4)(0) increased from mean ± SD -0.045 ± 0.12 μm to -0.109 ± 0.15 μm (P = .006, factor 2.42) in the PRK group and did not significantly increase in the LASIK group (mean ± SD -0.16 ± 0.17 μm to -0.17 ± 0.15 μm (P = .469, factor 1.08) at 6 mm pupil.

CONCLUSIONS

Visual outcome was excellent in both treatment groups. HOAs were still increased following LASIK by a factor of 1.23 but not PRK. Z(4)(0) was not induced by LASIK with the treatment algorithm but was negatively induced in PRK eyes.

Wavefront ablation profiles in refractive surgery: description, results, and limitations

PURPOSE

To provide an overview of the clinical results of different ablation profiles based on wavefront technology and discuss their characteristics and limitations.

METHODS

Literature review of studies reporting results of ablation profiles based on wavefront technology in virgin healthy eyes.

RESULTS

Over the past 10 years, a large number of studies comparing different treatment algorithms and newer excimer laser platforms have been published. Thirty-six clinical studies including 3637 eyes analyzing the clinical results obtained after wavefront-guided, wavefront-optimized, and Q-factor profiles have been reviewed. Although wavefront-driven profiles allowed reduction of the amount of induced optical aberrations with conventional ablations, thereby improving the quality of vision, it appears that no algorithm of treatment or excimer laser platform has demonstrated a clear superiority over another. Wound healing and unexpected biomechanical response to surgery affect the accuracy of customized treatments and produce variable results. In addition, it is difficult to rigorously analyze and compare findings among different studies because of the diverse variety in which the data are reported.

CONCLUSIONS

Despite several technological improvements over the years, wavefront ablation profiles have not consistently demonstrated superiority in terms of visual acuity and lower order aberrations compared to the standard procedure, although the induction of higher order aberrations has been reduced. The concept of an individualized eye model has emerged recently, based on the optical ray tracing algorithm, and could theoretically provide a higher level of customization, thus fulfilling the promise of "super vision."

Three-month clinical outcomes with static and dynamic cyclotorsion correction using the SCHWIND AMARIS

PURPOSE

To evaluate intraoperative static and dynamic cyclotorsions and postoperative outcomes on astigmatism and high-order aberration in astigmatic or aberrated eyes that underwent laser in situ keratomileusis treatments with advanced cyclotorsion control using the SCHWIND AMARIS.

METHODS

Fifty eyes (30 for aberration neutral and 20 for corneal wavefront) were treated. Treatments were planned with Custom Ablation Manager and ablations were performed using the SCHWIND AMARIS. Laser in situ keratomileusis flaps were cut with an LDV femtosecond laser. Cyclotorsional movements were evaluated for static cyclotorsion component (SCC) for mean and repeatability, and for dynamic cyclotorsion component (DCC) for mean and amplitude. Clinical outcomes were evaluated for predictability, refractive outcome, safety, and wavefront aberration.

RESULTS

Registration rates were 90% for SCC and 98% for DCC. SCC was within ± 5 degrees in 64% of cases. Repeatability of SCC was ± 1 degree in 88% of cases. Mean DCC was within ± 1 degree in 98% of cases, partly compensating for SCC. DCC amplitude was within ± 2 degrees in 84% of cases. At 3-month follow-up, 88% of eyes were within ± 0.50 diopter (D) of astigmatism. Mean defocus was -0.06 ± 0.24 D and astigmatism was 0.27 ± 0.20 D. Best spectacle-corrected visual acuity improved in 42% of eyes versus 2% losing 1 line. In corneal wavefront-customized treatments, coma, trefoil, spherical aberration, and root mean square high-order magnitudes at 6-mm analysis diameter were reduced by -0.04, -0.13, -0.04, and -0.10 μm, respectively.

CONCLUSIONS

Laser in situ keratomileusis with advanced cyclotorsion compensation using the SCHWIND AMARIS is safe and predictable and yields superior visual outcomes. Refractions and high-order aberrations were reduced to subclinical values without applying additional nomograms, showing the excellent performance of the system.

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.

Wavefront-optimized ablation versus topography-guided customized ablation in myopic LASIK: comparative study of higher order aberrations

BACKGROUND AND OBJECTIVE

To compare the outcomes of wavefront-optimized ablation and topography-guided ablation in fellow eyes of patients undergoing laser in situ keratomileusis (LASIK) for myopia.

PATIENTS AND METHODS

This prospective study included 84 patients who underwent LASIK in both eyes: wavefront-optimized ablation in one eye (group I) and topography-guided ablation in the fellow eye (group II). The Moria2 microkeratome with a 110 single-use head (Moria, Antony, France) was used to create a superior hinged flap and the Allegretto Wave Excimer Laser (Alcon/Wavelight Light Laser Technologie GmbH, Erlangen, Germany) for photoablation. The Allegretto wave analyzer was used to measure the ocular aberrations before and 6 months after LASIK. Refractive visual outcomes and ocular aberration changes were compared between the two treatment modalities.

RESULTS

Six months postoperatively, the mean uncorrected visual acuity of group II was statistically better than that of group I (P = .02). Seventy percent of group I and 83% of group II achieved a postoperative spherical equivalent refraction of ±0.5 diopters. The postoperative total root-mean-square of higher order aberrations (HOAs) of group II was smaller than that of group I, but the difference was not statistically significant (P = .51). There was a decrease in most of the individual terms of HOAs in group II, but it was only statistically significant in Z(3) (-1) (P = .04). The reverse occurred in group I, where most of the individual terms of HOAs increased, but it was not statistically significant. Significant improvement was only noted in Z(5) (3) (P = .05) and Z(5) (5) (P = .04).

CONCLUSION

Both wavefront-optimized ablation and topography-guided ablation provided good refractive results, but the latter induced fewer HOAs.

Six-month clinical outcomes of customized treatments minimized for depth and time in laser corneal refractive surgery

PURPOSE

Evaluating the application of 2 methods for minimizing the ablated tissue upon objective minimization of depth and time of Zernike-based customized ablations.

SETTING

Muscat Eye Laser Center, Muscat, Sultanate of Oman.

METHODS

Recently developed algorithms for selection of Zernike terms in customized treatments for refractive surgery were used. Clinical outcomes and tissue-saving attributes were evaluated on 2 groups [minimize depth (MD) and minimize volume (MV); 30 eyes each], plus a control group [corneal wavefront (CW); 30 eyes] with conventional customized approach. Clinical outcomes were evaluated in terms of predictability, safety, and contrast sensitivity and tissue-saving attributes in terms of saved depth and time for each condition (in micrometers, seconds, and percentage) and whether minimized depth or time were less than required for equivalent noncustomized treatments.

RESULTS

Ninety-three percent of treatments in the CW group, 93% in the MD group, and 100% in the MV group were within 0.50 diopters of spherical equivalent (SEq) postoperatively. Forty percent of treatments in the CW group, 34% in the MD group, and 47% in the MV group gained at least 1 line of best spectacle-corrected visual acuity postoperatively. Tissue-saving attributes showed an average saved depth of 8 μm (1-20 μm) and a saved time of 6 seconds (1-15 seconds) in the MD group and 6 μm (0-20 μm) and 8 seconds (2-26 seconds) in the MV group. Proposed corrections were always less deep and shorter than full wavefront corrections. In 43% of the MD cases, corrections were less deep, and in 40% of the MV cases, corrections were shorter than equivalent aberration-free treatments.

CONCLUSION

The minimization techniques compared here effectively reduced depth and time needed for ablation (up to a maximum of 50% and by 15% in average) without negatively affecting clinical outcomes postoperatively, yielding results equivalent to those of the full customization group.

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.

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.

Clinical outcomes of LASIK for myopia using the SCHWIND platform with ocular wavefront customized ablation

PURPOSE

To evaluate the clinical outcomes of aspheric ocular wavefront ablation profiles in LASIK treatments.

METHODS

Thirty eyes treated by ocular wavefront were retrospectively analyzed at 6-month follow-up. Custom Ablation Manager (CAM) software was used to plan wavefront-customized aspheric treatments, and the ESIRIS system was used to perform ablations (SCHWIND eye-tech-solutions). Outcomes were evaluated in terms of efficacy, predictability, refractive outcome, safety, and pre-and postoperative wavefront aberration analysis (SCHWIND Ocular Wavefront Analyzer).

RESULTS

At 6 months postoperatively, 47% of eyes achieved uncorrected visual acuity 20/20 or better. Average defocus was reduced from -3.49+/-2.38 diopters (D) preoperatively (range: -10.63 to 0.00 D) to -0.14+/-0.31 D postoperatively (range: -1.75 to 0.00 D). Astigmatism was reduced from -0.81+/-1.15 D (range: -4.25 to 0.00 D) to -0.25+/-0.37 D (range: -1.25 to 0.00 D). Eighty-six percent of eyes were within +/- 0.50 D. Best spectacle-corrected visual acuity (logMAR) improved from +0.12+/-0.08 (range: 0.0 to +0.2) to -0.05+/-0.13 (range: -0.2 to +0.2) (P=.04). The treatment did not change coma or spherical aberration, and reduced the trefoil from 0.21+/-0.13 microm (range: 0.05 to 0.53 microm) to 0.08+/-0.13 microm (range: 0.01 to 0.39 microm) (P=.002).

CONCLUSIONS

The study results indicate that the aspheric ocular wavefront customized CAM approach for planning ablation volumes is safe and effective.

Aspheric profile versus wavefront-guided ablation photorefractive keratectomy for the correction of myopia using the Allegretto Eye Q

PURPOSE

To compare the results of photorefractive keratectomy (PRK) with Q-factor customized aspheric ablation and wavefront-guided customized ablation for correction of myopia compound with astigmatism.

METHODS

Fifty-six patients were enrolled in this prospective controlled study. In each patient, one eye was randomly assigned for treatment with the Q-factor customized PRK (custom-Q study group) and the other eye treated with wavefront-guided customized PRK. Preoperative and 3-month postoperative manifest refraction, contrast sensitivity, visual acuity, aberrometry, and asphericity of the cornea were compared between the two groups. All eyes were treated with the Wavelight Eye-Q 400 Hz excimer laser in a single refractive surgery center by a single surgeon.

RESULTS

Uncorrected visual acuity (UCVA) improved to 20/20 or more and 20/25 or more in 34 eyes (60.7%) and 56 eyes (100%), respectively, in the wavefront-guided ablation group and in 36 eyes (64.2%) and 54 eyes (96.4%) in the custom-Q ablation group. All eyes had UCVA of 20/40 or better. A total of 54 eyes (96.4%) in the wavefront-guided ablation group and 56 (100%) in the custom-Q ablation group had spherical equivalent (SE) within -/+0.5 D. One eye in each group (2%) lost >or=2 lines of best-corrected visual acuity (BCVA). High order root mean square (RMS) in the wavefront-guided group was 0.3630-/+0.13 mum preoperatively and 0.427-/+0.17 at 3 months (p=0.2). In the custom-Q ablation group it was 0.329-/+0.092 preoperatively and 0.4730-/+0.181 at 3 months after PRK (p=0.08).

CONCLUSIONS

Regarding safety and refractive efficacy, custom-Q ablation profiles were clinically equivalent to wavefront-guided profiles in corrections of myopia up to -6.00 D and astigmatism up to 2.50 D.

Excimer laser correction of moderate to high astigmatism with a non-wavefront-guided aberration-free ablation profile: Six-month results

PURPOSE

To evaluate the postoperative clinical outcomes and higher-order aberrations (HOAs) in eyes with astigmatism greater than 2.00 diopters (D) that had laser in situ keratomileusis (LASIK) using a non-wavefront-guided aberration-free ablation profile.

SETTINGS

Private practice.

METHODS

This retrospective study evaluated the 6-month results of LASIK for astigmatism greater than 2.00 D. Standard examinations and preoperative and postoperative wavefront analyses were performed. Aspheric treatments with a non-wavefront-guided ablation profile were planned using software integrated into the Amaris flying-spot excimer laser system, which was used to perform the ablations. The LASIK flaps were created using an LDV femtosecond laser. Clinical outcomes were predictability, refractive outcomes, safety, efficacy, and wavefront aberration.

RESULTS

At 6 months, 84% of the 50 eyes evaluated achieved 20/20 or better uncorrected distance visual acuity (UDVA) and 40% achieved 20/16 or better UDVA. Forty-four percent of eyes were within +/-0.25 D of the attempted astigmatic correction, and 78% were within +/-0.50 D. The mean SE was -0.12 D +/- 0.25 (SD) and the mean astigmatism, 0.50 +/- 0.26 D. Corrected distance visual acuity (CDVA) improved in 36% of eyes; 4% of eyes lost 1 line of CDVA. The predictability slope for astigmatism was 0.97 and the intercept, -0.15 D. There were no clinically relevant changes in any aberration metric from preoperatively to postoperatively.

CONCLUSIONS

Excimer laser LASIK using a non-wavefront-guided aberration-free ablation profile yielded excellent visual outcomes. The preoperative astigmatism was reduced to subclinical values with no clinically relevant induction of HOA.

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

PURPOSE

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

SETTING

Four sites in Asia.

METHODS

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

RESULTS

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

CONCLUSION

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

Clinical outcomes of corneal wavefront customized ablation strategies with SCHWIND CAM in LASIK treatments

PURPOSE

To evaluate the clinical outcomes of aspheric corneal wavefront (CW) ablation profiles in LASIK treatments.

METHODS

Thirty eyes treated with CW ablation profiles were included after a follow-up of 6 months. In all cases, standard examinations including preoperative and postoperative wavefront analysis with a CW topographer (Optikon Keratron Scout) were performed. Custom Ablation Manager (CAM) software was used to plan corneal wavefront customized aspheric treatments, and the ESIRIS flying spot excimer laser system was used to perform the ablations (both SCHWIND eye-tech-solutions, Kleinhostheim, Germany). Clinical outcomes were evaluated in terms of predictability, refractive outcome, safety, and wavefront aberration.

RESULTS

In general, the postoperative uncorrected visual acuity and the best corrected visual acuity improved (p < 0.001). In particular, the trefoil, coma, and spherical aberrations, as well as the total root-mean-square values of higher order aberrations, were significantly reduced (p < 0.05) when the pre-existing aberrations were greater than the repeatability and the biological noise.

CONCLUSIONS

The study results indicate that the aspheric corneal wavefront customized CAM approach for planning ablation volumes yields visual, optical, and refractive results comparable to those of other wavefront-guided customized techniques for correction of myopia and myopic astigmatism. The CW customized approach shows its strength in cases where abnormal optical systems are expected. Apart from the risk of additional ablation of corneal tissue, systematic wavefront-customized corneal ablation can be considered as a safe and beneficial method.

Corneal Higher-Order Aberrations After Customized Aspheric Ablation and Conventional Ablation for Myopic Correction

PURPOSE

To investigate and compare the corneal wavefront aberrations and corneal asphericity after customized aspheric and conventional myopic ablation.

METHODS

Fifty-eight myopic patients from two laser centers were enrolled in this study. The patients were treated with laser in situ keratomileusis (LASIK) randomly with customized aspheric algorithm (32 patients, group A) and conventional algorithm (26 patients, group B). There was no significant difference in preoperative mean equivalent sphere (p = 0.954). The manifest refraction, corneal asphericity, and corneal wavefront data were taken into account to generate the customized aspheric ablation profile. Corneal wavefront aberrations, and corneal asphericity were analyzed and compared before and 6 months after the treatment.

RESULTS

Preoperatively, no significant difference was found in corneal asphericity and higher-order aberrations (HOAs) between two groups (p = 0.833 and p = 0.459, respectively). Root mean square (RMS) value of corneal HOAs, spherical aberration, and corneal asphericity increased postoperatively in both groups (p < 0.05), but the smaller increase was shown in group A (p < 0.05). The Zernike third-order aberration increased by 10% (p = 0.088) but without significance in group A compared with significant increase by 27% (p < 0.01) in group B.

CONCLUSIONS

The customized aspheric ablation induced smaller increase in corneal higher-order aberrations and corneal asphericity. It provides a good option for the customized myopic correction.

Aberration-neutral ablation pattern in hyperopic LASIK with the ESIRIS laser platform

PURPOSE

To analyze refractive power changes, topographical changes, and aberrations induction after aberration-neutral (Aberration-Free") hyperopic LASIK using the SCHWIND ESIRIS laser platform.

METHODS

Thirty-three consecutive eyes of 19 patients were evaluated retrospectively. The outcomes were analyzed at 3 months. In all cases, standard examinations and pre- and postoperative topographical and corneal wavefront analysis with a Keratron topographer (OPTIKON 2000 SpA) were performed. The preoperative mean spherical equivalent refraction was +2.61 +/- 1.39 diopters (D) (range: +0.75 to +6.00 D) with a mean cylinder of 0.67 +/- 0.74 D (range: 0.00 to 4.00 D). Ablations were performed with the SCHWIND ESIRIS excimer laser system. Topographical changes of Maloney index, simulated keratometry (Sim-K), and K-readings at 5 and 7 mm were evaluated.

RESULTS

Corneal aberrations up to the seventh order (36 Zernike terms) were measured. Corneal spherical aberration was +0.197 +/- 0.144 microm preoperatively and -0.040 +/- 0.206 microm postoperatively at the 6-mm analysis diameter. At 3 months postoperatively, 88% of eyes were within +/-0.50 D manifest refraction. Changes in refraction, Maloney indices, and Sim-K indices postoperatively were correlated with the intended correction. Induction of negative corneal spherical aberrations and increased prolate asphericity were correlated with the achieved defocus correction. No other Zernike mode was significantly correlated. Topographically, a corneal multifocality of <0.25 D was also observed.

CONCLUSIONS

Analyzing the topographical maps, the corneal power change of the Maloney indices correlated with the intended correction. With the aberration-neutral (SCHWIND Aberration-Free) pattern, patients with hyperopia up to +5.00 D were treated safely and with good predictability. The induced corneal aberrations were less than those calculated with the classical profile and compared to the literature.

Tissue-Saving Zernike Terms Selection in Customized Treatments for Refractive Surgery

Purpose

To study the possibility of performing customized refractive surgery minimising the amount of ablated tissue without compromising visual quality.

Methods

A new algorithm for the selection of an optimized set of Zernike terms in customized treatments for laser corneal refractive surgery was developed. Its tissue saving attributes have been simulated on 100 different wave aberrations at 6mm diameter. Outcomes were evaluated in terms of how much depth and volume was saved for each condition (in micrometers and in percentage), whether the proposed correction consists of either a full wavefront correction or an aberration-free treatment, and whether the proposed depth or volume was less than the one required for the equivalent aberration-free treatment.

Results

Simulated outcomes showed an average saved depth of 5μm (0-16μm), and an average saved volume of 95μl (0-127μl) or 11% saved tissue (0-66% saved tissue). Proposed corrections were always less deep than full wavefront corrections and in 59% of the cases were less deep than equivalent aberration-free treatments.

Conclusions

Even though Zernike modes decomposition is a mathematical description of the aberration, it is not the aberration itself. Not all Zernike modes affect the optical quality in the same way. The eye does not see through Zernike decomposition but with its own aberration pattern. However, it seems feasible to efficiently perform laser corneal refractive surgery in a customized form minimising the amount of ablated tissue without compromising the visual quality. Further clinical evaluations on human eyes are needed to confirm the preliminary simulated results presented herein.

Wavefront-guided versus wavefront-optimized laser in situ keratomileusis: contralateral comparative study

PURPOSE

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

SETTING

Medical and Vision Research Foundation, Tamil Nadu, India.

METHODS

This prospective comparative study comprised 27 patients who had wavefront-guided LASIK in 1 eye and wavefront-optimized LASIK in the fellow eye. The Hansatome (Bausch & Lomb) was used to create a superior-hinged flap and the Allegretto laser (WaveLight Laser Technologie AG), for photoablation. The Allegretto wave analyzer was used to measure ocular wavefront aberrations and the Functional Acuity Contrast Test chart, to measure contrast sensitivity before and 1 month after LASIK. The refractive and visual outcomes and the changes in aberrations and contrast sensitivity were compared between the 2 treatment modalities.

RESULTS

One month postoperatively, 92% of eyes in the wavefront-guided group and 85% in the wavefront-optimized group had uncorrected visual acuity of 20/20 or better; 93% and 89%, respectively, had a postoperative spherical equivalent refraction of +/-0.50 diopter. The differences between groups were not statistically significant. Wavefront-guided LASIK induced less change in 18 of 22 higher-order Zernike terms than wavefront-optimized LASIK, with the change in positive spherical aberration the only statistically significant one (P= .01). Contrast sensitivity improved at the low and middle spatial frequencies (not statistically significant) and worsened significantly at high spatial frequencies after wavefront-guided LASIK; there was a statistically significant worsening at all spatial frequencies after wavefront-optimized LASIK.

CONCLUSION

Although both wavefront-guided and wavefront-optimized LASIK gave excellent refractive correction results, the former induced less higher-order aberrations and was associated with better contrast sensitivity.

Topographic changes after hyperopic LASIK with the SCHWIND ESIRIS laser platform

PURPOSE

To analyze and compare refractive power changes with topographic changes after hyperopic LASIK using the ESIRIS laser platform.

METHODS

Sixty-six consecutive eyes of 37 patients were evaluated retrospectively. Outcomes were evaluated at 3 months. In all cases, standard examinations including pre- and postoperative topographic and corneal wavefront analysis with a Keratron topographer were performed. Preoperative mean spherical equivalent was +/- 2.74 diopters (D) with a mean cylinder of 0.67 D. The ESIRIS excimer laser system was used to perform ablations. Topographic changes of Maloney index, simulated keratometry (sim-K), and K-reading at 5 and 7 mm were evaluated.

RESULTS

Ninety-two percent of eyes were within +/- 0.50 D manifest refraction at 3 months postoperatively. Changes in refraction, Maloney indices, and sim-K indices after surgery were strongly correlated with the intended correction. Induction of negative corneal spherical aberrations and increased prolate asphericity was correlated with the achieved defocus correction. No other Zernike mode was significantly correlated. Topographically, an overcorrection within the central 3 mm and a gradual peripheral undercorrection also was observed.

CONCLUSIONS

Analyzing the topographic maps, the corneal power change of the Maloney indices correlated with the intended correction. After hyperopic LASIK, an overcorrection was observed in the 3-mm central zone, and progressive undercorrections were observed in the 5- and 7-mm zones.

[Aspheric profiles for refractive laser ablation of the cornea]

Conventional ablation profiles for excimer lasers for myopic refractive correction of the cornea are of spheric geometry. Therefore, they induce additional imaging aberrations into the optical system of the eye, most notably spherical aberration. This is a major cause of the observed deterioration of visual quality after such corrections, especially under low illumination and ensuing larger pupil diameter. Therefore, aspheric ablation profiles compromizing the preexisting imaging/visual quality of the eye as little as possible are currently being developed and optimized for all laser platforms. Employed methods include customized correction profiles on the basis of individual wavefront data of the anterior corneal topography on the one hand, and correction profiles that minimize the induced spherical aberration in a "standardized" way on the other hand. We demonstrate for a particular laser platform how such profiles must be developed and optimized. Mathematical theoretical calculations appear to be an indispensable but insufficient prerequisite. The biological reaction of the corneal stroma and epithelium ("biodynamic response") can only be determined experimentally and must lead to adjustment of the calculated ablation algorithm. The results show that aspheric profiles developed on this basis can lead to significant reduction of induced spherical aberration. The obtainable effect is, however, limited by the biological response and the ensuing peripheral ablation depth and volume.

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.