Evaluation of corneal functional optical zone after laser in situ keratomileusis

Effective optical zone: Differences between small-incision lenticule extraction and femtosecond LASIK for myopia

PURPOSE

To compare the effective optical zones (EOZs) of small-incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (F-LASIK) by utilizing topographic methods on the tangential curvature difference map at postoperative 1 year and to identify parameters linked to the EOZ alterations following both surgeries.

METHODS

Myopic patients who underwent SMILE or F-LASIK were included in the study. Patients with refractive error greater than -9.0 D sphere or -0.50 D of astigmatism were excluded from the study. EOZs were measured at postoperative 1 year by using the tangential curvature difference map of the Scheimpflug tomography system. Correlations between the EOZ alterations and relevant parameters were assessed.

RESULTS

In total, 59 eyes in the SMILE group and 65 eyes in the F-LASIK group were assessed. The decrease in EOZ compared with the programmed optical zone was significantly higher in the F-LASIK group ( P < 0.001). The increase in corneal asphericity was significantly relevant to the decrease in EOZin both groups according to the multiple regression analysis ( P < 0.001, B/95% CI: 0.62/0.34 and 0.90, standardized-Beta: 0.587 for the SMILE group; P < 0.001, B/95% CI: 0.74/0.41 and 1.07, standardized-Beta: 0.631 for the F-LASIK group).

CONCLUSION

The EOZ decreased 1 year after both SMILE and F-LASIK. The SMILE group showed less EOZ reduction than F-LASIK patients relative to the programmed optical zone. The decrease in EOZ was correlated with the increase in corneal asphericity in both groups.

Effective optical zone following small incision lenticule extraction: a review

Small incision lenticule extraction (SMILE) is a "flapless" keratorefractive surgery with excellent safety, efficacy, stability, and predictability for myopia correction. A recent global multicenter study also reported good refractive outcomes for hyperopic SMILE. SMILE has shown advantages including improved biomechanical strength, fewer dry eye symptoms, less corneal denervation, and fewer surgery-induced higher-order aberrations over laser in situ keratomileusis (LASIK). However, night vision complaints, including glare, halos, and starbursts, could still occur after SMILE. These symptoms have been proven to be closely related to the effective optical zone (EOZ), which is defined as the achieved area of corneal ablation. A larger postoperative EOZ may indicate better visual quality, making EOZ an important safety parameter for keratorefractive surgeries. As SMILE has gained wider application globally, the EOZ following SMILE has also been increasingly studied in the field of refractive surgery. This review provides an update on topics related to the EOZ after SMILE, including its measurement and influencing factors, aiming to benefit the personalization of the surgical algorithm and ultimately improve the visual quality after the SMILE procedure.

Effective Optical Zone and Centration Following SMILE and FS-LASIK for High Myopia Calculated With a Novel Method

PURPOSE

To compare the effective optical zone (EOZ) and centration in eyes with high myopia after small incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK) using a novel method.

METHODS

Forty eyes of 40 consecutive patients with high myopia scheduled for SMILE or FS-LASIK were enrolled in the study. The EOZ, optical zone decentration, and corneal aberrations were analyzed using Scheimpflug imaging. These values were then analyzed and compared between the two procedures 6 months after surgery.

RESULTS

The mean EOZ diameter for SMILE (4.41 ± 0.14 mm) was larger than that for FS-LASIK (4.24 ± 0.28 mm; P = .002), corresponding to reductions of 1.60 ± 0.11 and 1.71 ± 0.21 mm, respectively, compared with the programmed optical zone (POZ) (P = .007). Moreover, the total decentration for SMILE (0.33 ± 0.12 mm) was greater than that for FS-LASIK (0.27 ± 0.15 mm; P = .020). The induction of spherical aberration (SA) was lower with SMILE than with FS-LASIK (P = .007).

CONCLUSIONS

A larger EOZ and less SA were observed after SMILE than after FS-LASIK in eyes with high myopia. [J Refract Surg. 2023;39(11):736-740.].

Methods of Corneal Vertex Centration and Evaluation of Effective Optical Zone in Small Incision Lenticule Extraction

Inappropriate small incision lenticule extraction (SMILE) centration methods can affect the decentration of the effective optical zone (EOZ) after operation, which can subsequently lead to the decline of postoperative visual quality. We aimed to provide an overview of corneal vertex (CV) centration methods and an evaluation of the size and decentration of the EOZ in SMILE. We described the CV centration methods for patients with myopia, myopic astigmatism, hyperopia, and large kappa angle. The measurement methods of the EOZ were evaluated from the aspects of corneal morphology and corneal refractive power. Additionally, we summarized the advantages and disadvantages of measuring decentration based on topographic mapping and intraoperative video-captured images. Finally, we discussed the relationship between the EOZ and visual quality. Based on our review, clinicians should consider the following when choosing CV centration methods and evaluating EOZ postoperatively. First, the tear film mark center or topographic map comparison method is preferred for the correction of myopia, low myopic astigmatism, hyperopia, and large kappa angle (>0.2 mm). Triple marking centration is recommended for high myopic astigmatism (-3.5 diopters). Second, the total corneal power better reflects the change in refractive power than the topographic method. The measurement of the area rather than the diameter of the total corneal refractive power is more suitable for the evaluation of noncircular EOZs after high myopia astigmatism (<-2.0 diopters). Third, for the evaluation of decentration, the tangential curvature difference map method is preferred as it is not influenced by offset pupils. Finally, a large EOZ after SMILE may improve patient tolerance to decentration.

Evaluation of the Effects of Myopic Astigmatism Correction and Anterior Corneal Curvature on Functional Optical Zone After SMILE

PURPOSE

To evaluate the influence of different degrees of myopic astigmatism correction and preoperative anterior corneal curvature on the functional optical zone (FOZ) following small incision lenticule extraction (SMILE).

METHODS

In this retrospective study, 68 patients (106 eyes) treated with SMILE were grouped according to myopic astigmatism correction: control (0.00 diopters [D]), moderate astigmatism (-0.50 to -2.00 D), and high astigmatism (> -2.00 D). The FOZ was measured and compared between the three groups for 3 months. Correlations between attempted correction, anterior corneal curvature, corneal aberrations, and the FOZ were analyzed.

RESULTS

The preoperative mean treatment spherical equivalent was comparable among the three groups. The average FOZ was 5.06 ± 0.24 mm in the control group, 5.19 ± 0.25 mm in the moderate astigmatism group, and 5.35 ± 0.20 mm in the high astigmatism group The FOZ showed statistically significant differences among the three groups (P < .001), particularly between the high astigmatism group and the other two groups (P < .001 and .018). Correlation analysis showed that the total higher order aberrations, coma, and spherical aberration change were correlated with the FOZ (P < .001). Preoperative steep keratometry, average keratometry, and corneal astigmatism were significantly correlated with the FOZ (P < .05). The correlation remained after excluding the influence of attempted correction on the FOZ (P < .05). After adjusting for other risk factors using multiple linear regression analysis, there was still a significant positive association between preoperative steep keratometry and the FOZ (P < .001).

CONCLUSIONS

Patients with higher myopic astigmatism achieved a larger FOZ and less induced horizontal coma than the control and moderate astigmatism groups. A larger FOZ after SMILE can be achieved in eyes with steeper keratometry. [J Refract Surg. 2023;39(2):135-141.].

Changes of the effective optical zone after small-incision lenticule extraction and a correlation analysis

The objective of the study is to observe the changes in the effective optical zone (EOZ) after small incision lenticule extraction (SMILE) and explore possible correlations with some influencing factors. In total, 133 eyes after SMILE were divided into the mild to moderate myopia group (- 1.75 D to - 5.75 D, 70 eyes) and the high myopia group (- 6.00 D to - 9.50 D, 63 eyes). The postoperative EOZ was calculated by utilizing the corneal tangential curvature map. Changes in EOZ (△-OZ) were monitored and compared between the two groups. Pearson correlation analysis was conducted to determine the correlation between △-OZ and corneal high-order wavefront aberrations. Multicollinearity analysis and ridge regression analysis were performed to assess the correlation between △-OZ and some corneal parameters. After SMILE, the horizontal EOZ (H-EOZ), vertical EOZ (V-EOZ), and average EOZ (A-EOZ) were significantly smaller than the programmed optical zone (POZ) in both groups (p < 0.05). The difference between V-EOZ and POZ (△V-OZ) and the difference between A-EOZ and POZ (△A-OZ) showed more significant changes in the high myopia group than in the mild to moderate myopia group, and △V-OZ was significantly larger than the difference between H-EOZ and POZ (△H-OZ) in the high myopia group. In both groups, the total high-order aberration (T-HOA) and spherical aberration (SA) both increased after SMILE, and they had a similar significant negative correlation with A-EOZ. Moreover, there was a significant negative correlation between △-OZ and Km (X1), Q-value (X2), spherical equivalent (SE, X3), ablating depth (AD, X4) and △e (X6), and a significant positive correlation between △-OZ and △Q (X5). △H-OZ was expressed as Y1, △V-OZ as Y2, and △A-OZ as Y3. The multiple linear regression equations were as follows: Y1 = 3.683 - 0.065X1, Y2 = 1.549 - 0.469X2 - 0.059X3, Y3 = 4.015 - 0.07X1 - 0.03X3, Y1 = 1.337 - 0.005X4 + 0.413X5, Y2 = 1.265 + 0.469X5, and Y3 = 0.852 - 0.002X4 - 0.398X6. The correlation degree with △A-OZ was ranked as Km > △Q > Q-value > AD > e-value > △e > SE > △Km, as represented by the ridge regression analysis. The EOZ was irregularly reduced after SMILE, which should be taken into consideration in the design of POZ, especially for high myopia. Consideration of the refractive diopter and corneal topography is advised for the design of POZ, the latter of which has greater reference significance.

Changes in effective optical zone after small-incision lenticule extraction in high myopia

PURPOSE

To evaluate the four measurement approaches on the determination of effective optical zone (EOZ) using Scheimpflug tomography after small-incision lenticule extraction surgery in eyes with high myopia.

SETTING

Corneal refractive surgery conducted in an eye hospital in southern China.

DESIGN

This is a retrospective cohort study.

METHODS

In total, 74 subjects were recruited. EOZ was measured at 3 months postoperatively using vertex-based (EOZ_V), pupil-based (EOZ_P), 4 mm-ring-based total corneal refraction method (EOZ₄) and tangential curvature difference map method (EOZ_D), and their consistencies were compared. EOZs and planned optical zone (POZ) were compared and analyzed with eccentricity, ablation degree (AD) and total corneal aberrations.

RESULTS

At 3 months after surgery, the mean root mean square of ΔHOA, ΔComa, ΔTrefoil and ΔSA were 0.53 ± 0.27 μm, 0.36 ± 0.20 μm, 0.01 ± 0.84 μm and 0.16 ± 0.14 μm, respectively. EOZ_V, EOZ_P, EOZ₄ and EOZ_D were 5.87 ± 0.44 mm, 5.85 ± 0.45 mm, 4.78 ± 0.40 mm and 5.29 ± 0.27 mm, respectively, which were significantly smaller than POZ 6.48 ± 0.16 mm. Bland-Altman plots showed a good consistency among the four EOZs. The difference between the EOZ_V and EOZ_P was 0.02 mm within the range of clinically acceptable difference. In addition, the eccentricity was positively correlated with ΔHOA, ΔComa and ΔSA.

CONCLUSIONS

All 4 measurement approaches demonstrated the reduction of EOZs compared to POZ. The EOZ_V was the closest to POZ, followed by EOZ_P. The ΔEOZs showed no significant difference with eccentricity, AD and corneal aberrations.

Effective Optical Zone Following Small Incision Lenticule Extraction for Myopia Calculated With Two Novel Methods

PURPOSE

To evaluate the effective optical zone (EOZ) following small incision lenticule extraction in myopic eyes using two novel methods and investigate factors influencing postoperative EOZ.

METHODS

In this prospective study, 45 patients (45 eyes) with a mean spherical equivalent of -5.82 ± 1.58 diopters underwent SMILE and were observed during a 6-month follow-up. Postoperative EOZ was calculated using custom software that automatically distinguishes EOZ on the tangential curvature difference map (EOZc) and total corneal refractive power map (EOZp) of the Pentacam HR (Oculus Optikgeräte GmbH). The agreement between the two methods, the difference between postoperative EOZ and programmed optical zone (POZ), and its relationship with parameters including corrected spheres, cylinders, ablation ratio (ablation depth/central cornea thickness), and Q-value change were investigated.

RESULTS

The EOZc area was 20.76 ± 2.43 mm² (diameter: 5.04 ± 0.60 mm) and the EOZp area was 20.22 ± 4.70 mm² (diameter: 5.13 ± 0.30 mm). Both were significantly smaller than POZ (P < .001). Bland-Altman plots showed 4.44% (2/45) points located outside the 95% limits of agreement. EOZc and EOZp reductions were negatively related to corrected cylinders (r = -0.631, P < .001 and r = -0.594, P < .001, respectively). EOZp reduction was positively correlated with corrected spheres (r = 0.336, P = .024). Subgroup analysis revealed significant differences in EOZc and EOZp reduction between low and high astigmatism groups despite myopia degree.

CONCLUSIONS

EOZ after incision lenticule extraction, measured using two novel methods, was smaller than POZ. The reduction of EOZ was negatively correlated with the corrected cylinders. [J Refract Surg. 2022;38(7):414-421.].

Achieved and Functional Optical Zone in Myopic Eyes With High Astigmatism After Small Incision Lenticule Extraction

PURPOSE

To investigate the achieved optical zone and functional optical zone in myopic eyes with high astigmatism after small incision lenticule extraction (SMILE).

METHODS

Seventy-five eyes of 75 consecutive patients with myopia before SMILE were included and divided into two groups (no astigmatism group: without astigmatism vs high astigmatism group: with astigmatism > 2.00 diopters). The achieved optical zone, functional optical zone, and corneal aberrations were compared using Scheimpflug imaging at 6 months postoperatively. Correlations between corneal aberrations and functional optical zone were analyzed.

RESULTS

The mean achieved optical zone diameter was smaller in the no astigmatism group than in the high astigmatism group. There were no significant differences in achieved optical zone among the different meridians in each group. The mean functional optical zone diameter was significantly smaller in the no astigmatism group than in the high astigmatism group. Compared with the programmed optical zone, significant reduction of the functional optical zone was found in the two groups. The reduction of the functional optical zone was significantly smaller in the high astigmatism group than in the no astigmatism group, except for the 60°, 90°, and 120° meridians. There were significant correlations between the functional optical zone area and the induced corneal aberrations in the high astigmatism group, except for horizontal coma, whereas significant correlations of functional optical zone with total higher order aberrations and spherical aberration were detected in the no astigmatism group.

CONCLUSIONS

Myopic eyes with high astigmatism following SMILE had a circular achieved optical zone, but the functional optical zone was oval and larger than in eyes without astigmatism. Moreover, a lower spherical aberration was observed in the patients with high astigmatism. [J Refract Surg. 2022;38(4):243-249.].

Functional Optical Zone and Visual Quality After Small-Incision Lenticule Extraction for High Myopic Astigmatism

Introduction

The aim of this study was to compare the functional optical zone (FOZ) after correction of high myopic astigmatism and low myopic astigmatism by small-incision lenticule extraction (SMILE).

Methods

In this prospective study, 30 patients who received SMILE for high myopic astigmatism correction (cylinderical diopters ≤ − 2.0D) were enrolled in the high astigmatism group (HA). The control group comprised 40 patients who underwent SMILE for low myopic astigmatism correction (LA; cylinderical diopters ≥ − 0.5D). FOZ was delineated as the area outlined by a change of 0.5D relative to the power at the corneal vertex on the total corneal refractive power map. An ellipse-fitting program (MatLab) was used to calculate some parameters of the FOZ. Visual quality evaluations were also conducted, including evaluations of wavefront aberrations, optical quality, and intraocular scattering, and completion of a quality of life questionnaire. All of the right eyes were analyzed in the study.

Results

The preoperative average treatment spherical equivalent (− 5.77 ± 1.86D vs. − 6.49 ± 1.49D; P = 0.074), lenticule thickness (120.87 ± 23.27 μm vs. 118.53 ± 21.66 μm; P = 0.666), and programmed optical zone (6.58 ± 0.17 mm vs. 6.65 ± 0.18 mm; P = 0.104) were comparable between the HA and LA groups. The long axes (6.99 ± 1.14 mm vs. 5.32 ± 0.61 mm; P < 0.001), short axes (4.66 ± 0.96 mm vs. 4.23 ± 0.64 mm; P = 0.047), and area (25.90 ± 8.03 mm² vs. 17.92 ± 4.36 mm²; P < 0.001) of the FOZ were significantly larger in the HA group than in the LA group. The centration of the FOZ were comparable between the two groups (0.62 ± 0.25 mm vs. 0.70 ± 0.25 mm; P = 0.194). Postoperative spherical aberration was lower in the HA group than in the LA group (0.07 ± 0.05 μm vs. 0.14 ± 0.10 μm; P = 0.001). There was no significant difference in the ocular scatter index (0.80 ± 0.46 vs. 0.73 ± 0.46; P = 0.447), modulated transfer function (MTF)_cutoff (37.89 ± 9.79 cpd vs. 39.78 ± 7.45 cpd; P = 0.363), and Strehl in two dimensions (Strehl2D) ratio (0.20 ± 0.04 vs. 0.20 ± 0.04; P = 0.363) between the HA group and the LA group. There were no significant differences in the scores on quality of life between the HA and LA groups (45.88 ± 2.15 vs. 45.64 ± 1.84; P = 0.423). Correlation analysis revealed that increase in the spherical aberration was significantly correlated with the long axes, short axes and area in the FOZ in both groups.

Conclusion

With a comparable optical design and attempted correction in SMILE, the eyes with higher myopic astigmatism correction achieved larger FOZ than the eyes with lower myopic astigmatism correction. Consequently, less spherical aberration induction was created after higher myopic astigmatism correction. This result may be associated with less corneal volume sculpted by laser for the higher astigmatism treatment, leading to fewer biochemical responses and les change in corneal aspherity. Good retinal image quality and satisfied quality of life were achieved at a comparable level in both study groups.

The best optical zone for small-incision lenticule extraction in high myopic patients

Small-incision lenticule extraction (SMILE) is an effective and safe procedure for the correction of myopia due to minimally invasive and noncorneal flap surgery. However, the SMILE procedure has certain requirements for corneal cap thickness, attempted refractive correction, residual stromal bed thickness, and optical zone diameter, which sometimes make surgeons hesitant to choose SMILE or other refractive surgeries. The requirements limit its use in patients with high myopia. The purpose of this review was to find the optimal parameters of SMILE through discussing the best optical zone for high myopic patients, the visual quality of different optical zones, the choice of corneal cap thickness, and their effects on corneal biomechanical parameters, so surgeons can provide reference recommendations for patients with high myopia in choosing a reasonable and safe procedure.

Six modes of corneal topography for evaluation of ablation zones after small-incision lenticule extraction and femtosecond laser-assisted in situ keratomileusis

PURPOSE

To evaluate the ablation zone diameter (AZD) using six modes of corneal topography after small-incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK) for myopia and to compare the programmed and postoperative AZDs METHODS: This retrospective comparative study included 86 right eyes in 86 patients who underwent SMILE or FS-LASIK at the Shandong Eye Institute between June 2016 and August 2017. Data were collected preoperatively and at 1, 3, and 6 months postoperatively using the Pentacam system. The AZD was determined using six modes of corneal topography: postoperative axial curvature topography (PACT), postoperative tangential curvature topography (PTCT), difference-axial curvature topography (DACT), difference-tangential curvature topography (DTCT), postoperative front elevation topography (PFET), and difference-corneal thickness topography (DCTT). The difference between the programmed and postoperative AZDs was compared between the groups of two surgical procedures.

RESULTS

At 3 months, the AZDs measured by PTCT, DTCT, and PFET after SMILE showed a significant decrease, while the AZD by DACT revealed an increase (P < 0.001), and the AZDs measured by PACT, PTCT, DACT, DTCT, PFET, and DCTT after FS-LASIK were all significantly decreased (P < 0.001), as compared with the programmed ablation zone values. The AZDs measured by DACT and DTCT after 3 months were larger in the SMILE group (P < 0.001); likewise, the differences between the programmed and postoperative AZDs were lower in the SMILE group (P < 0.001). Furthermore, PACT, PTCT, DACT, DTCT, and PFET indicated acceptable inter-observer reliability (ICC > 0.75).

CONCLUSIONS

In the treatment of myopia, the achieved topographic ablation zones after FS-LASIK were smaller than the theoretically designed ones. The AZDs after SMILE were larger than those after FS-LASIK, with an equivalent programmed value. The DACT may be more suitable for measuring postoperative ablation zones in clinic with clearer borders and favorable repeatability. This method may be potential for the measurement of ablation zones and further research on the visual quality after refractive surgery.

Comparison of effective optical zone after small-incision lenticule extraction and femtosecond laser-assisted laser in situ keratomileusis for myopia

PURPOSE

To compare the effective optical zone (EOZ) after small-incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK).

SETTING

Jinan Mingshui Eye Hospital, Jinan, China.

DESIGN

Retrospective case series.

METHODS

Myopic patients who had small-incision lenticule extraction or FS-LASIK were enrolled in this retrospective study. Effective OZs were measured at 1 week, 1 month, and 3 months postoperatively, using the tangential curvature difference map of the Scheimpflug tomography system. Correlations between the changes in the EOZ and relevant parameters were analyzed 3 months postoperatively.

RESULTS

The study comprised 76 patients (76 eyes). The mean EOZs at 1 week, 1 month, and 3 months postoperatively were 5.39 ± 0.27 mm, 5.33 ± 0.30 mm, and 5.34 ± 0.23 mm in the small-incision lenticule extraction group and 5.06 ± 0.36 mm, 4.98 ± 0.39 mm, and 5.01 ± 0.31 mm in the FS-LASIK group, when the programmed OZ was 6.5 mm. The magnitude of decreases in EOZ was significantly smaller in the small-incision lenticule extraction group than in the FS-LASIK group at all timepoints after surgery (P < .01). There were significant correlations between changes in EOZ and corneal asphericity (P < .01). Epithelial thickening was positively correlated with EOZ reduction in the small-incision lenticule extraction group (r = 0.479, P < .01); however, no correlation was found between epithelial thickening and EOZ reduction in the FS-LASIK group (r = .324, P > .05).

CONCLUSIONS

Both small-incision lenticule extraction and FS-LASIK resulted in EOZ reduction during correction of myopia. However, small-incision lenticule extraction resulted in less reduction than FS-LASIK and was associated with corneal asphericity changes and epithelial thickening.

Functional Optical Zone and Centration Following SMILE and LASIK: A Prospective, Randomized, Contralateral Eye Study

PURPOSE

To compare centration and functional optical zone (FOZ) after small incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (LASIK).

METHODS

In this prospective, randomized, single-masked, paired-eyed, clinical trial, 70 patients received SMILE in one eye and LASIK in the other eye for myopia and myopic astigmatism. FOZ was calculated using custom software on 3-month postoperative refractive power maps (Pentacam HR; Oculus Optikgeräte GmbH, Wetzlar, Germany). Programmed treatment area was defined as the total area of the programmed OZ plus the transition zone. Centration was evaluated by the linear distance between FOZ centroid and the pupil center and the corneal apex.

RESULTS

The average preoperative spherical equivalent (-5.38 ± 1.65 vs -5.45 ± 1.61 diopters [D]), postoperative spherical equivalent (0.05 ± 0.39 vs 0.06 ± 0.39 D), uncorrected distance visual acuity (0.01 ± 0.13 vs 0.00 ± 0.08 logMAR), and corrected distance visual acuity (-0.07 ± 0.10 vs -0.07 ± 0.10 logMAR) were comparable in SMILE- and LASIK-treated eyes of the 60 patients with complete datasets (P > .419). Postoperative increase in spherical aberration was lower in SMILE than in LASIK (0.08 ± 0.16 vs 0.17 ± 0.18 µm, P = .002). The FOZ area was significantly larger in SMILE than in LASIK (30.25 ± 3.60 vs 29.21 ± 3.72 mm²), despite the smaller programmed OZ diameter (6.48 ± 0.08 vs 6.52 ± 0.11 mm) and smaller programmed treatment area (33.87 ± 0.81 vs 46.30 ± 2.61 mm², P < .037). Pupil centration (0.43 ± 0.21 vs 0.41 ± 0.22 mm) and apex centration (0.48 ± 0.24 vs 0.48 ± 0.22 mm) were comparable between SMILE and LASIK (P > .694).

CONCLUSIONS

SMILE created a larger FOZ than LASIK, despite the smaller programmed OZ. This may be due to a difference in the biomechanical response between the two procedures. Visual outcome and centration were comparable between SMILE and LASIK. [J Refract Surg. 2019;35(4):230-237.].

Changes of Functional Optical Zone After LASIK for Hyperopia and Hyperopic Astigmatism

PURPOSE

To evaluate which factors may influence the size of the postoperative functional optical zone after hyperopic LASIK.

METHODS

Thirty-three eyes with a mean spherical equivalent of +3.55 ± 1.28 diopters (D) underwent LASIK with a Technolas 217 C-LASIK laser (Bausch & Lomb Surgical, Munich, Germany). After 1 week and 1, 4, and 12 months, the authors examined refraction, corneal refractive power by means of computerized videokeratography (Technomed C-Scan; Baesweiler, Germany), and uncorrected/corrected distance visual acuity (UDVA/CDVA). According to the degree of hyperopia, they were divided into low hyperopia (spherical equivalent ≤ 3.00 D) and high hyperopia (spherical equivalent > 3.00 D) groups.

RESULTS

One year postoperatively, 82% of all eyes had a UDVA of 0.5 or better; in 88%, the spherical equivalent did not deviate more than 1.00 D from the attempted value. Three eyes were slightly undercorrected. After an initial overcorrection (-0.27 D) with subsequent regression, the refraction remained stable at +0.17 D from the fourth postoperative month (low hyperopia group: +0.14 D; high hyperopia group: +0.19 D after 1 year). After 1 year, the functional optical zone diminished by 32%; the reduction was more pronounced in eyes with higher hyperopia: -1.85 ± 1.09 mm (range: +0.5 to -3.4 mm) in the low hyperopia group (P < .0001) and -2.25 ± 1.24 mm (range: +1 to -3.9 mm) in the high hyperopia group (P < .0001). Preoperative spherical equivalent and preoperative corneal refractive power affected the postoperative size of the functional optical zone additively.

CONCLUSIONS

An expected small functional optical zone in high hyperopia may not be regarded as a compelling exclusion criterion, but can induce possible side effects such as glare and halos. [J Refract Surg. 2018;34(7):476-481.].

Functional Optical Zone After Small-Incision Lenticule Extraction as Stratified by Attempted Correction and Optical Zone

PURPOSE

To compare the functional optical zone (OZ) with different levels of myopia and different OZ groups after small-incision lenticule extraction.

METHODS

This retrospective study included 249 patients (120 men) after small-incision lenticule extraction correction. We grouped participants according to attempted correction [low: spherical equivalent (SE) > -3.0 D; moderate: -6.0 D ≥ SE ≥ -3.0 D; high: SE ≥ -6.0 D] and planned functional optical zone (PFOZ) (OZ-1: PFOZ ≤ 6.3 mm; OZ-2: 6.3 mm < PFOZ ≤ 6.5; OZ-3: PFOZ > 6.5 mm), and we compared the achieved functional optical zone (AFOZ) and total corneal aberration, using Scheimpflug imaging, 1 month postoperatively. Correlations between corneal aberration and AFOZ were analyzed.

RESULTS

The AFOZ was smaller than the PFOZ in all 3 refraction groups (reduction: low, 0.78 ± 0.72 mm; moderate, 1.22 ± 0.60 mm; and high: 1.49 ± 0.58 mm, P < 0.001). There was no difference in the AFOZ among the 3 OZ groups. Total corneal aberration increased more in the high myopia group (total higher-order aberration, coma, and spherical aberration, P < 0.001), which also correlated with the AFOZ.

CONCLUSIONS

The discrepancy between the AFOZ and PFOZ increased with greater attempted correction. Attempted correction and AFOZ influence corneal aberration.

Single-step transepithelial photorefractive keratectomy in high myopia: qualitative and quantitative visual functions

AIM

To investigate quantitative and qualitative optical outcomes of single-step transepithelial photorefractive keratectomy (TransPRK) in high myopia.

METHODS

In a prospective interventional case-series, 30 eyes with high myopia (-6.00 to -8.75 D) with (up to -3.00 D) or without astigmatism were enrolled from Bina Eye Hospital, Tehran, Iran. One-step TransPRK was performed with aberration-free aspherical optimized profile and SCHWIND AMARIS 500 laser. One-year follow-up results for refraction, visual acuities, vector analysis, ocular wave-front (OWF) and corneal wave-front (CWF) higher order aberrations (HOA), contrast sensitivity (CS), and post-operative haze were assessed.

RESULTS

After the surgery, both photopic and mesopic CSs significantly improved (both P<0.001). We detected significant induction of OWF coma and trefoil (P<0.001 for both) HOAs; CWF coma (P=0.002), spherical (P<0.001), and tetrafoil (P=0.003) HOAs in 6 mm analysis diameter; and CWF trefoil (P=0.04) HOA in 4 mm analysis diameter. The range of mean induction observed for various HOAs was 0.005-0.11 µm. The 86.7% of eyes reached an uncorrected distance visual acuity of 20/20 or better; 96.7% of eyes were within ±0.5 D of targeted spherical refraction. In vector analysis, mean correction index value was 1.03 and mean index of success was 0.22. By 12mo after the operation, no eye lost any number of corrected distance visual acuity lines. We detected no corneal haze greater than 1⁺ throughout the follow-up.

CONCLUSION

Our findings show promising effects of single-step TransPRK on quality of vision in high myopic eyes. It also improves refraction and visual acuity.

Comparison of visual outcomes after variable spot scanning ablation versus wavefront-optimized myopic LASIK

PURPOSE

To compare the refractive and visual outcomes of variable spot scanning ablation versus the wavefront-optimized ablation for myopia and myopic astigmatism.

METHODS

Fifty patients with myopia who underwent LASIK (100 eyes) were divided into two equal groups. Myopic correction performed using the variable spot scanning (VSS) ablation with the VISX STAR S4/IR platform (Abbott Medical Optics, Inc., Santa Ana, CA) (VSS group) and wavefront-optimized (WFO) ablation profile with the WaveLight Allegretto Wave Eye-Q platform (Alcon Laboratories, Inc., Fort Worth, TX) (WFO group). Manifest refraction, uncorrected distance visual acuity, and corrected distance visual acuity were obtained preoperatively and 1 day and 1 and 3 months postoperatively. Wavefront measurement and contrast sensitivity testing were done preoperatively and 3 months postoperatively.

RESULTS

Postoperative mean refractive spherical equivalent was -0.14 ± 0.2 diopters for the VSS group and -0.15 ± 0.28 diopters for the WFO group. Forty-eight eyes of the VSS group and 47 eyes of the WFO group were within ±0.5 diopters. Postoperative mean corrected distance visual acuity was 1.05 ± 0.13 for the VSS group and 1.06 ± 0.12 for the WFO group. The postoperative uncorrected distance visual acuity was 1.01 ± 0.16 for the VSS group and 1.01 ± 0.11 for the WFO group. The safety index was 1.12 for the VSS group and 1.06 for the WFO group, whereas the efficacy index was 1.07 for the VSS group and 1.01 for the WFO group. The mean induced positive spherical aberration was 0.041 ± 0.046 µm for the VSS group and 0.195 ± 0.171 µm for the WFO group (P < .001). Mesopic contrast sensitivity testing showed no statistically significant differences between groups at all tested spatial frequencies.

CONCLUSIONS

Both VSS and WFO treatments showed similar refractive and visual outcomes. Both induced significant positive spherical aberration, significantly more with WFO.

Small optical zones with aspheric profiles in laser refractive surgery for myopia: a surgical outcome and patient satisfaction study

PURPOSE

To assess the outcomes of small optical zone (OZ) ablations used in conjunction with large transition zones (TZ) and a highly aspheric treatment profile.

METHODS

Interventional case series of 39 consecutive patients with myopia or myopic astigmatism. Patient data included pre and postoperative refraction and visual acuities, laser treatment settings and pre and postoperative corneal topography as well as questionnaire responses about the use of glasses and the quality of vision postoperatively.

RESULTS

The mean preoperative spherical equivalent was -4.50±2.11 dioptres (D) and the mean OZ and TZ diameters were 4.5±0.5mm and 8.1±0.4mm, respectively. The mean patient age was 40.7±10.4 years. Manifest spherical refraction was within ±0.5D in 87% of patients (±1.0D in 99%) and cylindrical refraction within 0.5D in 79% (≤1.0D in 95%). The need to wear distance glasses postoperatively was associated with dissatisfaction with the quality of daytime vision (p=0.05) and unhappiness with night vision was associated with symptoms of halos (p=0.03) and starbursts (p=0.02). The proportion of patients reporting symptoms of dysphotopsias included: ghosting 0%; glare 2%; halos 10%; and starbursts 15%. There was a significant difference in the measured mean effective OZ diameter (4.8±0.3mm) compared to the mean programmed OZ (4.5±0.5mm, p=0.00).

CONCLUSIONS

Small ablation zones, when used in conjunction with a large diameter TZ, do not lead to a greater incidence of unwanted visual phenomena over that reported by many studies with larger OZs.

Anterior corneal optical irregularity measured by higher-order aberrations induced by a broad beam excimer laser

BACKGROUND

The aim was to analyse anterior corneal optical irregularity in patients receiving photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) with a conventional broad beam laser.

METHODS

Pre- and post-operative anterior corneal aberrations including Zernike coefficients and root mean squares of higher-order aberrations were measured and derived with a Placido-ring-based corneal topographer and wavefront software, respectively, from 768 right eyes of patients receiving either PRK or LASIK for myopia with a conventional broad beam excimer laser in National Taiwan University Hospital, Taipei, Taiwan. Multiple linear regression models selected by Mallows' Cp criteria were used to evaluate predictability of surgically induced aberrations and relevant factors.

RESULTS

Mean attempted spherical equivalent correction was -7.37 ± 2.33 D (range: -16.5 to -1.95). Root mean squares of higher-order aberrations and variances of Zernike coefficients all increased significantly after surgery (p < 0.01). All post-operative higher-order aberrations increased with the amount of attempted myopic correction and secondary astigmatism increased with attempted cylindrical correction. LASIK surgery induced less coma and third-order aberrations but more fifth- and sixth-order aberrations than PRK, although squared partial correlation coefficients were low. Larger optic and transitional zones meant fewer higher-order aberrations after surgery. Younger patients tended to have more surgically induced aberrations in the 3.0 mm pupil zone.

CONCLUSIONS

Anterior corneal optical irregularity increased tremendously after refractive surgery by conventional broad beam lasers and correlated with greater attempted myopic correction, younger age and a smaller treatment zone. The effect of corneal flaps on post-operative corneal irregularity differed trivially.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Comparison of the topographic ablation zone after photorefractive keratectomy for myopia using two different excimer lasers

PURPOSE

To compare the topographic features of eyes treated with photorefractive keratectomy (PRK) for myopia using two different excimer lasers.

METHODS

A total of 65 eyes in 39 patients treated with PRK (6.0-mm optical zone) using Technolas 217C and VISX S4 excimer lasers were evaluated retrospectively to determine the size of the topographic ablation zone.

RESULTS

The zones ablated using the VISX S4 had shorter diameters in both axes (-0.89+/-0.73, -1.59+/-0.49 mm; both P=0.00), whereas those ablated using the Technolas 217C had a longer diameter in the major axis (0.96+/-0.63 mm; P=0.00) and a shorter diameter in the minor axis (-0.39+/-0.59 mm; P=0.00). The theoretical ablated zone was a circle with a diameter of 6.0 mm. The Technolas 217C group tended to have oval cuts in comparison with the VISX S4 group, and the difference between the programmed (6.0 mm) and topographic diameters was significant in both groups.

CONCLUSIONS

There was a difference between the programmed and postoperative topographic diameters of the ablation zone. The postoperative ablation zone differed in shape and size according to the type of excimer laser.

Multizone model for postsurgical corneas: analysis of standard and custom LASIK outcomes

A multizone model for postsurgical corneal topography is presented and applied to a comparative analysis of the outcome of standard and customized myopic LASIK. The different zones are segmented automatically by a clustering algorithm. The algorithm uses a set of three local descriptors, which correspond to normalized physical magnitudes computed for each point of the corneal topography map: Gauss curvature, root-mean-square (RMS) fit error to an ellipsoid surface model, and distance to the center of the topographic map. Both presurgical and post-LASIK corneal topographies of 31 eyes were analyzed using monozone and multizone models. The patients were classified into three groups according to the different LASIK treatments applied: Allegretto, Zyoptix, and PlanoScan. For post-LASIK corneas, the multizone model provided a lower fit error, an average of 1.2+/-0.4 microm versus 2.4+/-0.7 microm (monozone). The comparative analysis of the three different LASIK treatments showed no improvement of custom over standard treatments. The outcomes of Zyoptix and PlanoScan were basically equivalent and consistent with previous findings: The higher-order aberration (HOA) increased by a factor of two. The increase in HOA was higher, by a factor of three, after the Allegretto treatment. The multizone model shows a higher-fidelity representation and permits a deeper understanding of the postsurgical cornea.

Higher Order Aberrations and Relative Risk of Symptoms After LASIK

PURPOSE

To understand what level of higher order aberrations increases the relative risk of visual symptoms in patients after myopic LASIK.

METHODS

This study was a retrospective comparative analysis of 103 eyes of 62 patients divided in two groups, matched for age, gender, pupil size, and spherical equivalent refraction. The symptomatic group comprised 36 eyes of 24 patients after conventional LASIK with different laser systems evaluated in our referral clinic and the asymptomatic control group consisted of 67 eyes of 38 patients following LADARVision CustomCornea wavefront LASIK. Comparative analysis was performed for uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), contrast sensitivity, refractive cylinder, and higher order aberrations. Wavefront analysis was performed with the LADARWave aberrometer at 6.5-mm analysis for all eyes.

RESULTS

Blurring of vision was the most common symptom (41.6%) followed by double image (19.4%), halo (16.7%), and fluctuation in vision (13.9%) in symptomatic patients. A statistically significant difference was noted in UCVA (P = .001), BSCVA (P = .001), contrast sensitivity (P < .001), and manifest cylinder (P = .001) in the two groups. The percentage difference between the symptomatic and control group mean root-mean-square (RMS) values ranged from 157% to 206% or 1.57 to 2.06 times greater.

CONCLUSIONS

Patients with visual symptoms after LASIK have significantly lower visual acuity and contrast sensitivity and higher mean RMS values for higher order aberrations than patients without symptoms. Root-mean-square values of greater than two times the normal after-LASIK population for any given laser platform may increase the relative risk of symptoms.

Efficacy of Measuring Visual Performance of LASIK Patients under Photopic and Mesopic Conditions

Introduction: The aim of the study was to compare the visual performance of LASIK eyes measured using high-contrast logMAR letter charts under bright (photopic) and dim (mesopic) conditions. Materials and Methods: A total of 46 subjects (35 ± 8 years of age) undergoing LASIK procedures were recruited for the study. The best spectacle-corrected visual acuity (BSCVA) of each subject was measured using the high-contrast ETDRS logMAR chart under photopic and mesopic conditions at 3 visits: preoperative (Pre), 1 month postoperative (Post1) and 3 months postoperative (Post3). The differences in logMAR scores for the right eyes only were analysed for the Pre-Post1 (n = 46), Pre-Post3 (n = 18) and Post1-Post3 (n = 16) comparisons. Results: The logMAR scores of subjects were worse at the 1-month postoperative visit than preoperatively, and improvement in visual performance was seen at the 3-month postoperative visit. These changes in visual performance became more evident under mesopic conditions. The means and standard errors of the differences in logMAR scores for the Pre-Post3 (0.097 ± 0.020) were slightly larger than those of the Pre-Post1 (-0.067 ± 0.019) and Post1-Post3 (0.031 ± 0.012) comparisons. Under mesopic conditions, the visual performance of the subjects was statistically significant for the 3 comparisons, but not under photopic conditions. Conclusion: High-contrast logMAR chart performed under mesopic conditions has the potential to replace visual acuity measured under photopic conditions in providing more reliable representation of postoperative visual outcomes of LASIK eyes. Eye doctors should consider performing this vision test routinely to gauge the success of LASIK surgery. Key words: Contrast sensitivity, logMAR chart, Visual acuity

Size of corneal topographic effective optical zone: comparison of standard and customized myopic laser in situ keratomileusis

PURPOSE

To investigate the corneal topographic effective optical zone (EOZ) in eyes after wavefront-guided myopic laser in situ keratomileusis (LASIK) and to compare them with the EOZ after standard LASIK.

DESIGN

Retrospective, case-control study.

METHODS

We evaluated the corneal topographic maps of 41 eyes of 25 consecutive patients who had CustomVue LASIK (CV LASIK) and 41 eyes of 23 patients who had standard LASIK with correction up to -7 diopters using the VISX Star S4 laser (VISX Inc, Santa Clara, California, USA). On the refractive map of the Humphrey Topography System, we defined the EOZ as the area outlined by a change of corneal power of 0.5 diopters from the power at the center of the pupil. We analyzed the differences in EOZs of the two ablation patterns and the correlation between EOZ and magnitude of refractive correction.

RESULTS

The mean postoperative EOZs were 17.9 +/- 3.7 mm(2) and 11.4 +/- 3.4 mm(2) after CV and standard LASIK, representing 60% and 40% of the laser-programmed optical zones, respectively (both P < .0001). There was no correlation between the postoperative EOZs and the magnitude of refractive correction for both ablations (all P > .05). In eyes with spherical correction (cylinder < or =0.25 diopters), CV LASIK increased the preoperative EOZ by 3.8 +/- 5.6 mm(2) (P = .018), whereas standard LASIK decreased EOZ by 4.5 +/- 5.2 mm(2) (P = .005).

CONCLUSION

CV LASIK created larger corneal topographic EOZs than standard ablation. In eyes with spherical correction, the preoperative EOZ was expanded by CV LASIK and reduced by standard LASIK.

Factors affecting the change in lower-order and higher-order aberrations after wavefront-guided laser in situ keratomileusis for myopia with the Zyoptix 3.1 system

PURPOSE

To identify factors that affect the change in lower- and higher-order wavefront aberrations after myopic wavefront-guided laser in situ keratomileusis (wg-LASIK).

SETTING

Department of Ophthalmology, Johann Wolfgang Goethe-University, Frankfurt am Main, Germany.

METHODS

Sixty myopic eyes of 32 patients were treated with wg-LASIK (Zyoptix version 3.1, Bausch & Lomb) and had an uneventful follow-up of 12 months. Wavefront errors were measured preoperatively and 12 months after LASIK and were computed for pupil diameters (PDs) of 3.5 mm and 6.0 mm. Multiple stepwise regression analysis was performed to assess the influence of patient age, spherical equivalent (SE), sphere, cylinder, optical zone (OZ) diameter, and the preoperative individual Zernike coefficients on lower- and higher-order aberration (HOA) change.

RESULTS

The mean preoperative SE was -5.59 diopters (D) +/- 2.20 (SD) (range -1.00 to -9.50 D); the mean OZ diameter was 6.70 +/- 0.68 mm (range 5.6 to 8.1 mm). Reduction in almost all Zernike coefficients was influenced significantly by the preoperative amount of the individual coefficient. The effect varied among the coefficients and was lower with the 6.0 mm PD. With the 3.5 mm PD, age, SE, sphere, cylinder, and OZ diameter did not have a significant effect on individual Zernike coefficients. With the 6.0 mm PD, SE and OZ diameter had a significant effect on the induction of Z4(0); the OZ diameter also had an effect on the induction of coma root mean square.

CONCLUSIONS

Three groups of factors influenced the change in HOAs: The negative correlation with the magnitude of preoperative HOA values reflected the effect of the wavefront-guided algorithm. The SE and OZ diameter affected the inadvertent induction of spherical aberrations. Randomly acting effects such as decentration or flap creation, which were not included in the model, affected the induction of HOAs, particularly coma-like terms.

Functional outcome and patient satisfaction after Artisan phakic intraocular lens implantation for the correction of myopia

PURPOSE

To determine patient satisfaction after Artisan phakic intraocular lens (PIOL) implantation to correct myopia.

DESIGN

Non-comparative prospective case series.

METHODS

One hundred twenty eyes of 60 patients who had undergone Artisan PIOL implantation to correct myopia were analyzed. A validated questionnaire that consisted of 66 satisfaction items were self-administered by patients 12 months after surgery. Clinical parameters (PIOL decentration, the difference between pupil size and PIOL optical zone, and optical aberrations) were measured. Main outcome measures of satisfaction scale scores (global satisfaction, quality of uncorrected and corrected vision, night vision, glare, day and night driving) were analyzed. Correlations with clinical parameters were obtained.

RESULTS

After surgery, 98.3% of patients were satisfied, and 73.3% of patients considered their night vision to be the same or better; 44.1% of patients reported more bothersome glare. The night vision score correlated with spheric aberration (r = -0.303; P = .020). The glare score correlated with the difference between scotopic pupil size and PIOL optical zone (r = -0.280; P = .030) and vertical coma (r = -0.337; P = .009). The night driving score correlated with postoperative spheric equivalent (r = 0.375; P = .009), total root mean square aberrations (r = -0.337; P = .017), higher order root mean square aberrations (r = -0.313; P = .027), and vertical coma (r = -0.297; P = .036).

CONCLUSION

Overall satisfaction after Artisan PIOL implantation for myopia is excellent. The quality of night vision and night driving were related to scotopic pupil size, individual higher order aberrations, and residual refractive error.

Comparison of LASIK Using the NIDEK EC-5000 Optimized Aspheric Transition Zone (OATz) and Conventional Ablation Profile

PURPOSE

To compare a new ablation algorithm termed the optimized aspheric transition zone (OATz) with the conventional laser ablation profile for correction of myopic astigmatism.

METHODS

LASIK using OATz profile #6 or using conventional ablation profile was performed on 98 eyes of 53 patients (OATz #6 group) and 111 eyes of 66 patients (control #6 group), respectively. Further, LASIK using OATz profile #5 or using the conventional ablation profile was performed on 109 eyes of 58 patients (OATz #5 group) and 109 eyes of 75 patients (control #5 group), respectively. The effective optical zone, uncorrected visual acuity, manifest refraction, aberrations, contrast sensitivity, and patient satisfaction at 3 months postoperatively were compared between the OATz #6 and control #6 groups and between the OATz #5 and control #5 groups.

RESULTS

The effective optical zones in the OATz #6 group (6.45 +/- 0.29 mm) or OATz #5 group (6.40 +/- 0.21 mm) were significantly larger than those in the control #6 group (6.33 +/- 0.27 mm) or control #5 group (6.26 +/- 0.25 mm) (P < .01), respectively. Uncorrected visual acuity and manifest refraction were similar in all groups. The changes in contrast sensitivity were significant and favored the OATz #6 (P < .01) and OATz #5 groups (P < .05). The patient satisfaction survey found no statistical difference at 3 months postoperatively.

CONCLUSIONS

Patients treated with the OATz profiles had better visual quality as measured by contrast sensitivity and also had larger effective optical zones as compared with those treated by the conventional ablation profile.

Influence of pupil and optical zone diameter on higher-order aberrations after wavefront-guided myopic LASIK

PURPOSE

To investigate the influence of pupil and optical zone (OZ) diameter on higher-order aberrations (HOAs) after myopic wavefront-guided laser in situ keratomileusis (LASIK).

METHODS

Twenty-seven myopic eyes of 19 patients were included. The mean preoperative spherical equivalent was -6.86 diopters (D) +/- 1.24 (SD) (range -4.25 to -9.5 D); the mean planned OZ diameter was 6.26 +/- 0.45 mm (range 5.7 to 7.1 mm). All patients had uneventful wavefront-guided LASIK (Zyoptix version 3.1, Bausch & Lomb) and an uncomplicated follow-up of 12 months. Wavefront measurements were performed with a Hartmann-Shack sensor in maximum mydriasis preoperatively and 12 months after LASIK. Wavefront errors were computed for pupil diameters (PDs) of 3.0, 3.5, 4.0, 5.0, 6.0, and 7.0 mm for the individual OZ diameter and for the individual mydriatic PD (7.93 +/- 0.46 mm). The impact of the relationship between pupil diameter and OZ diameter (fractional clearance [FC]) on HOA was described and quantified using curvilinear regression with a 4th-order polynomial fit.

RESULTS

There was a reproducible relationship between FC and the amount of induced HOA. The change in HOA root mean square and primary spherical aberration (Z(4)0) was significantly correlated with FC. If the OZ was 16.5% larger than the pupil (FC = 1.17), only half the amount of HOA was expected to be induced than if the OZ equaled the pupil. In contrast, an OZ that was 9% smaller than the pupil (FC = 0.91) resulted in an HOA induction 50% higher than at FC = 1.

CONCLUSION

The OZ zone to pupil ratio (fractional clearance) had a significant impact on HOA induction after wavefront-guided LASIK.

Effective corneal refractive diameter as a function of the object tangent angle in visual space

PURPOSE

To determine whether the currently accepted method of selecting a minimum optical zone diameter for laser refractive surgery that is equal to or slightly greater than the dark-adapted pupil diameter provides a sufficient diameter of corneal surface to focus light arising from objects in the paracentral and peripheral visual field.

SETTING

Department of Ophthalmology and Visual Sciences, Texas Tech University Health Sciences Center, Lubbock, Texas, USA.

METHODS

An optical model of the anterior segment was developed to calculate the effective corneal refractive diameter (ECRD), which is the diameter of the area of cornea that refracts all incident light rays arising from an object through the physical pupil (PP). This model incorporates the patient variables of central anterior chamber depth (ACD), central corneal curvature (K(c)), and the diameter of the apparent entrance pupil (EP). The model was expanded to incorporate distant objects off the line of sight (LOS), described by their angular displacement from the fixation object in visual space (the object tangent angle delta(ob)). Results were calculated for the 360 meridian degree visual field (ie, for all objects in visual space perceptually displaced from the fixation object by angle delta(ob)). The effect of the prolate nature of the cornea was also investigated.

RESULTS

The ECRD expanded rapidly as a function of PP and delta(ob) but was minimally influenced by K(c). Beyond a critical object tangent angle delta(c), light rays striking the corneal vertex were not refracted through the PP, and the ECRD became an annular surface centered on the corneal vertex. The delta(c) was not a function of K, but increased as the PP increased and decreased as the ACD increased. The prolate nature of the cornea had little influence on the ECRD, even for very peripheral light rays.

CONCLUSIONS

The ECRD expands rapidly when considering distant objects only slightly displaced from the LOS. A patient treated with an optical zone equal to or slightly greater than the dark-adapted pupil diameter may experience vision quality loss for paracentral and midperipheral objects even under conditions of ambient indoor lighting.

Functional outcomes and patient satisfaction after laser in situ keratomileusis for correction of myopia

PURPOSE

To determine subjective patient satisfaction and self-perceived quality of vision after laser in situ keratomileusis (LASIK) to correct myopia and myopic astigmatism.

SETTING

Department of Ophthalmology, Academic Hospital Maastricht, Maastricht, The Netherlands.

METHODS

A validated questionnaire consisting of 66 items was self-administered by 142 consecutive patients. Seven scales covering a specific aspect of quality of vision were formulated. Aspects included global satisfaction, quality of uncorrected and corrected vision, quality of night vision, glare, daytime driving, and night driving. Main outcome measures were responses to individual questions and scale scores, and correlations with clinical parameters including refractive outcome, uncorrected visual acuity, best corrected visual acuity, ablation depth, and scotopic pupil-optical zone disparity were obtained.

RESULTS

The mean score for the overall satisfaction was 4.1 +/- 0.71 (SD) (scale 0 to 5.0). A total of 92.2% of patients were satisfied or very satisfied with their surgery, 93.6% considered their main goal of surgery achieved, and 92.3% would choose to have LASIK surgery again. Satisfaction with uncorrected vision was 3.03 +/- 0.71. The mean score for glare was 3.0 +/- 0.9. At night, glare from lights was believed to be more important than before surgery by 47.2%. Glare from oncoming car headlights after surgery was reported by 58.4% and was believed to be more bothersome for night driving than before surgery by 52.8%. Night driving was rated more difficult than before surgery by 39.4%, whereas 59.3% had less difficulty driving at night. There was a significant correlation between the uncorrected vision score and the postoperative spherical equivalent (r = 0.245) and postoperative astigmatism (r = 0.265). There was no correlation between the glare or night vision scores and the degree of correction, the amount of ablation depth, or the disparity between the scotopic pupil and the optical zone.

CONCLUSIONS

Self-perceived uncorrected vision after LASIK surgery for the correction of myopia and myopic astigmatism appears to be very good and is related to the postoperative residual error. Although the majority of patients postoperatively experienced glare, particularly with driving at night, this was not related to the pupil-optical zone disparity or degree of correction.

Evaluation of a clinical aberrometer for lower-order accuracy and repeatability, higher-order repeatability, and instrument myopia

BACKGROUND

Refractive surgery has stimulated the development of aberrometers, which are instruments that measure higher-order aberrations. The purpose of this study was to test one clinical aberrometer, the Complete Ophthalmic Analysis System (COAS), for its accuracy, repeatability, and instrument myopia for measuring sphere and astigmatism and its repeatability for measuring higher-order aberrations.

METHODS

Aberrations of 56 normal eyes (28 subjects) were measured with and without cycloplegia using a COAS, a conventional autorefractor and by subjective refraction. We evaluated lower-order accuracy (sphere and astigmatism) of the COAS and autorefractor by comparing that data with that of subjective refraction. We also tested COAS lower- and higher-order repeatability for 5 measurements taken in less than 1 minute. We evaluated instrument myopia by comparing cycloplegic and noncycloplegic measurements of the same eye. Data were analyzed for a 5.0-mm-diameter pupil.

RESULTS

Mean COAS spherical error was between -0.1 and +0.4 diopters (D), depending on cycloplegia and the kind of sphere power computation selected. Cylinder power errors were less than 0.1 D. COAS repeatability coefficients were better than 0.25 D, and instrument myopia was less than 0.4 D. These were comparable with those of autorefraction. Higher-order repeatability was sufficient to allow reliable measurement of normal third-order aberrations and spherical aberration.

CONCLUSIONS

Accuracy, repeatability, and instrument myopia of the COAS are similar to those of a conventional autorefractor. Accuracy and repeatability are also similar to those of subjective refraction. Like an autorefractor, the COAS provides instantaneous, objective measurements of sphere and astigmatism, but it also measures higher-order aberrations. We found that it is capable of reliably measuring problematic higher-order aberrations and is therefore a valuable asset for modern clinical eye care.

Functional optical zone after myopic LASIK as a function of ablation diameter

PURPOSE

To analyze spherical aberrations in patients who had myopic laser in situ keratomileusis (LASIK) with different optical zones and varying degrees of attempted corrections.

SETTING

Laser Refractive Center, University of California, Los Angeles, USA.

METHODS

This retrospective analysis comprised 78 eyes of 56 consecutive patients who had LASIK for myopia with the Alcon LADARVision excimer laser. The preoperative and 3-month postoperative functional optical zones (FOZs), a measure of spherical aberrations, were assessed in each eye. The change in FOZs was analyzed by size of the primary optical zone and degree of attempted correction.

RESULTS

The mean preoperative FOZ was 6.1 mm +/- 0.6 (SD) and the mean 3-month FOZ, 5.2 +/- 1.0 mm. The mean decrease was 0.9 +/- 1.0 mm (P < .0001). The mean decreases were 0.005 +/- 0.7 mm, 0.7 +/- 0.9 mm, and 1.6 +/- 0.9 mm in the low, moderate, and high attempted correction groups, respectively (P < .05), and 1.3 +/- 0.9 mm, 1.2 +/- 1.0 mm, 0.5 +/- 1.3 mm, and 0.3 +/- 0.7 mm in optical zone groups of 6.0 to 6.5 mm, 6.6 to 7.0 mm, 7.1 to 7.5 mm, and 7.6 to 8.0 mm, respectively (P < .05).

CONCLUSIONS

Larger optical zones had fewer postoperative spherical aberrations. Higher attempted corrections had larger increases in spherical aberrations. Larger treatment diameters minimized postoperative spherical aberrations.

Effect of expanding the treatment zone of the Nidek EC-5000 laser on laser in situ keratomileusis outcomes

PURPOSE

To evaluate the effect of expanding the treatment zone of the Nidek EC-5000 laser on postoperative visual acuity as well as night glare and halos after laser in situ keratomileusis (LASIK) using 4 ablation zone diameters.

SETTING

Division of Ophthalmology, Evanston Northwestern Healthcare and Northwestern University Medical School, Glenview, Illinois, USA.

METHODS

This prospective study comprised 301 eyes of 154 consecutive patients who had LASIK in 1 or both eyes using the Nidek EC-5000 laser by 1 surgeon with experience in keratomileusis and excimer laser refractive surgery. A 6.5 mm optical zone was used with a transition zone 1.0 mm larger than the pupil under scotopic conditions (7.5, 8.0, 8.5, or 9.0 mm). Targeted correction was calculated according to a customized clinical nomogram. All patients were queried about glare and halos preoperatively and 3 months postoperatively using a questionnaire assigning numeric values to the degree of perceived visual disturbance (0 = no glare or halos, 1 = minimal, 2 = moderate, 3 = severe).

RESULTS

The baseline uncorrected visual acuity (UCVA) was 20/200 or worse in 293 eyes. The baseline best spectacle-corrected visual acuity was 20/20 or better. The mean preoperative refractive sphere was -6.33 diopters (D) +/- 2.80 (SD) (range -1.00 to -16.25 D) and the mean preoperative refractive cylinder, 0.86 +/- 0.83 D (range 0 to +3.25 D). Three months postoperatively, 78% of eyes had a UCVA of 20/20 and 99%, of 20/40 or better. Preoperatively, 94 eyes (31%) had glare and halos. At 3 months, glare, halos, or both were present in 19 eyes of 11 patients (6.3%) (P<.0001); in 14 eyes, patients reported less severe glare and halos postoperatively than preoperatively.

CONCLUSIONS

The use of a peripheral transition zone 1.0 mm larger than the pupil under scotopic conditions resulted in a low incidence of glare and halos postoperatively and did not adversely affect visual acuity. There was no increase in postoperative complications including corneal ectasia.

Topographic and biomechanical differences between hyperopic and myopic laser in situ keratomileusis

PURPOSE

To evaluate the size, shape, and uniformity of the videokeratographic functional optical zone (FOZ) after laser in situ keratomileusis (LASIK) in 2 cohorts of patients with equivalent amounts of preoperative myopic or hyperopic astigmatism.

SETTING

Pepose Vision Institute, St. Louis, Missouri, USA.

METHODS

Eyes with myopic or hyperopic astigmatism (n=27 in each group) that had LASIK with the Visx Star S3 laser were retrospectively selected to match for level of preoperative refractive error. Slit-scanning videokeratography was performed preoperatively and 6 months postoperatively and analyzed using custom software. The FOZ was calculated by analyzing refractive power maps using a region-growing algorithm. Difference maps were generated from slit images and compared for interval change in corneal elevation, tangential curvature, and refractive power. The difference maps were also averaged (mean difference maps) for each target population. A Zernike decomposition of corneal first-surface elevation was performed to compare postoperative values with baseline parameters.

RESULTS

The mean postoperative refractive sphere at 6 months was -0.17 diopter (D) +/- 0.66 (SD) and +0.25 +/- 0.85 D in the myopia group and hyperopia group, respectively, and the mean postoperative astigmatism, -0.49 +/- 0.32 D and -0.65 +/- 0.52 D, respectively (P=.11). Based on the refractive power maps, the mean preoperative and postoperative myopic FOZ was 33.09 +/- 7.30 mm(2) and 30.94 +/- 5.43 mm(2), respectively, and the mean hyperopic FOZ, 33.19 +/- 7.96 mm(2) and 37.99 +/- 6.88 mm(2), respectively. After LASIK, there was an increase in magnitude of negative anterior corneal surface spherical-like Zernike values in the myopia group (P<.0001) and an increase in magnitude of positive spherical-like Zernike values in the hyperopia group. Postoperatively, significant induction of corneal surface horizontal coma was noted in hyperopic eyes (P<.0001). Hyperopic eyes, on average, had larger topographic FOZs after LASIK, but with less uniformity of curvature and power change than myopic eyes.

CONCLUSIONS

Hyperopic LASIK, which involves more transition points along the ablation diameter, produced a less uniform topographic FOZ than typical myopic treatments. Less predictable biomechanical changes from the circumferential release of tension on collagen bundles after midperipheral hyperopic ablation and greater variation in beam centration and the angle of incidence may contribute to the greater variability in corneal curvature and power in hyperopic LASIK than in myopic LASIK.

Wavefront-guided LASIK with the Zyoptix 3.1 system for the correction of myopia and compound myopic astigmatism with 1-year follow-up

OBJECTIVE

To assess safety, efficacy, predictability, stability, and change in aberrations after wavefront-guided LASIK for myopia and myopic astigmatism.

DESIGN

Prospective, nonrandomized, self-controlled trial.

PARTICIPANTS

Wavefront-guided LASIK was performed in 97 eyes in a 1-year trial. Treated eyes had a mean subjective manifest spherical equivalent (SE) of -5.22+/-2.07 diopters (D), with a range of -0.25 to -9.00 D of myopia and 0 to -3.25 D of astigmatism.

INTERVENTION

After a microkeratome cut, a wavefront-based excimer ablation (Zyoptix 3.1) was performed. The full treatment to achieve emmetropia of an early nomogram provided by the system manufacturer was used in all procedures.

MAIN OUTCOME MEASURES

Safety, efficacy, predictability, and stability were evaluated at 1, 3, and 12 months postoperatively. Wavefront changes of higher order aberrations (HOAs) at 1 year were determined for pupil sizes of 3.5 and 6 mm.

RESULTS

At 1 year postoperatively, uncorrected visual acuity (VA) was 20/20 or better in 83% of the eyes, and 20/40 or better in 98%. The mean subjective manifest SE at 1 year was -0.25+/-0.43 D; it was within 0.50 D in 77% and within 1.0 D in 95%. No eye lost > or =2 lines of best spectacle-corrected VA (BSCVA) at 1 year postoperatively; 40 eyes gained 1 line of BSCVA, and 5 eyes gained 2 lines. The total HOA root mean square (RMS) increased on average by a factor of 1.23+/-0.57 with a 3.5-mm pupil; for the 6 mm pupil, the increase factor was 1.52+/-0.36. No change or reduction in the total HOA RMS was observed in 45.5% of the eyes for a 3.5-mm pupil and in 20.6% for a 6-mm pupil. There was a significant increase of primary spherical aberration (Z 4,0) by a factor of 4.11+/-10.17 for 3.5-mm pupils and 4.31+/-6.76 for 6-mm pupils.

CONCLUSIONS

Wavefront-guided LASIK using Zyoptix 3.1 is an effective and safe procedure for the treatment of myopia and myopic astigmatism. Although in close to half of the eyes HOAs could be reduced, there was still undercorrection and induction of HOAs with the algorithm employed.

Pupil size and night vision disturbances after LASIK for myopia

PURPOSE

To examine whether standardized, preoperative evaluation of pupil sizes can predict the risk of night vision visual disturbances after bilateral laser in situ keratomileusis (LASIK) for myopia.

METHODS

A prospective study was carried out involving 46 patients who underwent bilateral LASIK for myopia. Pupil sizes were measured before surgery using an infrared pupillometer under standardized settings. Pre- and postoperative refraction and best spectacle-corrected visual acuity (BSCVA) were registered. At the 3-month follow-up visit, the patients completed a questionnaire regarding night vision pre- and postoperatively.

RESULTS

The mean bilateral, spherical equivalent refraction (SE) was - 8.76 D (range 6.32 to - 12.0 D) preoperatively, and - 1.69 D (range 0 to - 4.38 D) postoperatively. The mean bilateral BSCVA was not changed by the operations. We found a significant correlation between large scotopic pupil sizes and the impression of worsened night vision (p < 0.01). A significant correlation between gender (males) and subjectively reduced night vision postoperatively was also found (p < 0.05).

CONCLUSION

Large pupil size measured preoperatively is correlated with an increased frequency of subjectively experienced post-LASIK visual disturbances during scotopic conditions. We recommend preoperative evaluation of pupil size in all patients prior to LASIK surgery.

[Current state of wavefront guided corneal surgery to correct refraction disorders]

The present review describes the current status of wavefront-guided corneal surgery and up-to-date results. Wavefront-guided LASIK procedures performed to date achieved uncorrected vision of i.o or better in a larger number of patients than with conventional LASIK surgery, but the "eagle eye" has remained the exception. In part of the patients reductions of higher order aberrations could be obtained, but in the majority of ca-ses an increase was observed. This increase was however less than with conventional LASIK surgery. Correction of higher order aberrations has not yet been perfected since the predictability of corrections appears to be deserving of improvement on the one hand and aberrations are still induced by the technique on the other hand.

Quality of vision and patient satisfaction after LASIK

PURPOSE

The purpose of this article is to review the literature and find characteristics that lead to improved patient satisfaction and better quality of vision.

RECENT FINDINGS

Flatter preoperative corneal curvature is a risk factor for starbursts after laser-assisted in situ keratomileusis (LASIK). Pupil size has not been found to be correlated with night vision symptoms. Wavefront-guided ablations reduce higher-order aberrations in comparison with traditional LASIK. Night vision symptoms are correlated with younger age, greater correction/increased ablation depth, enhancement, and decreased ablation diameter. Contrast sensitivity has been found to initially decrease after LASIK, returning to baseline 6 to 12 months postoperatively.

SUMMARY

LASIK has quickly become the refractive procedure of choice around the world. Quality of vision and patient satisfaction after LASIK can be difficult to assess because of the many variables that must be considered to accurately measure these endpoints. Preoperative characteristics such as: increased patient age, decreased corneal toricity, or increased pupil size reduce patient satisfaction. Intraoperative factors like decentration, ablation-zone size, active eye tracking, and wavefront guided ablations affect quality of vision. Finally, postoperative factors such as night vision symptoms, reduced contrast sensitivity, and re-treatment can lead to a decline in patient satisfaction. Eliminating or limiting these variables may lead to increased patient satisfaction and higher quality of vision after LASIK.

Wavefront-optimized ablation profiles

PURPOSE

To describe a method for calculating wavefront-optimized ablation profiles to precompensate for the spherical aberration and higher-order astigmatism induced by myopic, hyperopic, and astigmatic corneal laser corrections.

SETTING

IROC-Institut für Refraktive und Ophthalmo-Chirurgie, and Institute for Biomedical Engineering, Swiss Federal Institute of Technology, Zürich, Switzerland.

METHODS

The basic ablation profile for myopic, hyperopic, and astigmatic correction is derived from the 2nd-order Zernike representation of wavefront aberrations. Including 4th-order spherical aberration and higher-order astigmatism in the theoretical calculation of the ablation profile allows precompensation for the expected amount of higher-order aberrations (HOAs). The shapes of wavefront-optimized ablation profiles are compared with the shapes of "classic" ablation profiles for myopic and astigmatic corrections.

RESULTS

The introduction of precompensating spherical aberration and higher-order astigmatism leads to a more aspheric ablation profile with a significant increase in ablation depth (up to 35%) in the midperiphery of the optical zone. The central ablation depth remains unchanged in the myopic correction but increases by 3% in cylinder correction.

CONCLUSIONS

Wavefront-optimized ablation profiles provide a simple method to precompensate for the expected 4th-order spherical aberration and higher-order astigmatism in the average eye. Further clinical studies must be performed to prove the theoretical results; demonstrate the reduction in HOAs; and predict safety, predictability, and stability of wavefront-optimized ablation profiles.

Comparative Study of Ablation Profiles of Six Different Excimer Lasers

PURPOSE

To compare the morphological features of photorefractive ablations produced by six different excimer lasers.

METHODS

A spherocylindrical photoablation (-2.00 -2.00 x 90 degrees; 6-mm optical zone) was performed on regular fluence plates with six excimer lasers: Bausch & Lomb Technolas 217C, Schwind Esiris, Kera Technology Isobeam D200, Ladarvision 4000, Zeiss Meditec MEL 70 G-Scan, and Visx Star S3. Morphometric analysis of the fluence plates provided superficial measurements of the ablated areas.

RESULTS

Two areas were identified visually: a central area with a complete ablation of the metallic surface layer and a surrounding area with a partial ablation. The dimensions of the ablated areas were highly variable in the lasers tested. The major differences appeared in the total ablated area (ranging from 38.55 mm2 [Schwind] to 81.94 mm2 [Bausch & Lomb] and in the peripheral to total area ratio (ranging from 36.95% [Schwind] to 59.51% [Ladarvision]).

CONCLUSION

Large differences appeared in the superficial dimensions and contours of the ablations produced by different excimer lasers for the treatment tested in this study. It remains unknown how these different ablation patterns induce the same optical correction, but we assume that the depth of the ablation compensates for the differences in the surface extension of the ablated areas.