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.

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.

The effects of programmed optical zones on achieved corneal refractive power with myopic astigmatism after small incision lenticule extraction (SMILE): a vector analysis.

PURPOSE: To evaluate the effects of different programmed optical zones (POZs) on achieved corneal refractive power (CRP) with myopic astigmatism after small incision lenticule extraction (SMILE). METHODS: In total, 113 patients (113 eyes) were included in this retrospective study. The eyes were divided into two groups according to POZ: group A (6.5, 6.6, and 6.7 mm, n = 59) and group B (6.8, 6.9, and 7.0 mm, n = 54). Fourier vector analysis was applied to evaluate the error values between the attempted and achieved corneal refractive power (CRP). Alpins vector analysis was used to calculate surgically induced astigmatism (SIA), difference vector (DV), magnitude of error (ME), and astigmatism correction index (ACI). Multivariate regression analysis was performed to assess potential factors associated with the error values. RESULTS: The error values in the group with large POZ were closer to zero, and significantly associated with the POZ at 2 and 4 mm of the cornea (ß = - 0.50, 95% confidence interval [CI] [- 0.80, - 0.20]; ß = - 0.37, 95% CI [- 0.63, - 0.10], P < 0.05, respectively). For the correction of astigmatism, the values of SIA, ME, and ACI were lower in group B than in group A (P < 0.05). The fitting curves between TIA and SIA were y = 0.83x + 0.19 (R2 = 0.84) and y = 1.05x + 0.04 (R2 = 0.90), respectively. CONCLUSIONS: Smaller POZs resulted in higher error values between the achieved- and attempted-CRP in the SMILE procedure, which should be considered when performing surgery.

Comparison of visual quality after SMILE correction of low-to-moderate myopia in different optical zones.

OBJECTIVE: To compare the effects of different optical zones for small-incision lenticule extraction (SMILE) on postoperative visual quality in low-to-moderate myopia. METHODS: This retrospective case-control study involved patients who underwent SMILE using two optical-zone diameters: 6.5 mm (50 patients, 100 eyes) and 6.8 mm (50 patients, 100 eyes). Uncorrected visual acuity (UCVA), best corrected visual acuity, spherical equivalent (SE), corneal higher-order aberrations (HOAs), and subjective visual-quality questionnaire scores were assessed. RESULTS: Postoperatively, UCVA and SE did not differ between the two groups (P > 0.05). In both groups, corneal HOAs, spherical aberration, and coma significantly increased at 1 and 3 months postoperatively (P < 0.05), while trefoil was unchanged after surgery (P > 0.05). Corneal HOAs, spherical aberration, and coma significantly differed between the groups at 1 and 3 months (P < 0.05), while trefoil did not (P > 0.05). Visual-quality scores were higher in the 6.8 mm group than in the 6.5 mm group at 1 month (P = 0.058), but not at 3 months (P > 0.05). In both groups, subjective scores significantly decreased at 1 month (P < 0.05) and gradually returned to the preoperative level at 3 months (P > 0.05). The subjective visual-quality scores were negatively and positively correlated with pupillary and optical-zone diameter, respectively (P < 0.05 for both). Objective visual-quality indicators (HOAs, spherical aberration, and coma) were negatively correlated with optical-zone diameter (P < 0.05) but not pupillary diameter (P > 0.05). CONCLUSION: SMILE in different optical zones effectively corrected low-to-moderate myopia. The larger the optical-zone diameter, the better the early postoperative visual quality.

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 (EOZV), pupil-based (EOZP), 4 mm-ring-based total corneal refraction method (EOZ4) and tangential curvature difference map method (EOZD), 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. EOZV, EOZP, EOZ4 and EOZD 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 EOZV and EOZP 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 EOZV was the closest to POZ, followed by EOZP. The ΔEOZs showed no significant difference with eccentricity, AD and corneal aberrations.

Comparison of early visual quality in patients with moderate myopia using different optical zones in small incision lenticule extraction (SMILE).

BACKGROUND: The early visual qualities of patients with moderate myopia were evaluated after small incision lenticule extraction (SMILE) using different optical zones. METHODS: In this retrospective case study, 27 cases (51 eyes) were selected, including 10 cases in Group A (19 eyes), 6.6-6.8 mm in the optical zone, 10 cases in Group B (19 eyes), 6.4-6.5 mm in the optical zone, and 7 cases in Group C (13 eyes),6.1-6.3 mm in the optical zone. The following items were examined preoperatively and 1 month postoperatively: uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), spherical, cylinder, central corneal thickness (CCT), corneal mean curvature (CMC), total ocular aberrations (TA), total low order aberrations (tLOAs), defocus, astigmatism and total high order aberrations (tHOAs), spherical, coma, trefoil, modulation transfer function (MTF), MTFcutoff, SR, objective scatter index (OSI), point scatter function at 50 and 10% (PSF50%, PSF10%), and contrast visual acuity of 100, 20, and 9% (VA100%, VA20%, and VA9%). We compared the three groups by Kruskal-Wallis test. Wilcoxon signed ranks test was used for each group before and 1 month after surgeries. P< 0.05 was considered statistically significant. RESULTS: There was no significant difference in UCVA, BCVA, CCT, cylinder, and CMC in three groups preoperatively and 1 month postoperatively (P> 0.05). Comparison of the aberrations of the three groups showed statistically significant difference only in TA, tLOA, defocus, astigmatism and SA preoperatively, and trefoil 1 month postoperatively(P< 0.05). The postoperative TA, tLOAs, defocus, astigmatism and trefoil of the three groups were lower than those before surgeries (P< 0.05). The postoperative tHOAs of Group B and C was lower than those before surgeries (P< 0.05). The MTF results showed that before surgeries, there were significant differences in three groups (P< 0.05) in spatial frequencies 5~15 cycles per degree (cpd), and no differences in 20~30 cpd(P> 0.05), while no difference were observed in all spatial frequencies postoperatively (P> 0.05). Comparing the preoperative and postoperative MTF values for each group, the results showed that there was a significant difference in Group C at 5~20 cpd after surgeries(P< 0.05). There was no significant difference in MTFcutoff, SR, OSI, PSF50%, PSF10%, VA100%, VA20%, and VA9% in the three groups preoperatively (P> 0.05). One month after surgeries, higher VA9% values were measured for Group C compared to Group A and B (P < 0.05). There was no significant difference in each group before and after surgeries (P> 0.05). CONCLUSION: SMILE could improve the visual qualities of patients with moderate myopia. Reducing the surgical optical zone will only affect night vision slightly.

Comparison of refractive outcomes after photorefractive keratectomy with different optical zones using Mel 90 excimer laser.

BACKGROUND: A larger optical zone for photorefractive keratectomy may improve optical quality and stability. However, there is need for limiting ablation diameter in that a larger ablation diameter requires greater ablation depth, and minimizing ablation depth may reduce adverse effects on postoperative wound healing, haze and keratoectasia. In this study, we compared the changes in clinical outcomes and the degree of regression between a 6.0 mm optical zone and 6.5 mm optical zone following PRK. METHODS: The records of 95 eyes that had undergone PRK with a 6.0 OZ (n = 40) and a 6.5 OZ (n = 55) were retrospectively reviewed. We compared data including the spherical equivalent of manifest refraction (SE of MR), simulated K (Sim K), thinnest corneal thickness, change in thinnest corneal thickness (the initial value divided by corrected diopter [ΔTCT/CD]), Q value, corneal higher order aberrations (HOAs) and spherical aberration (SA) pre-operation, at 3 and 6 months postoperative and at the last follow-up visit (Mean; 20.71 ± 10.52, 17.47 ± 6.57 months in the 6.0 and 6.5 OZ group, respectively). RESULTS: There were no significant differences in the SE of MR, Sim K and UDVA between the 6.0 OZ group and the 6.5 OZ group over 1 year of follow-up after PRK, and the 6.0 OZ group required less ΔTCT/CD than the 6.5 OZ group. The 6.5 OZ group showed better results in terms of post-operative HOAs of RMS, SA and Q value. When comparing that pattern of change in Sim K, there was no significant difference between the 6.0 OZ group and the 6.5 OZ group. CONCLUSIONS: The clinical refractive outcomes and regression after PRK using Mel 90 excimer laser with a 6.0 OZ were comparable to those with a 6.5 OZ.

Changes in Corneal Dynamics and Effective Optical Zone After Transepithelial Photorefractive Keratectomy for Myopia.

Objectives: The objective of this study was to analyze the changes in the effective optical zones (EOZ) using topographic techniques on the tangential curvature difference map at post-operative 1-year following transepithelial photorefractive keratectomy (T-PRK) and to identify parameters linked to the EOZ alterations. Methods: The study comprised 55 eyes of 55 myopic patients who underwent T-PRK. EOZs were measured using the tangential curvature difference map of the Scheimpflug tomography system. Correlations between the EOZ alterations and relevant parameters were assessed. Results: The EOZ was significantly lower than the programmed optical zone (p<0.001). The decrease in the EOZ was significantly relevant to the decrease in mean keratometry (p=0.01, B/95% confidence interval [CI]: 0.139/0.033 and 0.244, standardized Beta: 0.346) and the increase in maximum keratometry (p=0.003, B/95% CI: 0.072/0.026 and 0.118, standardized Beta: 0.406). Conclusion: The EOZ decreased in the 1st year after T-PRK in eyes with myopia. The decrease in the EOZ was correlated positively with the decrease in mean and maximum keratometry. T-PRK may be an effective and safe surgery for the correction of mild-to-moderate myopia.

Comparative study of functional optical zone: small incision lenticule extraction versus femtosecond laser assisted excimer laser keratomileusis.

AIM: To investigate the size of functional optical zone (FOZ) after small incision lenticule extraction (SMILE) versus femtosecond laser assisted excimer laser keratomileusis (FS-LASIK) for myopia correction and potential associated factors for FOZ. METHODS: A total of 133 patients who received corneal refractive surgery in our hospital between November 2018 and July 2021 were retrospectively enrolled. There were 63 patients (123 eyes) in SMILE group and 70 patients (139 eyes) in FS-LASIK group. The size of FOZ was measured using Pentacam 3-dementional anterior segment analyzer before and 3mo after surgery, so as to analyze postoperative achieved functional optical zone (AFOZ) and its contributing parameters. RESULTS: When planned functional optical zone (PFOZ) was 6.5 mm for both groups, AFOZ was 1.45±0.27 and 1.67±0.25 mm smaller than preoperative FOZ in SMILE group and FS-LASIK group 3mo after surgery. AFOZ in SMILE group was significantly larger than that in FS-LASIK group (P<0.001). Variation of FOZ was negatively correlated with preoperative spherical equivalent (SE) and positively correlated with variation of mean keratometry value (ΔKm), variation of spherical aberration (ΔSA), and variation of Q-value (ΔQ, all P<0.001) in both groups. Multiple variable linear regression equations were ΔFOZ=1.354-0.1×pre-SE+0.336×ΔQ+1.462×ΔSA in SMILE group and ΔFOZ=1.512+0.137×ΔQ+0.468×ΔSA in FS-LASIK group. CONCLUSION: AFOZ is significantly smaller than preoperative FOZ in both SMILE and FS-LASIK groups. With the same PFOZ, larger AFOZ is achieved in SMILE group than in FS-LASIK group.

Impact of the pupil size - central optical zone diameter relationship on visual performance in aspheric multifocal contact lenses.

PURPOSE: To determine the impact of different central optical zone diameters (COZDs), obtained from pupil size, on the visual performance of presbyopic subjects fitted with centre-distance simultaneous-image multifocal contact lenses (SIMCLs). METHODS: Thirty-two presbyopic volunteers, between 45-58 years of age, participated in this prospective, controlled, double-blind study. Subjects were fitted with 5 centre-distance SIMCLs of variable COZD, determined from the measurement of pupil size under photopic light conditions and corresponding to 60, 70, 80, 90 and 100 % of pupil diameter. Subjects visual performance was evaluated through the measurement of distance, intermediate and near visual acuity (VA), "visual functional range" (VFR) obtained from the VA Defocus Curve (VADC) and Contrast Sensitivity Function (CSF), using a third-generation retina display iPad. RESULTS: Statistically significant differences were obtained for both distance (p = 0.01) and intermediate (p = 0.001) VA amongst designs. Best results were obtained with 80 % and 90 % COZDs compared to 60 %. No significant differences in VFR (p > 0.05) were obtained amongst the different COZDs. 90 and 100 % COZDs offered statistically significant better results at 6 and 18 cycles per degree (cpd) in the CSF, compared to the 60 and 70 % designs. CONCLUSIONS: SIMCLs with COZDs of 80-90 % and of 90-100% of photopic pupil diameter offered better distance and intermediate VA, without a decline in near performance, and superior contrast sensitivity at medium and high spatial frequencies respectively, compared to lower COZD designs.

Functional optical zone after wavefront-optimized versus wavefront-guided laser in situ keratomileusis.

Background: Many studies have used functional optical zone (FOZ) as a measure to compare different refractive laser treatment modalities. However, to our knowledge, no study has compared wavefront- optimized (WFO) and wavefront-guided (WFG) laser in situ keratomileusis (LASIK) using FOZ. We compared the FOZ after WFO versus WFG LASIK in patients with myopia and myopic astigmatism. Methods: In this prospective comparative study, we included 100 myopic eyes of 50 patients with or without astigmatism. They were divided into two groups according to the platform used: WFO or WFG femtosecond LASIK. Using Holladay's equivalent keratometry reading (EKR) report of Pentacam HR, FOZ was defined as a zone centered on the pupil center with a standard deviation (SD) of 0.5 D, around the mean EKR. The differences in FOZ between the two platforms were analyzed at 3 months postoperatively. Visual acuity, refractive error, corneal asphericity (Q-value), and root mean square of higher-order aberrations (RMS for HOAs) were evaluated and compared. Results: The mean (SD) of patient age was 26.64 (5.67) years. The preoperative characteristics of the two groups were comparable (all P > 0.05). The intended optical zone (IOZ) was 6 mm in both groups. The mean laser ablation depth was significantly greater in the WFG group (18 µm per D) than in the WFO group (16 µm per D) (P = 0.035). At 3 months postoperatively, the mean (SD) of FOZ diameter was 4.32 (0.94) mm (71.99% [15.68%] of intended optical zone) in the WFO group and 4.16 (1.13) mm (69.33% [18.78%] of intended optical zone) in the WFG group, with no significant difference between the two groups (P = 0.622). The change in corneal asphericity was greater in the WFG group than in the WFO group (P = 0.034). Postoperative mean corrected and uncorrected distance visual acuity, manifest refraction, and RMS for HOAs showed no significant difference between the two groups (all P > 0.05). Conclusions: We found that WFG LASIK resulted in greater ablation depth and change in corneal asphericity than WFO LASIK at 3 months postoperatively. However, there was no significant difference in FOZ diameter, refractive error, and RMS for HOAs between the two groups. Further research is needed to confirm these findings.

Effect of the Optical Zone Ablation Diameter on Higher Order Aberrations After Transepithelial Photorefractive Keratectomy: A Cohort Study.

OBJECTIVES: To study the effect of the optical zone diameter of ablation on higher order aberrations after transepithelial photorefractive keratectomy for myopia and myopic astigmatism. METHODS: In this historical cohort study in 2019, patients were grouped into 7-mm (Gr-1) and 6.5-mm optical zones of ablation (Gr-2). Topographic and higher order aberrations at analysis diameters of 2, 4, and 6 mm were measured before and six months after transepithelial photorefractive keratectomy. The changes in the five types of higher order aberrations in the 6.5 mm and 7 mm groups were compared. The pupillary diameter was correlated with the change in the higher order aberrations. RESULTS: We had 24 eyes of 12 patients in Gr-1 and 80 eyes of 40 patients in Gr-2. The trefoil type of higher order aberrations at 6 mm was significantly more prevalent in Gr-2 than in Gr-1 before surgery (p = 0.038). The change in spherical aberration six months after surgery compared with before was significantly more at 6 mm in the eyes of Gr-2 patients (p = 0.02). For the eyes managed by the 7-mm optical zone of ablation for transepithelial photorefractive keratectomy, the decline in the different types of higher order aberrations was significant. The pupillary diameter was positively correlated with the change in the third-order coma in Gr-2 (Spearman coefficient, p = 0.005). All the eyes had an uncorrected visual acuity of 0.0 LogMAR in Gr-1 and 95% in Gr-2 after surgery. CONCLUSIONS: The higher order aberrations six months after transepithelial photorefractive keratectomy were similar in eyes managed with 7-mm and 6.5-mm optical zone for ablation. But a lower aberration coefficient in eyes was managed by the 7-mm zone than the 6.5-mm zone of optical ablation at 6-mm analysis diameter.

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.

Comparison of 6.0 mm versus 6.5 mm Optical Zone on Visual Outcomes after LASIK.

Previous studies have demonstrated safety and efficacy using 6.0 and 6.5 mm optical zones in the WaveLight EX500 Excimer Laser System but have not evaluated if differing optical zone sizes influence refractive outcomes. This study examines visual outcomes between two study populations undergoing LASIK with either a 6.0 mm (1332 patients) or 6.5 mm (1332 patients) optical zone. Outcomes were further stratified by severity of myopia (low, moderate, and high) and astigmatism (low and high). Patients were matched by age and preoperative manifest sphere and cylinder. Postoperative measurements were then compared. The 6.5 mm group demonstrated better postoperative manifest refractive spherical equivalent (MRSE), manifest sphere, and absolute value of the difference in actual and target spherical equivalent refraction (|∆ SEQ|), within the total population, moderate myopia, and low astigmatism groups, but this did not lead to improved postoperative uncorrected distance visual acuity (UDVA) or best corrected distance visual acuity (CDVA). Though astigmatic correction and postoperative angle of error were similar between optical zone sizes, they were significantly worse with high myopia. Overall, this study demonstrates differences in visual outcomes between the 6.0 and 6.5 mm optical zone sizes that may warrant consideration; however, essentially, the results are comparable between them.

Myopic outcomes after excimer laser phototherapeutic keratectomy (PTK).

PURPOSE: To evaluate refractive outcomes following excimer laser phototherapeutic keratectomy (PTK). METHODS: A retrospective non-randomized review of refractive outcomes of 146 consecutive eyes treated with excimer laser PTK at the Rothschild Foundation, Paris, France. Inclusion criteria were all patients undergoing PTK laser using a flying spot excimer laser system (Wavelight Allegretto, Alcon Surgical, Inc.) from October 2016 to June 2018. Exclusion criteria were incomplete data, irregular astigmatism and dystrophies of uncertain diagnosis. Preoperative diagnoses included recurrent corneal erosion syndrome without dystrophy and Cogan corneal dystrophies. The primary outcome measure was the change in spherical equivalent (SEQ) at M1 post PTK. The secondary outcome measure was the creation of a regression equation for predicting refractive outcomes after PTK, by analyzing the effect of ablation depth (AD) and optical zone (OZ) diameter. RESULTS: Fifty-eight eyes of 54 patients were included. The mean OZ was 7.352 mm±0.622. The mean AD was 18.362µm±21.406. At M1 postoperatively, the mean SEQ was -2.485 D±2.628 and mean final SEQ was -1.052 D±1.260. Both OZ and AD were independent variables with significant effects on the final visual outcome. A regression equation for predicting refractive outcomes was established. No complications were observed. CONCLUSION: The Wavelight flying spot excimer laser system produces myopic outcomes following PTK. Both OZ and AD are significant variables. A regression equation was created and may aid in prediction of refractive outcomes following PTK.

Comparison of efficacy and visual outcomes after SMILE and FS-LASIK for the correction of high myopia with the sum of myopia and astigmatism from -10.00 to -14.00 dioptres.

PURPOSE: To compare the efficacy and visual outcomes after femtosecond laser small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) in correcting high myopia. METHODS: This prospective, randomized study included patients who underwent SMILE or FS-LASIK for the correction of high myopia [the sum of spherical and cylindrical error from -10.00 to -14.00 dioptres (D)]. Preoperative, 1-month (P1m), 3-months (P3m) and 6-months (P6m) postoperative outcomes were analysed and compared between the two procedures. RESULTS: Ninety-six right eyes of 96 patients (SMILE: n = 51, FS-LASIK: n = 45) were included. Both the (Attempted - achieved) sphere and the (attempted - achieved) spherical equivalent (SEQ) were greater in the FS-LASIK group at all three postoperative time-points (p < 0.001). The postoperative vector means of astigmatism were smaller in the SMILE group than in the FS-LASIK group. The differences between the optical zone of tissue removal (ROZ) during surgery and the postoperative functional optical zone (FOZ; ROZ-FOZ) were smaller in the SMILE group than in the FS-LASIK group. No significant difference was found between the two procedures in the delta-root mean square (RMS) of aberrations, except for delta-spherical aberration (SA) at P3m. CONCLUSIONS: Both SMILE and FS-LASIK are effective in correcting high myopia. SMILE resulted in less under-correction, less regression, a smaller decrease in the FOZ and a smaller increase in SA when compared to FS-LASIK, resulting in better visual outcomes with SMILE.

Stability of corneal topography and aberrometry after hyperopic laser in situ keratomileusis with a 500-Hz excimer laser platform: A 3-year follow-up study.

PURPOSE: The aim of this study is to analyze the long-term stability of the corneal topography, the functional optical zone, and the refractive stability throughout 3 years following laser in situ keratomileusis surgery for hyperopia using a 500-Hz excimer laser system. METHODS: This retrospective consecutive observational case series study comprised 66 eyes that underwent laser in situ keratomileusis to correct hyperopia with a postoperative follow-up of 3 years. Laser in situ keratomileusis procedures were performed using the SCHWIND Amaris 500-Hz excimer laser. Main outcomes measured were stability of the functional optical zone at corneal topography and corneal aberrometry. RESULTS: Statistically significant differences were found in simulated keratometry (K2 (steep meridian) and Km (mean keratometry)) between 3 and 36 months postoperatively (p ⩽ 0.01); these differences disappeared at 12 and 36 months (p ⩾ 0.18). No statistically significant changes were observed in the horizontal and vertical diameter of the functional optical zone throughout the whole follow-up (p ⩾ 0.07). A statistically significant difference was found in the spherical aberration between 3 and 36 months (p = 0.02); this difference disappeared when compared between 12 and 36 months (p = 0.72). Statistically significant correlations were detected between the vertical functional optical zone and coma root mean square (r = -0.510, p < 0.01) and between the vertical functional optical zone and spherical aberration (r = 0.441, p = 0.02) 36 months after surgery. CONCLUSION: Following 3 years of hyperopic laser in situ keratomileusis with a 500-Hz Amaris excimer laser, keratometry, functional optical zone, and corneal aberrations remain stable from 1 year after surgery. Topographical regression is not observed in hyperopic laser in situ keratomileusis with this excimer laser technology from 1 year after surgery.

Corneal functional optical zone under monocular and binocular assessment.

BACKGROUND: In this retrospective randomized case series, we compared bilateral symmetry between OD and OS eyes, intercorneal differences and Functional Optical Zone (FOZ) of the corneal aberrations. METHODS: Sixty-seven normal subjects (with no ocular pathology) who never had any ocular surgery were bilaterally evaluated at Augenzentrum Recklinghausen (Germany). In all cases, standard examinations and corneal wavefront topography (OPTIKON Scout) were performed. The OD/OS bilateral symmetry was evaluated for corneal wavefront aberrations, and FOZ-values were evaluated from the Root-Mean-Square (RMS) of High-Order Wavefront-Aberration (HOWAb). Moreover, correlations of FOZ, spherical equivalent (SE), astigmatism power, and cardinal and oblique astigmatism for binocular vs. monocular, and binocular vs. intercorneal differences were analyzed. RESULTS: Mean FOZ was 6.56 ± 1.13 mm monocularly, 6.97 ± 1.34 mm binocularly, and 7.64 ± 1.30 mm intercorneal difference, with all strongly positively correlated, showing that the diameter of glare-free vision is larger in binocular than monocular conditions. Mean SE was 0.78 ± 1.30 D, and the mean astigmatism power (magnitude) was 0.46 ± 0.52 D binocularly. The corresponding monocular values for these metrics were 0.78 ± 1.30 D and 0.53 ± 0.53 D respectively. SE, astigmatism magnitude, cardinal astigmatism component, and FOZ showed a strong correlation and even symmetry; and oblique astigmatism component showed odd symmetry indicating Enantiomorphism between the left and right eye. CONCLUSIONS: These results confirm OD-vs.-OS bilateral symmetry (which influences binocular summation) of HOWAb, FOZ, defocus, astigmatism power, and cardinal and oblique astigmatism. Binocular Functional Optical Zone calculated from corneal wavefront aberrations can be used to optimize refractive surgery design.

Predictability and stability of refraction with increasing optical zone diameter in hyperopic LASIK.

OBJECTIVE: We undertook a prospective nonrandomized study to assess refractive outcome and patient satisfaction with hyperopic laser in situ keratomileusis (LASIK) using variable optical zone diameters in correction of hyperopia of more than 4.00 diopters. METHODS: Fourteen adults (comprising 28 hyperopic eyes) underwent hyperopic LASIK correction for hyperopia of more than 4.00 diopters. The sample was divided into two groups. Group 1 included the right eyes of the 14 patients who underwent hyperopic LASIK using a 6.5 mm optical zone diameter. Group 2 comprised the left eyes of the same patients with the only difference being that the optical zone diameter was 6.0 mm. RESULTS: The mean age of the patients was 36.42 +/- 5.10 years. Group 1 eyes had a median (range) preoperative uncorrected visual acuity (UCVA) of 0.79 (0.52) and best-corrected visual acuity (BCVA) of 0.15 (0.08). Group 2 had a median preoperative UCVA of 0.79 (0.60) and BCVA of 0.15 (0.08). The median postoperative UCVA in Group 1 was 0.17 (0.21) and BCVA was 0.15 (0.13). In Group 2, the median postoperative UCVA was 0.30 (0.32) and BCVA was 0.15 (0.26). Group 1 had a median preoperative refraction of +5.37 (1.75) diopters and the median postoperative refraction at one week was -0.23 (1.25) diopters, at three months was +0.75 (0.75) diopters, and at six months was +0.75 (1.00) diopters. Group 2 had a median preoperative refraction of +5.00 (1.75) diopters, and the median postoperative refraction at one week was +0.13 (1.5) diopters, at three months was +1.00 (0.75) diopters and at six months +1.25 (1.25) diopters. The difference was statistically significant between groups 1 and 2. The difference within each group was also significant. Group 1 eyes were stabilizing after the three-month period in contrast with Group 2 in which the refractive changes continued throughout the follow-up period. CONCLUSION: Larger optical zone diameter in correction of hyperopia of more than 4.00 diopters was more predictable, stable and safe.