Measurement of the distance between corneal apex and pupil center in patients following small-incision lenticule extraction or implantable collamer lens implantation and its correlation with the surgical-induced astigmatism.

BACKGROUND: To investigate the change in the distance between corneal apex and pupil center after small-incision lenticule extraction (SMILE) or implantable collamer lens (ICL) implantation and its correlation with surgical-induced astigmatism (SIA). METHODS: This study included patients who had undergone SMILE (n = 112) or ICL implantation (n = 110) to correct myopia and myopic astigmatism. The angle kappa was measured using a Scheimpflug imaging device (Pentacam) and represented as Cartesian values between the pupil center and the corneal vertex (X, Y) and chord u ([Formula: see text]orientation), and was compared pre- and post-operative. RESULTS: Following SMILE, the magnitude of chord u[Formula: see text]) significantly increased in both eyes (Wilcoxon signed-rank test, OD: P<0.001; OS: P=0.007), while no significant change was observed in the orientation. A significant correlation was found between the J0 component of SIA and the change in the magnitude of chord u for both eyes (OD: R2=0.128, P<0.001; OS: R2=0.033, P=0.004). After ICL implantation, the orientation of the chord u was significantly different in the right eye (Wilcoxon signed-rank test, P = 0.008), and the Y-intercept significantly decreased in both eyes (Wilcoxon signed-rank test, P<0.001). A significant correlation was found between J0 of SIA and the change in the magnitude of chord u for the right eyes (R2=0.066, P=0.002). A significant correlation was found between J45 of SIA and the change in the magnitude of chord u for the left eyes (R2=0.037, P=0.044). CONCLUSIONS: The magnitude of the chord u increased following the SMILE procedure, whereas the Y-intercept significantly decreased after ICL implantation. SIA was related to the change in the magnitude of chord u.

Influence of corneal diameter on the accuracy of corneal tomography in patients with forme fruste keratoconus or thin corneas.

CLINICAL RELEVANCE: The detection of subclinical ectasia is important in preoperative screening for laser-refractive surgery. Previous studies have confirmed the impact of corneal diameter on the diagnostic accuracy of several ectasia indices in tomographically normal eyes. BACKGROUND: This study aimed to investigate the influence of corneal diameter on the diagnostic accuracy of Pentacam tomographic indices in eyes with forme fruste keratoconus (FFKC) and thin corneas. METHODS: One hundred and one eyes of 101 patients with FFKC (FFKC group), 104 eyes of 104 patients with a corneal thickness <490 µm (thin cornea group), and 200 eyes of 200 normal subjects (normal group) were analysed in the study. Pentacam ectasia indices were compared between the groups. RESULTS: The results of multiple linear regression analysis showed that the standardised coefficients for corneal diameter and overall deviation of normality (BAD-D) were -0.386, -0.552, and -0.552 for the FFKC, thin cornea, and normal groups, respectively (p < 0.001). Comparing for the classifications (normal versus abnormal) of the individual indices demonstrated that for corneal diameters ≤11.9 mm, the rates of abnormal cases were significantly higher in the FFKC group than in the normal group for seven indices and in the thin cornea group than normal group for nine indices. For corneal diameters >11.9 mm, the rates of abnormal cases were higher in the FFKC than normal group for three indices and higher in the thin cornea group than normal group for seven indices. CONCLUSION: Belin/Ambrosio Enhanced Ectasia display indices may underestimate the risk of ectasia in patients with large corneas, especially those with FFKC.

Risk factors associated with haptic malposition in eyes implanted with implantable collamer lenses.

PURPOSE: To examine the risk factors for haptic malposition in eyes with implantable collamer lens (ICL). SETTING: Eye and ENT Hospital, Fudan University, Shanghai, China. DESIGN: Prospective nonrandomized observational study. METHODS: This study included 134 (77.9%) of 172 initially enrolled patients who underwent ICL implantation and completed a 1-year follow-up. The extent of haptics present in the ciliary sulcus (ICS) was measured. Patients were categorized based on ICS count (0 to 4). The position of the haptics was quantified as the distance between the iris root and the terminal tip of ICL haptics (iris root to haptic tip, IRH). The related factors to the ICS count and its correlation with the central vault were analyzed. RESULTS: ICS distribution was 0 ICS in 19 eyes (14.2%), 1 in 22 eyes (16.4%), 2 in 32 eyes (23.9%), 3 in 29 eyes (21.6%), and 4 in 32 eyes (23.9%). Parameters like maximum ciliary body thickness (CBTmax, P = .008), iris-ciliary process distance (ICPD, P < .001), and ciliary process length ( P = .034) varied significantly across ICS groups. A multiple linear regression analysis revealed that the iris-ciliary angle ( P = .006), CBTmax ( P = .007), the distance between the sulcus-to-sulcus plane and the anterior crystalline lens surface (STSL, P = .035), and ICL size ( P = .015) were significantly associated with IRH. Spherical equivalents ( P = .042), STSL ( P = .001), and ICS count ( P = .020) significantly correlated with the central vault. CONCLUSIONS: Shortened ciliary process is a primary risk for haptic malposition. The ICS count significantly relates to the central vault.

Assessment of Keratoconus Risk in Very Asymmetric Ectasia Using Corneal Tomographic and Biomechanical Parameters.

Purpose: To investigate the relationship between corneal tomographic or biomechanical parameters and risk of keratoconus in very asymmetric ectasia (VAE). Methods: This retrospective case-control single-centre study included patients with VAE and normal controls. The VAE group had clinical ectasia in one eye and normal topography (VAE-NT) in the fellow eye; VAE-NT eyes were selected for analysis. The control group was selected from corneal refractive surgery candidates; the right eye was enrolled. Scheimpflug-based corneal tomography (Pentacam) and corneal biomechanical assessment (Corvis ST) were performed. Univariate and multivariable logistic regression were performed using Cox proportional hazards models to evaluate keratoconus-associated risk factors. A two-piecewise linear regression model was applied to examine the threshold effect of selected vital paragmeters on the risk of keratoconus according to a smoothing plot. Results: Threshold effect between tomographic integration and risk of keratoconus was observed. Discrepancy between the central corneal thickness and thinnest corneal thickness (discrepancy CCT vs TCT) greater than 5 µm, discrepancy between the apex corneal thickness and thinnest corneal thickness (discrepancy ACT vs TCT) greater than 3 µm, vector distance between CCT and TCT (distance CCT vs TCT) greater than 0.65 mm indicated a significant increased risk of keratoconus. Risk of keratoconus decreased when distance CCT vs TCT was less than 0.65 mm. Conclusion: Discrepancy CCT vs TCT, discrepancy ACT vs TCT, and distance CCT vs TCT can be used as indicators for risk assessment of early keratoconus.

Anterior Segment Characteristics of Eyes with Anterior Chamber Depth Less than 2.8 mm and Axial Length Greater than 25 mm.

INTRODUCTION: This study aimed to investigate anterior segment parameters of eyes, with anterior chamber depth (ACD) less than 2.8 mm and axial length greater than 25.0 mm. METHODS: This cross-sectional study included 180 myopic eyes of 180 consecutive patients with axial length greater than 25.0 mm. Patients were divided into low ACD (ACD < 2.8 mm, n = 56) and normal ACD (ACD ≥ 2.8 mm, n = 124) groups. Anterior segment parameters were measured using Scheimpflug imaging and ultrasound biomicroscopy. A general linear model was used to compare parameters between the two groups, after adjusting for age and spherical equivalent. RESULTS: Compared with the normal ACD group, the low ACD group had lower values for the following parameters: corneal diameter, trabecular-anterior iris surface angle, angle-opening distance at 500 µm, anterior chamber volume, anterior chamber width, anterior vault, iris thickness at 500 µm, ciliary sulcus-to-sulcus diameter, distance between cornea and sulcus, trabecular-ciliary process distance, maximum ciliary body thickness, ciliary process length, relative anterior vault, relative distance between cornea and sulcus, and relative lens position (general linear model, p < 0.05). In contrast, central corneal thickness, iris curvature, lens thickness, lens vault, and iris-ciliary angle were greater in the low ACD group (general linear model, p < 0.05). CONCLUSION: A smaller anterior segment, as well as a thicker and more anteriorly positioned lens, may correlate with shallow ACD in eyes with long axial length.

Comparison of Two Scheimpflug Systems in the Measurements of Eyes with Corneal Diameter Smaller than 11.1 mm.

INTRODUCTION: This article aimed to evaluate the measurements of ectasia parameters by two Scheimpflug-based tomography devices, Pentacam and Sirius, for eyes with different corneal diameters (CDs). METHODS: This cross-sectional research included subjects from the Fudan University EENT Hospital Refractive Center Database that were followed once a year for at least 3 years with unremarkable slit-lamp examination and normal topography. Pentacam and Sirius examinations were performed on these subjects and the ectasia indices were compared between different CD groups. RESULTS: The right eyes of 153 subjects were included (CD ≤ 11.1 mm, n = 50; 11.2-12 mm, n = 52; > 12.0 mm, n = 51). For the ectasia parameters from Pentacam, CD had the greatest influence on the deviation of normality of back elevation (Db, R2 = 0.371, ß = - 1.119, P < 0.001), overall deviation of normality (BAD-D, R2 = 0.305, ß = - 0.589, P < 0.001), and minimum pachymetric progression index (PPImin, R2 = 0.282, ß = - 0.131, P < 0.001). For parameters derived from Sirius, CD had the greatest influence on Baiocchi-Calossi-Versaci index of the back surface (BCVb, R2 = 0.138, ß = - 0.179, P < 0.001), keratoconus vertex of the back surface (KVb, R2 = 0.099, ß = - 2.273, P < 0.001), and BCV (R2 = 0.071, ß = - 0.078, P = 0.001). CD had little influence on surface asymmetry index of the front (SIf) and back surface (SIb), keratoconus vertex of the front surface (KVf), Baiocchi-Calossi-Versaci index of the front surface (BCVf), and Sirius classifier (P > 0.05). CONCLUSIONS: For Pentacam, CD mainly influenced indices related to back elevation (BE) and pachymetry progression, whereas for Sirius, CD mainly influenced indices related to BE and corneal aberration.

Influence of Ocular Residual Astigmatism on the Correction of Myopic Astigmatism by Toric Implantable Collamer Lens: A Comparative Study With Femtosecond Laser Small Incision Lenticule Extraction.

Purpose: To evaluate the influence of the origin of astigmatism on the correction of myopic astigmatism by toric implantable collamer lens (TICL) and compare it with femtosecond laser small incision lenticule extraction (SMILE). Methods: Ocular residual astigmatism (ORA) was determined by vector analysis using manifest refraction and Scheimpflug camera imaging of the anterior cornea. One-to-one matching between the TICL and SMILE groups was performed by preoperative manifest refractive astigmatism (RA) and ORA, tolerating a maximum difference of 0.50 diopter (D) for RA and 0.25 D for ORA. Patients of each group were further divided into groups according to ORA (high > 1.0 D; low ≤ 1.0 D). The baseline and 12-month postoperative data were analyzed. Data are expressed as mean ± standard deviation (SD). A value of p less than 0.05 was considered statistically significant. Results: For the TICL group, no significant differences in the postoperative RA, safety index, efficacy index, index of success (IOS), correction index (CI), and angle of error (AOE) were found between high (n = 36) and low ORA (n = 36) groups (Mann-Whitney U test, p > 0.05). For the SMILE group, the postoperative RA (high: -0.67 ± 0.43 D, low: -0.39 ± 0.29 D, Mann-Whitney U test, p = 0.003) and IOS (high: 0.50 ± 0.43, low: 0.25 ± 0.23, Mann-Whitney U test, p = 0.003) were greater in the high ORA group. When comparing TICL and SMILE groups, the mean postoperative RA (TICL: -0.48 ± 0.29 D, SMILE: -0.67 ± 0.43 D, Mann-Whitney U test, p = 0.03) and IOS (TICL: 0.32 ± 0.23, SMILE: 0.50 ± 0.43, Mann-Whitney U test, p = 0.03) were significantly higher in the SMILE group when the ORA was >1.0 D. Conclusion: Both TICL and SMILE are effective in correcting myopic astigmatism. ORA has a lesser effect on TICL than on SMILE.

Prognostic Nomograms Predicting Risk of Keratoconus in Very Asymmetric Ectasia: Combined Corneal Tomographic and Biomechanical Assessments.

Purpose: The aim of the study was to develop and validate a prognostic nomogram for subclinical keratoconus diagnosis using corneal tomographic and biomechanical integration assessments. Design: This is a retrospective case-control study. Methods: Setting: The study was carried out in a hospital setting. Patients: The study included patients with very asymmetric ectasia (VAE) and normal controls. Patients with VAE had defined clinical ectasia in one eye and normal topography (VAE-NT) in the fellow eye, and VAE-NT eyes were selected for analysis. VAE-NT was defined as stratified stage 0 using the ABCD keratoconus grading system. The normal control group was selected from corneal refractive surgery candidates at our clinic, and the right eye was enrolled. Observation Procedures: Scheimpflug-based corneal tomography (Pentacam) and corneal biomechanical assessment (Corvis ST) were performed. Main Outcome Measures: We performed multiple logistic regression analysis and constructed a simple nomogram via the stepwise method. The receiver operating characteristic (ROC) curve and discrimination and calibration of prognostic nomogram were performed by 500 bootstrap resamplings to assess the determination and clinical value, respectively. Results: A total of 59 VAE-NT and 142 normal eyes were enrolled. For differentiating normal and VAE-NT eyes, the values of specificity, sensitivity, and area under the ROC (AUROC) were 0.725, 0.610, and 0.713 for tomographic parameters, 0.886, 0.632, and 0.811 for biomechanical parameters, and 0.871, 0.754, and 0.849 for combined parameters, respectively. Combined parameters showed better predictability than separated tomographic or biomechanical parameters. Conclusion: Our nomogram developed with combined tomographic and biomechanical parameters demonstrated a plausible, capable, and widely implementable tool to predict risk of keratoconus. The identification of at-risk patients can provide advanced strategies to epitomize ectasia susceptibility.

Comparison of posterior corneal elevation after SMILE and FS-LASIK in correcting myopia over -9.0 diopters.

BACKGROUND: To compare the changes in posterior corneal elevation after small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) in correcting myopia over -9 diopters (D). METHODS: In this prospective comparative study, 82 eyes of 82 patients scheduled for refractive correction were recruited. Eyes were randomly assigned to the SMILE group (45 eyes, -10.43±0.92 D) or FS-LASIK group (37 eyes, -10.97±1.37 D). The posterior corneal surface was measured using a Scheimpflug camera (Pentacam, Oculus, Germany) preoperatively and at 1 day, 1 month, and 6 months after surgery. Posterior corneal elevation in the central point and central 4-mm area, and in various optical zones above the best-fit sphere, was analyzed. A P value of less than 0.05 was considered statistically significant. RESULTS: All surgeries were completed successfully. The safety index and efficacy index were 1.20 and 1.00, respectively, in the SMILE group, and was 1.10 and 0.90, respectively, in the FS-LASIK group. No significant difference existed in all analyzed data before and at 6 months after surgery in both the SMILE group and the FS-LASIK group. Changes in posterior corneal elevation after FS-LASIK were greater than after SMILE, with no statistical significance (P≥0.07). In the SMILE group, residual bed thickness was found to be moderately negatively correlated with changes in the elevation in the central area (P≤0.045); whereas it was positively correlated in the peripheral area (P=0.002). CONCLUSIONS: SMILE and FS-LASIK presented stable posterior corneal surface in correction of myopia over -9.0 D at the follow-up visit of 6 months.

Influence of Ocular Residual Astigmatism and Target-Induced Astigmatism on the Efficacy of the Implantation of a Toric Implantable Collamer Lens With Central Hole for Myopic Astigmatism Correction.

PURPOSE: To investigate the effects of ocular residual astigmatism (ORA) and target-induced astigmatism (TIA) on the efficacy of toric implantable collamer lens (TICL) with central hole for myopic astigmatism correction. METHODS: Retrospective case series. One hundred and eighteen eyes implanted with a TICL (V4c) from 118 patients were included. Subjective refraction and corneal topography were examined preoperatively, at 1 and 12 months postoperatively. The eyes were divided into the low-ORA ( ≤ 0.5 D) and high-ORA (>0.5 D) groups based on vector analysis, and into the low-TIA (≥0.75D and <2 D) and the high-TIA (≥2 D and ≤ 4 D) groups according to preoperative refractive astigmatism. Correction index (CI) and index of success (IOS) were compared between different groups. RESULTS: All surgeries were uneventful, and no complications occurred during follow-up. At 1 and 12 months postoperatively, no significant differences were found in CI or IOS values between the high and low ORA groups, while significantly higher CI and lower IOS were detected in the high-TIA group than in the low-TIA group (P < 0.05). No significant difference was found in CI between 1 and 12 months postoperatively in either group (P > 0.05). However, significantly lower IOS was found at 12 months compared with 1 month postoperatively for each group (P < 0.05). CONCLUSIONS: Toric implantable collamer lens (TICL) implantation is effective in correcting myopic astigmatism and is more effective in eyes with high TIA, while ORA has a minor effect.

Effect of brimonidine tartrate 0.2% ophthalmic solution on visual quality after implantable collamer lens implantation with a central hole.

PURPOSE: To investigate the effect of brimonidine tartrate 0.2% on visual quality after implantable collamer lens with a central hole (ICL V4c). METHODS: This study comprised 59 consecutive patients implanted with an ICL V4c. Brimonidine was administered randomly into one eye of the patients with symptomatic glare or halos 1 week postoperatively and the contralateral eye with artificial tears as the control group. Visual quality (measured by a optical quality analysis system), pupil size and refraction under scotopic light conditions were measured before and 0.5, 1.5, 3 and 6 h after administration of brimonidine. A symptom questionnaire was also evaluated. RESULTS: The visual quality improved and reached its maximum value, and the scotopic pupil size reached its minimum value 1.5 h after brimonidine administration, with a statistically significant difference seen from 0.5 to 3 h compared to baseline. No changes in refraction were seen after brimonidine. The questionnaire showed that symptoms of glare or halos could be eliminated after brimonidine in 58% of patients, be alleviated in 37% of patients and be unchanged in 5% of patient. However, 10% of patients experienced conjunctival congestion and some patients experienced reduced drug efficacy 1 month after treatment. CONCLUSION: Brimonidine can be used to improve night visual quality in early postoperative period after ICL V4c implantation. It helps patients to quickly adapt to the glare or halos.

Pentacam Scheimpflug Tomography Findings in Chinese Patients With Different Corneal Diameters.

PURPOSE: To investigate the Pentacam (Oculus Optikgeräte) Scheimpflug tomography findings in Chinese patients with different corneal diameters. METHODS: This prospective cross-sectional study included candidates for correction of myopia with normal tomography (ABCD keratoconus grading system, stage 0). The participants were grouped according to their horizontal corneal diameters. Pentacam ectasia detection indices were compared between different corneal diameter-based groups. RESULTS: A total of 643 eyes were included (corneal diameter ⩽ 11 mm, n = 206; 11 to 12 mm, n = 219; ⩾ 12 mm, n = 218). The corneal powers and the thinnest pachymetry were negatively correlated with corneal diameter (linear regression analysis, P < .001). However, the corneal astigmatism was positively correlated with corneal diameter (R2 = 0.03, P < .001). Both the front (FE) and back (BE) elevations were negatively correlated with corneal diameter (FE: R2 = 0.027, P < .001; BE: R2 = 0.274, P < .001). The three pachymetric progression indices (PPI) (minimum, maximum, and average) were negatively correlated with corneal diameter (PPImin: R2 = 0.164, P < .001; PPImax: R2 = 0.06, P < .001; PPIavg: R2 = 0.158, P < .001). The maximum Ambrósio's relational thickness (ARTmax) also was positively correlated with corneal diameter (R2 = 0.031, P < .001). Five normalized indices were negatively correlated with corneal diameter (deviation of normality of the front elevation [Df]: R2 = 0.122, P < .001; deviation of normality of the back elevation [Db]: R2 = 0.47, P < .001; deviation of normality of pachymetric progression [Dp]: R2 = 0.159, P < .001; deviation of normality of relational thickness [Da]: R2 = .031, P < .001; Belin/Ambrósio Enhanced Ectasia display: R2 = 0.32, P < .001) and Dt was positively correlated with corneal diameter (R2 = 0.015, P = .002). Additionally, it was noted that corneal diameter had the greatest influence on Db, Belin/Ambrósio Enhanced Ectasia display (BAD-D), and BE. CONCLUSIONS: Corneal diameter has an influence on the BAD parameters, especially Db, BAD-D, and BE, and therefore should be incorporated as an additional variable in BAD analysis. The analytical dimensions should be individualized for eyes with individual corneal diameter. [J Refract Surg. 2020;36(10):688-695.].

Correction to: Thickness profiles of the corneal epithelium along the steep and flat meridians of astigmatic corneas after orthokeratology.

An amendment to this paper has been published and can be accessed via the original article.

Thickness profiles of the corneal epithelium along the steep and flat meridians of astigmatic corneas after orthokeratology.

BACKGROUND: The aim of this study was to investigate the changes in corneal epithelial thickness along the principle meridians of astigmatic corneas after six months of overnight spherical myopic orthokeratology (OK) lens wear. METHODS: This is a prospective study. Fifty-seven subjects with up to 1.50 diopters (D) of corneal toricity wore spherical OK lenses for 6 months. Evaluations of OK lens fit, visual acuity, refractions and corneal toricity (CT) were performed. Fourier-domain optical coherence tomography (FD-OCT) was conducted to measure the corneal epithelial thickness (ET) along the principle meridians of corneal toricity over a diameter of 6 mm. The means of △ET of the same diameter at individual meridians (△ETSm and △ETFm) were calculated and compared. RESULTS: Visual acuity and refraction improved significantly after OK lens wear. △ETFm thinned more than △ETSm (P = 0.027) at 1.5 mm in radius. △ETSm thickened more than △ETFm at 2.5 mm (P = 0.019) and 3.0 mm (P = 0.036).∣△ETSm - △ETFm∣ were significantly correlated with the baseline central CT at 2.0 mm, 2.5 mm and 3.0 mm. ∣△ETSm - △ETFm∣was significantly correlated with the baseline peripheral CT at 2.5 mm. CONCLUSIONS: Overnight wear of spherical OK lenses resulted in differential changes in the thickness profiles of the corneal epithelium between the steep and flat meridians in eyes with corneal toricity.

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.

Decentration following femtosecond laser small incision lenticule extraction (SMILE) in eyes with high astigmatism and its impact on visual quality.

BACKGROUND: To measure the decentration following SMILE in eyes with high myopic astigmatism and investigate its impact on visual quality. METHODS: The prospective study was conducted to analyze patients who underwent SMILE for correction of myopia and myopic astigmatism ≥2.5D (high astigmatism group, HA) at the ophthalmology department, Eye and ENT hospital, Shanghai, China.. Patients with myopic astigmatism < 1.5D served as controls (low astigmatism group, LA). Decentration was measured using a Scheimpflug camera with a difference map of the tangential curvature at 12 months postoperatively. Also the associations between decentration from the coaxial sighted corneal light reflex (CSCLR) and the visual outcomes, correction efficacy of astigmatism, wavefront aberrations and objective scatter index (OSI) were analyzed. RESULTS: No significant differences were observed in the decentered distance between HA and LA in either eyes (OD: HA: 0.18 ± 0.10 mm, LA: 0.20 ± 0.14 mm, P = 0.659; OS: HA: 0.22 ± 0.11 mm, LA: 0.20 ± 0.11 mm, P = 0.637). The analysis across the three levels of decentration (< 0.1 mm, 0.1-0.2 mm, and > 0.2 mm) showed no significant association between decentration and visual outcomes of predictability, efficiency, safety, MTF cutoff, OSI, SR and OVs in both groups. Also no significant association was observed between decentration and postoperative astigmatism in either group. A significant relationship between the magnitude of decentration and induced coma and spherical aberration was observed in HA. CONCLUSIONS: The amount of decentration between HA and LA groups showed no differences. Decentration > 0.20 mm from CSCLR resulted in greater induction of coma and SA after SMILE in eyes with HA.

Comparison of Corneal Power and Astigmatism between Simulated Keratometry, True Net Power, and Total Corneal Refractive Power before and after SMILE Surgery.

Purpose. To compare the mean corneal power (Km) and total astigmatism (Ka) estimated by three methods: simulated keratometry (simK), true net power (TNP), and total corneal refractive power (TCRP) before and after femtosecond laser small incision lenticule extraction (SMILE) surgery. Methods. A retrospective, cross-sectional study. SimK, TNP, and TCRP from a Scheimpflug analyzer were obtained from 144 patients before and 6 months after SMILE surgery. Km and Ka were recorded as the mean of individual paracentral rings of 1.0 to 8.0 mm (R1 to R8). The surgically induced changes in Km (delta-simK, delta-TNP, and delta-TCRP) and Ka (delta-simKa, delta-TNPa, and delta-TCRPa) were compared to the changes in spherical equivalent of the cycloplegic refraction (delta-SE) and astigmatism (delta-RA). Results. Preoperatively, astigmatism values were greatest with simKa from R1 to R5 and greatest with TCRPa from R6 to R8. Astigmatism values were smallest with TNPa from R1 to R7. Postoperatively, astigmatism values were greatest with simKa from R1 to R5 and greatest with TCRPa from R6 to R8. Delta-TCRP3 and Delta-TCRP4 matched delta-SE most closely, and delta-TCRPa3 matched delta-RA most closely. Conclusions. TCRP proved to be the most accurate method in estimating corneal power and astigmatism both before and after SMILE surgery.

Comparison of femtosecond laser small-incision lenticule extraction and laser-assisted subepithelial keratectomy to correct myopic astigmatism.

PURPOSE: To compare the efficacy of correcting myopic astigmatism with femtosecond laser small-incision lenticule extraction (SMILE, Carl Zeiss Meditec AG) versus laser-assisted subepithelial keratectomy (LASEK). SETTING: The study was conducted at the Ophthalmology Department, Eye and ENT Hospital, Shanghai, China. DESIGN: A retrospective, cross-sectional study. METHODS: This study included patients who underwent small-incision lenticule extraction or LASEK for the correction of myopia and myopic astigmatism. Preoperative and 6-month postoperative astigmatism values were analyzed. The efficacies of the 2 surgeries to correct astigmatism were compared. RESULTS: A total of 180 right eyes of 180 patients (small-incision lenticule extraction: n = 113, LASEK: n = 67) were included. No significant difference was found between the 2 groups in the preoperative astigmatism (small-incision lenticule extraction: 1.16 ± 0.85D, LASEK: 1.16 ± 0.83D, P > .05) or the postoperative astigmatism (small-incision lenticule extraction: 0.35 ± 0.37D; LASEK: 0.31 ± 0.42D, P > .05), determined by manifest refraction. No significant difference was found between the 2 groups in surgically induced astigmatism vector (small-incision lenticule extraction: 1.13 ± 0.83D, LASEK: 1.01 ± 0.65D, P > .05). The correction index was higher for the small-incision lenticule extraction group (1.05 ± 0.53) than for the LASEK group (0.95 ± 0.21, P = .045). The postoperative astigmatism was significantly higher for the small-incision lenticule extraction group when the preoperative astigmatism was 1.0 D or less (small-incision lenticule extraction: 0.26 ± 0.30D, LASEK: 0.12 ± 0.20D, P = .007) and lower for the small-incision lenticule extraction group when the preoperative astigmatism was more than 2.0 D (small-incision lenticule extraction: 0.48 ± 0.37D, LASEK: 0.89 ± 0.46D, P = .002). CONCLUSIONS: An adjustment of nomograms for correcting low astigmatism (≤1.0 D) by small-incision lenticule extraction is suggested due to the tendency toward overcorrection, whereas a nomogram adjustment for tissue-saving ablation profile is needed for the correction of high astigmatism (>2.0 D) by LASEK due to the tendency toward undercorrection. FINANCIAL DISCLOSURE: The authors declare that they have no competing financial interests.

Corneal Power Distribution and Functional Optical Zone Following Small Incision Lenticule Extraction for Myopia.

PURPOSE: To evaluate corneal power distribution using the ray tracing method (corneal power) in eyes undergoing small incision lenticule extraction (SMILE) surgery and compare the functional optical zone with two lenticular sizes. METHODS: This retrospective study evaluated 128 patients who underwent SMILE for the correction of myopia and astigmatism with a lenticular diameter of 6.5 mm (the 6.5-mm group) and 6.2 mm (the 6.2-mm group). The data include refraction, correction, and corneal power obtained via a Scheimpflug camera from the pupil center to 8 mm. The surgically induced changes in corneal power (Δcorneal power) were compared to correction and Δrefraction. The functional optical zone was defined as the largest ring diameter when the difference between the ring power and the pupil center power was 1.50 diopters or less. The functional optical zone was compared between two lenticular diameter groups. RESULTS: Corneal power distribution was measured by the ray tracing method. In the 6.5-mm group (n=100), Δcorneal power at 5 mm showed the smallest difference from Δrefraction and Δcorneal power at 0 mm exhibited the smallest difference from correction. In the 6.2-mm group (n=28), Δcorneal power at 2 mm displayed the lowest dissimilarity from Δrefraction and Δcorneal power at 4 mm demonstrated the lowest dissimilarity from correction. There was no significant difference between the mean postoperative functional optical zones in either group when their spherical equivalents were matched. CONCLUSIONS: Total corneal refactive power can be used in the evaluation of surgically induced changes following SMILE. A lenticular diameter of 6.2 mm should be recommended for patients with high myopia because there is no functional difference in the optical zone.

Influence of intraocular astigmatism on the correction of myopic astigmatism by femtosecond laser small-incision lenticule extraction.

PURPOSE: To evaluate the influence of the origin of astigmatism on the correction of myopia or myopic astigmatism by femtosecond laser small-incision lenticule extraction (SMILE). SETTING: Ophthalmology Department, Eye and ENT Hospital, Shanghai, China. DESIGN: Prospective case series. METHODS: Small-incision lenticule extraction was performed to correct myopia or myopic astigmatism. Ocular residual astigmatism (ORA) was determined by vector analysis using manifest refraction and Scheimpflug camera imaging of the anterior cornea. Patients were divided into 2 groups according to ORA (high >1.0 diopter [D]; low ≤1.0 D), and procedural efficacy was compared. Patients were examined preoperatively and 1, 3, and 6 months postoperatively. RESULTS: This study comprised 122 right eyes of 122 patients. No significant difference was found in the preoperative manifest astigmatism (target-induced astigmatism [TIA]) between the low ORA group (n = 67) and high ORA group (n = 55). The mean postoperative manifest astigmatism was higher in the high ORA group at all postoperative timepoints (1 month: t = 2.182, P=.031; 3 months: t = 2.30, P=.023; 6 months: t = 2.193, P=.03). The mean index of success (postoperative astigmatism/TIA) was 0.68 in the high ORA group and 0.34 in the low ORA group 1 month postoperatively (t = 2.531, P=.013); 0.73 and 0.39, respectively, at 3 months (t = 2.689, P=.008); and 0.77 and 0.46, respectively, at 6 months (t = 2.105, P=.037). CONCLUSION: Small-incision lenticule extraction was effective in correcting astigmatism but may be less effective in correcting ORA.