Astigmatic Power Research Articles

Prediction of corneal back surface power - Deep learning algorithm versus multivariate regression.

The corneal back surface is known to add some against the rule astigmatism, with implications in cataract surgery with toric lens implantation. This study aimed to set up and validate a deep learning algorithm to predict corneal back surface power from the corneal front surface power and biometric measures. This study was based on a large dataset of IOLMaster 700measurements from two clinical centres. N=19,553measurements of 19,553 eyes with valid corneal front (CFSPM) and back surface power (CBSPM) data and other biometric measures. After a vector decomposition of CFSPM and CBSPM into equivalent power and projections of astigmatism to the 0°/90° and 45°/135° axes, a multi-output feedforward neural network was derived to predict vector components of CBSPM from CFSPM and other measurements. The predictions were compared with a multivariate linear regression model based on CFSPM components only. After pre-conditioning, a network with two hidden layers each having 12 neurons was derived. The dataset was split into training (70%), validation (15%) and test (15%) subsets. The prediction error (predicted corneal back surface power CBSPP - CBSPM) of the network after training and crossvalidation showed no systematic offset, narrower distributions for CBSPP - CBSPM and no trend error of CBSPP - CBSPM vs. CBSPM for any of the vector components. The multivariate linear model also showed no systematic offset, but broader distributions of the prediction error components and a systematic trend of all vector components vs. CFSPM components. The neural network approach based on CFSPM vector components and other biometric measures outperforms the multivariate linear model in predicting corneal back surface power vector components. Modern biometers can supply all parameters required for this algorithm, enabling reliable predictions for corneal back surface data where direct corneal back surface data are unavailable.

Magnitude of astigmatism – A comparison between eyes

PurposeAstigmatism is a highly prevalent refractive error and while studies typically focus to describe the axis symmetry between eyes, little is known about the refractive symmetry. Therefore, this study determined the astigmatic power symmetry between eyes in a large clinic population. MethodsA clinical chart review was conducted at three optometric practices in the United States, the United Kingdom and Canada and subjective refraction data from 88,891 patients 14–70 years of age who presented with at least −0.25DC refractive astigmatism in at least one eye were included in the analysis. Data were obtained at these practices between January 2014 and March 2017. The overall distribution (%) and magnitude (DC) of astigmatism was determined and refractive differences between eyes were identified. ResultsThe mean age of the patients was 42.1 ± 15.9 years and included 51,685 (58%) female and 37,206 (42%) male patients. In this data pool of 177,782 eyes, 10.9% required zero astigmatic correction, while 56.2% had astigmatism of −0.25 to −0.75DC. In total 23.9% of patients presented with astigmatism of at least −0.75DC in only one eye, while the other eye had 0 to −0.50DC. Overall, the difference in astigmatism between eyes was less than −0.75DC for 82.1% of astigmatic patients. For patients who presented with astigmatism of −1.00DC in the right eye, 80.8% of them had an astigmatic prescription of −1.00 ± 0.50DC in the left eye. For an astigmatic prescription of −4.00DC in the right eye, only 40.6% of patients exhibited astigmatism of −4.00DC ± 0.50DC in the left eye. ConclusionsThe majority of patients exhibited a difference in astigmatism between eyes of less than −0.75DC, however the refractive cylinder power symmetry was significantly lower in patients with higher refractive astigmatism.

Objective changes in astigmatism during accommodation.

Previous studies have shown small but clinically significant changes in the power and axis of astigmatism when the eye accommodates. Monocular objective measurements of the eye during accommodation, when the object approaches the eye without convergence, also reveal small astigmatic changes. Moreover, it is known that the eye exhibits ocular cyclotorsion at different gaze angles. Since accommodation and convergence normally occur simultaneously, we studied the change in the magnitude and axis of astigmatism during accommodation for different convergence angles. The left eye of 15subjects between 20 and 49years old (mean 28.5±9.7years) having ≤1.5D astigmatism was evaluated. Measurements were made using a Shack-Hartmann aberrometer for an accommodation range of +0.50D to -10D in 0.50D steps, and for four monocular convergence demands: 0°, 5°, 10° and 15°. Statistical analysis used power vectors to quantify the change in cylinder power and axis for each accommodation and convergence demand with age. Jackson cross-cylinder component J45 did not change during accommodation for all vergences tested. However, J0 changed by an average of -0.02D per dioptre of accommodation (D/Dacc) for convergence demands of 0°, 5° and 10° and -0.03D/Dacc for the 15° demand. This corresponds to an average cylinder power change of -0.05D/Dacc for convergences of 0°, 5° and 10° and -0.08D/Dacc for 15° of convergence. The cylinder axis always changed towards 90° (against-the-rule), and age did not play a significant role. Except for accommodation demands >4D, we did not find a clinically significant change in astigmatism for convergence angles up to 15º. The small changes in cylinder power and axis may be due to shifts in the position of the crystalline lens during accommodation.

Effects of Rebamipide on Differences in Power and Axis of Corneal Astigmatism Between Two Intra-patient Keratometric Measurements in Dry Eyes.

IntroductionThis study investigated the effect of rebamipide on discrepancies in the power and axis of astigmatism between two intra-patient keratometric measurements in patients with dry eyes.MethodsFifty-eight dry eyes (with a short tear breakup time [TBUT] of less than 5 s) were analyzed. Patients with dry eye were treated with 2% rebamipide ophthalmic suspension (group R) or Mytear® artificial tear ophthalmic solution (group M) for 4 weeks. TBUT and corneal higher-order aberrations (HOAs) were evaluated at baseline and 4 weeks after treatment. Astigmatism power and axis were measured twice during both evaluations, at 5-min intervals. Baseline and post-treatment measurements were compared. Changes in TBUT and HOAs, and intra-patient discrepancies in astigmatism power and axis measurements were evaluated.ResultsHOAs showed significant positive correlations with intra-patient differences in astigmatism power and axis (P < 0.001). At the 4-week post-treatment follow-up, TBUT increased, and HOAs and astigmatism power and axis discrepancies decreased in a significant number of patients in group R (P < 0.001). In group M, only differences in astigmatism power decreased in a significant number of cases (P = 0.005). The degree of change in the intra-patient difference in astigmatism power between the two post-treatment keratometric measurements was significantly greater in group R than in group M (P < 0.001). In group R, baseline HOAs exhibited a significant positive correlation with changes in HOAs and intra-patient differences in astigmatism power (both P < 0.001). In group M, baseline HOAs were only significantly correlated with changes in intra-patient differences in astigmatism power (P = 0.030).ConclusionIn dry eyes with short TBUTs, rebamipide significantly improved the corneal surface condition and significantly reduced intra-patient discrepancies in astigmatism power and axis measurements. Rebamipide may improve the accuracy of intraocular lens (IOL) power calculations in dry eyes, particularly when toric IOLs are implanted.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40123-021-00368-9.

Surgically induced astigmatism following single site and twin site phacotrabeculectomy augmented with mitomycin C.

To determine difference in surgically induced astigmatism (SIA), post-operative intraocular pressure (IOP) and axial length (AL) between single site and twin-site phacotrabeculectomy augmented with Mitomycin C (MMC). Prospective interventional randomised controlled study. In a prospective interventional comparative study, eligible patients were scheduled for phacotrabeculectomy. They were randomised to either group A: single site or group B: twin-site phacotrabeculectomy with MMC 0.2 mg/mL. Axial length was measured by using Zeiss IOL master I, pre-operatively and at 1, 3, 6 and 12 months post-operatively. Corneal topography was performed using Bausch and Lomb Orbscan I pre-operatively and at 3, 6 and 12 months post-operatively to analyse surgically induced astigmatism. Vector analysis was used to analyse the surgically induced astigmatism. One hundred and eight eyes of which 55 patients in group A, and 53 patients in group B were enroled for vector analysis. The mean preoperative astigmatic vector power was +0.89 ± 0.4 D and +0.97 ± 0.5 D in group A and B respectively. The mean post-operative astigmatic vector power was +0.78 ± 0.4 D in group A and +0.96 ± 0.5 D in group B at the end of 12 months. Corneal topography showed post-operative superior flattening (51.8% at 3 months and 55.4% at 12 months) in group A (P = 0.072) compared to superior steepening (59.6% at 3 months and 61.5% at 12 months) in group B (P = 0.977). The two commonly used techniques of combined cataract and glaucoma surgery proved to be efficacious without significant difference in surgical induced astigmatism.

Ratio of torus and equivalent power to refractive cylinder and spherical equivalent in phakic lenses - a Monte-Carlo simulation study.

Spherical and astigmatic powers for phakic intraocular lenses are frequently calculated using fixed ratios of phakic lens refractive power to refractive spherical equivalent, and of phakic lens astigmatism to refractive cylinder. In this study, a Monte-Carlo simulation based on biometric data was used to investigate how variations in biometrics affect these ratios, in order to improve the calculation of implantable lens parameters. A data set of over sixteen thousand biometric measurements including axial length, phakic anterior chamber depth, and corneal equivalent and astigmatic power was used to construct a multidimensional probability density distribution. From this, we determined the axial position of the implanted lens and estimated the refractive spherical equivalent and refractive cylinder. A generic data model resampled the density distributions and interactions between variables, and the implantable lens power was determined using vergence propagation. 50 000 artificial data sets were used to calculate the phakic lens spherical equivalent and astigmatism required for emmetropization, and to determine the corresponding ratios for these two values. The spherical ratio ranged from 1.0640 to 1.3723 and the astigmatic ratio from 1.0501 to 1.4340. Both ratios are unaffected by the corneal spherical / astigmatic powers, or the refractive cylinder, but show strong correlation with the refractive spherical equivalent, mild correlation with the lens axial position, and moderate negative correlation with axial length. As a simplification, these ratios could be modelled using a bi-variable linear regression based on the first two of these factors. Fixed spherical and astigmatic ratios should not be used when selecting high refractive power phakic IOLs as their variation can result in refractive errors of up to ±0.3 D for a 8 D lens. Both ratios can be estimated with clinically acceptable precision using a linear regression based on the refractive spherical equivalent and the axial position.

Management of Limbal Dermoids by Simple Excision in Young Children.

To report the visual outcomes, refractive results, and complications of simple excision for limbal dermoid in the first 8 years of life. This retrospective chart review included all children aged 8 years or younger who underwent excision of a grade I or II limbal dermoid without involvement of the visual axis between the years 2000 and 2019. Nineteen patients met the inclusion criteria. Their mean age was 4.2 ± 2.0 years (age range: 9 months to 8 years). The mean change in visual acuity was +1 ± 2.3 lines. The mean astigmatism was 3.20 ± 1.80 diopters (D) preoperatively and 3.50 ± 2.20 D at the last visit; the mean change in the astigmatism power was +0.20 ± 1.20 D (range: -1.50 to +2.75 D). Epithelial healing occurred in a mean of 8 days. No complications such as perforation were encountered. All patients had a good cosmetic outcome. Reepithelialization led to good cosmetic outcomes after this quick, simple, and uncomplicated procedure. There was no significant change in visual acuity or astigmatism, so amblyopia and astigmatism reduction are poor indications for limbal dermoid excision. Families should be counseled preoperatively that correction of the astigmatism and patching will remain essential in the postoperative management of amblyopia. [J Pediatr Ophthalmol Strabismus. 2021;58(3):196-201.].

Are changes in visual acuity and astigmatism after corneal cross-linking (CXL) in keratoconus predictable?

To evaluate changes in corrected distance visual acuity (CDVA), ratio of anterior and posterior corneal radii over the thinnest region of the cornea (ARC/PRC), and astigmatism after cross-linking (CXL) in keratoconus. Subjective refraction and ARC/PRC (using Pentacam™) were monitored over 1year in (I) keratoconus treated with routine CXL (n = 53), (II) relatively stable keratoconus (n = 23), and (III) age/gender matched controls (n = 24). CDVA (median, mode, interquartile range) improved significantly in group I, compared with groups II and III (p < 0.05), from 0.45 (0.60, 0.20-0.63) to 0.80 (0.95, 0.60-0.95); change in CDVA was associated with preop CDVA (p < 0.01 at all times postop). ARC/PRC (mean ± sd, 95% CI) changed from 1.362 (± 0.048, 1.347-1.377) to 1.425 (± 0.073, 1.401-1.449). CDVA and ARC/PRC remained stable in II and III. Significant relationships were revealed between logCDVA and ARC/PRC in I and II (at 12months, I rs = - 0.464, II rs - 0.449) and logCDVA at postop(y), log CDVA at preop(x1), and ARC/PRC at preop(x2) in I (at 12months, y = 0.356x1 - 1.312x2 + 1.806, r21 = 0.494, r22 = 0.203). Astigmatic power (mean ± sd, 95% CI) improved from - 3.10DC (± 1.52, - 3.55 to - 2.66) to - 2.53DC (± 1.24, - 2.90 to - 2.17) in I, and worsened from - 1.27DC (± 1.32, - 1.81 to - 0.73) to - 1.61DC (± 1.28, - 2.13 to - 1.09) in II. Vector analysis revealed in group I (a) the power of the surgically induced astigmatism (SIA) was linked to astigmatic power at preop and (b) the difference between the axis of astigmatism at preop(ø) and the axis of the SIA was linked to ø. CXL improved CDVA, increased the ARC/PRC ratio, and modified the association between CDVA and ARC/PRC. The change in CDVA was linked to preop CDVA and ARC/PRC values. The association between SIA and preop astigmatism implies there is not a simple cause and effect relationship with CXL.

본태적 난시도 그룹간 난시성 흐림이 대비감도에 미치는 영향

본태적 난시도 그룹간 난시성 흐림이 대비감도에 미치는 영향

Time to Keratometric Stability After Pterygium Excision and the Associated Factors: A Clinical Perspective.

PurposeTo determine the percentage of eyes with corneal astigmatic power stability and mean corneal keratometric power at 6-month post-pterygium excision, and to identify the time, and the associated factors, required to achieve stability.MethodsThis prospective observational study enrolled patients undergoing pterygium excision. Patients were evaluated for baseline characteristics and keratometric data before and every month after pterygium excision for six months using IOL Master 500® (Carl Zeiss, Meditec). Clinically stable corneal astigmatic power and keratometric power were, respectively, defined as changes in these parameters of less than 0.25 and 0.27 diopters after two consecutive visits. Time to corneal astigmatic and keratometric power stability, as well as factors associated with the stability, were analyzed.ResultsForty percent and 73.3% of eyes, respectively, demonstrated corneal astigmatic and corneal keratometric stability at six months post-operation. Within three months of reaching initial stability, the corneal astigmatic power and the mean keratometric power showed instability in 46.7% and 27.3% of patients, respectively. No patients with keratometric stability for more than three months became unstable during the study period. The extension of pterygium exceeding 3.0 mm was associated with a delay in time to corneal astigmatic stability (HRadjusted 0.41; 95% CI 0.19–0.89; P= 0.02).ConclusionAccording to the clinical relevance, 40% and 73% of patients, respectively, presented corneal astigmatic and keratometric stability within six months post-operation. Patients with a pterygium extension of more than 3 mm required a longer time for corneal astigmatic stability. It is recommended that keratometric stability be achieved for at least three months before commencing with additional procedures.

Surgical Treatment of Epiblepharon Effectively Alleviates Keratopathy but Not Astigmatism: A Case-Control Study Utilizing Vector Analysis in East Asian Children.

Purpose To identify an appropriate surgical indication of epiblepharon by comparing keratopathy and astigmatism outcomes after surgical and medical treatments for epiblepharon in Asian children. Methods Children diagnosed with epiblepharon (n = 82, age 5.93 ± 2.76 years) with >6 months of follow-up were enrolled. The clinical presentations and cycloplegic refractive status at the baseline and 3 and 6 months after treatment were compared between surgical (91 eyes from 47 children) and nonsurgical (67 eyes from 35 children) groups. The refractive and keratometric astigmatism at each time point were evaluated with vector analysis methods. For Thibos and Horner's method, the astigmatic power vector was decomposed into horizontal and oblique meridians (J0 and J45). However, the treatment-induced astigmatism (TIA) vectors were calculated by Alpins' method and depicted by the AstigMATIC software. Results In the surgical and nonsurgical groups, the baseline astigmatism magnitude was similar (2.22 ± 1.39 and 2.26 ± 1.46 D, p = 0.87). The rate of complete resolution of keratopathy at 6 months was 71.4% and 11.5%. The astigmatism magnitude in the surgical group differed among baseline and 3 months (2.25 ± 1.23 D) and 6 months postoperatively (1.97 ± 1.28 D) (p = 0.001). Power vector analyses confirmed a nuanced against-the-rule shift in the surgical group. This trend was especially observed in the subgroup of baseline astigmatism >2.0 D. However, the difference in the astigmatism magnitude between surgical and nonsurgical groups, even in highly astigmatic children, was not significant at 6 months. Conclusions The improvement of keratopathy in the surgical group was greater than that in the nonsurgical group in consideration of the more advanced severity in the surgery group at baseline. Decreased with-the-rule astigmatism can be observed at 6 months postoperatively, particularly among those with greater baseline astigmatism. However, the amount of change is small, and the outcome does not differ significantly from the nonsurgical treatment. Therefore, surgical indications should majorly base on the severity of symptoms and keratopathy.

Effect of Trabeculectomy on Corneal Astigmatism: A Hospital Based Study

Purpose: To find out the effect of trabeculectomy on corneal astigmatism among glaucoma patients.&#x0D; Study Design: Interventional case series.&#x0D; Place and Duration of Study: Al-Shifa Trust hospital, from August 2015 to February 2016.&#x0D; Methods: Thirty patients of glaucoma who were advised trabeculectomy were included in the study. Pre and post trabeculectomy data was collected by a structured clinical proforma. Snellen chart was used to measure visual acuity. Autorefracto-keratometer was used to find K-readings, corneal astigmatism and its axis. Data was entered in SPSS version 22. Descriptive analysis was done to report frequencies, percentages for qualitative variables and mean and SD for continuous variables. Paired sample t test was applied after the preliminary analysis to compare the corneal astigmatism pre and post trabeculectomy.&#x0D; Results: Out of 30 patients, majority (76%) were males. There was no statistically significant change found in visual acuity pre and post trabeculectomy (p-value &gt; 0.05). There was statistically significant difference of K1 (Horizontal) and K2 (Vertical) readings pre and post trabeculectomy (p &lt; 0.05). There was a statistically significant increase in overall corneal astigmatic power (p &lt; 0.05). Approximately 1.20D of astigmatism developed after trabeculectomy. There was no statistically significant difference between pre (94.0 ± 49.6) and post-operative corneal axis of astigmatism (87.6 ± 64.1).&#x0D; Conclusion: Trabeculectomy results in a significant change of corneal curvature in both meridians. This causes a change in post-operative visual acuity which in turn may adversely affect the compliance of patient towards surgical treatment. Patient should be informed and counselled about the possible visual outcomes after the trabeculectomy to preclude any distress that may occur following surgery.&#x0D; Key Words: Glaucoma, Trabeculectomy, Corneal Astigmatism, Visual acuity, Keratometry.

Predictability of Residual Postoperative Astigmatism After Implantation of a Toric Intraocular Lens Using Two Different Calculators.

PurposeTo compare predictability of postoperative refractive astigmatism (RA) using the Emmetropic Verifying Optical (EVO) Toric Formula v2.0 to one that accounts only for anterior corneal astigmatism.MethodsThis is a secondary analysis of de-identified data from a clinical trial including 9 sites across the United States. Preoperative biometry was used to predict postoperative RA with the implanted toric IOL using legacy enVista and EVO online calculators. The RA prediction error was computed between back-calculated postoperative RA and predicted residual RA. Outcome measures included vector (centroid) and arithmetic mean RA prediction error.ResultsComparison of calculators was based on 109 eyes, 97 (89%) of which were implanted with a toric IOL with an effective astigmatism power of 1.4 D or less. Centroid of the RA prediction errors was 0.37 D @ 178 and 0.17 D @ 090 for the legacy and EVO calculators, respectively (p < 0.0001). The proportion of eyes with an absolute RA prediction error ≤0.5 was 47.3% and 49.1% (p = 0.78), while the proportion of eyes ≤1.0 D was 82.7% and 89.1% (p = 0.03). Differences in the proportions ≤0.5 D existed for WTR (p = 0.015) but not ATR (p = 0.75) eyes. The proportion in which orientation of the predicted RA (ATR, WTR, or oblique) matched the actual RA was 62% and 78% for legacy and EVO calculators, respectively (p = 0.0029).ConclusionThe EVO Toric Formula v2.0 out-performed the legacy calculator with regards to predictions in eyes with low astigmatism.

Long-term Vector Outcomes of SMILE in Correcting Moderate to High With-the-Rule Astigmatism Under Astigmatism Axis Marked Condition.

To evaluate the vector outcomes of small incision lenticule extraction (SMILE) in correcting moderate to high myopic astigmatism under astigmatic axis marked condition. In a prospective, longitudinal, interventional study, 71 eyes (71 patients) that had with-the-rule preoperative cylinder refraction exceeding 1.50 diopters (D) were corrected with the VisuMax femtosecond laser (Carl Zeiss Meditec AG) at Zhongshan Ophthalmic Center. Refractive outcomes and astigmatic vector were evaluated preoperatively and at 1, 3, 6, and 30 months postoperatively. At 30 months postoperatively, the efficacy and safety indexes were 1.04 ± 0.18 and 1.15 ± 0.17, respectively. The magnitude of the surgically induced astigmatism (SIA) (2.13 ± 0.71 D at 1 month [P1m-pre = .018], 2.12 ± 0.72 D at 3 months [P3m-pre = .006], 2.13 ± 0.69 D at 6 months [P6m-pre = .010], and 2.19 ± 0.72 D at 30 months [P30m-pre < .001]) was slightly higher than that of the target induced astigmatism (TIA) (2.07 ± 0.69 D). Only the y-coordinate of the SIA vector had a significant overcorrection compared to that of the TIA vector (P1m-pre = .033, P3m-pre = .011, P6m-pre = .012, P30m-pre < .001). The corrected index (CI = |SIA|/|TIA|) varied from 1.03 ± 0.07 at 1 month to 1.06 ± 0.10 at 30 months, which was higher when correcting moderate astigmatism than when correcting high astigmatism (P = .041) at 30 months postoperatively. SMILE had long-term safety, efficacy, predictability, and stability when correcting moderate to high myopic astigmatism under astigmatism axis marked condition. Meanwhile, a cylinder overcorrection was observed due to the overcorrection of y-coordinate astigmatic power, which implied that the vector adjustment of the cylinder refraction nomogram should be considered. [J Refract Surg. 2020;36(9):585-591.].

Astigmatism Management with Intraocular Lens Surgery

Corneal astigmatism is common. More than 40% of patients undergoing cataract surgery have 1 diopter (D) power or more of astigmatism, which left untreated is visually significant. Because toric intraocular lenses (IOLs) are available, the current standard of care is to offer treatment of astigmatism at the time of cataract surgery. PubMed, MEDLINE, Embase databases, and the Cochrane Library were systematically searched from inception to October 2019. Search words included astigmatism, corneal astigmatism, toric IOLs, alignment, and IOL calculation. Studies evaluated included review articles regarding the origin and history of astigmatism, the diagnosis and management of the disease, and the history of surgical management options for astigmatism. Other studies evaluated in this review included clinical trials, meta-analyses, and retrospective analysis of surgical refractive outcomes. Prediction of refractive outcomes was evaluated with a review of IOL calculators and their use in lens prediction for cataract surgery. Evaluation of these articles also showed improved uncorrected visual acuity with the use of toric IOLs in patients undergoing cataract surgery. New diagnostic technology, new toricIOLs, updated lens formulas, intraoperative guidance, and advanced imaging technology and softwarehavecontributed to improvements in the surgical correction of astigmatism.

Mutual comparative analysis: a new topography-guided custom ablation protocol referencing subjective refraction to modify corneal topographic data

BackgroundSeveral planning algorithms have been developed for topography-guided custom ablation treatment (T-CAT), but each has its own deficiencies. The purpose of this study is to demonstrate the potential of a novel mutual comparative analysis (MCA) informed by manifest refraction and corneal topographic data and the patient’s subjective perception in correcting ametropia.MethodsThis retrospective review included patients with significant preoperative differences in the power or axis of astigmatism according to the manifest refraction and corneal topographic data (power > 0.75 D and/or axis > 10°). T-CAT planning was designed using MCA. Follow-ups were conducted for at least 6 months.ResultsSeventy-nine patients (121 eyes) were included. The mean preoperative deviation in the astigmatic power and axis were 0.72 ± 0.43 D and 20.18 ± 23.68°, respectively. The average oculus residual astigmatism (ORA) was 0.81 ± 0.32 D (range: 0.08–1.66 D). Six months postoperatively, the mean spherical equivalent refraction was 0.04 ± 0.42 D, and the mean cylinder was − 0.27 ± 0.24 D. The mean efficacy and safety indices were 1.10 and 1.15, respectively. The uncorrected distance visual acuity in 92% of the eyes was the same or better than the corrected distance visual acuity. The angle of error was ±5° in 61% of eyes and ± 15° in 84% of eyes. Residual astigmatism was ≤0.5 D in 91% of eyes. Optical quality and photopic contrast sensitivity did not change significantly (p > 0.05), and the scotopic contrast sensitivity decreased at 3, 6, and 12 cpd (p < 0.05). The vertical coma and horizontal coma of the anterior corneal surface significantly decreased postoperatively but increased during follow-up.ConclusionsThe MCA demonstrated safety, efficacy, accuracy, predictability, and stability and can be used as a complementary and feasible method for T-CAT.

The precision and agreement of corneal thickness and keratometry measurements with SS-OCT versus Scheimpflug imaging

PurposeTo assess the repeatability and reproducibility of swept-source optical coherence tomography (SS-OCT) and Scheimpflug system and evaluate the agreement between the two systems in measuring multiple corneal regions in children.MethodsPachymetric and keratometric maps for both systems were evaluated. Central, midperipheral and peripheral corneal thickness (CT), keratometry and astigmatism power vectors were recorded. The three outcomes yielded by the same observer were used to assess intraobserver repeatability. The differences in the mean values provided by each observer were used to evaluate interobserver reproducibility. Within-subject standard deviation, test-retest repeatability (TRT) and coefficient of variation (CoV) were used to analyze the intraobserver repeatability and interobserver reproducibility. Paired T-test and Bland-Altman were used to appraise interdevice agreement.ResultsSeventy-eight eyes of 78 children were included. The CoV was ≤2.12 and 1.10%, respectively, for repeatability and reproducibility. TRT and CoV were lower for central and paracentral CT measurements than for peripheral measurements. The SS-OCT device generated higher precision when acquiring CT data, whereas Scheimpflug system showed higher reliability when measuring corneal keratometry. Although the CT readings measured using SS-OCT were significantly thinner than Scheimpflug device (P < 0.001), the central and thinnest CT values were still of high agreement. The interdevice agreement of keratometry measurement was high for the central corneal region and moderate for the paracentral and peripheral areas.ConclusionsThe precision of CT measurements by SS-OCT was higher, while the reliability of keratometry measurements by the Scheimpflug system was higher in children. Apart from the measured values in the central corneal region, the thickness and keratometry readings should not be considered interchangeable between the two systems.

Refractive outcome of toric intraocular lens calculation in cases of oblique anterior corneal astigmatism.

To establish whether toric intraocular lens (IOL) calculation on the basis of anterior corneal measurements alone, in corneas with oblique anterior astigmatism, will result in a systematic overcorrection or undercorrection of postoperative refractive astigmatism, and to establish whether adjustment of oblique anterior corneal astigmatism to allow for the likely effect of posterior corneal astigmatism is needed in such eyes. The Queen Elizabeth Hospital, Department of Ophthalmology, Adelaide, South Australia. Retrospective case series. Data were collected from consecutive eyes with oblique anterior corneal astigmatism undergoing cataract surgery or refractive lens exchange. Toric IOL calculations were made using unadjusted anterior corneal astigmatism measurements and an astigmatically neutral technique. By comparison of targeted vs achieved astigmatic correction using vector analysis, the astigmatic power prediction error and angle of error were derived. In 50 eyes, the mean postoperatively measured refractive astigmatism was 0.42 diopters (D) (SD 0.33 D), the mean targeted refractive astigmatism was 0.15 (SD 0.18), and the vector-derived mean absolute prediction error was 0.23 D (SD 0.21). All 50 eyes (100%) fell at or within ±1.00 D of the target and 45 eyes (90%) at or within ±0.50 D. The geometric mean astigmatism correction index was 0.98, and the mean absolute angle of error was 8.63 degrees (SD 8.55). There is no systematic error attributable to posterior corneal astigmatism in toric IOL calculation and no need for adjustment of anteriorly measured corneal keratometric values for toric IOL calculation in eyes with oblique anterior corneal astigmatism. To do so may introduce an error in astigmatic outcome.

Characterization of a compact low-cost Stokes lens for astigmatism compensation in optical instruments.

Variable power cross-cylinder lenses (or Stokes lenses) have been widely known in the literature for decades. In this paper, we describe how to build a low-cost Stokes lens and discuss its calibration and its application to two significant cases. The construction is in virtue of a phoropter's Risley prism mount for assembling a couple of equal but opposite sign cylindrical lenses (we have selected $\,\pm 1.50$±1.50 D). Thus, variable astigmatic power is achieved by relative rotation of the lenses in opposite directions, and the resulting astigmatic axis is defined by the global rotation of the device. Calibration measurements are performed using an automatic lensmeter (Topcon CL-300) and an aberrometer (Zeiss iProfiler plus) for low and high order, respectively, aberration characterization. The proposed device has been adapted to a manual Topcon LM-8 lensmeter and to a regular Olympus BX-60 upright microscope for experimental validation concerning astigmatism compensation in a digital microscope and astigmatism cancellation in ophthalmic lenses, respectively. The device can be easily adapted to any ophthalmic/optic instrument for the compensation and/or measurement of astigmatism up to a maximum range of $|3|$|3| D of astigmatism.

Corneal Astigmatism Measurements Comparison among Ray-Tracing Aberrometry, Partial Coherence Interferometry, and Scheimpflug Imaging System.

Purpose To investigate interdevice agreement among corneal topography/ray-tracing aberrometry (iTrace), partial coherence interferometry (IOLMaster), and Scheimpflug imaging (Pentacam) for the measurement of corneal astigmatism. Methods The analysis included 90 eyes of 90 subjects without ocular disease. The main outcome measures were corneal cylinder power and axis of astigmatism. All corneal astigmatism measurements were converted to two perpendicular components by using vector analysis. Interdevice agreement was assessed using Bland–Altman analysis, paired sample t-test, and one-way analysis of variance. Results No significant interdevice difference existed in the astigmatism magnitude, cardinal component, and oblique component (all P > 0.05). On comparing iTrace wavefront and simulated keratometry (SimK) astigmatism, significant differences were observed in the astigmatism magnitude and oblique component (both P < 0.01), but not in the cardinal component (P=0.687). On comparing Pentacam pupil 3 mm and corneal vertex 3 mm axial astigmatism, significant difference was observed in the astigmatism magnitude (P < 0.001), but not in the cardinal and oblique components (both P > 0.05). Conclusions The iTrace, IOLMaster, and Pentacam devices could be used interchangeably for corneal astigmatism measurement. However, the measurement difference in iTrace wavefront and SimK astigmatism and Pentacam pupil 3 mm and vertex 3 mm axial astigmatism should be considered in clinic practice.