A New Method to Minimize the Standard Deviation and Root Mean Square of the Prediction Error of Single-Optimized IOL Power Formulas.

Purpose: The purpose of this study was to develop a simplified method to approximate constants minimizing the standard deviation (SD) and the root mean square (RMS) of the prediction error in single-optimized intraocular lens (IOL) power calculation formulas. Methods: The study introduces analytical formulas to determine the optimal constant value for minimizing SD and RMS in single-optimized IOL power calculation formulas. These formulas were tested against various datasets containing biometric measurements from cataractous populations and included 10,330 eyes and 4 different IOL models. The study evaluated the effectiveness of the proposed method by comparing the outcomes with those obtained using traditional reference methods. Results: In optimizing IOL constants, minor differences between reference and estimated A-constants were found, with the maximum deviation at -0.086 (SD, SRK/T, and Vivinex) and -0.003 (RMS, PEARL DGS, and Vivinex). The largest discrepancy for third-generation formulas was -0.027 mm (SD, Haigis, and Vivinex) and 0.002 mm (RMS, Hoffer Q, and PCB00/SN60WF). Maximum RMS differences were -0.021 and +0.021, both involving Hoffer Q. Post-minimization, the largest mean prediction error was 0.726 diopters (D; SD) and 0.043 D (RMS), with the highest SD and RMS after adjustments at 0.529 D and 0.875 D, respectively, indicating effective minimization strategies. Conclusions: The study simplifies the process of minimizing SD and RMS in single-optimized IOL power predictions, offering a valuable tool for clinicians. However, it also underscores the complexity of achieving balanced optimization and suggests the need for further research in this area. Translational Relevance: The study presents a novel, clinically practical approach for optimizing IOL power calculations.

Angle Kappa Influence on Multifocal IOL Outcomes.

PURPOSE: To characterize angle kappa and study the relationship between preoperative angle kappa and postoperative refractive accuracy, visual outcomes, and patient satisfaction in a large population of eyes with multifocal intraocular lens (MIOL) implantation. METHODS: A comprehensive electronic medical record chart review of 26,470 consecutive eyes that underwent immediate sequential bilateral cataract or refractive lens exchange with MIOLs was conducted. The primary outcome measures were postoperative monocular uncorrected distance visual acuity (UDVA), manifest refraction sphere and cylinder, spherical equivalent (SEQ), defocus equivalent (DEQ), subjective quality of vision at near, intermediate, and distance, and the likelihood of recommending the procedure. Relationships between preoperative angle kappa and postoperative outcomes were assessed with Pearson correlations. RESULTS: Angle kappa followed a right-skewed normal distribution (R2 = 0.99) with a mean ± standard deviation of 0.64 ± 0.27 mm. No clinically meaningful relationship was found between preoperative angle kappa and postoperative sphere, cylinder, SEQ, and DEQ, all with R2 ⩽ 0.0005. Similarly, there was no clinically meaningful relationship between preoperative angle kappa and postoperative UDVA (R2 = 0.001), postoperative satisfaction for near, intermediate, and distance vision (all R2 ⩽ 0.0023), or for recommending the MIOL surgery to friends and relatives (R2 = 0.0000). CONCLUSIONS: Preoperative angle kappa does not have a predictive clinical impact on postoperative MIOL visual outcomes, refractive accuracy, or subjective patient satisfaction. Angle kappa as a single variable cannot be used to determine MIOL candidacy. [J Refract Surg. 2023;39(12):840-849.].

Characterization of postoperative LASIK ectasia features on higher-order aberration excimer ablation maps.

BACKGROUND: To characterize anterior corneal higher-order aberration (HOA) excimer ablation map patterns in postoperative LASIK ectasia (POE) and to examine correlations between newly identified corneal HOA ablation map features of POE and known topographic indices. METHODS: Prospective multicenter non-interventional descriptive study. A total of 28 eyes from 22 POE patients were enrolled. The postoperative HOA ablation map was derived from Topolyzer Vario corneal imaging at the time of POE diagnosis. Features that recurred were identified and then analyzed. Correlations to Orbscan indices were studied. RESULTS: An arrangement of two elliptical paracentral ablation islands, deep inferior and shallow superior, in direct mirror-like opposition to each other, were identified on all HOA maps. The paracentral islands were accompanied by peripheral ablation crescents. The deep paracentral inferior island 'hot spot' coincided with the topographical apical POE cone and was highly reproducible in angular position (249.3 ± 17.3°). There was significant variation in ablation depth (shallow superior island: 11.5 ± 6.9 µm and deep inferior island: 32.5 ± 18.8 µm). The superior crescents had high variability in depth (34.8 ± 18.9 µm). Strong correlations were found between the corneal irregularity index and the ablation depth difference between the deep and shallow paracentral islands (R = 0.96; P < 0.0001). CONCLUSION: The corneal HOA excimer ablation map revealed a recurring, distinct, easily recognizable pattern in POE eyes. Validated Orbscan POE indices and HOA ablation map islands showed a strong correlation. It is possible to extract useful information from the corneal HOA ablation map, potentially making it suitable for diagnosing and monitoring POE although more studies are needed.

Impact of Single Constant Optimization on the Precision of IOL Power Calculation.

Purpose: The primary objective of this research is to examine how precision in intraocular lens calculation formulas can be impacted by zeroing the mean error through adjustments in the effective lens position value. Additionally, the study aims to evaluate how this modification influences outcomes differently based on the source of the prediction error. Methods: In order to analyze the impact of individual variables on the standard deviation, the study maintained all variables constant except for one at a time. Subsequently, variations were introduced to specific parameters, such as corneal curvature radius, keratometric refractive index, axial length, and predicted implant position. Results: According to our findings, when zeroing the mean error is applied to correct for inaccuracies in corneal power estimation, it results in a significant and exponential rise in standard deviation, thus adversely affecting the formula's precision. However, when zeroing is employed to compensate for prediction errors stemming from axial length measurements or predicted implant position, the effect on precision is minimal or potentially beneficial. Conclusions: The study highlights the potential risks associated with the indiscriminate but necessary zeroing of prediction errors in implant power calculation formulas. The impact on formula precision greatly depends on the source of the error, underscoring the importance of error source when analyzing variations in the standard deviation of the prediction error after zeroing. Translational Relevance: Our study contributes to the ongoing effort to enhance the accuracy and reliability of these formulas, thereby improving the surgical outcomes for cataract patients.

The Development of a Thick-Lens Post-Myopic Laser Vision Correction Intraocular Lens Calculation Formula.

PURPOSE: To describe the development of the post-myopic laser vision correction (LVC) version of the PEARL-DGS intraocular lens (IOL) calculation formula and to evaluate its outcomes on an independent test set. DESIGN: Retrospective, single-center case series. METHODS: A modified lens position prediction algorithm was designed along with methods to predict the posterior corneal curvature radius and correct the corneal power measurement error. A different set of previously operated eyes that underwent LVC was used to evaluate the prediction precision of the post-LVC formula. RESULTS: Post-LVC PEARL-DGS formula significantly reduced mean absolute error of prediction in comparison to Haigis-L, Shammas, and American Society of Cataract and Refractive Surgery (ASCRS) average formulas (P < .001). It exhibited similar postoperative refractive precision as the Barrett True-K No History formula (P = .61). CONCLUSION: The post-LVC formula development process described in this article performed as well as the state-of-the-art post-LVC formula on the present test set. Further studies are required to assess its efficacy in other independent sets.

A Simplified Method to Minimize Systematic Bias of Single-Optimized Intraocular Lens Power Calculation Formulas.

PURPOSE: To provide a simplified method to optimize lens constants to zero the mean prediction error (ME) of an intraocular lens (IOL) calculation formula, without the need to program the formula itself, by exploring the influence of IOL and corneal power on the refractive impact of variations in effective lens position. DESIGN: Theoretical development of an optimized formula and retrospective clinical evaluation on documented datasets. METHODS: Retrospective data from 8878 patients with cataracts with pre- and postoperative measurements available using 4 IOL models and 6 IOL power calculation formulas were examined. A schematic eye model was used to study the impact of small variations in effective lens position (ELP) on the postoperative spherical equivalent (SE) refraction. The impact of keratometry (K) and IOL power (P) on SE was investigated. A theoretical thick lens model was used to devise a formula to zero the average prediction error of an IOL power calculation formula. This was achieved by incrementing the predicted ELP, which could then be translated into an increment in the IOL constant. This method was tested on documented real-life postoperative datasets, using different IOL models and single-constant optimized IOL calculation formulas. RESULTS: For small variations in ELP, there was an exponential relationship between IOL power and the resultant postoperative refractive variation. The ELP adjustment necessary to zero the ME equated to a ratio between the ME and the mean of the following expression: 0.0006*(P2+2K*P) on the considered datasets. The accuracy of the values obtained using this formula was confirmed on documented postoperative datasets, and on published and nonpublished formulas. CONCLUSION: The proposed method allows surgeons without special expertise to optimize an IOL constant to nullify the ME on a documented dataset without coding the different formulas. The influence of individual eyes is proportional to the squared power of the implanted IOL.

Toric Trifocal Intraocular Lens for Refractive Lens Exchange: A Multi-center, Multi-surgeon Large Cohort Study.

PURPOSE: To assess the outcomes of a novel toric trifocal intraocular lens (IOL) for refractive lens exchange (RLE) in a large series of eyes with corneal astigmatism. METHODS: Consecutive eyes that underwent RLE with the PanOptix Toric IOL (Alcon Laboratories, Inc) were included. Outcomes measures included postoperative distance (UDVA), 60 cm intermediate (UIVA), and 40 cm near (UNVA) uncorrected visual acuity, manifest refraction, spherical and defocus equivalent, efficacy and safety indices, and vector analyses of refractive and toric IOL accuracy. RESULTS: A total of 4,933 eyes had a median follow-up of 3 months. UDVA of 20/20 and 20/40 was obtained in 65% and 99% of eyes monocularly and 87% and 100% binocularly, respectively. UIVA at 60 cm of 20/25 and 20/40 was achieved in 70% and 99% of eyes monocularly and in 77% and 100% binocularly, respectively. UNVA at 40 cm of 20/25 and 20/40 was achieved in 85% and 96% of eyes monocularly and in 95% and 100% binocularly, respectively. A total of 67%, 89%, 97%, and 99% of eyes had a SEQ within 0.25, 0.50, 0.75, and 1.00 diopter (D) of intended target (R2 = 0.99). Postoperative refractive astigmatism of 0.50, 0.75, and 1.00 D or less was achieved in 86%, 95%, and 98% of eyes. The vector analysis correction index and index of success were 1.04 ± 0.35 and 0.41 ± 0.31 for toric IOL accuracy and 1.00 ± 0.46 and 0.36 ± 0.55 for refractive accuracy, respectively. The 3- and 12-month post-RLE excimer laser enhancement rates were 1.1% (95% CI: 0.8% to 1.4%) and 7.6% (95% CI: 6.9% to 8.3%), respectively. CONCLUSIONS: The PanOptix Toric IOL performed well for a wide range of axial lengths and corneal astigmatism in eyes that had RLE. Most patients achieved effective uncorrected binocular near, intermediate, and distance vision for daily functioning. [J Refract Surg. 2023;39(5):302-310.].

mEYEstro software: an automatic tool for standardized refractive surgery outcomes reporting.

BACKGROUND: Standardization for reporting medical outcomes enables clinical study comparisons and has a fundamental role in research reproducibility. In this context, we present mEYEstro, a free novel standalone application for automated standardized refractive surgery graphs. mEYEstro can be used for single and multiple group comparisons in corneal and intraocular refractive surgery patients. In less than 30 s and with minimal user manipulation, mEYEstro automatically creates the required journal standard graphs while simultaneously performing valid statistical analyses. RESULTS: The software produces the following 11 standard graphs; Efficacy: 1. Cumulative uncorrected (UDVA) and corrected visual acuity (CDVA), 2. Difference between UDVA and CDVA, Safety: 3. Change in line of CDVA, Accuracy: 4. Spherical equivalent (SEQ) to intended target, 5. Attempted vs. achieved SEQ, 6. Defocus equivalent (DEQ) accuracy, 7. Refractive astigmatism accuracy, 8. Target-induced astigmatism vs. Surgically-induced astigmatism, 9. Correction index histogram, 10. Angle of error histogram, Stability: 11. SEQ stability over time. Percent proportions, means, standard deviations, Cohen's d effect sizes, and p-values are calculated and displayed on each graph. All graphs can be easily exported as high-resolution TIFF images for figures to use in scientific manuscripts and presentations. CONCLUSIONS: mEYEstro software enables clinicians, surgeons, and researchers, to easily and efficiently analyze refractive surgery outcomes using the standardized methodology required by several peer-reviewed ophthalmology journals.

Posterior Corneal Astigmatism Does Not Influence Manifest-Treated Topography-guided LASIK Outcomes.

PURPOSE: To investigate whether the magnitude of posterior corneal astigmatism (PCA) impacts refractive and visual outcomes of primary topography-guided laser in situ keratomileusis (LASIK) and to provide guidance on treating eyes with high PCA. METHODS: Comparative retrospective analysis of 4,541 consecutive eyes treated with Contoura (Alcon Laboratories, Inc) on the manifest refractive astigmatism. Standard outcomes of the 1,514 eyes with the lowest PCA (first tercile; low PCA group) were compared to the 1,514 eyes with the highest PCA (last tercile; high PCA group). Pearson correlation coefficient was used to assess relationships between variables. RESULTS: Preoperatively, 20.9% of eyes presented with PCA of 0.50 diopters (D) or greater. The mean PCA was 0.18 ± 0.07 D in eyes with low PCA, and 0.50 ± 0.11 D in eyes with high PCA. An equivalent number of eyes achieved a cumulative postoperative unilateral uncorrected distance visual acuity of 20/20 in both the low PCA and high PCA groups (95.3% vs 94.7%; P = .4489). The efficacy index of both low and high PCA eyes was identical (0.99 ± 0.06 vs 0.99 ± 0.08; P = .3192), as was the safety index (1.00 ± 0.02 vs 1.00 ± 0.03; P = .0110). The magnitude of preoperative PCA was weakly correlated with postoperative refractive astigmatism (R = 0.1323), but not with postoperative defocus equivalent (R = -0.0414) or spherical equivalent (R = -0.0128). CONCLUSIONS: PCA does not negatively impact the outcomes of topography-guided LASIK targeting the manifest refraction, having identical accuracy, efficacy, and safety in eyes with both low and high PCA. There is no scientific basis to measure and consider PCA in topography-guided LASIK planning software or nomograms if the excimer laser treatment input targets the manifest refraction. [J Refract Surg. 2022;38(12):780-790.].

Does Adjunctive Under-flap CXL Reduce Regression for Hyperopic LASIK?

PURPOSE: To investigate whether adding accelerated under-flap corneal cross-linking to hyperopic laser in situ keratomileusis (LASIK-ufCXL) affects postoperative stability and regression, visual and refractive outcomes, and subjective quality of vision. METHODS: This prospective comparative contralateral eye study included 51 patients with hyperopia (102 eyes) who received LASIK-ufCXL in the eye with highest defocus equivalent (DEQ) or randomized when DEQ equal, with the contralateral control eye receiving LASIK alone. After excimer ablation, 0.25% riboflavin was instilled on the stromal bed for 3 minutes. The flap was repositioned, followed by a total irradiation dose of 3.24 J ultraviolet A (UV-A) light administered to the corneal surface, using 18 mW/cm2 UV-A for 3 minutes. Postoperative hyperopic regression (stability) was the primary outcome measure, defined by the difference in spherical equivalent (SEQ) at 1 week and 24 months postoperatively. Secondary measures reported uncorrected distance visual acuity, corrected distance visual acuity, cylinder vector analysis, subjective quality of vision, subjective night vision disturbances, and corneal haze. RESULTS: At 24 months, the SEQ stability (P = .4273) and the magnitude of hyperopic regression (P = .5613) did not significantly differ between groups, with a small trend showing hyper-opic regression of 0.50 diopters or greater being less frequent in LASIK-ufCXL eyes. There were no significant differences in accuracy, efficacy, and safety (P > .05), with a small trend of more residual refractive astigmatism in the LASIK-ufCXL group (P = .3216, Cohen's d: -0.29). Subjective quality of vision trended inferior in LASIK-ufCXL eyes (P = .2237, Cohen's d: -0.25), with a greater haze grading (P = .0466, Cohen's d: 0.41). CONCLUSIONS: Postoperative regression and stability were statistically equivalent between hyperopic LASIK vs LASIK-ufCXL, with identical safety. There were small clinical trends of lower efficacy, accuracy, and subjective quality of vision in LASIK-ufCXL eyes. [J Refract Surg. 2022;38(12):770-779.].