Total keratometry in intraocular lens power calculations in eyes with previous laser refractive surgery

Effect of Posterior Keratometry and Corneal Radius Ratio on the Accuracy of Intraocular Lens Formulas After Myopic LASIK/PRK

PURPOSE

To investigate the impact of back-to-front corneal radius ratio (B/F ratio) and posterior keratometry (PK) on the accuracy of intraocular lens power calculation formulas in eyes after myopic laser in situ keratomileusis (LASIK)/photorefractive keratectomy (PRK) surgery.

METHODS

A retrospective, consecutive case series study included 101 patients (132 eyes) with cataract after myopic LASIK/PRK. Mean prediction error (PE), mean absolute PE (MAE), median absolute error (MedAE), and the percentage of eyes within ±0.25, ±0.50, and ±1.00 diopters (D) of PE were determined.

RESULTS

The Barrett True K-TK formula exhibited the lowest MAE (0.59 D) and MedAE (0.48 D) and the highest percentage of eyes within ±0.50 D of PE (54.55%) in total. In eyes with a B/F ratio of 0.70 or less and PK of -5.70 D or greater, the Potvin-Hill formula displayed the lowest MAE (0.46 to 0.67 D).

CONCLUSIONS

The Barrett True-TK exhibited the highest prediction accuracy in eyes after myopic LASIK/PRK overall. However, for eyes with a low B/F ratio and flat PK, the Potvin-Hill performed best. [J Refract Surg. 2024;40(9):e635-e644.].

Comparison of Legacy and New No-History IOL Power Calculation Formulas in Postmyopic Laser Vision Correction Eyes

PURPOSE

To compare the refractive accuracy of legacy and new no-history formulas in eyes with previous myopic laser vision correction (M-LVC).

DESIGN

Retrospective cohort study.

METHODS

Setting: Two academic centers Study Population: 576 eyes (400 patients) with previous M-LVC that underwent cataract surgery between 2019-2023. A SS-OCT biometer was used to obtain biometric measurements, including standard (K), posterior (PK), and total keratometry values (TK).

OBSERVATION PROCEDURES

Refractive prediction errors were calculated for 11 no-history formulas: two legacy M-LVC formulas, four new M-LVC formulas using K values only, and five new M-LVC formulas using K with PK or TK.

MAIN OUTCOME MEASURES

Heteroscedastic testing was used to evaluate relative formula performance, and formulas were ranked by root mean square error (RMSE).

RESULTS

New M-LVC formulas performed better than legacy M-LVC formulas. New M-LVC formulas with PK/TK values performed better than versions without PK/TK values. Among new M-LVC formulas with PK/TK values, EVO 2.0-PK was superior to Hoffer QST-PK (P < 0.005). Among new M-LVC formulas using K only, Pearl DGS-K and EVO 2.0-K were both superior to Hoffer QST-K and Barrett True K NH-K formulas (all P < 0.005).

CONCLUSIONS

Surgeons should favor using new no-history post M-LVC formulas over legacy post M-LVC formulas whenever possible. The top-performing M-LVC formulas (EVO 2.0-PK, Pearl DGS-PK, and Barrett True K-TK) utilized posterior corneal power values. Among formulas utilizing K alone, the EVO 2.0-K and Pearl DGS-K performed best.

Comparison of intraocular lens power prediction by American Society of Cataract and Refractive Surgery formulas and Barrett True-K TK in eyes with prior laser refractive surgery

PURPOSE

To evaluate the prediction accuracy of various intraocular lens (IOL) power calculation formulas on American Society of Cataract and Refractive Surgery (ASCRS) calculator and Barrett True-K total keratometry (TK) in eyes with previous laser refractive surgery for myopia.

METHODS

This retrospective study included eyes with history of myopic laser refractive surgery, which have undergone clear or cataractous lens extraction by phacoemulsification followed by IOL implantation. Those who underwent uneventful crystalline lens extraction were included. Eyes with any complication of refractive surgery or those with eventful lens extraction procedure and those who were lost to follow-up were excluded. Formulas compared were Wang-Koch-Maloney, Shammas, Haigis-L, Barrett True-K no-history formula, ASCRS average power, ASCRS maximum power on the ASCRS post-refractive calculator and the IOLMaster 700 Barrett True-K TK. Prediction error was calculated as the difference between the implanted IOL power and the predicted power by various formulae available on ASCRS online calculator.

RESULTS

Forty post-myopic laser-refractive surgery eyes of 26 patients were included. Friedman's test revealed that Shammas formula, Barrett True-K, and ASCRS maximum power were significantly different from all other formulas (P < 0.00001 for each). Median absolute error (MedAE) was the least for Shammas and Barrett True-K TK formulas (0.28 [0.14, 0.36] and 0.28 [0.21, 0.39], respectively) and the highest for Wang-Koch-Maloney (1.29 [0.97, 1.61]). Shammas formula had the least variance (0.14), while Wang-Koch-Maloney formula had the maximum variance (2.66).

CONCLUSION

In post-myopic laser refractive surgery eyes, Shammas formula and Barrett True-K TK no-history formula on ASCRS calculator are more accurate in predicting IOL powers.

Total and simulated keratometry measurements using IOLMaster 700 and Pentacam AXL after small incision lenticule extraction

PURPOSE

Calculating the intraocular lens (IOL) in patients after corneal refractive surgery presents a challenge. Because an overestimation of corneal power in cases undergone this surgery leading to a subsequent under-correction of IOL power. However, recent advancements in technology have eliable measurement of total corneal power. The aim of this research was to assess the agreement in simulated keratometry (SimK) and total keratometry (TK) values between IOLMaster 700 and Pentacam AXL.

METHODS

The study involved 99 patients (99 eyes) undergone small incision lenticule extraction (SMILE) surgery. Each patient underwent scans using IOL Master 700 and Pentacam AXL. The following parameters were recorded: SimK1, SimK2, Total K1 (TK1), and Total K2 (TK2) for IOLMaster 700; and SimK1, SimK2, True Net Power (TNP) K1, TNPK2, Total Corneal Refractive Power (TCRP) K1, and TCRP K2 for Pentacam AXL. Agreement between the two devices was evaluated using Bland-Altman plot, while paired t-test was utilized to compare any differences in the same parameter by both instruments.

RESULTS

The results revealed a strong correlation between the two devices.Noticeable comparability was identified for all SimK variables. However, there were noticeable differences in TK measurements as well as TK1-TNPK1, TK2-TNP K2, TK1-TCRP K1, and TK2-TCRP K2 parameters when comparing the two devices. The IOLMaster 700 consistently measured steeper values than the Pentacam AXL, with significant and clinically relevant differences of 1.34, 1.37, 0.87, and 0.95 diopters, respectively.

CONCLUSION

While there was a noticeable correlation between the IOLMaster 700 and Pentacam AXL in SimK measurements, a marked difference was noted in TK values. The two devices cannot be used interchangeably when quantifying TK values.

Intraocular Lens Power Calculation in Eyes After Myopic Laser Refractive Surgery and Radial Keratotomy: Bayesian Network Meta-analysis

PURPOSE

To compare the accuracy of formulas for calculating intraocular lens power in eyes after myopic laser refractive surgery or radial keratotomy.

DESIGN

Bayesian network meta-analysis.

METHODS

PubMed, Embase, the Cochrane Data Base of Systematic Reviews, and the Cochrane Central Register of Controlled Trials databases were searched for retrospective and prospective clinical studies published from January 1, 2012, to August 24, 2022. The outcome measurement was the percentage of eyes with a predicted error within the target refractive range (±0.50 diopter [D] or ±1.00 D).

RESULTS

Our meta-analysis includes 24 studies of 1172 eyes after myopic refractive surgery that use 12 formulas for intraocular lens power calculation. (1) A network meta-analysis showed that Barrett true-K no history, the optical coherence tomography (OCT) formula, and the Masket formula had a significantly higher percent of eyes within ±0.50 D of the goal than the Haigis-L formula, whereas the Wang-Koch-Maloney formula showed the poor predictability. Using an error criterion of within ±1.00 D, the same 3 formulas performed slightly better than the Haigis-L formula. Based on performance using both prediction error criteria, the Barrett true-K no history formula, OCT formula, and Masket formula showed the highest probability of ranking as the top 3 among the 12 methods. (2) A direct meta-analysis with a subset of 4 studies and 5 formulas indicated that formulas did not differ in percent success for either the ±0.5 D or ±1.0 D error range in eyes that had undergone radial keratotomy.

CONCLUSIONS

The OCT, Masket, and Barrett true-K no history formulas are more accurate for eyes with previous myopic laser refractive surgery, whereas no significant difference was found among the formulas for eyes that had undergone radial keratotomy.

Current Concepts and Recent Updates of Optical Biometry- A Comprehensive Review

One of the most recent advancements in the field of cataract surgery is optical biometry. With the advent of optical biometry ocular measurements are now simpler, quicker, and more precise. The devices have made intraocular lens (IOL) power calculations easier in difficult situations too, such as in cases with extremes of axial lengths, silicone filled eyes, cataract surgery in post-keratoplasty eyes, post Laser-Assisted in Situ Keratomileusis (LASIK) eyes, etc. The gold standard for IOL power calculation in the present day is by the use of optical biometry devices. The anatomical measurements by these devices are highly precise and because of these measurements and the incorporation of various IOL power calculation formulas the optical biometry devices give the accurate power and the post-operative visual outcome is highly satisfactory among the patients. The growing use of these devices has made cataract the most commonly performed refractive surgical procedure nowadays. In the current scenario, optical biometry has widespread acceptance in almost all countries and has many advantages over ultrasound or immersion biometry. Cataract surgeons can obtain easy and reliable measurements from these devices. Refractive surprises have also decreased considerably with their use. This article will comprehensively review the principles of the various optical biometry devices, the parameters used in each of the devices, the advantages and disadvantages, and add more like what all this article will add.

Accuracy of toric intraocular lens power calculation depending on different keratometry values using a novel network based software platform

Purpose

To compare different corneal keratometry readings (swept-source-OCT-assisted biometry and Scheimpflug imaging) with a novel software platform for calculation of toric intraocular lenses.

Setting

Department of Ophthalmology, Ludwig-Maximilians-University, Munich, Germany.

Design

Retrospective, non-randomized, clinical trial.

Methods

Twenty-three eyes undergoing toric intraocular lens implantation were included. Inclusion criteria were preoperative regular corneal astigmatism of at least 1.00 D, no previous refractive surgery, no ocular surface diseases and no maculopathies. Lens exchange was performed with CALLISTO eye (Zeiss). For each patient, the expected postoperative residual refraction was calculated depending on three different corneal parameters of two different devices: standard K-front (K) and total keratometry (TK) obtained by a swept-source-OCT-assisted biometry system (IOL Master 700, Zeiss) as well as total corneal refractive power (TCRP) obtained by a Scheimpflug device (Pentacam AXL, Oculus). Barrett's formula for toric intraocular lenses was used for all calculations within a novel software platform (EQ workplace, Zeiss FORUM®). Results were statistically compared with postoperative refraction calculated according to the Harris dioptric power matrix.

Results

The standard K values (mean PE 0.02 D ± 0.45 D) and TK values (mean PE 0.09 D ± 0.43 D) of the IOL Master 700 reached similar results (p = 0.96). 78% of eyes in both K and TK groups achieved SE within ±0.5 D of attempted correction and all eyes (100%) were within ±1.0 D of attempted correction in both groups. By contrast, the prediction error in the IOL calculation using the TCRP of the Scheimpflug device was significantly greater (mean PE -0.56 D ± 0.49 D; p = 0.00 vs. standard K and p = 0.00 vs. TK) with adjusted refractive indices. Thirty-nine and Ninety-one percentage of eyes in the TCRP group achieved SE within ±0.5 D (p = 0.008 K vs. TCRP and p = 0.005 TK vs. TCRP) and ± 1.0 D (p = 0.14 vs. TCRP) of attempted correction, respectively.

Conclusion

All three corneal parameters (standard K, TK, TCRP) performed well in calculating toric IOLs. The most accurate refractive outcomes in toric IOL implantation were achieved by IOL calculations based on swept-source-OCT-assisted biometry. The SS-OCT-based K-front and TK values achieve comparable results in the calculation of toric IOLs.

Differences Between Keratometry and Total Keratometry Measurements in a Large Dataset Obtained With a Modern Swept Source Optical Coherence Tomography Biometer

PURPOSE

This study aimed to explore the concept of total keratometry (TK) by analyzing extensive international datasets representing diverse ethnic backgrounds. The primary objective was to quantify the disparities between traditional keratometry (K) and TK values in normal eyes and assess their impact on intraocular lens (IOL) power calculations using various formulas.

DESIGN

Retrospective multicenter intra-instrument reliability analysis.

METHODS

The study involved the analysis of biometry data collected from ten international centers across Europe, the United States, and Asia. Corneal power was expressed as equivalent power and astigmatic vector components for both K and TK values. The study assessed the influence of these differences on IOL power calculations using different formulas. The results were analyzed and plotted using Bland-Altman and double angle plots.

RESULTS

The study encompassed a total of 116,982 measurements from 57,862 right eyes and 59,120 left eyes. The analysis revealed a high level of agreement between K and TK values, with 93.98% of eyes exhibiting an absolute difference of 0.25 D or less. Astigmatism vector differences exceeding 0.25 D and 0.50 D were observed in 39.43% and 1.08% of eyes, respectively.

CONCLUSIONS

This large-scale study underscores the similarity between mean K and TK values in healthy eyes, with rare clinical implications for IOL power calculation. Noteworthy differences were observed in astigmatism values between K and TK. Future investigations should delve into the practicality of TK values for astigmatism correction and their implications for surgical outcomes.

Performance of IOL calculation formulas that use measured posterior corneal power in eyes following myopic laser vision correction

PURPOSE

To compare the predictive accuracy of the biometer-embedded Barrett True-K TK and new total corneal power methods of intraocular lens (IOL) power calculation in eyes with prior laser vision correction (LVC) for myopia.

SETTING

Academic clinical practice.

DESIGN

Retrospective case series.

METHODS

IOL power formulas were assessed using measurements from a swept-source optical coherence biometer. Refractive prediction errors were calculated for the Barrett True-K TK, EVO 2.0, Pearl-DGS, and HofferQST, which use both anterior and posterior corneal curvature measurements. These were compared with the Shammas, Haigis-L, Barrett True-K No History (NH), optical coherence tomography, and 4-formula average (AVG-4) on the ASCRS postrefractive calculator, and to the Holladay 1 and 2 with non linear axial length regressions (H1- and H2-NLR).

RESULTS

The study comprised 85 eyes from 85 patients. Only the Barrett True-K TK and EVO 2.0 had mean numerical errors that were not significantly different from 0. The EVO 2.0, Barrett True-K TK, Pearl-DGS, AVG-4, H2-NLR, and Barrett True-K NH were selected for further pairwise analysis. The Barrett True-K TK and EVO 2.0 demonstrated smaller root-mean-square absolute error compared with the Pearl-DGS, and the Barrett True-K TK also had a smaller mean absolute error than the Pearl-DGS.

CONCLUSIONS

The Barrett True-K TK and EVO 2.0 formulas had comparable performance to existing formulas in eyes with prior myopic LVC.

Optimization of biometry for best refractive outcome in cataract surgery

High-precision biometry and accurate intraocular lens (IOL) power calculation have become essential components of cataract surgery. In clinical practice, IOL power calculation involves measuring parameters such as corneal power and axial length and then applying a power calculation formula. The importance of posterior corneal curvature in determining the true power of the cornea is increasingly being recognized, and newer investigative modalities that can estimate both the anterior and posterior corneal power are becoming the standard of care. Optical biometry, especially using swept-source biometers, with an accuracy of 0.01-0.02 mm, has become the state-of-the-art method in biometry. With the evolution of IOL formulas, the ultimate goal of achieving a given target refraction has also moved closer to accuracy. However, despite these technological efforts to standardize and calibrate methods of IOL power calculation, achieving a mean absolute error of zero for every patient undergoing cataract surgery may not be possible. This is due to inherent consistent bias and systematic errors in the measurement devices, IOL formulas, and the individual bias of the surgeon. Optimization and personalization of lens constants allow for the incorporation of these systematic errors as well as individual bias, thereby further improving IOL power prediction accuracy. Our review provides a comprehensive overview of parameters for accurate biometry, along with considerations to enhance IOL power prediction accuracy through optimization and personalization. We conducted a detailed search in PubMed and Google Scholar by using a combination of MeSH terms and specific keywords such as "ocular biometry," "IOL power calculations," "prediction accuracy of refractive outcome in cataract surgery," "effective lens position," "intraocular lens calculation formulas," and "optimization of A-constants" to find relevant literature. We identified and analyzed 121 relevant articles, and their findings were included.

An update on intraocular lens power calculations in eyes with previous laser refractive surgery

PURPOSE OF REVIEW

There is an ever-growing body of research regarding intraocular lens (IOL) power calculations following photorefractive keratectomy (PRK), laser-assisted in-situ keratomileusis (LASIK), and small-incision lenticule extraction (SMILE). This review intends to summarize recent data and offer updated recommendations.

RECENT FINDINGS

Postmyopic LASIK/PRK eyes have the best refractive outcomes when multiple methods are averaged, or when Barrett True-K is used. Posthyperopic LASIK/PRK eyes also seem to do best when Barrett True-K is used, but with more variable results. With both aforementioned methods, using measured total corneal power incrementally improves results. For post-SMILE eyes, the first nontheoretical data favors raytracing.

SUMMARY

Refractive outcomes after cataract surgery in eyes with prior laser refractive surgery are less accurate and more variable compared to virgin eyes. Surgeons may simplify their approach to IOL power calculations in postmyopic and posthyperopic LASIK/PRK by using Barrett True-K, and employing measured total corneal power when available. For post-SMILE eyes, ray tracing seems to work well, but lack of accessibility may hamper its adoption.

Cataract surgery following refractive surgery: Principles to achieve optical success and patient satisfaction

A growing number of patients with prior refractive surgery are now presenting for cataract surgery. Surgeons face a number of unique challenges in this patient population that tends to be highly motivated to retain or regain functional uncorrected acuity postoperatively. Primary challenges include recognition of the specific type of prior surgery, use of appropriate intraocular lens (IOL) power calculation formulas, matching IOL style with spherical aberration profile, the recognition of corneal imaging patterns that are and are not compatible with toric and/or presbyopia-correcting lens implantation, and surgical technique modifications, which are particularly relevant in eyes with prior radial keratotomy or phakic IOL implantation. Despite advancements in IOL power formulae, corneal imaging, and IOL options that have improved our ability to achieve targeted postoperative refractive outcomes, accuracy and predictability remain inferior to eyes that undergo cataract surgery without a history of corneal refractive surgery. Thus, preoperative evaluation of patients who will and will not be candidates for postoperative refractive surgical enhancements is also paramount. We provide an overview of the specific challenges in this population and offer evidence-based strategies and considerations for optimizing surgical outcomes.

Comparative analysis of IOL power calculations in postoperative refractive surgery patients: a theoretical surgical model for FS-LASIK and SMILE procedures

BACKGROUND

As the two most prevalent refractive surgeries in China, there is a substantial number of patients who have undergone Femtosecond Laser-assisted In Situ Keratomileusis (FS-LASIK) and Small Incision Lenticule Extraction (SMILE) procedures. However, there is still limited knowledge regarding the selection of intraocular lens (IOL) power calculation formulas for these patients with a history of FS-LASIK or SMILE.

METHODS

A total of 100 eyes from 50 postoperative refractive surgery patients were included in this prospective cohort study, with 25 individuals (50 eyes) having undergone FS-LASIK and 25 individuals (50 eyes) having undergone SMILE. We utilized a theoretical surgical model to simulate the IOL implantation process in postoperative FS-LASIK and SMILE patients. Subsequently, we performed comprehensive biological measurements both before and after the surgeries, encompassing demographic information, corneal biometric parameters, and axial length. Various formulas, including the Barrett Universal II (BUII) formula, as a baseline, were employed to calculate IOL power for the patients.

RESULTS

The Barrett True K (BTK) formula, demonstrated an mean absolute error (AE) within 0.5 D for both FS-LASIK and SMILE groups (0.28 ± 0.25 D and 0.36 ± 0.24 D, respectively). Notably, the FS-LASIK group showed 82% of results differing by less than 0.25 D compared to preoperative BUII results. The Barrett True K No History (BTKNH) formula, which also incorporates measured posterior corneal curvature, performed similarly to BTK in both groups. Additionally, the Masket formula, relying on refractive changes based on empirical experience, displayed promising potential for IOL calculations in SMILE patients compared with BTK (p = 0.411).

CONCLUSION

The study reveals the accuracy and stability of the BTK and BTKNH formulas for IOL power calculations in myopic FS-LASIK/SMILE patients. Moreover, the Masket formula shows encouraging results in SMILE patients. These findings contribute to enhancing the predictability and success of IOL power calculations in patients with a history of refractive surgery, providing valuable insights for clinical practice. Further research and larger sample sizes are warranted to validate and optimize the identified formulas for better patient outcomes.

Intraocular Lens Power Calculations in Keratoconus Eyes Comparing Keratometry, Total Keratometry, and Newer Formulae

PURPOSE

To compare the utility of keratometry vs total keratometry (TK) for intraocular lens power calculations in eyes with keratoconus (KCN) using KCN and non-KCN formulae.

DESIGN

Retrospective cohort study.

METHODS

This study was conducted at 2 academic centers and included 87 eyes in 67 patients who underwent cataract surgery between 2019 and 2021. Biometry measurements were obtained using a swept-source optical coherence tomography biometer (IOL Master 700). Refractive prediction errors, including root mean square error (RMSE), were calculated for 13 formulae. These included 4 classical formulae (Haigis, Hoffer Q, Holladay 1 [H1], and SRK/T), 5 new formulae (NF) (Barrett Universal II [BU2], Cooke K6, EVO 2.0, Kane, and Pearl-DGS), 3 KCN formulae (BU2 KCN: M-PCA, BU2 KCN: P-PCA, and Kane KCN), and H1 with equivalent keratometry reading values (H1-EKR). Formulae were ranked by RMSE. Friedman analysis of variance with post hoc analysis and H-testing was used for statistical significance testing.

RESULTS

KCN formulae had the lowest RMSEs in all eyes, and BU2 KCN:M-PCA performed the best among KCN formulae in all subgroups. In eyes with severe KCN, if TK values are unavailable, the BU2 KCN: P-PCA performed better than the top-ranked non-KCN formula (SRK/T). In eyes with nonsevere KCN, if TK values are unavailable, EVO 2.0 K was statistically superior to the next competitor (Kane K). H1-EKR had the highest RMSE.

CONCLUSIONS

KCN formulae and TK are useful for intraocular lens power calculations in KCN eyes, especially in eyes with severe KCN. The BU2 KCN: M-PCA using TK values performed best for eyes with all severities of KCN. For eyes with nonsevere KCN, the EVO 2.0 TK or K can also be used.

Accuracy of refractive outcomes using standard or total keratometry for intraocular lens power formulas in conventional cataract surgery

PURPOSE

To evaluate if total keratometry (TK) is better than standard keratometry (K) for predicting an accurate intraocular lens (IOL) refractive outcome in virgin eyes using four IOL power calculation formulas.

METHODS

447 eyes that underwent monofocal intraocular lens implantation were enrolled in this study. IOLMaster 700 (Carl Zeiss Meditech, Jena, Germany) was used for optical biometry. Prediction error (PE), mean absolute prediction error (MAE), median absolute prediction error (MedAE), proportions of eyes within ± 0.25 diopters (D), ± 0.50 D, ± 0.75 D, ± 1.00 D, ± 2.00 D prediction error, and formula performance index (FPI) were calculated for each K- and TK-based formula.

RESULTS

Overall, the accuracy of each TK and K formula was comparable. The MAEs and MedAEs showed no difference between most of the K-based and the TK-based formula; only the MAE of TK was significantly higher than that of K using the Haigis. The percent of eyes within ± 0.25 D PE for TK was not significantly different from that for K. The analysis of PE across various optical dimensions revealed that TK had no effect on the refractive results in eyes with different preoperative axial length, anterior chamber depth, keratometry, and lens thickness. The K-based Barrett Universal II formula performed excellently, showed the leading FPI score, and had the best refractive prediction outcomes among the four formulas.

CONCLUSION

TK and K can be used for IOL power calculation in monofocal IOL implantation cataract surgery in virgin eyes, as both are comparable. In all investigated formulas, the predictive accuracy of TK-based formulas is not superior to that of standard K-based formulas.

Comparison of intraocular lens power calculation formulas with and without total keratometry and ray tracing in patients with previous myopic SMILE

PURPOSE

To evaluate the prediction error (PE) variance and absolute median PE of different intraocular lens (IOL) calculation formulas including last-generation formulas such as Barrett True-K with K, Okulix and total keratometry (TK)-based calculations with Haigis, and Barrett True-K in a simulation model in post-small-incision lenticule extraction (SMILE) eyes.

SETTINGS

Department of Ophthalmology, University Hospital Marburg, Marburg, Germany.

DESIGN

Prospective study.

METHODS

Preoperative measurements included IOL power calculation before and after SMILE surgery. The target refraction was set to be the lowest myopic refractive error in pre-SMILE eyes. The IOL power targeting at the lowest myopic refractive error in pre-SMILE eyes was selected for the post-SMILE IOL calculation of the same eye. The difference between the predicted refraction of pre- and post-SMILE eyes with the same IOL power was defined as IOL difference. The refractive change induced by SMILE was defined as the difference between preoperative and postoperative manifest refraction.

RESULTS

98 eyes from 49 patients underwent bilateral myopic SMILE. The PE variance of Okulix was not significantly different compared with Barrett True-K with TK ( P = .471). The SDs of the mean PEs were ±0.413 D (Haigis-TK), ±0.453 D (Okulix), ±0.471 D (Barrett True-K with TK), ±0.556 D (Haigis-L), and ±0.576 D (Barrett True-K with K). The mean absolute PE was 0.340 D, 0.353 D, 0.404 D, 0.511 D, and 0.715 D for Haigis-TK, Okulix, Barrett True-K with TK, Barrett True-K with K, and Haigis-L, respectively. The highest percentage of eyes within ±0.50 D was achieved by Okulix, followed by Haigis-TK, Barrett True-K with TK, Barrett True-K with K, and Haigis-L.

CONCLUSIONS

Results suggest that Haigis in combination with TK, Okulix, and Barrett True-K with and without TK offer good options for accurate IOL power calculation after SMILE. Haigis-L showed a tendency for myopic shift in eyes after previous SMILE.

Standard vs total keratometry for intraocular lens power calculation in cataract surgery combined with DMEK

PURPOSE

To compare the prediction accuracy of standard keratometry (K) and total keratometry (TK) for intraocular lens (IOL) power calculation in eyes undergoing combined cataract surgery and Descemet membrane endothelial keratoplasty (triple DMEK).

SETTING

Tertiary care academic referral center.

DESIGN

Retrospective case series.

METHODS

Review of 83 eyes (63 patients) that underwent triple DMEK between 2019 and 2021. Biometry measurements were obtained using a swept-source optical biometer (IOLMaster 700). 63 eyes were used for statistical analysis. Mean error, mean absolute error (MAE), SD, median absolute error, maximum absolute error, root mean squared prediction error, and the percentage of eyes within prediction errors of ±0.50 diopters (D) and ±1.00 D were calculated for 9 multivariate and third-generation formulas using K and TK values (Barrett Universal II, Yeo EVO 2.0, Cooke K6, Kane, Pearl-DGS, Haigis, Holladay 1, Hoffer Q, and SRK/T). Formulas were additionally tested by using the prediction for an IOL power 1 D below the IOL used (IOLup1D).

RESULTS

For all formulas, MAE was lower for K than for TK by an average of 0.21 D. The lowest MAE value observed was 0.67 D for "adjusted" SRK/T using K, and the highest MAE values observed were 1.24 D and 1.24 D for nonadjusted Hoffer Q and Haigis using TK, respectively. Overall, lower MAE values were observed for multivariate formulas and SRK/T.

CONCLUSIONS

In triple DMEK eyes, the prediction accuracy of K was higher than that of TK. The most accurate formulas were SRK/T and multivariate formulas using K with the IOLup1D adjustment.

Comparison of the Predictive Accuracy of Intraocular Lens Power Calculations after Phototherapeutic Keratectomy in Granular Corneal Dystrophy Type 2

Granular corneal dystrophy type 2 (GCD2) is an autosomal dominant disease affecting vision. Phototherapeutic keratectomy (PTK) is advantageous in removing vision-threatening corneal opacities and postponing keratoplasty; however, it potentially disturbs accurate intraocular lens (IOL) power calculation in cataract surgery. The myopic/hyperopic Haigis-L method with or without the central island has been reported; nevertheless, an optimal method has not yet been established. To compare the predictive accuracy of post-PTK IOL power calculations in GCD2, the retrospective data of 30 eyes from July 2017 to December 2020 were analyzed. All GCD2-affected eyes underwent post-PTK standard cataract surgery using the WaveLight EX500 platform (Alcon Laboratories, Inc., Fort Worth, TX, USA) under a single surgeon. The mean prediction error (MPE) and absolute error (MAE) with the myopic/hyperopic Haigis-L, Barrett Universal II, Barrett True-K, Haigis, and SRK/T by standard keratometry (K) and total keratometry (TK), where possible, were analyzed. Barrett Universal II and SRK/T showed significantly superior MPE, and MAE compared with the myopic/hyperopic Haigis-L method. TK was not significantly superior to K in the same formula. In conclusion, this study suggests that these biometries and formulas, especially Barrett Universal II and SRK/T, are potentially useful in IOL power calculation in GCD2 after PTK.

Comparative Analysis of Corneal Parameters Performed with GalileiG6 and OCT Casia 2

BACKGROUNDS

To compare keratometry (Ks and Kf), astigmatism (Ast.), and the astigmatism axes (Ax.) of the posterior surface of the cornea; the total, central cornea thickness (CCT); and the thinnest corneal thickness (TCT) measured using two different measurement methods.

METHODS

Patients qualified for cataract surgery at the Chair and Clinical Department of Ophthalmology, Division of Medical Science in Zabrze, Medical University of Silesia, Katowice, Poland, were included in the study and monitored with the following two devices: OCT-CASIA2 and Dual Scheimpflug Analyzer GalileiG6. Our work was a randomized, prospective study in which compliance with the agreement of measurements between the devices was evaluated using the Bland-Altman method.

RESULTS

A total of 110 patients (62 females and 48 males) were examined. Overall, 100 eyes of patients that qualified for cataract surgery were enrolled in the study. No statistically significant difference was observed for Total-Ks and Total-Kf. A significant difference was observable for the following parameters: total Ks-ax, total Kf-ax, the total power of astigmatism, and in all parameters of the part of the cornea and corneal thickness (CCT and TCT).

CONCLUSIONS

The measurements obtained using Casia2 and the Dual Scheimpflug Analyzer GalileiG6 were significantly different and not interchangeable except for total Ks and Kf.

Lower refractive prediction accuracy of total keratometry using intraocular lens formulas loaded onto a swept-source optical biometer

PURPOSE

To compare refractive outcomes calculated using intraocular lens (IOL) power calculation formulas loaded onto the IOLMaster 700 with the employment of anterior keratometry (K) and total keratometry (TK).

METHODS

A total of 225 eyes of 225 patients underwent uneventful cataract surgery and implantation of a single model of nontoric monofocal IOL by a single surgeon. All eyes underwent preoperative ocular biometric measurements with the IOLMaster 700. Refractive outcomes, including the mean numerical prediction error (MNE); standard deviation (SD); adjusted mean absolute prediction error (MAE); adjusted median absolute prediction error (MedAE); percentages of eyes with adjusted prediction error (PE) within ± 0.25, ± 0.50, ± 0.75, and ± 1.00 diopter; and IOL Formula Performance Index (FPI), were compared between the K-based formula and the TK-based formula of Barrett Universal II (BUII), Haigis, SRK/T, Holladay 2, and Hoffer Q. Axial length (short, medium, and long) subgroup analyses and anterior and posterior keratometry (flat, medium, and steep) subgroup analyses were conducted.

RESULTS

The K-based formula performed better than the TK-based formula in the accuracy of refractive prediction of each IOL calculation formula: BUII-K (FPI 0.690), BUII-TK (0.677), Haigis-K (0.617), Haigis-TK (0.584), SRK/T-K (0.608), SRK/T-TK (0.595), Holladay 2-K (0.419), Holladay 2-TK (0.406), Hoffer Q-K (0.364), and Hoffer Q-TK (0.356). The subgroup analyses of refractive prediction outcomes showed that TK influenced the refractive outcomes in eyes with relatively normal ranges of axial length and anterior keratometry.

CONCLUSIONS

Using TK instead of K leads to lower refractive prediction accuracy of the IOL power calculation formulas loaded on the IOLMaster 700.

Application of total keratometry in ten intraocular lens power calculation formulas in highly myopic eyes

Background

The accuracy of using total keratometry (TK) value in recent IOL power calculation formulas in highly myopic eyes remained unknown.

Methods

Highly myopic patients who underwent uneventful cataract surgery were prospectively enrolled in this prospective comparative study. At one month postoperatively, standard deviation (SD) of the prediction errors (PEs), mean and median absolute error (MedAE) of 103 highly myopic eyes were back-calculated and compared among ten formulas, including XGboost, RBF 3.0, Kane, Barrett Universal II, Emmetropia Verifying Optical 2.0, Cooke K6, Haigis, SRK/T, and Wang-Koch modifications of Haigis and SRK/T formulas, using either TK or standard keratometry (K) value.

Results

In highly myopic eyes, despite good agreement between TK and K (P > 0.05), larger differences between the two were associated with smaller central corneal thickness (P < 0.05). As to the refractive errors, TK method showed no differences compared to K method. The XGBoost, RBF 3.0 and Kane ranked top three when considering SDs of PEs. Using TK value, the XGboost calculator was comparable with the RBF 3.0 formula (P > 0.05), which both presented smaller MedAEs than others (all P < 0.05). As for the percentage of eyes within ± 0.50 D or ± 0.75 D of PE, the XGBoost TK showed comparable percentages with the RBF 3.0 TK formula (74.76% vs. 66.99%, or 90.29% vs. 87.38%, P > 0.05), and statistically larger percentages than the other eight formulas (P < 0.05).

Conclusions

Highly myopic eyes with thinner corneas tend to have larger differences between TK and K. The XGboost enhancement calculator and RBF 3.0 formula using TK showed the most promising outcomes in highly myopic eyes.

Measurements of Anterior and Posterior Corneal Curvatures with OCT and Scheimpflug Biometers in Patients with Low Total Corneal Astigmatism

Background: Posterior keratometry measurements are evolving features of the optical biometers. The differences between devices have bigger impact for the low astigmatism values. The majority of adults present the corneal astigmatism below 1.5 D. Objectives: To compare the total corneal astigmatism measured with two different technologies in cataract patients with corneal astigmatism below 1.5 D. Material and Methods: Three automated exams were performed on each of the two devices: swept-source optical coherence tomography (SS-OCT) and Scheimpflug biometers. The anterior and total corneal astigmatism and power were analysed. Statistical comparisons were performed for within-subject standard deviation, repeatability, Bland−Altman and vector analysis. Results: Twenty-nine eyes of twenty-seven patients were included. The limits of agreement between anterior and total corneal astigmatism were narrower for the SS-OCT than for the Scheimpflug biometer (−0.16 to 0.29 D and −0.40 to 0.39 D, respectively). The >0.5 D difference between SS-OCT and Scheimpflug total astigmatism was noticed in 5 (17%) of cases. The difference between mean total keratometric power for both devices was statistically significant (0.2 D, p < 0.001). SS-OCT total corneal flat measurements had worse repeatability than Scheimpflug (p = 0.007). Conclusions: For the corneal astigmatism <1.5 D, the difference between anterior and total corneal astigmatism measured with SS-OCT was clinically not significant. The mean anterior and total keratometry values obtained with Scheimpflug and SS-OCT biometers are not interchangeable.

Predictability of pseudophakic refraction using patient-customized paraxial eye models

PURPOSE

To determine whether patient-customized paraxial eye models that do not rely on exact ray tracing and do not consider aberrations can accurately predict pseudophakic refraction.

SETTING

Bascom Palmer Eye Institute, Miami, Florida.

DESIGN

Prospective study.

METHODS

Cataract surgery patients with and without a history of refractive surgery were included. Manifest refraction, corneal biometry, and extended-depth optical coherence tomography (OCT) imaging were performed at least 1 month postoperatively. Corneal and OCT biometry were used to create paraxial eye models. The pseudophakic refraction simulated using the eye model was compared with measured refraction to calculate prediction error.

RESULTS

49 eyes of 33 patients were analyzed, of which 12 eyes from 9 patients had previous refractive surgery. In eyes without a history of refractive surgery, the mean prediction error was 0.08 ± 0.33 diopters (D), ranging from -0.56 to 0.79 D, and the mean absolute error was 0.27 ± 0.21 D. 31 eyes were within ±0.5 D, and 36 eyes were within ±0.75 D. In eyes with previous refractive surgery, the mean prediction error was -0.44 ± 0.58 D, ranging from -1.42 to 0.32 D, and the mean absolute error was 0.56 ± 0.46 D. 7 of 12 eyes were within ±0.5 D, 8 within ±0.75 D, and 10 within ±1 D. All eyes were within ±1.5 D.

CONCLUSIONS

Accurate calculation of refraction in postcataract surgery patients can be performed using paraxial optics. Measurement uncertainties in ocular biometry are a primary source of residual prediction error.

Leftover Astigmatism: The Missing Link Between Measured and Calculated Posterior Corneal Astigmatism

PURPOSE

To quantify the total eye astigmatism that is not accounted for by measurement of anterior corneal astigmatism and posterior corneal astigmatism and knowledge of intraocular lens (IOL) astigmatism and assess whether it is correlated with candidate sources of or correlates with leftover astigmatism.

METHODS

Vector subtraction of anterior corneal, posterior corneal, and IOL astigmatism from total eye astigmatism as represented by spectacle astigmatism to yield a value of "leftover" astigmatism that is neither corneal nor lenticular. This value was derived in a series of eyes following cataract surgery. This novel entity was examined for correlation with candidate sources of or correlates with leftover astigmatism.

RESULTS

In 103 pseudophakic eyes with known IOL toricity, mean leftover astigmatism was 0.71 ± 0.43 diopters. This was significantly correlated with against-the-rule anterior corneal astigmatism (P < .001).

CONCLUSIONS

Leftover astigmatism is clinically substantial. Because it is included in IOL cylinder power calculations based on refractive outcome, it may explain why methods of IOL cylinder power calculation using refractive outcome-based adjustments to anterior corneal astigmatism (previously described as adjustments for "posterior corneal astigmatism") are more successful than adjustment on the basis of measured posterior corneal astigmatism. [J Refract Surg. 2022;38(9):559-564.].

Biometry and Intraocular Lens Power Calculation in Eyes with Prior Laser Vision Correction (LVC) - A Review

BACKGROUND

An intraocular lens (IOL) calculation in eyes that have undergone laser vision correction (LVC) poses a significant clinical issue in regards to both patient expectation and accuracy. This review aims to describe the pitfalls of IOL power calculation after LVC and give an overview of the current methods of IOL power calculation after LVC.

REVIEW

Problems after LVC derive from the measurement of anterior corneal radii, central corneal thickness, asphericity, and the predicted effective lens position. A central issue is that most conventional 3rd generation formulas estimate lens position amongst other parameters on keratometry, which is altered in post-LVC eyes.

CONCLUSION

An IOL power calculation results in eyes with prior LVC that are notably impaired in eyes without prior surgery. Effective corneal power including anterior corneal curvature, posterior corneal curvature, CCT (central corneal thickness), and asphericity is essential. Total keratometry in combination with the Barrett True-K, EVO (emmetropia verifiying optical formula), or Haigis formula is relatively uncomplicated and seems to provide good results, as does the Barrett True-K formula with anterior K values. The ASCRS ( American Society of Cataract and Refractive Surgery) calculator combines results of various formulae and averages results, which allows a direct comparison between the different methods. Tomography-based raytracing and the Kane and the Castrop formulae need to be evaluated by future studies.

Comparing Standard Keratometry and Total Keratometry Before and After Myopic Corneal Refractive Surgery With a Swept-Source OCT Biometer

Background

More recently, the swept-source OCT biometer-IOLMaster 700 has provided direct total corneal power measurement, named total keratometry. This study aims to evaluate whether standard keratometry (SK) and total keratometry (TK) with IOLMaster 700 can accurately reflect the corneal power changes induced by myopic corneal refractive surgery.

Methods

In this study, the biometric data measured with the swept-source OCT biometer—IOLMaster 700 before and 3 months after the myopic corneal refractive surgery were recorded. The changes of biological parameters, including SK, posterior keratometry (PK), and TK, and the difference between SK and TK were compared. In addition, the changes of SK and TK induced by the surgery were compared with the changes of spherical equivalent at the corneal plane (ΔSEco).

Results

A total of 74 eyes (74 patients) were included. The changes of SK, PK, TK, axial length, anterior chamber depth, and lens thickness after refractive surgery were all statistically significant (all p < 0.01), while the change of white-to-white was not (p = 0.075). The difference between SK and TK was −0.03 ± 0.10D before the corneal refractive surgery and increased to −0.78 ± 0.26D after surgery. The changes of SK and the changes of TK induced by the surgery had a good correlation with the changes of SEco (r = 0.97). ΔSK was significantly smaller than ΔSEco, with a difference of −0.65 ± 0.54D (p < 0.01). However, the difference between ΔTK and ΔSEco (0.10 ± 0.50D) was not statistically significant (p = 0.08).

Conclusions

Using SK to reflect the changes induced by the myopic corneal refractive surgery may lead to underestimation, while TK could generate a more accurate result. The new parameter, TK, provided by the IOLMaster 700, appeared to provide an accurate, objective measure of corneal power that closely tracked the refractive change in corneal refractive surgery.

Comparison of Mean Corneal Power of Annular Rings and Zones Using Swept-Source Optical Coherence Tomography

This study aims to investigate differences in the mean corneal power of annular zones (corneal power measured over the inner annular zone of difference diameters) and rings (corneal power measured over a ring of different diameters) centered on the corneal apex using the swept-source optical coherence tomography technique. The mean anterior axial curvature (AAC), posterior axial curvature (PAC), and total corneal power (TCP) centered on the corneal apex with the annular rings (0−2 mm, 2−4 mm, 4−6 mm, and 6−8 mm) and zones were assessed using the ANTERION device. The paired-sample t-test was used for data comparison. For the 0−2 mm comparison, the AAC, PAC, and TCP values of rings and zones were interchangeable. For the 2−4 mm comparison, the AAC of the rings was lower than that of the zones (p = 0.004), and the TCP values of the rings were higher than that of the zones (p < 0.001). For the 4−6 mm comparison, the AAC of the rings was lower than that of the zones (p < 0.001), and the PAC and TCP values of the rings were higher than that of the zones (both p < 0.001). For the 6−8 mm comparison, the AAC of the rings was lower than that of the zones (p < 0.001), and the PAC and TCP values of the rings were higher than that of the zones (both p < 0.001). Comparisons between AAC and TCP in each sub-region showed significant differences both in the rings (p < 0.001) and the zones (p < 0.008). Differences in the AAC, PAC, and TCP measured at different diameters (2−4 mm, 4−6 mm, and 6−8 mm) of the rings and zones, centered on the corneal apex, should be noticed in clinical practice. As the diameter increases, the difference between the rings and the zones in terms of AAC, PAC, and TCP increase as well. Clinicians should also pay attention to differences between AAC and TCP for the rings and the zones within the same annular region.

Intraocular lens power calculations in eyes with previous corneal refractive surgery: Challenges, approaches, and outcomes

In eyes with previous corneal refractive surgery, difficulties in accurately determining corneal refractive power and in predicting the effective lens position create challenges in intraocular lens (IOL) power calculations. There are three categories of methods proposed based on the use of historical data acquired prior to the corneal refractive surgery. The American Society of Cataract and Refractive Surgery postrefractive IOL calculator incorporates many commonly used methods. Accuracy of refractive prediction errors within ± 0.5 D is achieved in 0% to 85% of eyes with previous myopic LASIK/photorefractive keratectomy (PRK), 38.1% to 71.9% of eyes with prior hyperopic LASIK/PRK, and 29% to 87.5% of eyes with previous radial keratotomy. IOLs with negative spherical aberration (SA) may reduce the positive corneal SA induced by myopic correction, and IOLs with zero SA best match corneal SA in eyes with prior hyperopic correction. Toric, extended-depth-of-focus, and multifocal IOLs may provide excellent outcomes in selected cases that meet certain corneal topographic criteria. Further advances are needed to improve the accuracy of IOL power calculation in eyes with previous corneal refractive surgery.

Advancements in intraocular lens power calculation formulas

PURPOSE OF REVIEW

We review recent studies comparing intraocular lens (IOL) formulas with an emphasis on selection of the highest performing formulas based on patient axial length, age, and history of previous corneal refractive surgery.

RECENT FINDINGS

The Barrett Universal II formula based on a theoretical model has consistently demonstrated high accuracy. The Olsen four-factor formula using ray tracing optics and the Hill-RBF calculator using artificial intelligence have also demonstrated good prediction results after being updated. Notably, the Kane formula, incorporating artificial intelligence, has overall shown the best performance for all axial lengths. Although newly developed and updated IOL formulas have improved refractive prediction in patients with short or long axial length eyes or prior history of corneal refractive surgery, these challenging cases still require special consideration. The Barrett True-K formula has shown accurate results regardless of preoperative data in eyes with previous myopic refractive surgery.

SUMMARY

Advancements in optical biometry and IOL calculation formulas continue to improve refractive outcomes. The clinician can optimize refractive outcomes in the majority of patients with the use of formulas that have shown consistent results and accuracy in several large studies.

A Multicenter Study of the Distribution Pattern of Posterior-To-Anterior Corneal Curvature Radii Ratio in Chinese Myopic Patients

Estimation of corneal refractive power (CRP) is of crucial importance to refractive and cataract surgery. The ratio of posterior to anterior curvature radii of the cornea (P/A ratio) is one of the key factors to determine the actual CRP (True-K). While the traditional method to calculate the CRP (Sim-K) is based on a constant P/A ratio (0.82), it is suggested that the P/A ratio varies in different people and exhibits a distribution pattern, which may have an impact on the accuracy of CRP estimation and postoperative refractive outcome. In this multicenter study, we aimed to investigate the distribution pattern of the P/A ratio in a large number of myopic patients, and further explore the relationship between P/A ratio and ΔK (the difference between True-K and Sim-K). We found that distribution of the P/A ratio ranged from 0.72 to 0.86 with an average value of 0.82 ± 0.01. The compensation effect of the refractive power of the posterior on the anterior surface of the cornea decreased with the increase of P/A ratio. There was a significant correlation between P/A ratio and ΔK in all eyes (r = 0.9764, P &lt; 0.0001). A change of 0.1 in P/A ratio could cause a change of 0.75 D in ΔK. Our study suggests that the actual P/A ratio should be taken into consideration in refractive and cataract surgery when calculating the CRP and power of the intraocular lens in eyes with significantly deviated P/A ratios.

Comparison of Corneal Power Calculation by Standard Keratometry and Total Keratometry in Eyes With Previous Myopic FS-LASIK

PURPOSE

To compare the accuracy of Total Keratometry (TK) and standard keratometry (K) with the IOLMaster 700 (Carl Zeiss Meditec) in evaluating the corneal refractive change in eyes with previous myopic femtosecond laser-assisted LASIK (FS-LASIK).

METHODS

A series of consecutive patients who had undergone myopic FS-LASIK was prospectively enrolled. The refractive change in spherical equivalent (ΔSE) was defined as the difference between the preoperative target correction entered into the laser software and the postoperative cycloplegic refraction. The difference between the postoperative and the preoperative K (ΔK) and the difference between the postoperative and the preoperative TK (ΔTK) were compared to the ΔSE. Only the right eye of each patient was selected for the statistical analysis.

RESULTS

Twenty-five eyes of 25 patients were enrolled. The mean ΔSE was -4.41 ± 1.68 diopters (D). The mean ΔK (-3.82 ± 1.60 D) revealed a statistically significant underestimation of the laser-induced refractive change (P < .0001), whereas the mean ΔTK (-4.36 ± 1.78 D) did not show any significant difference (P = .45). The difference between ΔK and ΔTK was statistically significant (P < .0001). Linear regression between the laser-induced refractive change and the individual difference between the postoperative K and TK disclosed a statistically significant relationship (r = -0.6930, r² = 0.4803, P < .0001), thus revealing that higher refractive corrections increase the difference between the postoperative values of K and TK.

CONCLUSIONS

TK does not underestimate the laser-induced corneal changes and can be considered a reliable option for intraocular lens power calculation after myopic excimer laser surgery. [J Refract Surg. 2021;37(12):848-852.].

Comparing prediction accuracy between total keratometry and conventional keratometry in cataract surgery with refractive multifocal intraocular lens implantation

We aimed to compare refractive outcomes between total keratometry using a swept-source optical biometer and conventional keratometry in cataract surgery with refractive multifocal intraocular lens (IOL) implantation. We included patients who underwent cataract surgery with refractive multifocal IOL implantation. The IOL power was calculated using conventional formulas (Haigis, SRK/T, Holladay 2, and Barrett Universal II) as well as a new formula (Barrett TK Universal II). The refractive mean error, mean absolute error, and median absolute error were compared, as were the proportions of eyes within ± 0.25 diopters (D), ± 0.50 D, and ± 1.00 D of prediction error. In total 543 eyes of 543 patients, the absolute prediction error of total keratometry was significantly higher than that of conventional keratometry using the SRK/T (P = 0.034) and Barrett Universal II (P = 0.003). The proportion of eyes within ± 0.50 D of the prediction error using the SRK/T and Barrett Universal II was also significantly higher when using conventional keratometry than total keratometry (P = 0.010 for SRK/T and P = 0.005 for Barrett Universal II). Prediction accuracy of conventional keratometry was higher than that of total keratometry in cataract surgery with refractive multifocal IOL implantation.

Current Developments in Corneal Topography and Tomography

Introduction: Accurate assessment of the corneal shape is important in cataract and refractive surgery, both in screening of candidates as well as for analyzing postoperative outcomes. Although corneal topography and tomography are widely used, it is common that these technologies are confused. The aim of this study was to present the current developments of these technologies and particularly distinguish between corneal topography and tomography. Methods: The PubMed, Web of Science and Embase databases were the main resources used to investigate the medical literature. The following keywords were used in various combinations: cornea, corneal, topography, tomography, Scheimpflug, Pentacam, optical coherence tomography. Results: Topography is the study of the shape of the corneal surface, while tomography allows a three-dimensional section of the cornea to be presented. Corneal topographers can be divided into large- and small-cone Placido-based devices, as well as devices with color-LEDs. For corneal tomography, scanning slit or Scheimpflug imaging and optical coherence tomography may be employed. In several devices, corneal topography and tomography have been successfully combined with tear-film analysis, aberrometry, optical biometry and anterior/posterior segment optical coherence tomography. Conclusion: There is a wide variety of imaging techniques to obtain corneal power maps. As different technologies are used, it is imperative that doctors involved in corneal surgery understand the science and clinical application of devices for corneal evaluation in depth.

Cataract surgery after myopic laser in situ keratomileusis: objective analysis to determine best formula and keratometry to use

PURPOSE

To objectively determine which formula/keratometry combination was best for calculating intraocular lens (IOL) sphere power in eyes with a history of myopic laser in situ keratomileusis (LASIK).

SETTING

One practice in the United States.

DESIGN

Retrospective, unmasked, nonrandomized chart review.

METHODS

Consecutive patients undergoing cataract surgery after previous myopic LASIK were included. Eyes had to have a postoperative refraction at least 3 weeks postoperatively. IOL power was calculated with the ASCRS online postrefractive IOL calculator using anterior keratometry and recalculated using total corneal power (TK). The accuracy of treatment was calculated and compared between different formulas and keratometry methods including intraoperative aberrometry (IA).

RESULTS

Data from 101 eyes, 44 of which had TK available, were analyzed. Using TK, the Wang-Koch-Maloney formula had the highest percentages of eyes with expected spherical equivalent refractive errors within 0.50 diopter (D) and 1.00 D of plano (57% and 87%, respectively). With anterior keratometry, the Barrett True-K formula had the highest percentages (64% and 92%, respectively) but was not significantly better than the Wang-Koch-Maloney formula, with expected errors within ±0.50 and ±1.00 D (P > .2, McNemar test). Expected sphere results based on IA were not significantly different than for Barrett True-K within ±0.50 D or within ±1.00 D (P > .2, McNemar test).

CONCLUSIONS

Using TK in existing post-LASIK formulas did not seem beneficial. The formulas might have to be optimized for use with TK. The best expected results were obtained with the Barrett True-K and Haigis-L formulas using anterior keratometry. IA did not seem to materially improve results.

Intraocular lens power calculation using adjusted corneal power in eyes with prior myopic laser vision correction

PURPOSE

To evaluate the prediction accuracy of the intraocular lens (IOL) power calculation using adjusted corneal power according to the posterior/anterior corneal curvature radii ratio in the Haigis formula (Haigis-E) in patients with a history of prior myopic laser vision correction.

METHODS

Seventy eyes from 70 cataract patients who underwent cataract surgery and had a history of myopic laser vision correction were enrolled. The adjusted corneal power obtained with conventional keratometry (K) was calculated using the posterior/anterior corneal curvature radii ratio measured by a single Scheimpflug camera. In eyes longer than 25.0 mm, half of the Wang-Koch (WK) adjustment was applied. The median absolute error (MedAE) and the percentage of eyes that achieved a postoperative refractive prediction error within ± 0.50 diopters (D) based on the Haigis-E method was compared with those in the Shammas, Haigis-L, and Barrett True-K no-history methods.

RESULTS

The MedAE predicted using the Haigis-E (0.33 D) was significantly smaller than that obtained using the Shammas (0.44 D), Haigis-L (0.43 D), and Barrett True-K (0.44 D) methods (P < 0.001, P = 0.001, and P = 0.014, respectively). The percentage of eyes within ± 0.50 D of refractive prediction error using the Haigis-E (78.6%) was significantly greater than that produced using the Shammas (57.1%), Haigis-L (58.6%), and Barrett True-K (61.4%) methods (P = 0.025).

CONCLUSION

IOL power calculation using the adjusted corneal power according to the posterior/anterior corneal curvature radii ratio and modified WK adjustment in the Haigis formula could improve the refraction prediction accuracy after cataract surgery in eyes with prior myopic laser vision correction.

Agreement between Scheimpflug Camera and the Swept-source Optical Coherence Tomography Measurements in Keratometry and Higher-order Aberrations

PURPOSE

To evaluate the compatibility of corneal curvature and astigmatism, and higher-order aberrations (HOAs) measured by the Scheimpflug camera Pentacam HR and the swept-source optical coherence tomography ANTERION.

METHODS

This prospective study included normal subjects with no ophthalmic history. Steep keratometry (K), flat K, astigmatism and its axis of the anterior and posterior surfaces, total corneal power, and HOAs using the two instruments were compared. To compare the mean values of the measurements, a paired t-test was used. Bland-Altman analysis was applied to assess the agreement between the two devices.

RESULTS

Fifty-three eyes of 53 subjects were evaluated. There were statistically significant differences for steep K, astigmatism, and vector J0, J45 in the anterior surface and total corneal power between the two devices (p &lt; 0.05). There were also significant differences in the most of the keratometric values of the posterior corneal surface (p &lt; 0.05) except J0 (p = 0.410). Both devices showed strong positive correlations in steep K, flat K, astigmatism (r &gt; 0.81, p &lt; 0.001) with wide ranges of a 95% limit of agreement. Vectoral components were significantly correlated (r &gt; 0.78, p &lt; 0.001) with narrow 95% limit of agreement, except J45 of the posterior surface (r = 0.39, p = 0.004). In the corneal HOAs, there were statistically significant differences in the vertical coma, horizontal trefoil, spherical aberration, and root mean square of each fifth- and sixth-order Zernike coefficient (p = 0.043, p = 0.041, p &lt; 0.001, p &lt; 0.001, and p &lt; 0.001, respectively). Other HOAs showed moderate to strong positive correlations (r &gt; 0.37, p &lt; 0.05). Most HOAs, except for the horizontal trefoil, showed clinically acceptable agreements. The total root mean square of HOAs was not significantly different between the two devices (p = 0.122).

CONCLUSIONS

Most of the keratometric values cannot be used interchangeably. However, the vectoral component of astigmatism showed clinically good agreement. Several HOAs have statistically significant differences; however, almost all HOAs showed acceptable agreements, except for the horizontal trefoil.

Prediction accuracy of conventional and total keratometry for intraocular lens power calculation in femtosecond laser-assisted cataract surgery

This study evaluated the accuracy of total keratometry (TK) and standard keratometry (K) for intraocular lens (IOL) power calculation in eyes treated with femtosecond laser-assisted cataract surgery. The retrospective study included a retrospective analysis of data from 62 patients (91 eyes) who underwent uneventful femtosecond laser-assisted cataract surgery with Artis PL E (Cristalens Industrie, Lannion, France) IOL implantation by a single surgeon between May 2020 and December 2020 in Severance Hospital, Seoul, South Korea. The new IOLMaster 700 biometry device (Carl Zeiss Meditec, Jena, Germany) was used to calculate TK and K. The mean absolute error (MAE), median absolute error (MedAE), and the percentages of eyes within prediction errors of ± 0.25 D, ± 0.50 D, and ± 1.00 D were calculated for all IOL formulas (SRK/T, Hoffer-Q, Haigis, Holladay 1, Holladay 2, and Barrett Universal II). There was strong agreement between K and TK (intraclass correlation coefficient = 0.99), with a mean difference of 0.04 D. For all formulas, MAE tended to be lower for TK than for K, and relatively lower MAE and MedAE values were observed for SRK/T and Holladay 1. Furthermore, for all formulas, a greater proportion of eyes fell within ± 0.25 D of the predicted postoperative spherical equivalent range in the TK group than in the K group. However, differences in MAEs, MedAEs, and percentages of eyes within the above prediction errors were not statistically significant. In conclusion, TK and K exhibit comparable performance for refractive prediction in eyes undergoing femtosecond laser-assisted cataract surgery.

Comparison of total keratometry with corneal power measured by optical low-coherence reflectometry and placido-dual Scheimpflug system

PURPOSE

To compare the total keratometry (TK) and astigmatism measurements in eyes with cataract using automated keratometry of swept-source optical coherence tomography (ss-OCT), optical low-coherence reflectometry (OLCR), simulated keratometry (SimK), and total corneal power (TCP) of combined placido-dual Scheimpflug imaging system.

SETTING

The study was conducted at LV Prasad Eye Institute, Hyderabad, India.

DESIGN

Retrospective evaluation of electronic medical records of patients who were evaluated for cataract surgery.

METHODS

Twenty-eight eyes of 28 patients were included in the study. All patients evaluated for cataract surgery underwent corneal power measurements using three devices: ssOCT, OLCR, and combined placido-dual Scheimpflug imaging were included in the study. Vector analysis was performed to evaluate corneal astigmatism and Bland-Altman analysis was conducted to evaluate the limits of agreement of similar parameters among devices.

RESULTS

The mean TK was statistically significantly different from the keratometry obtained from optical biometers and values measured by the Scheimpflug imaging system. The magnitude of mean difference was greater between TK and TCP (0.75 ± 0.25) compared to other variables. The mean difference in astigmatism between TK, ss-OCT-K (0.09 ± 0.12, p = 0.48), OCLR-K (0.10 ± 0.48, p = 0.91), and TCP (0.09 ± 0.47, p = 0.31) was not statistically significant but was statistically significant between TK and SimK values (0.23D ± 0.49D). The axis of orientation (<20°) of astigmatism was comparable (100%, 28 eyes) between two keratometry variables measured by ss-OCT.

CONCLUSION

There appears to be a greater correlation of automated keratometry, and TK values obtained from ss-OCT compared to other variables studied. The measurements from TK, Simk, and TCP cannot be used interchangeably.

Prediction accuracy of standard and total keratometry by swept-source optical biometer for multifocal intraocular lens power calculation

We aimed to compare the refractive outcomes of cataract surgery with diffractive multifocal intraocular lenses (IOLs) using standard keratometry (K) and total keratometry (TK). In this retrospective observational case series study, a total of 302 patients who underwent cataract surgery with multifocal IOL implantation were included. Predicted refractive outcomes were calculated based on the current standard formulas and a new formula developed for TK using K and TK, which were obtained from a swept-source optical biometer. At 2-month postoperatively, median absolute prediction errors (MedAEs) and proportion of eyes within ± 0.50 diopters (D) of predicted postoperative spherical equivalent (SE) refraction were analyzed. There was no significant difference between MedAEs or proportion of eyes within ± 0.50D of predicted refraction from K and TK in each formula. In TFNT00 and 839MP IOL cases, there was no difference between MedAEs from K and TK using any formula. In 829MP IOL cases, MedAE from TK was significantly larger than that from K in Barrett Universal II/Barrett TK Universal II (P = 0.033). In 677MY IOL cases, MedAE from TK was significantly larger than that from K in Haigis (P = 0.020) and Holladay 2 (P = 0.006) formulas. In the subgroup analysis for IOL, there was no difference between the proportion of eyes within ± 0.50 D of predicted refraction from K and TK using any formula. TFNT00 and 839MP IOLs were favorable with TK, with 677MY IOL with K and 829MP IOL being in a neutral position, which necessitates the study that investigates the accuracy of the new TK technology.

Refractive Precision of Ray Tracing IOL Calculations Based on OCT Data versus Traditional IOL Calculation Formulas Based on Reflectometry in Patients with a History of Laser Vision Correction for Myopia

Purpose

To compare the refractive predictability of ray tracing IOL calculations based on OCT data versus traditional IOL calculation formulas based on reflectometry in patients with a history of previous myopic laser vision correction (LVC).

Patients and Methods

This was a prospective interventional single-arm study of IOL calculations for cataract and refractive lens exchange (RLE) patients with a history of myopic LVC. Preoperative biometric data were collected using an optical low coherence reflectometry (OLCR) device (Haag-Streit Lenstar 900) and two optical coherence tomography (OCT) devices (Tomey Casia SS-1000 and Heidelberg Engineering Anterion). Traditional post LVC formulas (Barret True-K no-history and Haigis-L) with reflectometry data, and ray tracing IOL calculation software (OKULIX, Panopsis GmbH, Mainz, Germany) with OCT data were used to calculate IOL power. Follow-up examination was 2 to 3 months after surgery. The main outcome measure, refractive prediction error (RPE), was calculated as the achieved postoperative refraction minus the predicted refraction.

Results

We found that the best ray tracing combination (Anterion-OKULIX) resulted in an arithmetic prediction error statistically significantly lower than that achieved with the best formula calculation (Barret True-K no-history) (−0.13 D and −0.32 D, respectively, adjusted p = 0.01), while the Barret TK NH had the lowest SD. The absolute prediction error was 0.26 D and 0.35 D for Anterion-OKULIX and Barret TK NH, respectively, but this was not statistically significantly different. The Anterion-OKULIX calculation also had the highest percentage of eyes within ± 0.25, compared to both formulas and within ±0.50 and ±0.75 compared to the Haigis-L (p = 0.03).

Conclusion

Ray tracing calculation based on OCT data from the Anterion device can yield similar or better results than traditional post LVC formulas. Ray tracing calculations are based on individual measurements and do not rely on the ocular history of the patient and are therefore applicable for any patient, also without previous refractive surgery.

Comparison of ocular biometric measurements in patients with cataract using three swept-source optical coherence tomography devices

BACKGROUND

Precise measurement of ocular biometry is critical for determining intraocular lens power. Newly developed swept-source optical coherence tomography (SS-OCT) - based ocular biometric devices, ANTERION and CASIA2 provide ocular biometric measurements as IOLMaster 700. This study aimed to assess agreement between three devices.

METHODS

This retrospective comparative study includes patients with cataract who underwent ocular biometric measurements with three devices, ANTERION, CASIA2, and IOLMaster 700, at Seoul National University Hospital, in April 2020. Anterior keratometry, total keratometry, central corneal thickness (CCT), anterior chamber depth (ACD), lens thickness (LT), and axial length (AL) were the main parameters for the comparison. To assess the agreement between the devices, intraclass coefficient (ICC) and Bland-Altman analysis with 95% limits of agreement (LoA) were used.

RESULTS

A total of 47 eyes of 29 patients were measured with three devices. Average anterior keratometry showed excellent agreement (ICC ≥ 0.989), and the mean difference was less than 0.1 D. However, the ICC of the total average keratometry ranged from 0.808 to 0.952, and the difference was more than 0.43 D. The AL measured by ANTERION and IOLMaster 700 showed excellent agreement (ICC = 0.999), and the mean difference was 0.005 mm. The ANTERION and IOLMaster 700 did not obtain AL in six (12.8%) and three (6.4%) cases, respectively (P = 0.001 by Fisher's exact test). The CCT, ACD, and LT also showed excellent agreement (ICC > 0.9).

CONCLUSIONS

The new SS-OCT-based devices, ANTERION, and CASIA2 showed a good agreement with IOLMaster 700 in measuring ocular biometry except for the total keratometry. The AL of ANTERION and IOLMaster 700 showed excellent agreement.