Intraocular Lens Power Calculation Research Articles

Comparison of refractive outcomes obtained with two swept-source OCT-based optical biometers after cataract surgery: A study of 152 eyes

To compare two swept-source OCT optical biometers, the Anterion® (Heidelberg Engineering GmbH, Heidelberg, Germany) and the IOLMaster 700® (Carl Zeiss Meditec AG, Jena, Germany), in the analysis of biometric data, intraocular lens (IOL) calculation and postoperative spherical equivalent predictability. This was a real-life, single-center, retrospective study including 152 eyes of 81 consecutive patients referred for cataract surgery. All patients were examined with the IOLMaster 700® and the Anterion®. Biometric data (axial length [AL], anterior chamber depth [ACD], mean keratometry [Km], K1 [flat keratometry], K2 [steep keratometry] and axis, TK1 [flat total keratometry], TK2 [steep total keratometry], central pachymetry, lens thickness [LT], white-to-white distance [WTW]), IOL calculation with the SRK/T formula, and postoperative refractive outcome at 1 month were compared. All biometric measurements were significantly different between the two biometers. Correlations were excellent for AL, pachymetry, ACD, LT and keratometry measurements, and for the IOL calculation (r>0.96, intraclass correlation coefficient=1). The IOL power for emmetropia was similar between both biometers when the SRK/T formula was used (20.84±3.24D versus 20.86±3.29D, P=0.61). The mean postoperative spherical equivalent prediction error calculated using the SRK/T formula was 0.03±0.5D for the IOLMaster 700® versus 0.01±0.47D for the Anterion® (P=0.12). This study showed excellent correlation and agreement for the biometric measurements and the IOL power calculation with the SRK/T formula between both biometers.

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Comparison of Different Intraocular Lens Power Calculation Formulas in Eyes with Primary Angle Closure.

To compare the accuracy of six intraocular lens power calculation formulas, Barrett Universal Ⅱ (BU Ⅱ), Haigis, Hoffer QST, HolladayⅠ, Kane and SRK/T, in eyes with primary angle closure disease (PACD). Xiamen University Affiliated Xiamen Eye center, Xiamen, Fujian, China. Prospective case series. Patients diagnosed with PACD and cataract and met the indication for cataract surgery were enrolled in the study. Six intraocular lens power calculation formulas were used to calculate refractive diopter. Percentage of eyes with prediction error (PE) within ±0.50D, and the median absolute prediction error (MedAE) were compared to determine the accuracy of different formulas in PACD patients. Subgroup analysis was performed according to axial length (AL). The accuracy of Barrett Universal Ⅱ was compared between PACD patients and age-related cataract patients. 105 patients (105 eyes) with PACD and 35 patients (35 eyes) with age-related cataract were enrolled in the study. Haigis, Kane and Barrett Universal Ⅱ formula achieved a comparable outcome and outperformed over the other three formulas in PACD patients. Subgroup analysis showed that the group with long AL has lower values of MedAE. PE was significantly positively correlated with AL and negatively correlated with relative lens position (RLP) when calculated use Barrett Universal Ⅱ and Kane. Haigis, Kane and Barrett Universal Ⅱ formula achieved a comparable outcome and outperformed over the other three formulas in PACD patients.

Accuracy of Intraocular lens power calculation in pediatric traumatic cataract.

To evaluate the prediction error (PE) in pediatric traumatic cataract surgery involving primary or secondary intraocular lens implantation (IOL) and the factors affecting it. Retrospective data of unilateral traumatic cataract eyes of children aged ≤16 years were collected between February 2019 and March 2022 at a tertiary eye care hospital. Absolute PE was calculated by deducting the target refraction from the observed refraction at 6 weeks postsurgery following suture removal. Simulated PE was calculated in eyes with corneal scar replacing the affected eye keratometry (K) with the K of the fellow eye and standard K (44D) and was then compared with absolute PE. Fifty children with a mean age of 9.5 years (2-16 years) were included. Mean absolute PE was 1.63 ± 1.8D (0 to 9D). Absolute PE was not affected by the age at surgery, method of biometry, duration of injury, type of cataract surgery, position of IOL, and preoperative keratometry. The absolute PE was affected by axial length (AXL) being <1.5D in AXL of 22.73 ± 0.84 mm, <1.5-2D in AXL of 22.07 ± 0.61 mm, and >2D in AXL of 22.01 ± 0.74 mm (P = 0.039) in univariate analysis. In multivariate analysis, none of the factors affected the absolute PE. In 34 eyes with corneal scar, higher variability in PE was observed. The standard K resulted in greater simulated PE as compared to the affected eye average K in eyes with scar involving the visual axis. Absolute PE following pediatric traumatic cataract was studied. It was higher in shorter AXLs. In corneal scar involving the visual axis, using the fellow eye K yielded lesser simulated PE as compared to standard K.

Comparison of SRK/T with Kane formula for prediction of refractive outcome after phacoemulsification: Insights from a South Asian patient group

BackgroundPhacoemulsification stands as the most commonly conducted ocular procedure. Biometry represents an art with numerous generations of formulas introduced to enhance refractive prediction accuracy. The Sanders Retzlaff Kraff theoretical (SRK/T), a third-generation formula that merges linear regression and a theoretical eye model, and the Kane formula, a fourth-generation formula incorporating theoretical optics, regression, and artificial intelligence, embody our focal points. Our aim is to compare post-operative refractive outcomes utilizing SRK/T and Kane formulae for calculating intraocular lens (IOL) power in senile cataract patients undergoing phacoemulsification featuring a hydrophilic acrylic, monofocal IOL. MethodsThis prospective, interventional institutional study engaged 70 patients, totaling 74 eyes. They were categorized into two groups: Group A employed the SRK/T for IOL power calculation, while Group B used the Kane formula. Quantel Medical® A-scan biometer was employed. A comparison was drawn between both formulae in terms of mean absolute error (MAE) and median absolute error (MedAE), with the utilization of IBM SPSS 20 and a significance level of p < 0.05. ResultsThe MAE for the SRK/T and Kane formulae stood at 0.18 ± 0.82 D and 0.24 ± 0.94 D, respectively, while the MedAE recorded values of 0.16 D and 0.155 D, correspondingly (p < 0.05). ConclusionWithin this South Asian cohort of senile cataract patients, the SRK/T formula demonstrated a marginally improved refractive outcome, evidenced by a reduced mean absolute error.

Accuracy of 14 intraocular lens power calculation formulas in extremely long eyes.

To compare the accuracy of 14 formulas in calculating intraocular lens (IOL) power in extremely long eyes with axial length (AL) over 30.0mm. In this retrospective study, 211 eyes (211 patients) with ALs > 30.0mm were successfully treated with cataract surgery without complications. Ocular biometric parameters were obtained from IOLMaster 700. Fourteen formulas were evaluated using the optimized A constants: Barrett Universal II (BUII), Kane, Emmetropia Verifying Optical (EVO) 2.0, PEARL-DGS, T2, SRK/T, Holladay 1, Holladay 2, Haigis and Wang-Koch AL adjusted formulas (SRK/Tmodified-W/K, Holladay 1modified-W/K, Holladay 1NP-modified-W/K, Holladay 2modified-W/K, Holladay 2NP-modified-W/K). The mean prediction error (PE) and standard deviation (SD), mean absolute errors (MAE), median absolute errors (MedAE), and the percentage of prediction errors (PEs) within ± 0.25 D, ± 0.50 D, ± 1.00 D were analyzed. The Kane formula had the smallest MAE (0.43 D) and MedAE (0.34 D). The highest percentage of PE within ± 0.25 D was for EVO 2.0 (37.91%) and the Holladay 1NP-modified-W/K formulas (37.91%). The Kane formula had the highest percentage of PEs in the range of ± 0.50, ± 0.75, ± 1.00, and ± 2.00 D. There was no significant difference in PEs within ± 0.25, ± 0.50 ± 0.75 and ± 1.00 D between BUII, Kane, EVO 2.0 and Wang-Koch AL adjusted formulas (P > .05) by using Cochran's Q test. The Holladay 2modified-W/K formula has the lowest percentage of hyperopic outcomes (29.38%). The BUII, Kane, EVO 2.0 and Wang-Koch AL adjusted formulas have comparable accuracy for IOL power calculation in eyes with ALs > 30.0mm.

Accuracy of 20 Intraocular Lens Power Calculation Formulas in Medium-Long Eyes.

The aim of this work is to compare 20 intraocular lens (IOL) power calculation formulas in medium-long eyes (24.50-25.99mm) in terms of root mean square absolute error (RMSAE), median absolute error (MedAE), and percentage of eyes with prediction error (PE) within ± 0.50 D. The data of patients who underwent uneventful phacoemulsification between January 2017 and September 2023 were reviewed. Pre-surgery IOL power was calculated using Holladay1, SRK/T, Hoffer Q, Holladay 2, and Haigis. Three months after phacoemulsification, refraction was measured. Post-surgery IOL power calculations were performed utilizing the following formulas: Barrett Universal II, Kane, K6, Olsen (OLCR), Olsen (standalone), PEARL-DGS, Ladas Super Formula AI (LSF AI), T2, EVO, VRF, Hoffer QST, Castrop, VRF-G, Karmona, and Naeser 2. RMSAE, MedAE, and percentage of eyes with PE within ± 0.25 D, ± 0.50 D, ± 0.75 D and ± 1.00 were calculated. One hundred twenty-four eyes with axial length ranges between 24.52 and 25.97mm were studied. The SRK/T formula yielded the lowest RMSAE (0.206) just before Holladay 1 (0.260) and T2 (0.261). In terms of MedAE, the best outcome was obtained by SRK/T (0.12) followed by Barrett Universal II (0.15) and LSF AI (0.15). The highest percentage of eyes with prediction error within ± 0.50 D was achieved by SRK/T, T2, and Holladay 1 (97.58, 93.55, and 93.55%, respectively). Third-generation formulas (SRK/T, Holladay 1) provided highly accurate outcomes in medium-long eyes and still can be wildly used to calculate IOL power.

Comparison of IOL power formulas in eyes with a flat cornea

PurposeTo assess and compare accuracy of intraocular lens (IOL) power calculation performed with old generation, new generation and artificial intelligence (AI)-based formulas in eyes with flat corneas. DesignPatients with a tomography-derived mean keratometry <42 D were retrospectively recruited among those who underwent uncomplicated phacoemulsification with intracapsular IOL implantation in two different tertiary care centers. Mean prediction error (ME), mean absolute prediction error (MAE) and incidence of MAE>0.25D were calculated for Barrett Universal II (BUII),EVO 2.0, Hoffer QST, Kane, Olsen-C, Pearl-DGS and SRK/T formulas. Linear correlation between MAE and axial length was also calculated for each formula. ResultsEighty (80) eyes with a mean keratometry of 41.4 ± 0.6 D (range 40.6–41.9 D) were recruited. The SRK/T significantly differed from both the Olsen-C (p = 0.022) and the BUII (p = 0.048) in ME. The EVO 2.0, the Hoffer QST, the Kane and the PEARL-DGS showed a significantly lower MAE compared to all other formulas (p < 0.001) and a significant lower incidence of MAE>0.25D (p < 0.001), MAE>0.50 D (p < 0.001) and MAE>1.0 D (0.002). ConclusionFormulas based on AI and on the theory of vergence show superior accuracy in IOL power calculation in corneas with low mean keratometry; their MAE is not correlated to axial length.

Impact of segmented optical axial length on the performance of intraocular lens power calculation formulas.

To investigate the difference between the segmented axial length (AL) and the composite AL on a swept-source optical coherence tomography biometer and to evaluate the subsequent effects on artificial intelligence intraocular lens (IOL) power calculations: the Kane and Hill-RBF 3.0 formulas compared with established vergence formulas. National Hospital Organization, Tokyo Medical Center, Japan. Retrospective case series. Consecutive patients undergoing cataract surgery with a single-piece IOL were reviewed. The prediction accuracy of the Barrett Universal II, Haigis, Hill-RBF 3.0, Hoffer Q, Holladay 1, Kane, and SRK/T formulas based on 2 ALs were compared for each formula. The heteroscedastic test was used with the SD of prediction errors as the endpoint for formula performance. The study included 145 eyes of 145 patients. The segmented AL (24.83 ± 1.89) was significantly shorter than the composite AL (24.88 ± 1.96, P < .001). Bland-Altman analysis revealed a negative proportional bias for the differences between the segmented AL and the composite AL. The SD values obtained by Hoffer Q, Holladay 1, and SRK/T formulas based on the segmented AL (0.52 diopters [D], 0.54 D, and 0.50 D, respectively) were significantly lower than those based on the composite AL (0.57 D, 0.60 D, and 0.52 D, respectively, P < .01). The segmented ALs were longer in short eyes and shorter in long eyes than the composite ALs. The refractive accuracy can be improved in the Hoffer Q, Holladay 1, and SRK/T formulas by changing the composite ALs to the segmented ALs.

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.

Precision in IOL Calculation for Cataract Patients with Prior History of Combined RK and LASIK Histories.

This study aimed to evaluate the accuracy of 12 intraocular lens (IOL) power calculation formulae for eyes that have undergone both radial keratotomy (RK) and laser assisted in situ keratomileusis (LASIK) surgery to determine the efficacy of various IOL calculations for this unique patient group. Currently, research on this surgical topic is limited. In this retrospective study, 11 eyes from 7 individuals with a history of RK and LASIK who underwent cataract surgery at Hoopes Vision were analyzed. Preoperative biometric and corneal topographic measurements were performed. Subjective refraction was obtained postoperatively. Twelve different intraocular lens (IOL) power calculations were used: Barrett True K No History, Barrett True K (prior LASIK, Prior RK history), Barrett Universal 2, Camellin-Calossi-Camellin (3C), Double K-Modified Holladay, Haigis-L, Galilei, OCT, PEARL-DGS, Potvin-Hill, Panacea, and Shammas. The rankings of mean arithmetic error (MAE), from least to greatest, were as follows: 3C (0.088), Haigis-L-L (-0.508), Shammas (-0.516), OCT Average (-0.538), Barrett True K (-0.557), OCT RK (-0.563), Galilei (-0.570), IOL Master (-0.571), OCT LASIK (-0.583), Barrett True K No History (-0.597), Pearl-DGS (-0.606), Potvin-Hill SF (-0.770), Potvin-Hill TNP (-0.778), Panacea (-0.876), and Barrett Universal 2 (-1.522). The 3C formula achieved the greatest percentage of eyes within ±0.25 D of target range (91%), while Haigis-L, Shammas, Galilei, Potvin Hill, Barrett True K, IOL Master, PEARL-DGS, and OCT formulae performed similarly, achieving 45% of eyes within ±0.75D of target refraction. This study demonstrates the accuracy of the lesser known 3C formula in IOL calculation, particularly for patients who have undergone both RK and LASIK. Well-known formulae, such as Haigis-L, Shammas, and Galilei, which are used by the American Society of Cataract and Refractive Surgery (ASCRS), are viable options, although 3C formulae should be considered in this patient population. Furthermore, larger studies can confirm the best IOL power formulas for post-RK and LASIK cataract patients.

Accuracy of new intraocular lens power calculation formula for short and long eyes using segmental refractive indices.

To evaluate the accuracy of a new intraocular lens power calculation formula using segmental refractive index-based axial length (AL). Chukyo Eye Clinic, Nagoya, Japan. Retrospective observational study. This study included patients undergoing preoperative examination for cataract surgery with the new Barrett True AL (BTAL) and Emmetropia Verifying Optical (EVO) formulas using segmental refractive index, and conventional Barrett Universal II (BU II) formula using equivalent refractive index. The predicted refractive error of each formula was compared with the postoperative subjective spherical equivalent. The mean prediction error (MPE) in the short AL group (≤ 22 mm; 44 eyes) was 0.32 ± 0.40 D for BU II, 0.22 ± 0.37 D for BTAL, and 0.10 ± 0.37 D for EVO (P < 0.0001). MPE in the long AL group (≥ 26 mm; 92 eyes) was 0.01 ± 0.32 D for BU II, 0.04 ± 0.32 D for BTAL, and 0.09 ± 0.32 D for EVO (P < 0.0001). In patients with an AL ≥ 28 mm, BU II showed a myopic trend in 57.1% of cases, while BTAL and EVO showed a hyperopic trend in 71.4%. The MPE for patients with an AL ≥ 28 mm was -0.16 ± 0.34 D for BU II, 0.18 ± 0.33 D for BTAL, and 0.16 ± 0.32 D for EVO (P < 0.0001). The new EVO and BTAL formulas showed higher accuracy than BU II in short eyes, whereas there was no difference in long eyes.

Performance of a simplified strategy for formula constant optimisation in intraocular lens power calculation.

To investigate the performance of a simple prediction scheme for the formula constants optimised for a mean refractive prediction error. Analysis based on a dataset of 888 eyes before and after cataract surgery with IOL implantation (Hoya Vivinex). IOLMaster 700 biometric data, power of the implanted lens and postoperative spherical equivalent refraction were used to calculate the optimised constants (.)opt for SRKT, HofferQ, Holladay and Haigis formula with an iterative nonlinear optimisation. For detuning start values by ±1.5 from (.)opt, the predicted formula constants (.)pred were calculated and compared with (.)opt. Formula performance metrics mean (MPE), median (MEDPE), mean absolute (MAPE), median absolute (MEDAPE), root mean squared (RMSPE) and standard deviation (SDPE) of the formula prediction error were analysed for (.)opt and (.)pred. (.)pred - (.)opt showed a 2nd order parabolic behaviour with maximal deviations up to 0.09 at the tails of detuning and a minimal deviation up to -0.01 for all formulae. The performance curves of different metrics of PE as functions of detuning variations show that the formula constants for zeroing MPE and MEDPE yield almost identical formula constants, optimisation for MAPE, MEDAPE and RMSPE yielded formula constants very close to (.)opt, and optimisation for SDPE could result in formula constants up to 0.5 off (.)opt which is unacceptable for clinical use. This simple prediction scheme for formula constant optimisation for zero mean refraction error performs excellently in our monocentric dataset, even for larger deviations of the start value from (.)opt. Further studies with multicentric data and larger sample sizes are required to investigate the performance in a clinical setting further.

Predictability of Existing IOL Formulas After Cataract Surgery in Patients with a Previous History of Radial Keratotomy: A Retrospective Cohort Study and Literature Review.

This study aims to evaluate the accuracy of 12 different intraocular lens (IOL) power calculation formulas for post-radial keratotomy (RK) eyes. The investigation utilizes recent advances in topography/tomography devices and artificial intelligence (AI)-based calculators, comparing the results to those reported in current literature to assess the efficacy and predictability of IOL calculations for this patient group. In this retrospective study, 37 eyes from 24 individuals with a history of RK who underwent cataract surgery at Hoopes Vision Center were analyzed. Biometry and corneal topography measurements were taken preoperatively. Subjective refraction was obtained 6 months postoperatively. Twelve different IOL power calculations were used, including the American Society of Cataract and Refractive Surgery (ASCRS) post-RK online formula, and the Barrett True K, Double K modified-Holladay 1, Haigis-L, Panacea, Camellin-Calossi, Emmetropia Verifying Optical (EVO) 2.0, Kane, and Prediction Enhanced by Artificial Intelligence and output Linearization-Debellemanière, Gatinel, and Saad (PEARL-DGS) formulas. Outcome measures included median absolute error (MedAE), mean absolute error (MAE), arithmetic mean error (AME), and percentage of eyes achieving refractive prediction errors (RPE) within ± 0.50 D, ± 0.75 D, and ± 1 D for each formula. A search of the literature was also performed by two independent reviewers based on relevant formulas. Overall, the best performing IOL power calculations were the Camellin-Calossi (MedAE = 0.515 D), the ASCRS average (MedAE = 0.535 D), and the EVO (MedAE = 0.545 D) and Kane (MedAE = 0.555 D) AI-based formulas. The EVO and Kane formulas along with the ASCRS calculation performed similarly, with 48.65% of eyes scoring within ± 0.50 D of the target range, while the Equivalent Keratometry Reading (EKR) 65 Holladay formula achieved the greatest percentage of eyes scoring within ± 0.25 D of the target range (35.14%). Additionally, the EVO 2.0 formula achieved 64.86% of eyes scoring within the ± 0.75 D RPE category, while the Kane formula achieved 75.68% of eyes scoring within the ± 1 D RPE category. There was no significant difference in MAE between the established and newer generation formulas (P > 0.05). The Panacea formula consistently underperformed when compared to the ASCRS average and other high-performing formulas (P < 0.05). This study demonstrates the potential of AI-based IOL calculation formulas, such as EVO 2.0 and Kane, for improving the accuracy of IOL power calculation in post-RK eyes undergoing cataract surgery. Established calculations, such as the ASCRS and Barrett True K formula, remain effective options, while under-utilized formulas, like the EKR65 and Camellin-Calossi formulas, show promise, emphasizing the need for further research and larger studies to validate and enhance IOL power calculation for this patient group.

Effect of Long-Acting Diquafosol Sodium on Astigmatism Measurement Repeatability in Preoperative Cataract Cases with Dry Eyes: A Multicenter Prospective Study.

Dry eye can compromise corneal astigmatism measurement repeatability during preoperative cataract surgery examination. No previous studies have analyzed the effectiveness of long-acting 3% diquafosol sodium (LA-DQS) on astigmatism measurement repeatability. This research assessed the effect of LA-DQS on astigmatism measurement repeatability in preoperative patients with cataract and short tear break-up time (TBUT) type dry eyes in both eyes of the same patient. Correlations between repeatability and TBUT, corneal high-order aberrations (HOAs), and corneal astigmatism magnitude were also analyzed. In total, 122 eyes (61 patients) with short TBUT-type dry eye were enrolled. Preoperatively, only one eye of all patients was treated with LA-DQS for 4 weeks. TBUT and corneal HOAs were checked using CASIA 2 before and 4 weeks post-treatment. The cylindrical power and meridian of astigmatism were measured at 3- and 4-week post-treatment using IOLMaster 700. Power vectors J0 and J45 were used for astigmatism calculations. Repeatability of astigmatism measurements was assessed as the within-subject standard deviation (Sw). The relative effects of TBUT and HOAs on J0 Sw and J45 Sw were also analyzed. Comparative changes in these variables were evaluated between treated and non-treated eyes, with additional analysis of their correlations. Treated eyes exhibited significant improvements in TBUT, HOAs, and post-treatment measurements of J0 Sw and J45 Sw at 3 and 4 weeks. In non-treated eyes, J0 Sw and J45 Sw showed significant correlation with TBUT and corneal HOAs. HOAs showed stronger relative associations with J0 Sw and J45 Sw than TBUT. In non-treated eyes, no significant correlation was found between cylindrical power and astigmatism measurement repeatability. In short TBUT-type dry eye, preoperative treatment with LA-DQS significantly improved astigmatism measurement repeatability. This may improve the precision of intraocular lens (IOL) power calculations regardless of the magnitude of corneal astigmatism, especially when toric IOLs are used.

Assessing the Impact of Tropicamide on Anterior Segment Parameters in Diabetic Patients: A Randomized Clinical Trial.

Evaluation of anterior segment parameters is crucial in ophthalmic procedures such as intraocular surgeries and contact lens fitting. However, the use of tropicamide in diabetic patients presents challenges due to its potential impact on biometric measurements. This study aims to investigate and compare the effects of 0.5% and 1% tropicamide on anterior segment parameters in diabetic patients. This double-masked randomized clinical trial enrolled 98 patients with diabetes mellitus. Participants were randomly assigned to receive either 0.5% or 1% tropicamide. Anterior segment parameters were measured using Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) before and 30 minutes after tropicamide administration. Parameters included anterior chamber depth (ACD), anterior chamber volume (ACV), anterior chamber angle (ACA), keratometry, central corneal thickness (CCT), white-to-white distance (WTW), and pupillary diameter (PD). Both concentrations of 0.5% and 1% tropicamide induced significant changes in anterior segment parameters. There was a notable increase in PD (2.99 ± 0.62, 3.11 ± 0.55, respectively, both P-values < 0.001), ACD (both 0.10 ± 0.05, both P-values < 0.001), ACV (16.69 ± 9.56, 17.51 ± 9.26, respectively, both P-values < 0.001), and WTW (0.06 ± 0.14,0.03 ± 0.30, respectively, both P-values < 0.001), along with a decrease in ACA (-3.50 ± 10.65, -3.30 ± 6.87, P-value< 0.001 and P-value=0.001,respectively), and CCT (-6.10 ± 8.06,-6.39 ± 9.97,respectively, both P-values < 0.001) post-dilation. However, no significant changes were observed in keratometry (front Km (-0.03 ± 0.19, -0.04 ± 0.21, respectively), back Km (0.01 ± 0.05, 0.004 ± 0.05, respectively), P-values> 0.05). Both concentrations of tropicamide exhibited comparable effects on anterior segment parameters in diabetic patients. These post-dilation changes should be considered for accurate intraocular lens power calculation and decision-making for cataract, phakic intraocular lens, and refractive surgeries.

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

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. Department of Ophthalmology, Ludwig-Maximilians-University, Munich, Germany. Retrospective, non-randomized, clinical trial. 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. 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. 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 Simulated Keratometry and Total Corneal Power in Eyes With Keratoconus and a Formula to Improve IOL Power Calculation Results.

To compare simulated keratometry (SimK) and total corneal power (TCP) in keratoconic eyes, to determine whether the differences are systematic and predictable and to evaluate an adjusted TCP-based formula for intraocular lens (IOL) power calculation. In a consecutive series of keratoconic eyes, measurements of SimK, TCP, posterior keratometry, and anterior and posterior corneal asphericities (Q-values) were retrospectively collected. The difference between SimK and TCP was linearly correlated to the biometric parameters. In a separate sample of keratoconic eyes that had undergone cataract surgery, IOL power was calculated with the Barrett Universal II, Hoffer QST, Holladay 1, Kane, and SRK/T formulas using the SimK and an adjusted TCP power. The respective prediction errors were calculated. A total of 382 keratoconic eyes (271 patients) were enrolled. An increasing overestimation of SimK by TCP was detected from stage I to III, with a significant correlation between the SimK and TCP difference and SimK in the whole sample (P < .0001, r2 = 0.1322). Approximately 7% of cases presented an underestimation of SimK by TCP. IOL power calculation with the adjusted TCP improved outcomes, achieving a maximum of 80% of eyes with a prediction error within ±0.50 diopters with the Hoffer QST, Holladay 1, and Kane formulas. Overall, SimK overestimated TCP. Such a difference could not be predicted by any variable. The proposed TCP-adjustment formula (TCPadj = TCP + 0.56 diopters) in keratoconic eyes for IOL power calculation might be valuable for improving refractive outcomes. [J Refract Surg. 2024;40(4):e253-e259.].

Intraocular lens power calculation: angle κ and ocular biomechanics

Purpose: To study the effect of ocular biomechanics on the prediction error of intraocular lens (IOL) power calculation. Setting: Centro Hospitalar Universitário do Porto, Porto, Portugal. Design: Prospective longitudinal study. Methods: This study included 67 subjects. Before cataract surgery subjects underwent biometry with IOLMaster 700 and biomechanical analysis with Corvis Scheimpflug technology. The targeted spherical equivalent was calculated with SRK-T and Barrett Universal II. Associations between prediction error (PE), absolute prediction error (AE), and biometric and biomechanical parameters were performed with stepwise multivariate linear correlation analysis. Results: Using the SRKT formula, there was association between PE and Corvis Biomechanical Index (CBI, B = −0.531, P = .011) and between AE and the horizontal offset between the center of the pupil and the visual axis (angle κ, B = −0.274, P = .007). Considering the Barret Universal II formula, PE was independently associated with anterior chamber depth (B = −0.279, P = .021) and CBI (B = −0.520, P = .013) and AE was associated with angle κ (B = −0.370, P = .007). Conclusions: A large angle κ may reduce the predictability of IOL power calculation. Ocular biomechanics likely influence the refractive outcomes after IOL implantation. This study showed that eyes with softer corneal biomechanics had more myopic PE. This may relate to anteriorization of the effective lens position. Dynamic measurements may be the way to progress into future formulas.