Accuracy Of Intraocular Lens Power Calculation Research Articles

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.

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.

Surgeons need to know more about IOL design for accurate power calculation.

Improvement in biometry and formulas have raised the bar for accurate IOL power calculation. However, when we look closely at the performance of a specific IOL model, we often find that the prediction error varies with the implant power. This phenomenon has no explanation other than the optic design of the IOL has shifted over the power range, thereby disrupting the assumptions of the calculations. By this report we call the industry to be more transparent and disclose the basic information about the IOL design that is important for accurate IOL power calculation. The relevant information concerns: the refractive index, the central optic thickness, the anterior and posterior curvature radii, the toricity location, the spherical aberration and haptic angulation. The goal is to predict possible shifts in principal planes or IOL position over the power range causing a refractive surprise if not corrected for.

Theoretical Impact of Intraocular Lens Design Variations on the Accuracy of IOL Power Calculations.

To ascertain the theoretical impact of optical design variations of the intraocular lens (IOL) on the accuracy of IOL power formulas based on a single lens constant using a thick lens eye model. This impact was also simulated before and after optimization. We modeled 70 thick-lens pseudophakic eyes implanted with IOLs of symmetrical optical design and power comprised between 0.50 D and 35 D in 0.5-step increments. Modifications of the shape factor resulting in variations in the anterior and posterior radii of an IOL were made, keeping the central thickness and paraxial powers static. Geometry data from three IOL models were also used. Corresponding postoperative spherical equivalent (SE) were computed for different IOL powers and assimilated to a prediction error of the formula due to the sole change in optical design alone. Formula accuracy was studied before and after zeroization on a uniform and non-uniform realistic IOL power distribution. The impact of the incremental change in optic design variability depended on the IOL power. Design modifications theoretically induce an increase in the standard deviation (SD), Mean Absolute Error (MAE), and Root Mean Square (RMS) of the error. The values of these parameters reduce dramatically after zeroization. While the variations in optical design can affect refractive outcomes, especially in short eyes, the zeroization of the mean error theoretically reduces the impact of the IOL's design and power on the accuracy of IOL power calculation.

Visual Outcomes of Cataract Surgery in Patients With Keratoconus Using Toric and Non-toric Lenses

To compare the accuracy and outcomes of different intraocular lens (IOL) power calculation formulas in eyes with keratoconus undergoing cataract surgery with toric and non-toric IOLs. This was a consecutive retrospective case series study including patients from the Cornea Service at the Department of Ophthalmology and Visual Sciences at the University of British Columbia, Vancouver, Canada, from 2000 to 2020. Keratoconus was diagnosed based on corneal topography and clinician opinion. Patients who underwent topography-guided photorefractive keratectomy, intracorneal ring segments implantation, or corneal transplant were excluded. The manifest spherical equivalent, prediction errors, and median absolute errors were calculated. Descriptive statistics were expressed as mean ± standard deviation. There were 160 eyes from 101 patients; 136 eyes received non-toric lenses and 24 eyes received toric lenses. Most patients had mild disease (< 48.00 diopters [D]) when stratified by steep keratometry values. Patients with severe disease (> 53.00 D) were significantly more hyperopic following surgery (P < .05). The Barrett Universal II (0.26 D, inter-quartile range [IQR] = 0.4), Holladay 2 (0.31, IQR = 1.2), and SRK/T (0.42, IQR = 0.86) formulas had the lowest median absolute error. The postoperative prediction error following toric lens insertion was not significantly different than following non-toric lens insertion, and the mean absolute astigmatism was significantly reduced with toric lenses. The Barrett Universal II, Holladay 2, and SRK/T were the most accurate IOL power calculation formulas in patients with keratoconus undergoing cataract surgery. Hyperopic surprise was increased in severe keratoconus. Toric IOLs may be considered in patients with mild keratoconus. [J Refract Surg. 2023;39(5):319-325.].

Comparison of Intraocular Lens Power Calculation formulas with and without Total Keratometry and Ray tracing in patients with previous myopic SMILE.

This study evaluated the prediction error (PE) variance and absolute median PE of different IOL calculation formulae including last generation formulae 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-SMILE eyes. Department of Ophthalmology, University Hospital Marburg, Germany. Design: Prospective study. 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 (IOL-Diff). The refractive change induced by SMILE was defined as the difference between preoperative and postoperative manifest refraction (SMILE-Diff). 98 eyes from 49 patients underwent bilateral myopic SMILE. The PE variance of Okulix was not significantly different compared to Barrett True-K with TK (P=0.471). The standard deviation (SD) 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 were 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. Our 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.

Comparison of the accuracy of three intraocular lens power calculation formulas in cataract patients with prior radial keratotomy

PurposeTo compare the accuracy of three intraocular lens (IOL) formulas in Chinese cataract patients with prior radial keratotomy (RK).MethodsMedical records of cataract patients with prior RK at Beijing Tongren Hospital were retrospectively analysed. The absolute error (AE) was calculated as the absolute difference between the actual postoperative spherical equivalent and the predicted spherical equivalent. The AE and percentages of eyes with AE within 0.5D, 1.0D, and 2.0D for three formulas [Barrett True-K, Holladay 1 (D–K), Haigis] were calculated and compared.ResultsForty-seven eyes of 28 cataract patients were included. The Median AE (MedAE) was significantly different among the three formulas (P < 0.001). The MedAE was lowest for the Barrett True-K formula (0.62), followed by the Haigis (0.76), and Holladay 1 (D–K) (1.16). The percentages of eyes with AE within 0.5D, and 1.0D were significantly different among the 3 formulas (P = 0.009, and P < 0.001). The Barrett True-K formula achieved the highest percentages (46.8%) of eyes with AE within 0.5D. Haigis achieved the highest percentages (70.21%) of eyes with AE within 1.0 D.ConclusionsBarrett True-K is the most accurate IOL power calculation formula among the 3 formulas and Haigis is an alternative choice. Considering the relatively lower accuracy of IOL formulas in cataract patients with prior RK, newer and more accurate IOL formulas are desirable.

Accuracy of Intraocular Lens Power Calculation in Pediatric Secondary Implantation: In-the-Bag Versus Sulcus Placement

To compare the effects of secondary in-the-bag vs ciliary sulcus intraocular lens (IOL) implantation on the accuracy of IOL power calculation in pediatric eyes. Prospective nonrandomized interventional study. Pediatric aphakic eyes that underwent either in-the-bag or ciliary sulcus secondary IOL implantation were included. The mean prediction error (PE), mean absolute error (MAE), median absolute error, and percentages of eyes with PE within ±0.25 diopter (D), ±0.50 D, ±0.75 D, and ±1.00 D were calculated and compared using SRK/T formula. One hundred fourteen eyes (38.26%) received in-the-bag IOL implantation and 184 (61.74%) underwent ciliary sulcus IOL implantation. Compared with the sulcus group, the capsular group displayed significantly lower MAE and higher percentage of eyes within ±0.50 D of PE (MAE: 0.90 vs 1.56 D; ±0.50 D: 40.40% vs 14.29%, both P < .001). The eyes receiving in-the-bag IOL implantation (sulcus IOL implantation β: -1.060, 95% CI: -1.415 to -0.705; P < .001), unilateral (β: 0.647, 95% CI: 0.144-1.150; P=.012), or with deeper anterior chamber depth (β: 0.362, 95% CI: 0.068-0.656; P=.016) were prone to maintain hyperopia (PE > 0). To reduce PE, when the predicted capsular IOL power was between 11.50 and 30.00 D, the power of a sulcus-implanted IOL should be reduced by 0.50 to 2.50 D accordingly (the exact amount of reduction is positively related to the predicted power). In-the-bag implantation yielded smaller PE in pediatric eyes undergoing secondary IOL implantation. Adjustment of IOL power for ciliary sulcus implantation is required to reduce PE, and the amount of adjustment is positively correlated with the IOL power predicted by SRK/T formula.

Assessment of the influence of keratometry on intraocular lens calculation formulas in long axial length eyes.

Hyperopic surprises tend to occur in axial myopic eyes and other factors including corneal curvature have rarely been analyzed in cataract surgery, especially in eyes with long axial length (≥ 26.0mm). Thus, the purpose of our study was to evaluate the influence of keratometry on four different formulas (SRK/T, Barrett Universal II, Haigis and Olsen) in intraocular lens (IOL) power calculation for long eyes. Retrospective case series. A total of 180 eyes with axial length (AL) ≥ 26.0mm were divided into 3 keratometry (K) groups: K ≤ 42.0 D (Flat), K ≥ 46.0 D (Steep), 42.0 < K < 46.0 D (Average), and all the eyes were underwent phacoemulsification cataract surgery with Rayner (Hove, UK) 920H IOL implantation. Prediction errors (PE) were compared between different formulas to assess the accuracy of different formulas. Multiple regression analysis was performed to investigate factors associated with the PE. The mean absolute error was higher for all evaluated formulas in Steep group (ranging from 0.66 D to 1.02 D) than the Flat (0.34 D to 0.67 D) and Average groups (0.40 D to 0.74D). The median absolute errors predicted by Olsen formula were significantly lower than that predicted by Haigis formula (0.42 D versus 0.85 D in Steep and 0.29 D versus 0.69 D in Average) in Steep and Average groups (P = 0.012, P < 0.001, respectively). And the Olsen formula demonstrated equal accuracy to the Barrett II formula in Flat and Average groups. The predictability of the SRK/T formula was affected by the AL and K, while the predictability of Olsen and Haigis formulas was affected by the AL only. Steep cornea has more influence on the accuracy of IOL power calculation than the other corneal shape in long eyes. Overall, both the Olsen and Barrett Universal II formulas are recommended in long eyes with unusual keratometry.

IOL Power Calculations and Cataract Surgery in Eyes with Previous Small Incision Lenticule Extraction.

Small incision lenticule extraction (SMILE), with over 5 million procedures globally performed, will challenge ophthalmologists in the foreseeable future with accurate intraocular lens power calculations in an ageing population. After more than one decade since the introduction of SMILE, only one case report of cataract surgery with IOL implantation after SMILE is present in the peer-reviewed literature. Hence, the scope of the present multicenter study was to compare the IOL power calculation accuracy in post-SMILE eyes between ray tracing and a range of empirically optimized formulae available in the ASCRS post-keratorefractive surgery IOL power online calculator. In our study of 11 post-SMILE eyes undergoing cataract surgery, ray tracing showed the smallest mean absolute error (0.40 D) and yielded the largest percentage of eyes within ±0.50/±1.00 D (82/91%). The next best conventional formula was the Potvin–Hill formula with a mean absolute error of 0.66 D and an ±0.50/±1.00 D accuracy of 45 and 73%, respectively. Analyzing this first cohort of post-SMILE eyes undergoing cataract surgery and IOL implantation, ray tracing showed superior predictability in IOL power calculation over empirically optimized IOL power calculation formulae that were originally intended for use after Excimer-based keratorefractive procedures.

Evaluation of IOL power calculation with the Kane formula for pediatric cataract surgery.

To assess the accuracy of the Kane formula for intraocular lens (IOL) power calculation in the pediatric population. The charts of pediatric patients who underwent cataract surgery with in-the-bag IOL implantation with one of two IOL models (SA60AT or MA60AC) between 2012 and 2018 in The Hospital for Sick Children, Toronto, Ontario, CanFada, were retrospectively reviewed. The accuracy of IOL power calculation with the Kane formula was evaluated in comparison with the Barrett Universal II (BUII), Haigis, Hoffer Q, Holladay 1, and Sanders-Retzlaff-Kraff Theoretical (SRK/T) formulas. Sixty-two eyes of 62 patients aged 6.2 (IQR 3.2-9.2) years were included. The SD values of the prediction error obtained by Kane (1.38) were comparable with those by BUII (1.34), Hoffer Q (1.37), SRK/T (1.40), Holaday 1 (1.41), and Haigis (1.50), all p > 0.05. A significant difference was observed between the Hoffer Q and Haigis formulas (p = 0.039). No differences in the median and mean absolute errors were found between the Kane formula (0.54 D and 0.91 ± 1.04 D) and BUII (0.50 D and 0.88 ± 1.00 D), Hoffer Q (0.48 D and 0.88 ± 1.05 D), SRK/T (0.72 D and 0.97 ± 1.00 D), Holladay 1 (0.63 D and 0.94 ± 1.05 D), and Haigis (0.57 D and 0.98 ± 1.13 D), p = 0.099. This is the first study to investigate the Kane formula in pediatric cataract surgery. Our results place the Kane among the noteworthy IOL power calculation formulas in this age group, offering an additional means for improving IOL calculation in pediatric cataract surgery. The heteroscedastic statistical method was first implemented to evaluate formulas' predictability in children.

Update and understanding of optical biometer

With advances in technology that allow for more accurate measurement of ocular biometric characteristics and the availability of sophisticated methods for calculating intraocular lens (IOL) power, cataract surgery has evolved into a refractive operation. Patient expectations have been raised as a result of this, as well as free and simple access to information about the latest technology. After cataract surgery, there is a greater demand than ever for life without spectacles. Newer advances in optical biometry, such as swept-source optical coherence tomography, combined with the availability of highly accurate IOL power calculation formulae, including artificial intelligence-based formulae, have the potential to enable surgeons to achieve near-perfect outcomes in the majority of their patients. Understanding the benefits and limitations of currently available cutting-edge technologies and equations and applying them to the cataract surgical practice is required to hit the bull’s eye in terms of goal refraction.

Accuracy of intraocular lens power calculation using Scheimpflug tomography and OKULIX ray-tracing software in paracentral corneal scarring not interfering with postoperative refraction

Purpose The aim of this study was to evaluate the accuracy of intraocular lens (IOL) power calculation using Scheimpflug tomography and OKULIX ray-tracing software in cases of paracentral corneal scarring. Patients and methods The study was conducted on 40 consecutive eyes: 20 with corneal scarring and coexisting cataract and 20 controls with clear cornea, for whom uneventful phacoemulsification and IOL implantation was performed. Preoperatively, Scheimpflug tomography and OKULIX ray-tracing software and third-generation IOL power calculation formulas were used for IOL power calculation. Accuracy of IOL power calculation was evaluated by subtracting the expected and achieved spherical refraction, 3 months postoperatively and was recorded as the mean absolute error (MAE). The distance uncorrected visual acuity for each eye was measured preoperatively and 3 months postoperatively; the visual acuity was scored and converted to the logarithm of the minimum angle of resolution (LogMar) for statistical analysis. Results In cases of corneal scarring, all eyes (100%) yielded a postoperative spherical refraction which differed by less than 1 D from the predicted. In 16 (80%) eyes, the postoperative spherical refraction was within 0.50 D from the expected. The MAE was 0.2 D in cases of corneal scarring, which did not differ significantly from the controls (MAE=0.1 D), P=0.142. In corneal scarring cases, the distance uncorrected visual acuity showed significant improvement from 1.3 LogMar (Snellen’s equivalent 20/400), preoperatively, to 0.5 LogMar (Snellen’s equivalent 20/60), 3 months postoperatively. Conclusion Scheimpflug tomography combined with OKULIX ray-tracing software for the calculation of IOL power provided accurate results in cases of corneal scarring.

OKULIX ray-tracing software versus third generation formulas: compatibility or superiority?

Purpose The aim of this retrospective study was to compare the accuracy of intraocular lens (IOL) power calculation using the OKULIX ray-tracing software compared with third generation IOL power calculation formulas. Patients and methods The study included 80 consecutive eyes of 80 patients (26 males and 54 females, with a mean age of 58.8±15.1 years), for whom phacoemulsification and IOL implantation was performed following biometry using the OKULIX ray-tracing software and third-generation IOL power calculation formulas for IOL power calculation. Accuracy of IOL power calculation was investigated by subtracting the attempted and achieved spherical equivalent 1 month postoperatively and was recorded as the mean absolute error. Results OKULIX ray-tracing software calculated IOL power was 17.1±8.5 diopters (D), which was statistically significantly different from Sanders, Retzlaff, Kraff (SRK)-T, Hoffer Q, SRK II, and Holladay formulas (16.7±8.3, 16.6±8.7, 16.8±8, and 16.7±8.5 D, respectively, P<0.001). The OKULIX ray-tracing software mean absolute error was 0.2±0.2 D, which was statistically significantly less than that of the SRK-T, Hoffer Q, SRK II, and Holladay formulas (0.5±0.5, 0.6±0.5, 0.8±0.7, and 0.6±0.5 D, respectively, P<0.001). Conclusions The OKULIX ray-tracing software seems to deliver reliable and more accurate results in comparison to the third generation IOL power calculation formulas.

Comparison of Intraocular Lens Power Estimation by Optical Biometry and Ultrasound Biometry in Cataract Surgery

Introduction: The evolution of modern technologies for cataract surgery has made it crucial for aiming emmetropia with highly defined vision. The key factor responsible for postoperative emmetropia is an accurate biometry, along with various other factors. Ultrasonic biometry is the gold standard method of Intraocular Lens (IOL) power calculation but the corneal indentation with the probe underestimate the axial length and result in a myopic shift which is overcome by the newer optical biometry devices, including swept source optical coherence biometry which uses infrared light to measure the ocular distances. Aim: To determine the precision and accuracy of IOL power calculation by ultrasound A-scan and optical IOL master and their refractive outcomes. Materials and Methods: This prospective, and observational study was conducted between September 2019 to February 2021 in 155 patients with cataract undergoing phacoemulsification in Kalinga Institute of Medical Sciences, KIIT University, Bhubaneswar, Odisha, India. All subjects underwent comprehensive ocular examination and biometry with two formulae {Sanders-RetzlaffKraff (SRK) and Holladay-I}. Biometry included corneal curvature (keratometry), axial length, anterior chamber depth, IOL power calculation, predicted refractive error. There were two broad groups. One group underwent biometry by ultrasound A-scan and the other group underwent optical biometry by IOL Master 700. The IOL power was calculated with the two formulae in both the groups. Comparisons between variables measured using the IOL master and A-scan were done using paired t-test. The p-values &lt;0.05 were considered statistically significant. Results: In a 18 month period, 155 eyes were consecutively enrolled in the study. The mean age of all enrolled patients was 62.1±8.65 years (range 34-80 years) with male:female ratio of approximately 1.25:1. The mean axial length measured by IOL master was higher (23.15 ± 0.85) than that by A-scan (22.96±0.81 diopters) with a mean difference of 0.197±0.35 mm (p-value &lt;0.001, paired t-test). The mean predicted IOL power was 20.81±1.84 diopters by IOL master and 21.13±1.62 by A-scan by SRK-II formula (p-value &lt;0.001). While mean predicted IOL power with Holladay-I by IOL Master 700 was 20.61±1.92 and 21.44±1.98 diopters by A-scan with a mean difference (-0.82±0.76 diopters) with a significant p-value &lt;0.001. Bland-Altman analysis plots showed almost perfect agreement between both methods regarding predicted IOL power. Conclusion: The swept source Optical Coherence Tomography (OCT) based IOL master 700 proved to be a faster non contact device to use with a shorter learning curve, higher accuracy in average axial length eye and less refractive surprises.

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.

Нюансы предоперационной подготовки пациентов перед экстракцией катаракты. Что мы упускаем из виду при проведении биометрии, расчете ИОЛ и оценке состояния глаза?

Modern cataract surgery is increasingly regarded as a refractive procedure. The focus has shifted from practicing and refining surgical steps towards personalized intraocular lens (IOL) choice based on the eye parameters of each individual. The best possible refractive outcome is now the priority. All components of biometry contribute to IOL power calculation accuracy. Therefore, any errors, a method of evaluating each parameter, and a technician’s experience are important. In addition, refraction, macular disorders, and prior surgical procedures affect IOL choice, preoperative care, and the extent of surgery. Moreover, subsequent changes in the IOL position that results in refractive errors after cataract surgery (this depends on the formula for IOL power calculation) should also be considered. The accuracy of IOL power calculation is affected by the inaccuracy of current biometry techniques and postoperative changes of the globe. Personalization of theoretical formulas provides better accuracy of IOL power calculations to meet modern trends in intraocular correction. Supplements containing macular pigments prevent macular degeneration and protect the macular zone. Keywords: cataract, refraction, cataract surgery, biometry, IOL power calculation, IOL power calculation formulas, retina, age-related macular degeneration. For citation: Movsisyan A.B., Egorov A.E. Nuances of preoperative care before cataract extraction. What do we overlook when performing biometry, calculating IOL power, and examining the eye? Russian Journal of Clinical Ophthalmology. 2021;21(3):159–163 (in Russ.). DOI: 10.32364/2311-7729-2021-21-3-159-163.

Comparison of Aphakic Refraction and Biometry-Based Formulae for Secondary In-The-Bag and Sulcus-Implanted Intraocular Lens Power Estimation in Children

Purpose: The aim of the study was to compare the accuracy of refractive outcomes in children undergoing secondary in-the-bag or cilliary sulcus intraocular lens (IOL) implantation, using aphakic refraction (AR)-based formulae (Hug and Khan) and biometry-based formulae (Holladay 1, Hoffer Q, SRK/T, and SRK II). Methods: In this retrospective study, a total of 65 eyes of 44 patients who underwent secondary in-the-bag or cilliary sulcus IOL implantation were included and divided into 2 groups: 39 eyes of the in-the-bag IOL group and the other 26 eyes of the sulcus-implanted IOL group. Holladay 1, Hoffer Q, SRK/T, and SRK II formulae were employed depending on the biometric data, while Hug and Khan formulae were used based on preoperative AR. The prediction error (PE) and the absolute value of predicted error (APE) were compared between the 2 groups and formulae. Results: In the in-the-bag IOL group, nonsignificant differences of APE were found among the 6 formulae, while the Holladay 1, Hoffer Q, SRK/T, and SRK II all demonstrated a significant hyperopic shift of median PE value compared to the Hug formula (p < 0.05, all), and Holladay 1 and SRK II also showed a significant hyperopic shift of PE compared to the Khan formula (p < 0.05, both). Higher percentages of eyes with PE <1 D were found using Hoffer Q and SRK/T. In the sulcus-implanted group, the Holladay 1, Hoffer Q, and SRK/T had a significantly smaller median value of APE than the Hug and Khan formulae (p < 0.05, all), and the SRK II had a significantly smaller median value of APE than the Hug formula (p < 0.05), while Holladay 1 had the lowest value of APE. Higher percentages of eyes within PE <1 D were found using Holladay 1, Hoffer Q, and SRK/T, while the highest one was SRK/T. Significantly larger hyperopic shifts of median PE value using all the 6 formulae were found in eyes with sulcus-implanted IOL than eyes with in-the-bag implanted IOL (p < 0.05, all). In the eyes of with in-the-bag implanted IOL, the Hug and Khan formulae had significantly smaller APE values when compared with the eyes with sulcus-implanted IOL (p < 0.05, both). Conclusions: Whether IOL was in the bag or implanted in the sulcus, almost all the formulae showed hyperopic shift, SRK/T showed the best accuracy. Biometry-based formulae were superior to AR-based formulae in accuracy of IOL power calculation, especially when IOL was implanted in the sulcus. In-the-bag IOL implantation should always be with higher priorities, especially when using AR-based formulae in IOL power calculation.

Update on Intraocular Lens Power Calculation Study Protocols: The Better Way to Design and Report Clinical Trials

It was almost 40 years ago when one of the authors (K.J.H.) published an organized system to quantify the accuracy of intraocular lens (IOL) power calculation formulas, methods, and instruments. At the behest of the editor of the American Journal of Ophthalmology, the IOL Power Club (along with a statistician) published an editorial in 2015 modernizing and quantifying the proper protocols for these studies. Over the past decade, so many new optical biometers, formulas, and methods (whose accuracies have yet to be completely tested) have been introduced that we were asked to modernize and update these guidelines yet again to help others design and report correctly the results of clinical studies on IOL power calculation and biometry for 2020. We evaluated guidelines to enroll patients, including visual acuity minimums, exclusion of bilateral eyes, sample size issues, demographics (age, gender, and ethnicity), and whether such studies should not be performed using the same data that were used to develop the formula being tested. We showed the absolute need for constant optimization, which formulas should be tested for comparison, refraction measurement (testing distance), as well as the analysis of the prediction error (median and mean absolute errors; standard deviation; range of errors; percentage of eyes with a prediction within ±0.25 diopter [D], ±0.50 D, ±0.75 D, and ±1.00 D; and interquartile displays) and statistical methods of analyses. We present methods of ranking formula accuracy, including the new Haigis IOL Formula Performance Index. We also point out the issues of who programmed the formulas being tested, that all formulas used in the study must be referenced, and the software version number of all instruments used in the study should be stated clearly. The definition of anterior chamber depth should be stated as measured from the corneal epithelium to the lens. We hope that these recommendations will help researchers to improve the validity and accuracy of their studies with the ultimate goal to improve the accuracy of IOL power calculation.

Refractive outcomes and accuracy of IOL power calculation with the SRK/T formula for sutured, scleral-fixated Akreos AO60 intraocular lenses.

Scleral fixation of intraocular lenses has become a popular procedure for treating aphakia in the absence of capsular support. However, the lens formulas used to predict refractive outcomes were designed for in-the-bag lens placement. This study evaluates the accuracy of the SRK/T formula in predicting a target postoperative refraction when suturing a scleral-fixated intraocular lens (IOL) implant 3mm posterior to the limbus. This is a retrospective, case series including 20 eyes of 20 patients who underwent scleral fixation of Akreos AO60 IOLs (Bausch & Lomb, Rochester, NY) by a single surgeon at the OSU Wexner Medical Center. Preoperative measurements were performed with optical biometry, and IOL power was calculated with the SRK/T formula. Following surgery, the actual refractive spherical equivalent (SE) was performed and compared with the preoperative prediction. Prediction error (PE), defined as the deviation of actual postoperative SE refraction in diopters (D) from preoperative predicted SE refraction, was the primary outcome measure. The mean attempted (predicted) SE was - 1.12 D (± 0.87). Mean achieved SE was - 0.96 D (± 1.04). Mean PE (actual postoperative SE versus predicted preoperative SE) was 0.16 D (± 0.69). A total of 9 eyes (45%) were within ± 0.5 D of the predicted SE, 16 eyes (80%) were within ± 1.0 D, and all 20 eyes (100%) were within ± 1.5 D. IOL power calculation using the SRK/T formula with optical biometry demonstrates reliable postoperative refractive outcomes in patients undergoing scleral fixation of an IOL (Akreos AO60). Further studies are needed to refine the predictive value of the SRK/T and other formulas for application in scleral fixation of IOLs.