Calculation formulas and influence factors of effective lens position / 中华实验眼科杂志

Cataract extraction is often combined with the implantation of intraocular lens (IOL) with the diopter matching the operated eye to restore optimal visual function after surgery.However, there are often errors between the actual refractive power of the operated eye and the predicted value.One of the major causes of postoperative refractive error is the change in IOL position compared with the expected position.In order to improve the accuracy of postoperative refraction prediction, Holladay proposed to introduce the concept of effective lens position (ELP) into the IOL diopter calculation formula.The differences in the parameters and algorithms incorporated in the calculation of ELP lead to differences in the accuracy of IOL calculation formulas.With the application of multi-parameter calculation methods, especially the formula based on the artificial intelligence algorithm, the accuracy of IOL calculation formula has been significantly improved.ELP is also affected by various factors such as differences in ocular anatomy, IOL design and material, and surgical procedures, especially the factors affecting the stability of the capsular bag that increase the difficulty of accurately predicting ELP.Therefore, the changes in postoperative ELP need to be further discussed in order to obtain more accurate postoperative refraction.This article aimed to give a review of the development of calculation formulas and the influencing factors of ELP.

Predicción de la posición efectiva del lente intraocular y su relación con los planos del cristalino / Prediction of the effective intraocular lens position and its relationship to crystalline lens planes

RESUMEN La cirugía de catarata es uno de los procedimientos quirúrgicos más frecuentes de toda la medicina. El objetivo de la técnica es eliminar el cristalino opacificado y sustituirlo con lentes intraoculares para lograr una rehabilitación de la función visual. El cálculo preciso de la posición efectiva del lente es crítico para lograr un buen resultado refractivo. Esta es la única variable que no puede medirse en el preoperatorio y que debe predecirse, por lo que representa uno de los retos más grande para el cirujano de catarata, ya que puede influir ampliamente en el resultado visual del paciente. Investigaciones recientes proponen nuevos parámetros para la estimación de la posición efectiva del lente, que están relacionados con la geometría del cristalino. Se realizó una búsqueda con el objetivo de describir la importancia de una adecuada estimación de la posición efectiva del lente y para conocer las últimas fórmulas propuestas para el cálculo del lente. Se encontraron estudios de investigación recientes en varias partes del mundo que proponen nuevas fórmulas basadas en parámetros anatómicos del cristalino. Se utilizó la plataforma Infomed, específicamente la Biblioteca Virtual de Salud, con todos sus buscadores(AU)

ABSTRACT Cataract surgery is one the most common surgeries within medicine. The technique's objective is the removal of the natural lens of the eye that has developed an opacification, and its replacement with an intraocular lens to provide optimal visual acuity. An accurate assessment of the effective lens position is critical to achieve a good postoperative refractive outcome. This is the only variable that cannot be measured in the preoperative period and most be predicted, therefore it represents one of the greatest challenge for the cataract surgeon, since it can greatly influence the visual outcome of the patient. Recent research proposes new parameters of the estimation of the effective lens position that are related to the geometry of the lens. Research has been made in order describe the importance of an adequate estimation of the effective lens position and to learn more about the lastest formulas proposed for its calcutation. Many studies proposed new formulas based on lens geometry parameters. The Infomed platform, specifically the Virtual Health Library, was used with all its search engines(AU)

Swivel haptics anterior capsule-fixated intraocular lens

The purpose of the study is to report the feasibility of implantation of a new design of anterior capsule-fixated intraocular lens (IOL). The new IOL design is a foldable, hydrophilic, open-loop posterior chamber IOL with two extra polymethyl methacrylate swivel haptics created on the optic surface to capture the anterior capsulotomy after the IOL is implanted in the bag. In the pilot phase, the new IOL was implanted in 10 eyes of 10 patients of which 8 eyes underwent phacoemulsification and 2 eyes had laser cataract surgery. The mean spherical equivalent changed from *1.75 D to ?0.75 D at 6 months. Postoperatively, from 1 week to 6 months, all eyes showed stable refraction and anterior chamber depth with no evidence of decentration. Subjective questionnaire revealed high patient satisfaction with no complaints of dysphotopsia. No intra- or postoperative complications such as swivel haptic breakage, iris chafing, pigment dispersion, postoperative uveitis, or endophthalmitis occurred in any of the eyes necessitating explantation of the IOL. The new IOL design was feasible to implant and provided satisfactory outcomes in terms of no dysphotopsias and stable effective lens position.

Preliminary evaluation of an algorithm to minimize the power error selection of an aspheric intraocular lens by optimizing the estimation of the corneal power and the effective lens position / 国际眼科杂志(Guoji Yanke Zazhi)

?AIM: To evaluate the refractive predictability achieved with an aspheric intraocular lens ( IOL ) and to develop a preliminary optimized algorithm for the calculation of its power ( PIOL ) .?METHODS:This study included 65 eyes implanted with the aspheric IOL LENTIS L-313 ( Oculentis GmbH ) that were divided into 2 groups:12 eyes (8 patients) with PIOL≥23. 0 D (group A), and 53 eyes (35 patients) with PIOL<23. 0 D ( group B ). The refractive predictability was evaluated at 3mo postoperatively. An adjusted IOL power ( PIOLadj ) was calculated considering a variable refractive index for corneal power estimation, the refractive outcome obtained, and an adjusted effective lens position ( ELPadj ) according to age and anatomical factors.?RESULTS: Postoperative spherical equivalent ranged from -0. 75 to +0. 75 D and from -1. 38 to +0. 75 D in groups A and B, respectively. No statistically significant differences were found in groups A (P=0. 64) and B (P=0. 82 ) between PIOLadj and the IOL power implanted ( PIOLReal ) . The Bland and Altman analysis showed ranges of agreement between PIOLadj and PIOLReal of +1. 11 to -0. 96 D and +1. 14 to -1. 18 D in groups A and B, respectively. Clinically and statistically significant differences were found between PIOLadj and PIOL obtained with Hoffer Q and Holladay I formulas (P<0. 01).?CONCLUSION: The refractive predictability of cataract surgery with implantation of an aspheric IOL can be optimized using paraxial optics combined with linear algorithms to minimize the error associated to the estimation of corneal power and ELP.

Positional accommodative intraocular lens power error induced by the estimation of the corneal power and the effective lens position.

Purpose: To evaluate the predictability of the refractive correction achieved with a positional accommodating intraocular lenses (IOL) and to develop a potential optimization of it by minimizing the error associated with the keratometric estimation of the corneal power and by developing a predictive formula for the effective lens position (ELP). Materials and Methods: Clinical data from 25 eyes of 14 patients (age range, 52–77 years) and undergoing cataract surgery with implantation of the accommodating IOL Crystalens HD (Bausch and Lomb) were retrospectively reviewed. In all cases, the calculation of an adjusted IOL power (PIOLadj) based on Gaussian optics considering the residual refractive error was done using a variable keratometric index value (nkadj) for corneal power estimation with and without using an estimation algorithm for ELP obtained by multiple regression analysis (ELPadj). PIOLadj was compared to the real IOL power implanted (PIOLReal, calculated with the SRK‑T formula) and also to the values estimated by the Haigis, HofferQ, and Holladay I formulas. Results: No statistically significant differences were found between PIOLReal and PIOLadj when ELPadj was used (P = 0.10), with a range of agreement between calculations of 1.23 D. In contrast, PIOLReal was significantly higher when compared to PIOLadj without using ELPadj and also compared to the values estimated by the other formulas. Conclusions: Predictable refractive outcomes can be obtained with the accommodating IOL Crystalens HD using a variable keratometric index for corneal power estimation and by estimating ELP with an algorithm dependent on anatomical factors and age.

Estimation of Intraocular Lens Power Calculation after Myopic Corneal Refractive Surgery: Using Corneal Height in Anterior Segment Optical Coherence Tomography

PURPOSE: To investigate the feasibility of estimating effective lens position (ELP) and calculating intraocular lens power using corneal height (CH), as measured using anterior segment optical coherence tomography (AS-OCT), in patients who have undergone corneal refractive surgery. METHODS: This study included 23 patients (30 eyes) who have undergone myopic corneal refractive surgery and subsequent successful cataract surgery. The CH was measured with AS-OCT, and the measured ELP (ELP(m)) was calculated. Intraocular lens power, which could achieve actual emmetropia (P(real)), was determined with medical records. Estimated ELP (ELP(est)) was back-calculated using P(real), axial length, and keratometric value through the SRK/T formula. After searching the best-fit regression formula between ELP(m) and ELP(est), converted ELP and intraocular lens power (ELP(conv), P(conv)) were obtained and then compared to ELP(est) and P(real), respectively. The proportion of eyes within a defined error was investigated. RESULTS: Mean CH, ELP(est), and ELP(m) were 3.71 +/- 0.23, 7.74 +/- 1.09, 5.78 +/- 0.26 mm, respectively. The ELP(m) and ELP(est) were linearly correlated (ELP(est) = 1.841 x ELP(m) - 2.018, p = 0.023, R = 0.410) and ELP(conv) and P(conv) agreed well with ELP(est) and P(real), respectively. Eyes within +/-0.5, +/-1.0, +/-1.5, and +/-2.0 diopters of the calculated P(conv), were 23.3%, 66.6%, 83.3%, and 100.0%, respectively. CONCLUSIONS: Intraocular lens power calculation using CH measured with AS-OCT shows comparable accuracy to several conventional methods in eyes following corneal refractive surgery.

Estimation of Intraocular Lens Power Calculation after Myopic Corneal Refractive Surgery: Using Corneal Height in Anterior Segment Optical Coherence Tomography

PURPOSE: To investigate the feasibility of estimating effective lens position (ELP) and calculating intraocular lens power using corneal height (CH), as measured using anterior segment optical coherence tomography (AS-OCT), in patients who have undergone corneal refractive surgery. METHODS: This study included 23 patients (30 eyes) who have undergone myopic corneal refractive surgery and subsequent successful cataract surgery. The CH was measured with AS-OCT, and the measured ELP (ELP(m)) was calculated. Intraocular lens power, which could achieve actual emmetropia (P(real)), was determined with medical records. Estimated ELP (ELP(est)) was back-calculated using P(real), axial length, and keratometric value through the SRK/T formula. After searching the best-fit regression formula between ELP(m) and ELP(est), converted ELP and intraocular lens power (ELP(conv), P(conv)) were obtained and then compared to ELP(est) and P(real), respectively. The proportion of eyes within a defined error was investigated. RESULTS: Mean CH, ELP(est), and ELP(m) were 3.71 +/- 0.23, 7.74 +/- 1.09, 5.78 +/- 0.26 mm, respectively. The ELP(m) and ELP(est) were linearly correlated (ELP(est) = 1.841 x ELP(m) - 2.018, p = 0.023, R = 0.410) and ELP(conv) and P(conv) agreed well with ELP(est) and P(real), respectively. Eyes within +/-0.5, +/-1.0, +/-1.5, and +/-2.0 diopters of the calculated P(conv), were 23.3%, 66.6%, 83.3%, and 100.0%, respectively. CONCLUSIONS: Intraocular lens power calculation using CH measured with AS-OCT shows comparable accuracy to several conventional methods in eyes following corneal refractive surgery.

Theoretical and Clinical Comparison of the Hoffer Q and SRK/T Formulas

PURPOSE: To evaluate the biometric conditions causing increased disparity in the calculation of intraocular lens (IOL) power between the Hoffer Q and SRK/T formulas. METHODS: A prospective comparative study was conducted on 365 uneventful, cataract surgeries performed at a tertiary care center by one surgeon. The IOL power was calculated using both the Hoffer Q and SRK/T formulas with A-scan biometry. For a selected IOL power, the expected disparity between the 2 formulas (EDF) was measured and the EDF value was used to categorize the cases. The resultant error associated with each formula was determined at postoperative 6 weeks. KAL was defined as the product of mean corneal power (K) and axial length (AL). Postoperative errors of both formulas were calculated and their association with preoperative biometry measurements analyzed. RESULTS: In 17.8% of the cases, the EDF was larger than 0.4 D, possibly leading to different IOL diopter recommendations. The EDF value and the product of corneal curvature and axial length were significantly correlated (R2 = 0.855, p < 0.001). Multiple regression analysis of causative preoperative biometric factors on the postoperative formula errors showed that astigmatism, anterior chamber depth (ACD), and lens thickness (LT) were significantly associated with Hoffer Q error and SRK/T error. CONCLUSIONS: Overall, both formulas performed very well when recommending the correct IOL power. The cause of disparity between the predicted refraction for the 2 formulas was more associated with KAL than K or AL alone. Astigmatism, ACD, and LT were the causative factors for the postoperative errors in both formulas.

Effects of Axial Length and Vitrectomy on Refractive Error after Cataract Surgery Using SRK/T Formula

PURPOSE: To investigate the error tendency between preoperative target diopter and postoperative manifest refraction in cataract surgery cases and the effect of axial length and vitrectomy on refractive error (RE). METHODS: We retrospectively studied 90 eyes of 90 patients who underwent cataract surgery. The power of intraocular lens (IOL) was calculated by SRK/T formula. Patients were devided into four groups based on axial length (AXL) and the past history of vitrectomy. RESULTS: The mean of RE showed no significant difference between groups. But an increasing AXL was associated with increased myopic shift with normal range AXL (24.4 mm) (r = 0.718, p < 0.001). In vitrectomized eyes, it showed no significant refractive shift with both normal range and long AXL. CONCLUSIONS: When determining IOL power using SRK/T formula in nonvitrectomized eyes, postoperative refractive shift based on axial length should be considered.

Posición efectiva del lente intraocular en la facoemulsificación diagnosticado por biomicroscopia ultrasónica / Effective position of the intraocular lens diagnosed with ultrasonic biomicroscopy in phacoemulsification

OBJETIVO: Determinar la posición efectiva del lente intraocular en la facoemulsificación diagnosticado por biomicroscopia ultrasónica y su relación con la "sorpresa refractiva" posquirúrgica. MÉTODOS: Se realizó un estudio descriptivo y prospectivo de una muestra de 176 ojos de 100 pacientes operados de catarata por facoemulsificación con la técnica de Pre chop, en el Servicio de Microcirugía Ocular del Instituto Cubano de Oftalmología "Ramón Pando Ferrer", a los que se le determinó la posición efectiva del lente intraocular en la facoemulsificación diagnosticado por biomicroscopia ultrasónica y su relación con la "sorpresa" refractiva posquirúrgica. RESULTADOS: La mayoría de los pacientes estudiados, fueron del sexo masculino de la tercera edad, se diagnóstico la posición efectiva del lente intraocular en saco-surco por biomicroscopia ultrasónica, con lo que se logró la mejor agudeza visual corregida posoperatoria en todos los grupos de estudio, la distancia de la cara posterior del iris al lente intraocular, diagnosticada por biomicroscopia ultrasónica, en pacientes con lente intraocular en saco capsular demostró un valor constante, la mayoría de pacientes normo corregidos tenían el lente intraocular en saco capsular, los lente intraocular ubicados en la posición saco-surco, cuya háptica se encontraba con mayor angulación, tenían un cilindro posoperatorio promedio mayor, no se encontraron diferencias significativas entre el cilindro posoperatorio promedio obtenido. CONCLUSIONES: Queda demostrada la importancia de la biomicroscopia ultrasónica en la determinación de la posición del lente intraocular en los pacientes operados. Es determinante la localización del lente intraocular en el defecto refractivo posoperatorio, se destaca en la posición saco surco la existencia de un cilindro posoperatorio mayor.

OBJECTIVE: To determine the effective position of the intraocular lens in the phacoemulsiphication diagnosed by ultrasonic biomicroscopy and its relationship to the postsurgical refractive surprise. METHODS: A prospective and descriptive study was performed in a sample of 176 eyes from 100 patients, who had been operated on from cataract with phacoemulsiphication using Pre Chop technique in the Ocular Microsurgery Service of "Ramón Pando Ferrer" Cuban Institute of Ophthalmology". The effective position of their intraocular lens diagnosed by ultrasonic biomicroscopy in the phacoemulsiphication and their relationship to the post surgery refractive surprise was determined. RESULTS: Most of the studied patients were older adult males. The ultrasonic biomicroscopy diagnosed the effective position of the intraocular lens in sac-sulcus to achieve the best postoperative corrected visual acuity in all the studied groups. The distance from the posterior face of the iris to the intraocular lens found in patients with intraocular lens in capsular sac showed a constant value. Most of the normocorrected patients had their intraocular lens in the capsular sac whereas the intraocular lens located in sac-sulcus position, whose haptics exhibited bigger angle, had bigger postoperative average cylinder, no significant differences were found among the postoperative average cylinders. CONCLUSIONS: The importance of the ultrasonic biomicroscopy is demonstrated in the determining the position of the intraocular lens in the surgical patients. The location of the intraocular lens is decisive in the postoperative refractive defect; bigger postoperative cylinder was more often found in the sac-sulcus position.