Research on Calculation of the IOL Tilt and Decentration Based on Surface Fitting

The tilt and decentration of intraocular lens (IOL) result in defocussing, astigmatism, and wavefront aberration after operation. The objective is to give a method to estimate the tilt and decentration of IOL more accurately. Based on AS-OCT images of twelve eyes from eight cases with subluxation lens after operation, we fitted spherical equation to the data obtained from the images of the anterior and posterior surfaces of the IOL. By the established relationship between IOL tilt (decentration) and the scanned angle, at which a piece of AS-OCT image was taken by the instrument, the IOL tilt and decentration were calculated. IOL tilt angle and decentration of each subject were given. Moreover, the horizontal and vertical tilt was also obtained. Accordingly, the possible errors of IOL tilt and decentration existed in the method employed by AS-OCT instrument. Based on 6–12 pieces of AS-OCT images at different directions, the tilt angle and decentration values were shown, respectively. The method of the surface fitting to the IOL surface can accurately analyze the IOL’s location, and six pieces of AS-OCT images at three pairs symmetrical directions are enough to get tilt angle and decentration value of IOL more precisely

Full OCT anterior segment biometry: An application in cataract surgery

In vivo three-dimensional (3-D) anterior segment biometry before and after cataract surgery was analyzed by using custom highresolution high-speed anterior segment spectral domain Optical Coherence Tomography (OCT). The system was provided with custom algorithms for denoising, segmentation, full distortion correction (fan and optical) and merging of the anterior segment volumes (cornea, iris, and crystalline lens or IOL), to provide fully quantitative data of the anterior segment of the eye. The method was tested on an in vitro artificial eye with known surfaces geometry at different orientations and demonstrated on an aging cataract patient in vivo. Biometric parameters CCT, ACD/ILP, CLT/ILT Tilt and decentration are retrieved with a very high degree of accuracy. IOL was placed 400 οm behind the natural crystalline lens, The IOL was aligned with a similar orientation of the natural lens (2.47 deg superiorly), but slightly lower amounts (0.77 deg superiorly). The IOL was decentered superiorly (0.39 mm) and nasally (0.26 mm). © 2013 Optical Society of America.This study has been funded by Spanish Government Grant FIS2011-25637 and European Research Council Grant ERC-2011-AdG-294099 to S. Marcos.Peer Reviewe

The Balanced Two-String Technique for Sulcus Intraocular Lens Implantation in the Absence of Capsular Support

Purpose. To describe and explore an alternative approach for sulcus intraocular lens (IOL) implantation in the absence of capsular support. Methods. The commonly available one-piece poly(methyl methacrylate) (PMMA) lens is stabilized in the sulcus by two intraocular horizontal strings of 10/0 polypropylene suture passed through the lens dialing holes in opposite directions to achieve a mechanical balance. The horizontal strings of 10/0 polypropylene work as a rail track for the IOL optics, allowing some side to side lens adjustment even following wound closure. The stability of the IOL was tested in vitro. Six aphakic patients underwent in-sulcus IOL secondary implantation using the balanced two-string technique. Patients were followed up for a minimum of six months. Best spectacle corrected vision was assessed. Lens centration and lens tilt were measured by anterior segment optical coherence tomography (AS-OCT). Results. All patients had successful lens insertion. Best spectacle corrected visual acuity (BSCVA) improved in all patients. Lens decentration ranged between 0.21 mm and 0.9 mm (average 0.53 mm). Lens tilt ranged between 1.2° and 2.8° (average 2.17°). Conclusion. The mechanically balanced two-string technique is an alternative option for sulcus IOL implantation in absence of capsular support, allowing lens centration adjustment with no additional risks

Biometric measurements in the crystalline lens: applications in cataract surgery

En esta tesis, hemos desarrollado una nueva metodología para medir el desalineamiento de la IOL implantada en pacientes con cirugía de cataratas a partir de imágenes de OCT en-face del segmento anterior. También hemos cuantificado la forma y la topografía 3D del cristalino del ojo in vivo, sus propiedades ópticas y sus cambios con la anterior y posterior del cristalino, y cambios estructurales con la edad. La metodología de OCT cuantitativa y modelos de ojo personalizados en pacientes han sido validados en pacientes operados de cirugía de cataratas, mediante comparaciones de las aberraciones simuladas y medidas en los mismo pacientes, y han permitido comprender la contribución relativa de los factores ópticos geométricos y quirúrgicos relacionados con la calidad de la imagen, como la identificación del centrado óptimo de la IOL. Estos son clave en los cálculos avanzados de la potencia de la IOL, la optimización de la selección individual o diseño de IOLs personalizados que puedan proporcionar una solución visual óptima al paciente.Departamento de Cirugía, Oftalmología, Otorrinolaringología y FisioterapiaDoctorado en Ciencias de la Visió

Evaluating techniques to improve visual performance with and assessment of premium intraocular lenses

Premium Intraocular Lenses (IOLs) such as toric IOLs, multifocal IOLs (MIOLs) and accommodating IOLs (AIOLs) can provide better refractive and visual outcomes compared to standard monofocal designs, leading to greater levels of post-operative spectacle independence. The principal theme of this thesis relates to the development of new assessment techniques that can help to improve future premium IOL design. IOLs designed to correct astigmatism form the focus of the first part of the thesis. A novel toric IOL design was devised to decrease the effect of toric rotation on patient visual acuity, but found to have neither a beneficial or detrimental impact on visual acuity retention. IOL tilt, like rotation, may curtail visual performance; however current IOL tilt measurement techniques require the use of specialist equipment not readily available in most ophthalmological clinics. Thus a new idea that applied Pythagoras’s theory to digital images of IOL optic symmetricality in order to calculate tilt was proposed, and shown to be both accurate and highly repeatable. A literature review revealed little information on the relationship between IOL tilt, decentration and rotation and so this was examined. A poor correlation between these factors was found, indicating they occur independently of each other. Next, presbyopia correcting IOLs were investigated. The light distribution of different MIOLs and an AIOL was assessed using perimetry, to establish whether this could be used to inform optimal IOL design. Anticipated differences in threshold sensitivity between IOLs were not however found, thus perimetry was concluded to be ineffective in mapping retinal projection of blur. The observed difference between subjective and objective measures of accommodation, arising from the influence of pseudoaccommodative factors, was explored next to establish how much additional objective power would be required to restore the eye’s focus with AIOLs. Blur tolerance was found to be the key contributor to the ocular depth of focus, with an approximate dioptric influence of 0.60D. Our understanding of MIOLs may be limited by the need for subjective defocus curves, which are lengthy and do not permit important additional measures to be undertaken. The use of aberrometry to provide faster objective defocus curves was examined. Although subjective and objective measures related well, the peaks of the MIOL defocus curve profile were not evident with objective prediction of acuity, indicating a need for further refinement of visual quality metrics based on ocular aberrations. The experiments detailed in the thesis evaluate methods to improve visual performance with toric IOLs. They also investigate new techniques to allow more rapid post-operative assessment of premium IOLs, which could allow greater insights to be obtained into several aspects of visual quality, in order to optimise future IOL design and ultimately enhance patient satisfaction

Evaluation of modern intraocular lenses

Accommodating Intraocular Lenses (IOLs), multifocal IOLs (MIOLs) and toric IOLs are designed to provide a greater level of spectacle independency post cataract surgery. All of these IOLs are reliant on the accurate calculation of intraocular lens power determined through reliable ocular biometry. A standardised defocus area metric and reading performance index metric were devised for the evaluation of the range of focus and the reading ability of subjects implanted with presbyopic correcting IOLs. The range of clear vision after implantation of an MIOL is extended by a second focal point; however, this results in the prevalence of dysphotopsia. A bespoke halometer was designed and validated to assess this photopic phenomenon. There is a lack of standardisation in the methods used for determining IOL orientation and thus rotation. A repeatable, objective method was developed to allow the accurate assessment of IOL rotation, which was used to determine the rotational and positional stability of a closed loop haptic IOL. A new commercially available biometry device was validated for use with subjects prior to cataract surgery. The optical low coherence reflectometry instrument proved to be a valid method for assessing ocular biometry and covered a wider range of ocular parameters in comparison with previous instruments. The advantages of MIOLs were shown to include an extended range of clear vision translating into greater reading ability. However, an increased prevalence of dysphotopsia was shown with a bespoke halometer, which was dependent on the MIOL optic design. Implantation of a single optic accommodating IOL did not improve reading ability but achieved high subjective ratings of near vision. The closed-loop haptic IOL displayed excellent rotational stability in the late period but relatively poor rotational stability in the early period post implantation. The orientation error was compounded by the high frequency of positional misalignment leading to an extensive overall misalignment of the IOL. This thesis demonstrates the functionality of new IOL lens designs and the importance of standardised testing methods, thus providing a greater understanding of the consequences of implanting these IOLs. Consequently, the findings of the thesis will influence future designs of IOLs and testing methods

A Numerical Exploration of the Crystalline Lens: from Presbyopia to Cataracts and Intraocular Lenses

Esta tesis aborda, de forma numérica, la resolución de tres problemas relacionados con el cristalino. En primer lugar, se ha construido un modelo de elementos finitos del cristalino humano para abordar la simulación de la acomodación, gracias a la incorporación de la contracción muscular del músculo ciliar. El modelo se ha validado con resultados experimentales comparando con Ramasubramanian & Glasser, 2015. Con el mismo modelo, se ha estudiado como afecta el cambio de las propiedades mecánicas de los tejidos del cristalino en la pérdida de amplitud de la acomodación con la edad para entender si la rigidización de los tejidos juega un papel importante en la presbicia. La conclusión principal del estudio numérico ha sido que las propiedades mecánicas y tensiones iniciales de la cápsula del cristalino proporciona la fuerza necesaria para acomodar, es decir, cambiar su curvatura para enfocar de cerca. Especificamente, el ratio de rígidez entre el núcleo y el cristalino gobierna cómo el cristalino cambia de forma. Con la edad, se produce una rigidización del núcleo, y el incremento de la relación entre ambas rigideces (núcleo y corteza) podría ser el principal responsable de la pérdida de la amplitud de acomodación con la edad. En segundo lugar, se ha estudiado la estabilidad biomecánica de diferentes diseños de lentes intraoculares (IOL). Las IOLs sustituyen las funciones del cristalino en pacientes con cataratas, es por ello necesario garantizar su estabilidad en el interior del saco para garantizar una visión adecuada. Entre los aspectos estudiados destaca la caracterización mecánica de los materiales acrílicos con los que se fabrican las lentes. Para ello, se han combinado ensayos uniaxiales con ensayos de indentación. Éstos últimos se han utilizado para caracterizar la respuesta visco-elástica del material. El definir la respuesta del material mediante modelos visco hiperelásticos es necesario para posteriormente analizar la estabilidad de la IOL mediante elementos finitos. Este análisis se ha defino a dos niveles, en un primer nivel se analiza la estabilidad de la IOL simulando el ensayo establecido en la norma ISO 11979-3:2012. Esta norma es de obligado cumplimiento para los fabricantes antes de introducir un nuevo diseño en el mercado. Se ha realizado un estudio estadístico para estudiar el efecto de la geometría de los hápticos tipo C-loop en la estabilidad mecánica de la IOL, obteniendo que el entronque, la unión entre el háptico y la lente, es el parámetro más influyente. Para validar la metodología numérica, se fabricaron varios diseños y se analizaron experimentalmente para comparar los resultados correspondientes con biomarcadores mecánicos (desplazamiento axial, rotación y la inclinación de la IOL) que están relacionados con la calidad visual resultante de la IOL. En un segundo nivel, se ha simulado la respuesta de la IOL en el interior del saco capsular, estudiando la influencia de diferentes parámetros del paciente, como geometría y propiedades mecánicas del saco. También se ha analizado la influencia de parámetros de la cirugía de la catarata, como es el diámetro y posición de la capsulorexis. En este último nivel, se ha estudiado tanto la respuesta instantánea, es decir, tras la cirugía, como a largo plazo, cuando sucede la huella de fusión (fusion footprint) entre la cápsula y la IOL. Para que los modelos computacionales sean de ayuda a los cirujanos o puedan servir en tiempo real, se ha planteado una metodología basada en inteligencia artificial. En este caso la base de datos de partida corresponde a modelos numéricos altamente fiables y con ellos, se genera datos con los que se entrena la red neuronal. En esta tesis, se estudia la estabilidad de la IOL en función del diámetro de compresión del paciente y la edad, que a su vez influye en las propiedades mecánicas del saco. Por último, se ha evaluado experimentalmente la influencia del material de la IOL (hidrófobo o hidrofílico) y su geometría durante la inyección de la IOL en el saco, registrando la fuerza de inyección que debe realizar el cirujano. De cara a evitar complicaciones (se dañe la IOL o el tejido corneal) durante la cirugía, es conveniente que la fuerza a ejercer sea baja. Se ha comprobado que su valor está fuertemente influenciado por el material de la lente.¿Por qué el cristalino es de vital importancia?El cristalino es el responsable tanto del cambio dinámico de la potencia refractiva del ojo a través del mecanismo de acomodación como de la corrección de las aberraciones de la córnea. El cambio óptico dinámico es consecuencia de un cambio geométrico del cristalino. Sin embargo, a medida que el cristalino envejece, disminuye este cambio óptico dinámico y se opacifica, lo que da lugar a las dos patologías comúnmente asociadas al envejecimiento como es, la presbicia y las cataratas. Por este motivo, en esta tesis doctoral se ha profundizado en el estudio mecánico del cristalino y tras su sustitución mediante una lente intraocular artificial durante la cirugía de catarata. La metodología establecida pueden ayudar en un futuro tanto al diseño de nuevos implantes como a los oftalmólogos a seleccionar la IOL adecuada a cada paciente para mejora su calidad visual.This thesis addresses three different case studies related to the crystalline lens. Firstly, the mechanical causes of the loss of accommodation amplitude with age, called presbyopia, were analysed through the finite element method. A high-fidelity simulation of the mechanism of accommodation including the contraction of the ciliary muscle was developed. This allowed us to analyse accommodation in depth, showing that although the lens capsule provides the force to accommodate, the stiffness ratio between the lens cortex and lens nucleus could have a higher effect on how the lens changes its shape. Secondly, the biomechanical stability of intraocular lenses (IOLs) was analysed. IOLs are essential for post-cataract patients as they substitute the functions of the crystalline lens. In this thesis, a wide variety of solutions were addressed: from the visco- and hyper-elasticity characterisation of IOL acrylic materials from depth sensing indentation and uniaxial tests to the simulation of the IOL biomechanical stability inside the capsular bag. We also performed a high-fidelity simulation of the IOL compression standards tests required by the IOLs to be commercialised and the results obtained were compared with clinical data. Lastly, we developed a patient-specific methodology to customise the IOL haptic design. Most of the numerical methology developed is intended to be used in the IOL pre-design phase to avoid costs and time. Thirdly, the IOL delivery during cataract surgery according to haptic and material design and injector characteristics was experimentally studied to avoid any possibility of IOL and eye damage. Apart from the injector size, the IOL material was the most influential parameter in the force exerted in IOL delivery. Why is the crystalline lens of vital importance? The crystalline lens is the responsible for both the dynamic change of the refractive power of the eye through the mechanism of accommodation and the correction of cornea aberrations. The dynamic optical change is consequence of change of the lens shape. However, as the lens ages over time, it decreases this dynamic optical change and becomes cloudy, what leads to the two most common lens-related pathologies, presbyopia and cataracts. Therefore, it is of utmost importance to study the lens mechanics and all issues related to the artificial intraocular lens that substitutes the lens during cataract surgery.<br /

Intraocular Lens

The first clinical application of intraocular lens (IOL) goes back to 1949 when Dr. Harold Ridley successfully implanted a PMMA IOL into an eye on 29 November 1949. This innovation is a big step forward for cataract surgery. With development of the IOL material and biocompatibility, more and more IOL types have been used in clinical ophthalmology. This book is the fruit of worldwide cooperation between clinical teams. In this book we discuss the IOL materials and design, aberration and astigmatism correction with IOL, entopic phenomenon of IOL, myopia and phakic IOL, and secondary IOL techniques. We believe that this content provides the readers with a comprehensive knowledge of the latest developments of IOL

Optical impact of correcting elements

Elementos correctores tales como lentes intraoculares (LIO) y lentes de contacto (LC) se usan comúnmente en oftalmología para corregir los errores de refracción, la presbicia y las cataratas. Por ello, estos elementos ópticos están en el centro de la investigación científica y el desarrollo. El impacto óptico de estos elementos es el tema principal de esta tesis doctoral. El impacto óptico se refiere a los resultados ópticos que inducen estos elementos en el sistema óptico del ojo humano. El impacto visual también se simula y se calcula con el fin de encontrar las diferencias entre la óptica y la calidad visual de un modelo de ojo humano con diferentes elementos correctores. Por lo tanto, la presente tesis versa sobre el desarrollo de modelos utilizando simulaciones en un entorno de programación para abordar el impacto óptico y visual de los elementos ópticos aplicados en las discapacidades relacionadas con el envejecimiento y proponer alternativas a los enfoques actuales. Todos los diseños de esta tesis son acerca de LIOs y LCs que están diseñadas siguiendo características generales y no siguiendo pautas específicas de una patente o un elemento que está protegido por derechos de autor. En el primer capítulo hay una introducción general del tema. Hay información sobre la biología del ojo humano y sus diferentes partes. Hay una descripción de la función acomodativa y cómo se ve afectada por la presbicia. Al final se enumeran algunos métodos de corrección de la presbicia tales como LIOs y LCs. También hay una breve descripción sobre los modelos de ojo humano en general. En el segundo capítulo, hay un estudio comparativo sobre los modelos de ojo humano que se utilizan en las ciencias de la visión. En este capítulo, se hace una comparación entre tres modelos de ojo teóricos, los modelos de ojos de Navarro, el de Arizona y el de Liou-Brennan. La comparación es acerca de la capacidad de estos modelos para simular la acomodación y si los resultados que producen son los mismos o si hay diferencias y dónde se produces éstas. En el tercer capítulo, se realiza un estudio sobre la distribución de la potencia dióptrica entre las superficies anterior y posterior de una LIO monofocal. En este capítulo se comprueba si la superficie anterior o posterior de una LIO es óptima para llevar la mayor cantidad de potencia dióptrica de la LIO. También se comprueba en cuál de las dos superficies de una LIOS asférica tiene que ser diseñada la asfericidad para una mejor calidad óptica. En el cuarto capítulo se lleva a cabo un estudio sobre los resultados ópticos y visuales. El estudio trata sobre LIOs monofocales diseñadas en modelos de ojos humanos personalizados. La personalización está en la superficie corneal anterior que se altera con datos topográficos de pacientes reales. Las LIOs se combinan con diseños de LCs y sus diseños están optimizados o no con el fin de probar la diferencia entre sus impactos. También hay un estudio de diferentes desajustes tales como descentramientos e inclinaciones con el fin de probar la tolerancia de los diseños en tales condiciones. En el quinto capítulo, hay una continuación del estudio anterior. Las LIOs bifocales difractivas están diseñadas en el mismo grupo de modelos de ojos humanos personalizados y se comparan los resultados ópticos y visuales. Las LIOs se prueban sin la combinación de LCS en este estudio. También hay una comparación de diferentes desajustes (descentramientos e inclinaciones) con el fin de comparar la tolerancia de los diseños en tales condiciones para distancias de lejos y cerca. Y finalmente en el sexto capítulo se diseña un sistema telescópico intraocular con diferente posicionamiento en el modelo del ojo. La posición del telescopio cambia los resultados ópticos y visuales producidos. También hay una comparación del desajuste entre los diseños que comprueba la calidad de la imagen proyectada en la retina.Correcting elements such as intraocular lenses (IOL) and contact lenses (CL) are commonly used in ophthalmology in order to correct refractive errors, presbyopia and cataract. Thus, these optical elements are in the center of scientific research and development. The optical impact of these elements is the main subject of this Doctoral Thesis. The optical impact refers to the optical results that these elements induce in the optical system of the human eye. The visual impact is also simulated and calculated in order to find the differences between the optical and the visual quality of a human eye model with correcting elements. Thus, then present Thesis is about developing models using simulations in a computer-programming environment to address the optical and visual impact of optical elements applied in elderly-related disabilities and to propose alternatives to current approaches. All the designs in this Thesis are about IOLs and CLs that are designed following general characteristics and not specific guidelines of a patent or an element that is copyrighted. In the first chapter, there is a general introduction of the topic. There is information about the human eye biology and its different parts. There is a description of the accommodation function and how is affected by presbyopia. In the end there are listed some methods of correction of the presbyopic effects, such as IOLs and CLs. There is also a short description about the human eye models in general. In the second chapter, there is a comparative study about human eye models that are used in vision sciences. In this chapter, a comparison between three theoretical eye models is done, the Navarro, the Arizona and the Liou-Brennan eye models. The comparison is about the ability of these models to simulate accommodation and if the results that they produce are the same or if there are differences and where these differences are due to. In the third chapter, there is a study about the dioptric power distribution between the anterior and posterior surfaces of a monofocal IOL. In this chapter is tested whether the anterior or the posterior surface of an IOL is optimal to carry the largest amount of dioptric power of the IOL. It is also tested on which of the two surfaces the asphericities of an aspheric IOL have to be designed for better optical quality. In the fourth chapter, a study about optical and visual results is taking place. The study is about monofocal IOLs that are designed in customized (personalized) human eye models. The customization is on the anterior corneal surface that is altered with topographic data from real patients. The IOLs are combined with CLs designs and their designs are either optimized or non-optimized, in order to test the difference between their impacts. There is also a study of different misalignments such as decentrations and tilts, in order to test the tolerance of the designs in such conditions. In the fifth chapter, there is a continuation of the previous study. Diffractive bifocal IOLs are designed in the same group of personalized human eye models and the optical and visual results are compared. The IOLs are tested without the combination of CLs in this study. There is also a comparison of different misalignments (decentrations and tilts) in order to compare the designs’ tolerance in such conditions for far and near target distances. And finally in the sixth chapter, an intraocular telescopic system is designed with different positioning in the eye model. The position of the telescope changes the optical and visual results produced. There is also a misalignment comparison between the designs that tests the image projection quality on the retinal plane of the model

Aspheric intraocular lens in cataract surgery

This thesis, by prior publication, encompasses an overview and critical analysis of 6 publications on aspheric intraocular lenses (IOLs) carried out at St. Thomas’ Hospital, Guy’s & St. Thomas’ NHS Foundation Trust, London between 2006 2012. The focus is on two areas: the visual and optical performance of aspheric IOLs with different values of asphericity, and their effect on posterior capsule opacification (PCO). Chapter 1 describes the history of IOLs and the evolution of aspheric IOLs. It also presents relevant optical concepts. The three publications presented in Chapter 2 compare aspheric IOLs with spherical IOLs. The results come from two prospective, randomised, fellow-eye comparison studies: one comparing a spherical Alcon AcrySof SN60AT versus the aspheric Alcon AcrySof SN60WF (with negative asphericity), which partially corrects corneal spherical aberrations, and the other comparing the Zeiss AcriSmart 36A (with negative asphericity), which partially corrects corneal spherical aberrations, and the Bausch & Lomb Akreos MI60 (with neutral asphericity), which has zero spherical aberration. The third publication reports changes in vertical coma after implantation of all the above lenses and additionally includes data on two spherical IOLs from a previous study by our group (the three piece Alcon MA60AC IOL and the plate haptic HumanOptic MC611MI IOL). For this study, the data were divided according to their asphericity and not design. To avoid confounding from aberrometric differences due to astigmatism and surgical techniques, standard incision sizes of 2.75 mm and 2.4 mm were used in the two felloweye, randomised studies and a single surgeon performed all the surgeries using same incision size for each study. Results demonstrated that the aspheric IOLs significantly reduced spherical aberration, improved mesopic contrast sensitivity and reduced depth-of-focus. Asphericity differences up to 20 μm were not associated with depth-of-focus and the degree of asphericity was not associated with best-corrected distance visual acuity. The vertical coma varied within IOL groups of the same asphericity but there was no statistically significant difference between the two spherical IOLs (AcrySof SN60AT and AcrySof MA60AC). Further critical analysis of our data already published showed no statistically significant difference in mean vertical coma between the AcrySof MA60AC (-0.060 ± 0.211μm) with that of Akreos MI60 (- 0.042 ± 0.148μm) (p=0.70) and AcriSmart 36A (-0.034 ± 0.141μm) (p=0.58) even though the AcrySof MA60AC, Akreos MI60 and AcriSmart 36A IOLs had different asphericity. This may be due to the difference in the IOL designs, decentration and difference in the sample sizes between groups. Chapter 3 discusses the findings of three publications related to posterior capsule opacification (PCO). The first publication is an in vitro study assessing posterior optic square edges of various commercially available spherical and aspherical IOLs. Results demonstrated hydrophilic IOLs had less sharp square edges compared to hydrophobic IOLs. Although these in vitro results are potentially significant, there are currently no in vivo studies on the lenses used to compare our results with. The other two publications are based on the PCO outcomes from the prospective, randomised, fellow-eye studies described above. There was no difference in the PCO rates between hydrophobic spherical AcrySof SN60AT and aspheric AcrySof SN60WF IOLs of the same design at 2 years. In contrast, we found a significant increase in the PCO with both the hydrophilic acrylic AcriSmart 36A and Akreos MI60 IOLs (one with negative asphericity and one with neutral asphericity). Variation in asphericity did not appear to be an important factor contributing to the PCO but it was apparent that the edge design and material of the IOL were important with regards to the PCO formation. Finally, since these publications, some of manufacturers have changed their IOL models and today a majority of the IOLs have are aspheric and have a sharp edge profile. The overall, benefit of using aspheric IOLs seems to be limited as it is dependent on the natural pupil size