Intraocular lenses (IOLs) are used in the cataract treatment for surgical replacement of the opacified crystalline lens. Before being implanted they have to pass the strict quality control to guarantee a good biomechanical stability inside the capsular bag, avoiding the rotation, and to provide a good optical quality. The goal of this study was to investigate the influence of the material and haptic design on the behavior of the IOLs under dynamic compression condition. For this purpose, the strain–stress characteristics of the hydrophobic and hydrophilic materials were estimated experimentally. Next, these data were used as the input for a finite-element model (FEM) to analyze the stability of different IOL haptic designs, according to the procedure described by the ISO standards. Finally, the simulations of the effect of IOL tilt and decentration on the optical performance were performed in an eye model using a ray-tracing software. The results suggest the major importance of the haptic design rather than the material on the postoperative behavior of an IOL. FEM appears to be a powerful tool for numerical studies of the biomechanical properties of IOLs and it allows one to help in the design phase to the manufacturers.
Intraocular lens (IOL) is an artificial implant substituting natural crystalline lens which is non-transparent due to cataract. Incorrect location of the IOL in the eyeball (e.g. its shift or tilt) causes significant deterioration of patient’s vision. The analysis of Purkinje images (i.e. reflections from successive refracting surfaces in the eye) enables to determine the real IOL location and thus helps in evaluating the retinal image quality. The experimental setup for Purkinje images recording consists of illuminator, composed of a number of infrared LEDs, telecentric lens and detector (CCD camera). Analysis of mutual position of particular reflections enables to evaluate the lens location in respect to the corneal axis. The actual measurements are realized on artificial eye model, what allows to estimate the precision of the algorithm applied in the calculations. In the future the experimental set-up will be adapted to measure the eyes of real patients.
An optomechanical model of human eye containing artificial cornea and a cuvette with immersion liquid is developed.
An artificial implantable intraoculer lens (IOL) inserted into the cuvette stands for the eye crystalline lens. A special
mechanical handle holding the IOL enables to move and rotate it thus simulationg possible errors during lens
implantation procedure. The "retinal" image is recorded with the high resolution CCD camera. The image of Siemens
star serves as qualitative measure of "retinal" image, while more quantitatively data come from Modulation Transfer
Function obtained by the analysis of the images of sinusoidal tests generated on the computer screen. The whole eye
model can be used for investigation of the impact of type and location of the IOL on the optical performance.
Cataract is one of the most frequent reasons of blindness all around the world. Its treatment relies on removing the
pathologically altered crystalline lens and replacing it with an artificial intraocular lens (IOL). There exists plenty
of types of such implants, which differ in the optical materials and designs (shapes). However one of the important
features, which is rather overlooked in the development of the intraocular implants is the chromatic aberration and its
influence on the retinal image quality. In this study authors try to estimate the influence of the design and optical
material of the implant on the retinal image quality in the polychromatic light, taking into consideration several
exemplary types of IOLs which are commercially available. Authors also propose the partially achromatized hybrid
IOLs, the longitudinal chromatic aberration (LCA)of which reduces the total LCA of the phakic eye to the level
of a healthy eye's LCA. Several image characteristics, as the polychromatic Point Spread Function (PSF) and
the Modulation Transfer Function (MTF) and the polychromatic encircled energy are estimated. The results of
the simulations show the significance of the partial chromatic aberration correction.
Cataract, or opacity of crystalline lens in the human eye is one of the most frequent reasons of blindness nowadays. Removing the pathologically altered crystalline lens and replacing it with artificial implantable intraocular lens (IOL) is practically the only therapy in this illness. There exist a wide variety of artificial IOL types on the medical market, differing in their material and design (shape).
In this paper six exemplary models of IOL's made of PMMA, acrylic and silicone are considered. The retinal image quality is analyzed numerically on the basis of Liou-Brennan eye model with these IOL's inserted. Chromatic aberration as well as polychromatic Point Spread Function and Modulation Transfer Function are calculated as most adequate image quality measures.
The calculations made with ZemaxTM software show the importance of chromatic aberration correction.
A typical proceeding in cataract is based on the removal of opaque crystalline lens and inserting in its place the artificial
intraocular lens (IOL). The quality of retinal image after such procedure depends, among others, on the parameters of the
IOL, so the design of the implanted lens is of great importance. An appropriate choice of the IOL material, especially in
relation to its biocompatibility, is often considered. However the parameter, which is often omitted during the IOL design is
its chromatic aberration. In particular lack of its adequacy to the chromatic aberration of a crystalline lens may cause
In order to fit better chromatic aberration of the eye with implanted IOL to that of the healthy eye we propose a hybrid - refractive-diffractive IOL. It can be designed in such way that the total longitudinal chromatic aberration of an eye with
implanted IOL equals the total longitudinal chromatic aberration of a healthy eye.
In this study we compare the retinal image quality calculated numerically on the basis of the well known Liou-Brennan
eye model with typical IOL implanted with that obtained if the IOL is done as hybrid (refractive-diffractive) design.
The influence of changes of both crystalline lens and intraocular lens (IOL) misalignment on the retinal image quality was investigated. The optical model of the eye used in investigations was the Liou-Brennan model, which is commonly considered as one of the most anatomically accurate. The original crystalline lens from this model was replaced with an IOL, made of rigid polymethylmethacrylate, in a way that recommend obligatory procedures. The modifications that were made both for crystalline lens and IOL were the longitudinal, the transversal, and the angular displacement.
The aim of our study was to define such shape of videokeratometric Placido disc based illuminator that would guarantee quasi flat image formation and due to that sharp and reliable information of corneal geometry receiving. The new shape of surface, which Placido rings would be painted on, is "cigar" like and was the result of our model study. Now analytical comparison with existing, commercially used videokeratometric illuminator was performed. Such cylindrical illuminator is used in the Tomey TMS-3 videotopographer. The study relied upon simple analytical path of rays calculations. The calculations were performed for 17 rays in inproportionate configuration at the entrance pupil plane. The results show the difference between image surfaces created by both illuminators on the average cornea. The image surface formed by introduced stimulator is much more flatter than the image of TMS-3 illuminator. This means that in order to receive sharp images providing reliable data, one can use the camera with smaller depth of sharpness.