Intraocular lens (IOL) is an artificial lens implanted into the eye in order to restore correct vision after the removal
of natural lens cloudy due to cataract. The IOL prolonged stay in the eyeball causes the creation of different changes
on the surface and inside the implant mainly in form of small-size local defects such as vacuoles and calcium deposites.
Their presence worsens the imaging properties of the eye mainly due to occurence of scattered light thus deteriorating
the vision quality of patients after cataract surgery. It is very difficult to study influence the effects of these changes
on image quality in real patients. To avoid these difficulties two other possibilities were chosen: the analysis of the image
obtained in an optomechanical eye model with artificially aged IOL as well as numerical calculation of the image
characteristics while the eye lens is burdened with adequately modeled defects.
In experiments the optomechanical model of an eye consisting of a glass “cornea”, chamber filled with liquid
where the IOL under investigation was inserted and a high resulution CCC detector serving as a “retina” was used.
The Modulation Transfer Function (MTF) of such “eye” was evaluated on the basis of image of an edge. Experiments
show that there is significant connection between ageing defects and decrease in MTF parameters.
Numerical part was performed with a computer programme for optical imaging analysis (OpticStudio Professional,
Zemax Professional from Radiant Zemax, LLC). On the basis of Atchison eye model with lens burdened with defects
Modulation Transfer Functio was calculated. Particular parameters of defects used in a numerical model were based
on own measurements. Numerical simulation also show significant connection between ageing defects and decrease
of MTF parameters. With this technique the influence of types, density and distribution of local defect in the IOL
on the retinal image quality can be evaluated quickly without the need of performing very difficult and even dangereous
experiments on real human patients.
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.
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.
Investigation of children vision is one of the most important tasks in pediatric medical care. According to World Health Organization screening done with rapid and simple tests should be considered as initial step of such care. Thanks to simple screening tests it is possible to identify children who probably are burden with eye problems and to distinguish them from the children with correct vision.
Typical test for screening 6-years-old children (beginning their school education) includes, among others, evaluation of visual acuity for far and/or near and evaluation of binocular vision.
This contribution describes the methods and results of screening program covering 21 elementary schools and 450 children in Strzelin County (Lower Silesia). Visual acuity was measured with help of SCOLATESTTM and binocular vision with RANDOM DOT E STEREOTEST. Additionally color recognition was tested with Ishihara Children Plates. The results suggest that almost 29% of investigated children have refraction error (9% being myopes and 20% being hyperopes), and 9% has problems with binocular vision.
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 diffractive structure (holographic lens: HL, diffractive optical element: DOE) can be included into compound
objective as one of its parts making a hybrid objective.
In this paper a possibility of correcting field aberrations in a triplet hybrid objective is analyzed. The solutions for
aplanatic correction in the case of achromate, apochromate and quasi-superachromate are presented and illustrated with
exemplary objectives. Correction of field curvature is considered in the case of hybrid triplet achromate.
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 simplest achromatic hybrid lens consists of a refractive (glass) lens with a diffractive microstructure deposited on one of its surfaces. In such lens the reasonable aberration correction is possible only for very limited aperture and field angles. Better possibilities of aberration correction appear if we split the refractive lens onto two identical parts separated by certain distance and locate the diffractive element between the glass lenses. We show that in such way it is possible to obtain hybrid lens of the same or even smaller aberrations for substantially greater aperture and field angles.
Visual quality depends on many factors of different nature and therefore it is not easy to define. Different measures are used to describe vision quality, such as: two point resolution, visual acuity, contrast sensitivity function (CSF) etc. We concentrate especially on CSF. There are two important factors affecting character of CSF. One of them is connected with the Optical Transfer Function (OTF) of the eye and the second one with the retinal response. Typically CSF is measured in incoherent light. Due to it is dependence on both mentioned above factors simultaneously it is impossible to extract the information on the eye optical system only. We hope that additional information offered by CSF measured in coherent light can help to solve this problem.
Spectacle lens is a very particular optical imaging element of great practical importance. Although its construction is very simple some demands are specific (in particular remarkable shift of output pupil). A number of classic spectacle lens designs is known for long time, however some new possibilities of aberration correction appear if we use a hybrid (diffractive refractive). Hybrid lens is an optical system composed of a classic refractive (glass) lens and a diffractive microstructure deposited on one of its surfaces. Imaging properties of such lens can be expressed in terms of dimensionless parameters(formula available in paper)(describing the distribution of focusing power between diffractive and refractive part). By proper choice of parameter η we can compensate chromatic aberration. Thanks to other free parameters
spherical aberration and astigmatism can be corrected also what is reasonable choice for spectacle lens. In this contribution the possibilities of particular Seidel aberration correction of hybrid lens will be presented. As an illustration some examples of spectacle hybrid lenses will be shown and its imaging characteristics compared with imaging characteristics of commercially available refractive lenses.
In ophthalmology and optometry a number of measures are used for describing quality of human vision such as resolution, visual acuity, contrast sensitivity function, etc. In this paper we will concentrate on the vision quality understood as a resolution of periodic object being a set of equidistant parallel lines of given spacing and direction. The measurement procedure is based on presenting the test to the investigated person and determining the highest spatial frequency he/she can still resolve. In this paper we describe a number of experiments in which we use test tables illuminated with light both coherent and incoherent of different spectral characteristics. Our experiments suggest that while considering incoherent polychromatic illumination the resolution in blue light is substantially worse than in white light. In coherent illumination speckling effect causes worsening of resolution. While using laser light it is easy to generate a sinusoidal interference pattern which can serve as test object. In the paper we compare the results of resolution measurements with test tables and interference fringes.
Human beings receive predominant percentage of the information about the environment thanks to their sense of vision. Therefore the vision quality is one of the most important parameters determining our well-being. By the vision quality we understand the possibility of perceiving light and darkness, colors and shadows, differentiating details form background and recognition of various objects. Vision quality depends on number of factors connected with the optical system of an eye, the light detection by retina, transmission of neural signals from eye to brain and the psychological process of signal interpretation. Vision quality is thus a complex idea.
The computer method of visual acuity measurement is described in the paper. Optotypes of different size and orientation are presented to the subject who answers if he recognizes them or not. Basing on the subject's answers, recorded by computer, we construct psychometric function from which we calculate parameters describing VA. The method can be used in investigation of the accommodation or changes in overall state of the subject.
Hybrid lens is a classic two-spherical glass lens with a diffractive microstructure deposited on one of its surfaces. The imaging properties of such lens depend on four parameters: two radii of curvature of both surfaces constituting two-spherical and two parameters describing the geometry of diffractive microstructure. The III-order aberration coefficients depend explicit on those parameters. Additionally the location of input pupil alters also the expression for aberrations. By proper choice of the said parameters it is possible to construct achromatic hybrid lens with corrected spherical aberration and coma, astigmatism or field curvature alternatively. In the paper we present the algorithm of necessary calculations and illustrate the results with such image characteristics as spot diagrams, wave aberrations or point spread function of the exemplary lenses.
Diffractive optics is more and more widely used nowadays. One of its most important applications is diffractive imaging element (DIE). The DIE can be a lens (Holo-lens, diffractive lens, hybrid lens) or a part of complex imaging system (e.g. an aberration corrector). Apart of such problems occurring when dealing with DIE as its design, manufacture or copying the problem of its control is important. By this we mean the measurement of wavefront generated by DIE, i.e. the evaluation of wavefront aberrations. To this aim we propose two different experimental methods: one of them employs diffraction interferometer, the other one holographic shearing interferometer.
The possibilities of aberration correction in the case of a single lens are limited. It is well known that, if classic glasses are used, it is impossible to compensate spherical aberration. It can be, however, minimized by proper choice of the ratio between the first and second surface radii of curvature (referred here as (zetz) ). It is possible also, in cost of uncorrected spherical aberration, to compensate III order coma. Additional possibilities of aberration correction occur, however, if a thin diffractive structure is deposited on one of the lens surface. Such lens is usually referred as a hybrid (diffractive-refractive) lens. The diffractive structure typically corresponds to the holographic lens generated by the interference of two spherical waves. The ratio of these waves radii of curvature is treated as a parameter (called here (beta) ) describing fully aberration properties of this structure. A focusing power of the diffractive part typically is only a small fraction ((eta) ) of total focusing power of a hybrid lens, so the diffractive part acts mainly as aberration corrector. Aberration properties of hybrid lens are determined by two parameters: (zetz) and (beta) so it is possible to achieve simultaneous correction of aperture aberrations: spherical aberration and coma. In the paper formulas describing the III-order aberration coefficients were used for calculating the values of parameters (zetz) and (beta) assuring such correction for several values of parameter (eta) and different locations of object plane. The calculations were performed with help of the MATHCAD programme. Basing on the results a number of hybrid lenses (collimating and imaging) were designed. Their imaging quality was then evaluated by numerical calculation of aberration spots. Estimated values of such image characteristics as the aberration spot moment of inertia or third order moment of the spots distribution enable to compare the imaging quality.
In the case of a single-element imaging system, aplanatic correction is of major importance. It can be achieved for single holographic lens, if recorded on a spherical surface. For this reason, however, a diffractive microstructure of high spatial frequency has to be recorded. From technological point of view, a combination of classic, glass lens giving most part of overall refractive power with a diffractive structure of relatively low spatial frequency acting as an aberration corrector seems to be more advantageous. In this paper the possibility of aplanatic correction if assuming that the object point is located in infinity and both refractive surfaces are spherical is analyzed.
In the case of a simple, one-piece optical imaging element the possibility of aplanatic correction is important. Such a correction can be obtained for a single holo-lens recorded on spherical surface. This needs, however, relatively high spatial frequency to be recorded. From the technological point of view the combination of classic spherical lens with a diffractive structure of relatively low spatial frequency seems much more convenient. Such hybrid lens is a single element consisting of diffractive and refractive parts. Even if one of the lens surfaces is flat (and on this surface the diffractive structure is deposited) it is possible to obtain the aplanatic correction for selected locations of the object point.
Third order aberrations of the hybrid (glass-holographic) lenses with spherical and plano-convex surfaces and pupil in contact are considered. The paper includes some analytical results obtained by computer ray tracing method.
Personal computers cause wide use of numerical methods for analysis of optical systems. The very important feature of algorithms applied for this purpose is their time efficiency. A fast algorithm for investigating the image quality of the hybrid lenses (i.e. glass lenses with hologram structure deposited on one of its surfaces) is presented in this paper.
A single holographic lens recorded with spherical waves can be used as a satisfactory Fourier transforming lens. By proper choice of the input pupil location where the object transparency illuminated with parallel light beam is placed a Fourier spectrum of this object free from spherical aberration and astigmatism can be obtained. The influence of the remaining coma is negligible if the relative aperture is not too high. It is also possible to diminish coma by recording the holographic lens on a spherical surface. However, full coma correction is not desirable, because compensation of distortion is then impossible. The uncompensated distortion leads to the deformation of the Fourier transform scale, but this fault is easy to correct by simple re-scaling at the recording step or subsequent image processing.
Diffractive lenses can be obtained by recording the interference pattern originated by interference of two different spherical waves. The imaging quality of such optical elements usually is described in terms of III-order aberrations. The aberration coefficients depend on the radii of curvature of waves used for the lens recording and location of its input pupil. The imaging quality also depends on such factors as image contrast and background illumination level (due to scattered light). Those factors do not result from aberrations, but are dependent on the type of recording process. Namely, light diffraction occurs on the system of fringes of profile depending on the transmittance-versus-exposure characteristics of the recording material. Several types of lenses including kinoform, linear, nonlinear, and binary amplitude, as well as linear and binary phase diffractive lenses of the same III-order aberrations, are investigated. Point spread function and incoherent transfer function numerically calculated are compared. The other factor influencing the imaging quality is modulation transfer function of the recording material. The different local spatial frequency of the diffractive lens microstructure corresponds to the different local diffraction efficiency. This effect is similar to apodising and also can change the imaging characteristics. Four typical material modulation transfer functions are considered: linear, parabolic, hyperbolic, and band-pass -- typical for photothermoplastics. The resulting point spread functions and incoherent transfer functions are calculated for diffractive lenses with aberrations: one having uncompensated astigmatism, the other with considerable coma.
The imaging quality of holographic lenses depends on parameters that include the shape of a holographic lens surface or an input pupil position. Based on the formulas for third-order aberration coefficients derived for such cases, conditions that ensure the correction of aperture and field aberrations are given. The possibility of joint correction of spherical aberration, coma, and astigmatism is discussed. The formulas presented are illustrated with a number of examples; two types of holo-lenses are taken into account: imaging and focusing. For imaging quality assessment an aberration spot calculation method based on numerical evaluation of an appropriate diffraction integral is used. The results of this method are compared with the results of imaging quality estimation using the geometrical ray tracing method.
Holographic optical elements (HOEs) become more and more important in modern optics. The most important application of HOEs is a holographic lens working as an imaging element. It is often used in monochromatic light because in polichromatic light the image location strongly depends on wavelength, which is usually a great disadvantage. However, in some cases this drawback can be changed into an advantage when a spectral device is regarded. This single diffractive lens can be applied as a basic element of monochromator or spectroscope. In a spectroscope, an input slit is illuminated by polichromatic light of which the spectral content is to be investigated. Each wavelength is focused into a different point and can be observed at the same time. For spectroscopy of good quality all light spots should be small and spatially separated. There are some difficulties in obtaining such spots sensibly separated along direction different from an optical axis. This difficulty disappears when we regard a monochromator. In a monochromator an input slit is illuminated by the light of continuous spectrum. Each wavelength is focused in a different point along optical axis. By moving an output slit one can choose an image of proper wavelength. For reasons stated above our investigations are limited to the monochromator. To establish optimum geometry parameters of this device it is necessary to analyze the sphero-chromatic aberration of a single holo- lens.
The possibility of application of a holographic lens for Fourier spectrum analysis is discussed. A set of parameters describing a holo-lens, including location of its input pupil and curvature of its surface, are proposed according to the results of III order aberration analysis. Recording holo-lens on spherical surface creates the possibility of coma correction. The assumption that the input pupil is not in contact with the lens (as it is the case of Fourier transforming setup) enables change in astigmatism, field curvature, and distortion; the latter being very important for the lens used in Fourier spectrum analysis. The imaging quality of the proposed lens was investigated numerically by evaluating aberration spots for different spatial frequency components.
In studying the imaging quality of holographic lenses, many studies confine their scope to the examination of the third-order aberration theory and pay special attention to the possibility of coma correction. By a suitable choice of the recording geometry of the holo-lens it is possible to obtain aplanatic correction. However, the analysis of imaging quality based on numerical modeling of imaging which enables calculation of the aberration spot shape suggests that such correction does not necessarily give satisfactory results. Better imaging quality can be obtained for the other (nonaplanatic) holo-lens of the same spherical aberration and astigmatism, in spite of some non-zero coma. Further improvement can be achieved by slight compensation of coma obtained by curving of the holo-lens substrate and simultaneous correction of astigmatism following from the input pupil shift. The conclusions are confirmed by calculated aberration spots and incoherent transfer functions.