Application of 3-Dimensional Printing Technology to Construct an Eye Model for Fundus Viewing Study

Objective

To construct a life-sized eye model using the three-dimensional (3D) printing technology for fundus viewing study of the viewing system.

Methods

We devised our schematic model eye based on Navarro''s eye and redesigned some parameters because of the change of the corneal material and the implantation of intraocular lenses (IOLs). Optical performance of our schematic model eye was compared with Navarro''s schematic eye and other two reported physical model eyes using the ZEMAX optical design software. With computer aided design (CAD) software, we designed the 3D digital model of the main structure of the physical model eye, which was used for three-dimensional (3D) printing. Together with the main printed structure, polymethyl methacrylate(PMMA) aspherical cornea, variable iris, and IOLs were assembled to a physical eye model. Angle scale bars were glued from posterior to periphery of the retina. Then we fabricated other three physical models with different states of ammetropia. Optical parameters of these physical eye models were measured to verify the 3D printing accuracy.

Results

In on-axis calculations, our schematic model eye possessed similar size of spot diagram compared with Navarro''s and Bakaraju''s model eye, much smaller than Arianpour''s model eye. Moreover, the spherical aberration of our schematic eye was much less than other three model eyes. While in off- axis simulation, it possessed a bit higher coma and similar astigmatism, field curvature and distortion. The MTF curves showed that all the model eyes diminished in resolution with increasing field of view, and the diminished tendency of resolution of our physical eye model was similar to the Navarro''s eye. The measured parameters of our eye models with different status of ametropia were in line with the theoretical value.

Conclusions

The schematic eye model we designed can well simulate the optical performance of the human eye, and the fabricated physical one can be used as a tool in fundus range viewing research.     

Biomechanical modeling of eye trauma for different orbit anthropometries

In military, automotive, and sporting safety, there is concern over eye protection and the effects of facial anthropometry differences on risk of eye injury. The objective of this study is to investigate differences in orbital geometry and analyze their effect on eye impact injury. Clinical measurements of the orbital aperture, brow protrusion angle, eye protrusion, and the eye location within the orbit were used to develop a matrix of simulations. A finite element (FE) model of the orbit was developed from a computed tomography (CT) scan of an average male and transformed to model 27 different anthropometries. Impacts were modeled using an eye model incorporating lagrangian-eulerian fluid flow for the eye, representing a full eye for evaluation of omnidirectional impact and interaction with the orbit. Computational simulations of a Little League (CD25) baseball impact at 30.1m/s were conducted to assess the effect of orbit anthropometry on eye injury metrics. Parameters measured include stress and strain in the corneoscleral shell, internal dynamic eye pressure, and contact forces between the orbit, eye, and baseball. The location of peak stresses and strains was also assessed. Main effects and interaction effects identified in the statistical analysis illustrate the complex relationship between the anthropometric variation and eye response. The results of the study showed that the eye is more protected from impact with smaller orbital apertures, more brow protrusion, and less eye protrusion, provided that the orbital aperture is large enough to deter contact of the eye with the orbit.     

Beneficial effect of daidzin in dry eye rat model through the suppression of inflammation and oxidative stress in the cornea

Present investigation evaluates the effect of daidzin in dry eye rat model through the suppression of inflammation and oxidative stress in the cornea. Briefly, electron spine resonance was used for the estimation of radical scavenging activity of daidzin and COX Fluorescent Activity Assay Kit was used for the estimation of PGS activity. Dry eye rat model was developed by removing the lacrimal gland and effect of daidzin was evaluated in dry eye rat model by estimating the fluorescein score, tear volume and expressions of heme oxigenase (HO-1), TNF α, Interlukin 6 (IL-6), matrix metallopeptidase 9 (MMP-9) and PGS-2. Result of the present study suggested that daidzin possess tyrosyl radical scavenging activity and thereby decreases the oxidative stress. Activity of PGS significantly increases in dry eye which was inhibited by daidzin treatment due to competitive inhibition of PGS. It also recovers the tear volume in dry eye rat model in which lacrimal gland was removed. Thus corneal erosion was improved by daidzin in dry eye rat model. Thus present study concludes that treatment with daidzin protects the cornea in dry eye rat model by suppression inflammation and oxidative stress.     

The effects of simulating a realistic eye model on the eye dose of an adult male undergoing head computed tomography

In head computed tomography, radiation upon the eye lens (as an organ with high radiosensitivity) may cause lenticular opacity and cataracts. Therefore, quantitative dose assessment due to exposure of the eye lens and surrounding tissue is a matter of concern. For this purpose, an accurate eye model with realistic geometry and shape, in which different eye substructures are considered, is needed. To calculate the absorbed radiation dose of visual organs during head computed tomography scans, in this study, an existing sophisticated eye model was inserted at the related location in the head of the reference adult male phantom recommended by the International Commission on Radiological Protection (ICRP). Then absorbed doses and distributions of energy deposition in different parts of this eye model were calculated and compared with those based on a previous simple eye model. All calculations were done using the Monte Carlo code MCNP4C for tube voltages of 80, 100, 120 and 140 kVp. In spite of the similarity of total dose to the eye lens for both eye models, the dose delivered to the sensitive zone, which plays an important role in the induction of cataracts, was on average 3% higher for the sophisticated model as compared to the simple model. By increasing the tube voltage, differences between the total dose to the eye lens between the two phantoms decrease to 1%. Due to this level of agreement, use of the sophisticated eye model for patient dosimetry is not necessary. However, it still helps for an estimation of doses received by different eye substructures separately.     

Computer simulation of hydraulic flows in a human eye

A two-dimensional computer model was developed to describe hydraulic flows inside the human eye. The flow field was described by coupled Navier-Stokes and Darcy equations. The velocity and pressure profiles in the chambers, the wall, and the vitreous body of the normal eye were obtained using the finite-element method. The model includes the filtration of fluid from the retinal capillary and its drainage through the choroid. The applications of this model include the investigation of the contribution of convection and diffusion to the transport of drugs and study of the kinetics of biodistribution in the eye.     

Dosimetric comparison between realistic ocular model and other models for COMS plaque brachytherapy with <Superscript>103</Superscript>Pd, <Superscript>131</Superscript>Cs,and <Superscript>125</Superscript>I radioisotopes

Nowadays, Monte Carlo calculations are commonly used for the evaluation of dose distributions and dose volume histograms in eye brachytherapy. However, currently available eye models have simple geometries, and main substructures of the eye are either not defined in details or not distinguished at all. In this work absorbed doses of eye substructures have been estimated for eye plaque brachytherapy using the most realistic eye model available, and compared with absorbed doses obtained with other available eye models. For this, a medium-sized tumour on the left sides of the right eye was considered. Dosimetry calculations were performed for four different eye models developed based on a literature review, and using a 12 mm Collaborative Ocular Melanoma Study plaque containing ¹³¹Cs, ¹⁰³Pd, and ¹²⁵I sources. Obtained results illustrate that the estimated doses received by different eye substructures strongly depend on the model used to represent the eye. It is shown here that using a non-realistic eye model leads to a wrong estimation of doses for some eye substructures. For example, dose differences of up to 35% were observed between the models proposed by Nogueira and co-workers and Yoriyaz and co-workers, while doses obtained by use of the models proposed by Lesperance and co-workers, and Behrens and co-workers differed up to 100 and 63% as compared to the situation when a realistic model was used, respectively. Moreover, comparing different radionuclides showed that the most uniform dose distribution in the considered tumour region was that from ¹³¹Cs, with a coefficient of variation of 33%. In addition, considering the realistic eye model, it was found that the radiosensitive region of the lens received more than the threshold dose of cataract induction (0.5 Gy), for all investigated radionuclides.     

Eye color prediction using single nucleotide polymorphisms in Saudi population

BackgroundDNA prediction of eye color represent one application of the externally visible characteristics (EVC), which attained growing interest in the field of DNA forensic phenotyping. This is mainly due to its ability to narrow the pool of suspects without the need to compare any retrieved DNA material from the crime scene to a reference DNA. Several methods and multiplex genetic panel were proposed with variable prediction accuracy between different populations. However, such panel was not previously tested in the Saudi population, nor any populations of the Middle East and North Africa origin.MethodA panel of eleven single nucleotide polymorphisms (SNPs) was tested for their association with three eye colors (brown, hazel, and intermediate) in 80 volunteer Saudi individuals. SNPs and haplotype association test with eye colors were performed to identify the top significant SNPs with the three eye colors. Also, multinomial logistic regression was used to construct the prediction model using a training set of 60 subjects, and a validation set of 20 subjects. The goodness of fit parameter of the model to correctly predicts each eye color as compared to the other was performed.ResultsEye color was significantly associated with rs12913832, rs7170852, and rs916977 that are located within HERC2. SNP rs12913832 was the top significant SNP (p-value = 1.78E?15) that accounted for the association in this region, as the other SNPs were not significant after adjusting for rs12913832. A prediction model containing five SNPs showed high prediction accuracy with Area Under the receiver operating characteristic Curves (AUC) equals to 0.95 and 0.83 for brown and intermediate eye colors, respectively. However, the model’s performance was very low for predicting the hazel eye color with AUC equals 0.75.DiscussionDespite the small sample size of our study, we reported very significant SNP associations with eye color. Our model to predict eye colors based on DNA material showed high accuracy for brown and intermediate eye colors. The eye color prediction-model underperformed for the hazel eye colors, suggesting that larger sample size, as well as more comprehensive set of SNPs, could improve the model-prediction accuracy.     

萤火虫复眼光学模型重叠成象的研究与模拟

以北京萤火虫复眼结构与生理参数为依据,基于已知的梯度折射率透镜特征,对复眼的整个光学系统进行模型化.模型的尺寸与折射率分布依据实际晶锥的测量值.通过对模型复眼的光线追迹,证明北京萤火虫复眼是一个折射重叠型复眼.重叠孔径以内入射的平行光线在视网膜水平形成一半宽度为一定值的模糊圈.利用计算机光线追迹模拟了复眼的重叠成象过程,随着象平面与晶锥近端距离的增加,信号光线的数目也逐渐增加,信噪比逐渐提高,在视网膜水平达到最大值.     

A fluid-structure interaction problem in biomechanics: prestressed vibrations of the eye by the finite element method.

The object of this work has been to develop a mechanical and numerical model of the eye submitted to vibrations, and in particular, to calculate the influence of intraocular pressure (IOP) on the eye resonance frequencies. Our mechanical model of the eye relies upon the theory of the mechanics of continuous media. The numerical model results from a model analysis of the vibrations of the eye using a finite element method (FEM) for discretization. The eye can be schematically represented as a prestressed shell, filled by an inviscid barotropic compressible fluid, which leads us to formulate and solve a problem of vibrations of a coupled fluid-structure system. The corneoscleral shell has been modeled as a thin and thick shell, taking into account material nonlinearities in the thick case. Numerical results obtained for the attached eye demonstrate a fair sensitivity of the resonance frequencies to the variations of the IOP; thus, founding the interest of the surveillance of the resonance frequency of the eye.     

New determinations of the eye rotation center and criteria for the formation of its membrane in terms of the floating eye model and experimental support of the latter

It is well known that the eye is a phylogenetically stabilized body with rotation properties. The eye has an elastic cover and is filled with uniform fluid. According to the theory of covers and other concepts on the configuration of turning fluid mass we concluded that the eyeball has an elliptic configuration. Classification of the eyeball is here presented with simultaneous studies of the principles of the eye situation. The parallelism between the state and different types of heterophory and orthophory was studied. To determine normal configuration it is necessary to have in mind some principles of achieving advisable correct situation of the eye in orbit. We determined the centre of the eye rotation and showed that it is impossible to situate it out of the geometrical centre of the eyeball. It was pointed out that for adequate perception the rotation centre must be situated on the visual axis. Using the well known theory of floating we experimentally determined that the centre of the eye rotation lies on the level of the floating eye, just on the point of cross of the visual line with the optical axis. It was shown experimentally on the basis of recording the eye movements in the process of eyelid closing that weakening of the eye movements is of gravitational pattern and proceeds under the action of stability forces, which directly indicates the floating state of the eye. For the first time using the model of the floating eye it was possible to show the formation of extraeye vacuum by straining the back wall. This effect can be obtained without any difficulty, if the face is turned down. The role of negative pressure in the formation of the eye ametropy, as well as new conclusions and prognostications about this new model are discussed.     

Functional significance of a floating eye model

The role of the floating eye model in the organization of situating and producing eye micromovements was studied. There is presented a hydromechanical model of orthophoria of latent and obvious squint. It is shown that the multiformity of obvious squint depends on the variety of combinations of nonuniform forces in the right eye aparting from the left one, which is the result of nonuniform deviations of both eyes from the norm, and heterophoria is the result of combinations of uniform forces aparting and of analogous deviations of both eyes form. It is shown that the concomittant squint is caused by the existence of different polar heterophoria at both eyes, and their multiformity is the result of their various combinations. The essential necessity of the eye floating for the organization of micromovements--eye tremor and drift is established. It is shown that the eye tremor which takes place under incomplete tetanus of the musole is possible only at optimal equilibrium of the eye and absence of friction they both are at floating. The non-muscle moving character of the eye drift is revealed. It proceeds under the influence of hydromechanical forces of aparting and nonequilibrated gravity of the cornea as a result of weakening of the eye movement muscle under fixation. The cause of the optic, axis divergence (OA) with optic line (OL) and the necessity with it of postnatal development of the eye dioptrics under active influence of the motor apparatus was discovered. Physiology of the eye floating, new conclusions and a hypothesis concerning the model are discussed.     

Astragalus IV ameliorates the dry eye injury in rabbit model via MUC1-ErbB1 pathway

The therapeutic effects and potential mechanisms of astragaloside IV on a rabbits dry eye model induced by benzalkonium chloride (BAC) was examined. In our study, a BAC-induced dry eye rabbit model was treated with eye drops containing astragaloside IV (5, 10 μM) or solvent four times a day. The clinical evaluations, such as tear break-up time (BUT) and Schirmer tear test (STT), were performed on days 0, 7, 14, 21, and 28. On day 28, the cornea and bulbar conjunctiva tissues (left eye and right eye) were collected with histology, and immunofluorescent staining conducted. The levels of MUC1 and ErbB1in the corneas were determined by realtime quantitative PCR (qRT-PCR) and the proteins levels of MUC1 and ErbB1 were detected by Western blot. It was demonstrated that both astragaloside IV (5, 10 μM) treatments resulted in an increased STT and BUT on days 7, 14, 21 and 28. Additionally, the astragaloside IV (5, 10 μM)-treated group showed increasing PAS-positive goblet cells than model group (0 μM). Moreover, the MUC1 in model group (0 μM) was decreased, while the expression of MUC1 in astragaloside IV (5, 10 μM) group was increased. Furthermore, astragaloside IV had a protective effect on BAC-induced rabbits’ dry eye and demonstrated clinical improvements, which indicated that astragaloside IV served as a potential protective agent in the clinical treatment of dry eye.Key words: Astragaloside IV, dry eye model, MUC1, ErbB1     

Control of human eye movements: II. a model for the extraocular plant mechanism

Control of eye movements is essential in accomplishing visual or perceptive tasks. The brain and central nervous system process retinal information and send nervous signals to the extraocular muscles, which exert forces that cause the eye to move. A model for the human extraocular plant, which consists of the nervous input signals, the extraocular muscles, the orbit and the globe, is proposed. The derivation is based on anatomical and physiological data as well as experiments concerned with a variety of eye movements under normal and abnormal conditions. The nervous activity controlling eye movements was estimated from electromyography and single unit studies of the extraocular nuclei. The equations describing muscle properties were discussed in a previous paper by the authors; these results were incorporated into the present model. The characteristics of the isolated globe and its visco-elastic interaction with the orbit were computed from length- tension curves and isotonic experiments. Simulations using the resulting representation accurately depicted the isotonic experiments on the isolated globe and on the total extraocular plant, the isometric forces during three different types of eye movements, and the weighted globe experiment. A future paper will show that the model accurately simulates normal eye movements of different types and amplitudes.     

A ‘tachometer’ feedback model of smooth pursuit eye movements

A new model of smooth pursuit eye movements is presented. We begin by formally analyzing the stability of the proportional-derivative (PD) model of smooth pursuit eye movements using Pontryagin's theory. The PD model is the linearized version of the nonlinear Krauzlis-Lisberger (KL) model. We show that the PD model fails to account for the experimentally observed dependence of the eye velocity damping ratio and the oscillation period on the total delay in the feedback loop. To explain the data, a new `tachometer' feedback model, based on an efference copy signal of eye acceleration, is proposed and analyzed by computer simulation. The model predicts some salient features of monkey pursuit data and suggests a functional role for the extraretinal input to the medial superior temporal area (MST). Received: 9 February 1995 / Accepted in revised form: 13 June 1995     

Dynamic response of intraocular pressure and biomechanical effects of the eye considering fluid-structure interaction

The vibration characteristics of shell structures such as eyes have been shown to vary with intraocular pressure (IOP). Therefore, vibration characteristics of the eye have the potential to provide improved correlation to IOP over traditional IOP measurements. As background to examine an improved IOP correlation, this paper develops a finite element model of an eye subject to vibration. The eye is modeled as a shell structure filled with inviscid pressurized fluid in which there is no mean flow. This model solves a problem of a fluid with coupled structural interactions of a generally spherically shaped shell system. The model is verified by comparing its vibrational characteristics with an experimental modal analysis of an elastic spherical shell filled with water. The structural dynamic effects due to change in pressure of the fluid are examined. It is shown that the frequency response of this fluid-solid coupled system has a clear increase in natural frequency as the fluid pressure rises. The fluid and structure interaction is important for accurate prediction of system dynamics. This model is then extended to improve its accuracy in modeling the eye by including the effect of the lens to study corneal vibration. The effect of biomechanical parameters such as the thicknesses of different parts of the eye and eye dimensions in altering measured natural frequencies is investigated and compared to the influence of biomechanical parameters in Goldmann applanation tonometry models. The dynamic response of the eye is found to be less sensitive to biomechanical parameters than the applanation tonometry model.     

Continuity versus split and reconstitution: exploring the molecular developmental corollaries of insect eye primordium evolution

Holometabolous insects like Drosophila proceed through two phases of visual system development. The embryonic phase generates simple eyes of the larva. The postembryonic phase produces the adult specific compound eyes during late larval development and pupation. In primitive insects, by contrast, eye development persists seemingly continuously from embryogenesis through the end of postembryogenesis. Comparative literature suggests that the evolutionary transition from continuous to biphasic eye development occurred via transient developmental arrest. This review investigates how the developmental arrest model relates to the gene networks regulating larval and adult eye development in Drosophila, and embryonic compound eye development in primitive insects. Consistent with the developmental arrest model, the available data suggest that the determination of the anlage of the rudimentary Drosophila larval eye is homologous to the embryonic specification of the juvenile compound eye in directly developing insects while the Drosophila compound eye primordium is evolutionarily related to the yet little studied stem cell based postembryonic eye primordium of primitive insects.     

Selenium Compound Protects Corneal Epithelium against Oxidative Stress

The ocular surface is strongly affected by oxidative stress, and anti-oxidative systems are maintained in corneal epithelial cells and tear fluid. Dry eye is recognized as an oxidative stress-induced disease. Selenium compound eye drops are expected to be a candidate for the treatment of dry eye. We estimated the efficacy of several selenium compounds in the treatment of dry eye using a dry eye rat model. All of the studied selenium compounds were uptaken into corneal epithelial cells in vitro. However, when the selenium compounds were administered as eye drops in the dry eye rat model, most of the selenium compounds did not show effectiveness except for Se-lactoferrin. Se-lactoferrin is a lactoferrin that we prepared that binds selenium instead of iron. Se-lactoferrin eye drops suppressed the up-regulated expression of heme oxygenase-1, cyclooxygenase-2, matrix metallopeptidase-9, and interleukin-6 and also suppressed 8-OHdG production in the cornea induced by surgical removal of the lacrimal glands. Compared with Se-lactoferrin, apolactoferrin eye drops weakly improved dry eye in high dose. The effect of Se-lactoferrin eye drops on dry eye is possibly due to the effect of selenium and also the effect of apolactoferrin. Se-lactoferrin is a candidate for the treatment of dry eye via regulation of oxidative stress in the corneal epithelium.     

The use of cycloferon in the therapy of experimental herpetic keratitis]

The cycloferon efficacy was investigated in the treatment of experimental herpesvirus kerato-conjunctivitis in rabbits. The model was demonstrated to reflect the main aspects of herpesvirus eye lesions in humans. Cycloferon application similarly to that of known interferon inducer poludan has been shown to enhance processes of inflammation and subsequent regeneration of eye tissues as well as to decrease mortality of animals due to the generalization of infection.     

Prediction of globe rupture caused by primary blast: a finite element analysis

Although a human eye comprises less than 0.1% of the frontal body surface area, injuries to the eye are found to be disproportionally common in survivors of explosions. This study aimed to introduce a Lagrangian–Eulerian coupling model to predict globe rupture resulting from primary blast effect. A finite element model of a human eye was created using Lagrangian mesh. An explosive and its surrounding air domain were modelled using Eulerian mesh. Coupling the two models allowed simulating the blast wave generation, propagation and interaction with the eye. The results showed that the peak overpressures caused by blast wave on the corneal apex are 2080, 932.1 and 487.3 kPa for the victim distances of 0.75, 1.0 and 1.25 m, respectively. Higher stress occurred at the limbus, where the peaks for the three victim distances are 25.5, 14.1 and 6.4 MPa. The overpressure threshold of globe rupture was determined as 2000 kPa in a small-scale explosion. The findings would provide insights into the mechanism of primary blast-induced ocular injuries.