糖尿病动物模型及其在DR的应用

糖尿病动物模型(DM模型)是糖尿病研究的基础。DM模型基础上建立的DR模型为糖尿病性视网膜病变提供很好的病理模型,在糖尿病性视网膜病变研究中起很重要的作用。DM模型主要可分为化学物质诱导性模型、自发性遗传性动物模型、胰腺部分切除模型和转基因模型等4种。其建立方法各有优缺点.实验性糖尿病动物模型价格低廉,可操作性强,并且在一定程度上符合人类糖尿病形成的病理过程,成为目前研究糖尿病的最主要动物模型,特别是STZ注射模型最为普遍;而基因敲除复制模型随着技术的发展,将有广阔的发展前景。     

The changing disparity energy model

Changing disparity is a possible cue for stereomotion perception. We propose the changing disparity energy model, a physiologically plausible model for neurons tuned to changing disparity. This model combines the disparity and motion energy models commonly used to model cortical neuron outputs. The model outputs are consistent with psychophysical experiments indicating that stereomotion speed discrimination thresholds for dynamic random dot stereograms are higher than for random dot stereograms. Thus, these experimental results are not necessarily strong evidence for the existence of an inter-ocular velocity difference cue. The model also predicts a relationship between the speed discrimination threshold ratio and the dot density.     

Combining information in different color-coding mechanisms to facilitate visual search

An earlier experiment using a yes-no procedure with a search accuracy task [A.L. Nagy, G. Thomas, Distractor heterogeneity, attention, and color in visual search tasks, Vision Research, 43 (2003) 1541-1552] showed that observers could combine information in different cardinal color mechanisms to facilitate search performance. In the experiments reported here we attempted to replicate these results with a forced-choice procedure and tested three different models of the manner in which information in different feature coding mechanisms is combined. One model was a linear summing model in which signals in different mechanisms are linearly summed in a mechanism under the control of attention. The summed signals are used to guide attention to likely targets. The second model was a nonlinear selection model in which signals in one mechanism are used to select stimuli for attention. A decision is then based on signals generated by the selected stimuli in a mechanism other than the one that is used for selection. The third model was the linear separability model, which suggests that the chromaticity of the target stimulus must be separated from the chromaticities of the distractor stimuli by a straight line in a chromaticity diagram for efficient search. Results favored the nonlinear selection model over the linear summing model and the linear separability model.     

Predicting visual fixations on video based on low-level visual features

To what extent can a computational model of the bottom-up visual attention predict what an observer is looking at? What is the contribution of the low-level visual features in the attention deployment? To answer these questions, a new spatio-temporal computational model is proposed. This model incorporates several visual features; therefore, a fusion algorithm is required to combine the different saliency maps (achromatic, chromatic and temporal). To quantitatively assess the model performances, eye movements were recorded while naive observers viewed natural dynamic scenes. Four completing metrics have been used. In addition, predictions from the proposed model are compared to the predictions from a state of the art model [Itti's model (Itti, L., Koch, C., & Niebur, E. (1998). A model of saliency-based visual attention for rapid scene analysis. IEEE Transactions on Pattern Analysis and Machine Intelligence 20(11), 1254-1259)] and from three non-biologically plausible models (uniform, flicker and centered models). Regardless of the metric used, the proposed model shows significant improvement over the selected benchmarking models (except the centered model). Conclusions are drawn regarding both the influence of low-level visual features over time and the central bias in an eye tracking experiment.     

Visual perception of extent and the geometry of visual space

The question of how perceived extents are related to the corresponding physical extents is a very old question that has not been satisfactorily answered. The common model is that perceived extent is proportional to the product of image size and perceived distance. We describe an experiment that shows that perceived extents are substantially larger than this model predicts. We propose a model that accounts for our results and a large set of other results. The principal assumption of the model is that, in the computation of perceived extent, the visual angle signal undergoes a magnifying transform. Extent is often perceived more accurately than the common model predicts, so the computation is adaptive. The model implies that, although the perception of location and the perception of extent are related, they not related by Euclidean geometry, nor by any metric geometry. Nevertheless, it is possible to describe the perception of location and extent using a simple model.     

An automated system of strabismus management. A direct approach using a "reverse" model

Until now computer models of strabismus have consisted of lengthy calculations based on oculomotor physiology. Such models have been able to demonstrate the pattern of strabismus that would arise from any given muscle abnormality and/or operation. However, it has been difficult to use such models to guide strabismus surgery because the surgeon requires a model that works in the opposite direction. The surgeon requires a model whose input is the pattern of strabismus and output is the muscle operation required. Such a model is described here. Instead of consisting of calculations based on physiology the new model consists of a store of most of the information capable of being generated by an existing strabismus model together with an efficient search procedure. In this paper the potential of the new model is demonstrated by its application to a case of paralytic strabismus.     

基于Micro—CT成像的听骨链有限元建模方法

目的利用Micro-CT扫描数据建立中耳听骨链三维有限元模型。方法用Micro—CT扫描成人颞骨标本,将获得的图像数据通过MicroView、Mimics等软件进行三维重建。再将模型转入其有限元分析（finite element analysis,FEA）模块的Remesh环境中进行调整、细化及面网格优化,通过SOLIDEWORK软件转换为实体网格。结果初步形成的三维几何模型可较清晰地辨别鼓室腔、听小骨和内耳系统,但部分图像不同程度存在噪点。最终形成了FEA软件可识别的成人中耳听骨链三维有限元网格模型,网格划分后的听骨链有限元模型中,完整听骨链的节点数降低,由原来包括805个不合理节点在内的12498个节点降低到2050个,在此基础上建立的有限元模型共1350个8节点四面体单元。结论结合Micro—CT技术及Mimics软件的三维建模方法可以快速获得较精确的听骨链三维数据,是建立听骨链三维有限元模型的有效途径。（中国眼耳鼻喉科杂志,2009．9．83。85）     

Visual working memory is better characterized as a distributed resource rather than discrete slots

A recent important debate in the field of visual working memory has focused on whether it represents a small set of high-precision representations (the "slot" model) or all items in parallel (the "resource" model). When faced with a large number of items, the slot model claims that high-precision representations of several items are stored and no information is retained about the other items, whereas the resource model claims that some imperfect information about each of the items can be stored. In this study, the observers tried to memorize and then recall six (out of eight possible) colors. The distribution of their scores (i.e., the number of correct responses) was modeled, and the empirical pattern of distribution fitted precisely with the prediction of the resource model but clearly differed from that of the slot model. Dependence analysis also revealed that the reports of items were approximately independent of each other, suggesting that all of the items were represented in parallel, as predicted by the resource model but not by the slot model. Overall, the data favored the resource model, not the slot model.     

Use of Fieldmaster automated perimeter for the detection of early visual field changes in glaucoma

The efficacy of automated suprathreshold perimetry with Fieldmaster automated perimeter (model 101 PR and 200) was evaluated in the screening for very early glaucomatous visual field defects which failed to be detected with kinetic perimetry using a Goldmann perimeter. Evaluation of 117 eyes with elevated intraocular pressure revealed a small, relative defect in the central field in 14 eyes which was confirmed by static perimetry with a Tübinger perimeter. Although Fieldmaster model 200 is equipped with more target positions than model 101 PR, detectability of early defects was almost identical between two models. Automated suprathreshold perimetry with either model of Fieldmaster perimeter is useful in detecting the early changes which may be missed by kinetic perimetry with a Goldmann perimeter. Based on the difference in the false positive rate (45.6% with model 200 vs 26.7% with model 101 PR) the screening with 101 PR seems to be more rewarding.     

An abbreviated assessment of ocular exposure to ultraviolet radiation

Individual behaviour has a very large effect on determining the exposure of the eye to solar radiation. To be able to examine the relationship between ocular exposure to ambient ultraviolet radiation and ocular disease, a model was developed previously that assessed cumulative ocular exposure from individual information on work and leisure activities. In this paper, we present a simplified version of the model that uses data on exposure during the middle of the day (9 a.m. to 3 p.m. solar time) during the northern 'summer' months (April to September). The ocular exposure determined by the simplified model is highly correlated with the full model ( r =0.98) and the simplified model predicts 62% of the total ocular exposure. This model should be useful for future epidemiologic studies of sun exposure and eye disease.     

A mathematical model of factors that influence the performance of accommodative intraocular lenses

In this work a mathematical model of capsule movement during pseudophakic accommodation is described to allow identification and evaluation of factors that may explain the variation in effect of accommodative intraocular lenses (IOLs) between patients. The model assumes that increasing vitreous pressure pushes the lens capsule forward as a circular diaphragm and that this movement is from a fixed fulcrum. With an IOL in situ, the capsule is taken to have a non-uniform thickness due to the presence of the anterior capsulorhexis. The model assumes a uniform capsular elasticity and ignores contributions from cellular elements such as posterior capsule opacification. Using our model and a regression formula to calculate capsular bag size, taking into account axial length and keratometry values, we are able to predict accommodative effect in individual patients. By simple geometry we have developed a mathematical model to identify variables that are important in pseudophakic accommodation. It provides the basis for the development of a more complex model that would address the movement of a lens taking into account the influence of the zonular system during accommodation.     

一种新型的可检测不同人工晶状体植入术后功能视力的模型眼

目的:通过这种新型的模型眼比较各种人工晶状体(以Tecnis为代表的非球面晶状体、以Array为代表的多焦晶状体及以EPOCH为代表的传统单焦球面晶状体)植入术后的功能视力。方法:我们这种新型的模型眼是根据理论模型眼的光学特性设计而来的。该模型眼是由一个焦距为35mm的球面设计的摄影镜头、一个置于房水的人工晶状体、一个电荷耦合照相机(CCDcamera)构成,图像分析采用目前国际上标准的商业化遥感处理软件系统。结果:模型眼和人眼具有相似的调制传递函数(modula-tiontransferfrequency,MTF)。模型眼所成的像和植入人工晶状体的眼睛所成的像相似,光阑的孔径和人工晶状体的屈光度可以改变,也可将镜片置于摄影镜头之前。结论:该模型眼能够即时的给出人工晶状体植入术后所成的像,让我们可以直接观察到模型眼构成的图像而不是数据,并能显示出各种人工晶状体的差异。     

An abbreviated assessment of ocular exposure to ultraviolet radiation.

Individual behaviour has a very large effect on determining the exposure of the eye to solar radiation. To be able to examine the relationship between ocular exposure to ambient ultraviolet radiation and ocular disease, a model was developed previously that assessed cumulative ocular exposure from individual information on work and leisure activities. In this paper, we present a simplified version of the model that uses data on exposure during the middle of the day (9 a.m. to 3 p.m. solar time) during the northern 'summer' months (April to September). The ocular exposure determined by the simplified model is highly correlated with the full model (r = 0.98) and the simplified model predicts 62% of the total ocular exposure. This model should be useful for future epidemiologic studies of sun exposure and eye disease.     

Computational analysis of vertebrate phototransduction: combined quantitative and qualitative modeling of dark- and light-adapted responses in amphibian rods

We evaluated the generality of two models of vertebrate phototransduction. The approach was to quantitatively optimize each model to the full waveform of high-quality, dark-adapted (DA), salamander rod flash responses. With the optimal parameters, each model was then used to account for signature, qualitative features of rod responses from three experimental paradigms (stimulus/response, "S/R suite"): (1) step responses; (2) the intensity dependence of the period of photocurrent saturation (Tsat vs. ln(I)); and (3) light-adapted (LA) incremental flash sensitivity as a function of background intensity. The first model was the recent successful model of Nikonov et al. (1998). The second model replaced the instantaneous Ca2+ buffering used in the Nikonov et al. model with a dynamic buffer. The results showed that, in the absence of the dynamic Ca2+ buffer, the Nikonov et al. model does not have sufficient flexibility to provide a good fit to the flash responses, and, using the same parameters, reproduce the salient features of the S/R suite--critical features at step onset and offset are absent; the Tsat function has too shallow a slope; and the model cannot generate the empirically observed I-range of Weber-Fechner LA behavior. Some features could be recovered by changing parameters, but only at the expense of the fit to the reference (Ref) data. When the dynamic buffer is added, the model is able to achieve an acceptable fit to the Ref data while reproducing several features of the S/R suite, including an empirically observed Tsat function, and an extended range of LA flash sensitivity adhering to Weber's law. The overall improved behavior of the model with a dynamic Ca2+ buffer indicates that it is an important mechanism to include in a working model of phototransduction, and that, despite the slow kinetics of amphibian rods, Ca2+ buffering should not be simulated as an instantaneous process. However, neither model was able to capture all the features with the same parameters yielding the optimal fit to the Ref data. In addition, neither model could maintain a good fit to the Ref data when five key biochemical parameters were held at their current known values. Moreover, even after optimization, a number of important parameters remained outside their empirical estimates. We conclude that other mechanisms will need to be added, including additional Ca2+-feedback mechanisms. The present research illustrates the importance of a hybrid qualitative/quantitative approach to model development, and the limitations of modeling restricted sets of data.     

Simulation of movement detection by direction-selective ganglion cells in the rabbit and squirrel retina

A veto-gate model of movement detection by direction-selective ganglion cells in the vertebrate retina, first proposed by Barlow and Levick (1965), provides the basis for a model described in this study. The model is a simple network consisting basically of (1) two subunits that have receptive fields with a center-surround organization and an adaptational gain control, (2) a lateral inhibitory pathway, (3) a site of nonlinear interaction, followed by (4) a leaky temporal integrator. The model is tested by comparing its basic properties to those reported in the physiological literature on rabbit and squirrel direction-selective retinal ganglion cells. It is shown that the physiological findings on sensitivity to flashes, moving spots or slits, and phi-movement stimuli, can be mimicked quite well by our model. Similarities between the component processes of the subunits and known retinal processes are pointed out. The simulation studies shed a new light on some of the known properties and suggest several new, more revealing, physiological experiments. Such experiments are necessary to develop a full specification of this type of model and to fix more parameter values than is possible at present. Results of some critical experiments are predicted to enable physiologists to falsify or corroborate the model. The simulation studies also help to distinguish use from abuse of this type of model in explanations of psychophysical findings. For example, neither the most complete Barlow-Levick detector nor any stripped-down versions that retain a temporally extended lateral inhibition (which is essential to mimick the physiological findings), respond well to moving random-pixel arrays.     

Individualized optimization of the screening interval for diabetic retinopathy: a new model

Introduction: Screening programmes for diabetic retinopathy follow guidelines that ensure that vision‐threatening complications are detected even when the disease progression is fast. This implies that patients with slow disease progression will be recommended examinations more often than needed. Method: On the basis of previously defined individual risk factors, multiple logistic regression was used to develop a model for individualized determination of the screening interval in diabetic retinopathy, while adjusting for the fact that in the data set used to construct the model, the screening interval acted as a time‐dependent confounder. The model was tested on 1372 patients screened during year 2000. Results: It was possible to construct a model for calculating the optimal screening interval in low‐risk patients in whom the recommended screening interval was longer than 12 months. When the probability of reaching a treatment requiring event was set to 0.5%, none of the patients reached a treatment end‐point in a validation of the model, and the screening interval was prolonged on average 2.9 times in patients with type 1 diabetes and 1.2 times in those with type 2 diabetes. The predictive strength of the model depended on the number of variables included. Conclusions: It is possible to construct a model for optimizing the examination interval during screening for diabetic retinopathy in low‐risk patients. The model can potentially be improved by identifying unknown or unmeasured confounders and by including knowledge of risk factors before and after the examination on the basis of which the prediction is made.     

A mathematical model for tear drainage through the canaliculi

PURPOSE: Tear drainage through the canaliculi has been extensively studied experimentally but there has been no attempt to develop a quantitative model for this process. In this paper, we develop a mathematical model for the tear drainage through the canaliculi. METHODS: The mathematical model is based on the experimental findings of Doane, according to which the muscle action during a blink drives the tear drainage. In this paper, mathematical models are developed for the tear flow and the canalicular deformation, and the model equations are solved to predict the tear drainage rates. RESULTS: The drainage rates depend on various physiological parameters. The time to attain a steady state during the drainage process can vary from about 0.0010 s to 0.0546 s, and the tear drainage rate can vary from 0.10 microl/min to 4.00 microl/min for a normal tear film, for physiologically reasonable values of various system parameters. CONCLUSIONS: The model predictions agree with various physiological experiments, at least qualitatively. The model also helps resolve the differences between various tear drainage experiments.     

Selective rod degeneration and partial cone inactivation characterize an iodoacetic acid model of Swine retinal degeneration

PURPOSE. Transgenic pigs carrying a mutant human rhodopsin transgene have been developed as a large animal model of retinitis pigmentosa (RP). This model displays some key features of human RP, but the time course of disease progression makes this model costly, time consuming, and difficult to study because of the size of the animals at end-stage disease. Here, the authors evaluate an iodoacetic acid (IAA) model of photoreceptor degeneration in the pig as an alternative model that shares features of the transgenic pig and human RP. METHODS. IAA blocks glycolysis, thereby inhibiting photoreceptor function. The effect of the intravenous injection of IAA on swine rod and cone photoreceptor viability and morphology was followed by histologic evaluation of different regions of the retina using hematoxylin and eosin and immunostaining. Rod and cone function was analyzed by full-field electroretinography and multifocal electroretinography. RESULTS. IAA led to specific loss of rods in a central-to-peripheral retinal gradient. Although cones were resistant, they showed shortened outer segments, loss of bipolar cell synaptic connections, and a diminished flicker ERG, hallmarks of transition to cone dysfunction in RP patients. CONCLUSIONS. IAA provides an alternative rod-dominant model of retinal damage that shares a surprising number of features with the pig transgenic model of RP and with human RP. This IAA model is cost-effective and rapid, ensuring that the size of the animals does not become prohibitive for end-stage evaluation or therapeutic intervention.     

Cortical dynamics of figure-ground segmentation: shine-through

The shine-through effect occurs when a brief offset vernier target is followed by a grating of non-offset vernier elements. Rather than mask the target, this stimulus sequence produces a percept of the target vernier occluding the mask elements. We analyzed the dynamics of the 3D LAMINART model of depth perception and found that it explains the appearance of shine-through for these stimuli. The model explanation proposes that shine-through is due to a combination of false binocular disparity matches between the target and the central element of the mask, and a weakening of between disparity competition due to spatial competition and boundary grouping. Simulations of the model demonstrate that its behavior closely matches empirical data on the properties of shine-through. The model is contrasted with an alternative explanation of shine-through, and novel mask conditions are studied that allow for empirical tests of the model hypotheses.     

Darkness filling-in: a neural model of darkness induction.

A model of darkness induction based on a neural filling-in mechanism is proposed. The model borrows principles from both Land's Retinex theory and BCS/FCS filling-in model of Grossberg and colleagues. The main novel assumption of the induction model is that darkness filling-in signals, which originate at luminance borders, are partially blocked when they try to cross other borders. The percentage of the filling-in signal that is blocked is proportional to the log luminance ratio across the border that does the blocking. The model is used to give a quantitative account of the data from a brightness matching experiment in which a decremental test disk was surrounded by two concentric rings. The luminances of the rings were independently varied to modulate the brightness of the test. Observers adjusted the luminance of a comparison disk surrounded by a single ring of higher luminance to match the test disk in brightness.