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。     

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.     

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.     

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.     

C57BL／6小鼠葡萄球菌性角膜感染模型的建立及相关研究

目的以乙基亚硝基脲（ENU）诱变技术建立小鼠葡萄球菌性角膜感染模型,探讨其主要条件致病菌的生物学特性。方法以ENU（150mg／kg）腹腔注射10周龄雄性C57BL／6小鼠,60d后与其同品系雌性小鼠配种,F1代小鼠中发现角膜混浊小鼠,以具有角膜混浊表型小鼠与C57BL／6小鼠回交的方式繁育。对角膜混浊小鼠角膜感染菌进行分离、培养、纯化、鉴定,并使用不同抗生素进行药物敏感试验。结果建立了稳定的小鼠葡萄球菌性角膜感染模型。从自发性角膜混浊（B6一Co）小鼠眼部成功分离纯化了松鼠葡萄球菌,筛选出了对该菌敏感及耐药的抗生素。对该菌敏感的抗生素有阿奇霉素、克林霉素、氯霉素、庆大霉素、利福平、四环素、阿米卡星、复方新诺明、米诺环素、左氟沙星、头孢噻吩、头孢噻肟、呋喃唑酮;对该菌耐药的抗生素有头孢西丁、青霉素、氨苄西林、新生霉素;属于中间态的抗生素为呋喃妥因。结论C57BL／6小鼠葡萄球菌性角膜感染模型为自发性动物模型,系凝固酶阴性葡萄球菌感染所致,以松鼠葡萄球菌为主。     

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.     

Some aspects of the mechanics of accommodation

A minimal model for the mechanics of accommodation is presented. The main components of the model are ciliary muscle, zonular system, elastic lens, and elastic choroid. Using estimates for physical properties of as many of the components as possible, the model can be made consistent with most available evidence. One exception is that ciliary muscle is required to be stronger than suggested in earlier physiological work.     

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.     

Dual nonlinearities regulate contrast sensitivity in pattern discrimination tasks

Many current psychophysical models propose that visual processing in cortex is hierarchical, with nonlinearities sandwiched between linear stages of processing. In earlier publications, we proposed a model of this type to account for masking effects found with spatial frequency and orientation discriminations. Our model includes two nonlinear mechanisms that regulate contrast sensitivity in early cortical mechanisms. The first is a local within-pathway nonlinearity that accelerates at low contrasts but is compressive at high. The second is a pooled nonlinear gain control process that operates over a broad range of neurons with different tuning characteristics. Here, we test predictions of the model for spatial frequency discriminations. The model predicts that at low contrasts, adding a grating mask oriented parallel to test gratings will improve discrimination performance via operation of the within-pathway nonlinearity, analogous to the "dipper effect" found with contrast discriminations. Adding an orthogonally oriented mask is predicted to have no effect at low contrasts, where pooled gain control processes contribute little to performance. At high contrasts, the model predicts that performance will asymptote and become independent of contrast with either parallel or orthogonal masks. The results confirm model predictions.     

A model of spatiotemporal signal processing by primate cones and horizontal cells

A model of spatiotemporal signal processing by the cone-horizontal cell circuit in the primate outer retina is developed and validated using measurements on the H1 horizontal cell from the literature. The model extends an earlier temporal model that mainly addressed the regulation of sensitivity by the cones. Three elements are added to the earlier model to describe the full spatiotemporal processing by horizontal cells. First, the feedback gain from horizontal cells to cones is made adaptive, depending on field size. Second, the spatial filtering by the horizontal dendritic tree is modeled as a two-component spatial filter. Third, an adaptive temporal low-pass filter is added, also depending on field size. The resulting model adequately describes all available measurements on spatiotemporal processing in macaque H1 cells. The adaptive feedback gain is argued to contribute to negative afterimages and chromatic adaptation in human vision.