Physicochemical Properties of Vitreous Body and Development of Artificial Vitreous Body

玻璃体是一种含有胶原蛋白和透明质酸的脆弱凝胶聚合物网络的分数仅为约1-2%，其余为水。玻璃体位于晶状体和视网膜之间，占眼睛整体体积的80%。玻璃体的功能应该是保持眼球的形状，吸收外界的机械冲击，维持眼球的内平衡，调节晶状体的位置。新鲜玻璃体的外观是透明的，因此，玻璃体被认为是一个均匀的组织。迄今为止的许多研究表明，体外牛玻璃体的散射光强度和动态均匀分布，受外界条件变化的影响，透明质酸呈线圈状。这些研究将有助于更好地了解玻璃体疾病的功能和机制。通过对不同条件下的膨胀行为和动态光散射的宏观观察，研究了牛玻璃体的相平衡特性和结构动力学特性。结果表明，玻璃体在不同的外部条件下，会发生各向同性或各向异性的收缩。当pH < 4和钙离子浓度（e 1 mol/L）改变时，玻璃体在保持形状的同时坍塌，而在甲醇和水的混合溶剂中，玻璃体沿轨道轴坍塌。通过对玻璃体散射光的动力学观察，得到了显示两个独立扩散系数的强度自相关函数。在1-1.5 mm的焦深范围内，扩散系数与位置无关。当钙离子浓度接近临界阈值（1 mol/L）时，测量到的散射光强度和扩散系数出现发散现象。也就是说，观察到动态模式的减速伴随着“静态”散射强度的增加。散射光强度和扩散系数的发散行为是可逆的。这表明钙离子浓度发生相变。经γ辐照交联的聚乙烯醇（PVA）水凝胶被评估为一种可能的玻璃体替代品。通过一系列的实验，观察到部分病例术后眼压升高，玻璃体腔内出现炎症变化。实验中使用了食蟹猕猴。玻璃体切除术后玻璃体腔内注射PVA凝胶，临床随访采用眼镜、眼压测定、眼底摄影、视网膜电图（ERG）、趋化性、光斑细胞计。3个月后进行光镜和电镜组织病理学检查。结果，眼科检查结果无明显变化。未见眼压异常升高。ERG未显示有意义的振幅减弱。从耀斑细胞计的光子计数来看，没有观察到明显的血水屏障和血视网膜屏障破裂。组织病理学检查显示视网膜各层完整，无明显组织损失。然而，在注射PVA凝胶的眼睛中，在一些标本中发现一些内视网膜空泡。综上所述，PVA凝胶在这些实验中耐受性良好。具有类似玻璃体网状结构的凝胶表现出最好的生物相容性，但其长期生物相容性有待进一步研究。聚乙烯醇凝胶是一个很好的玻璃体替代品。少

The vitreous body is a tenuous gel that contains collagen and hyaluronic acid.4 The fraction of the polymer network is only about 1-2%, and the remaining is water. The vitreous body is located between the lens and the retina, and comprises 80% of the overall volume of eye. The functions of the vitreous body are supposed to keep the shape of the eyeball, to absorb the external mechanical shock, to maintain the homoeostasis of the eye, and to regulate the position of the lens. The appearance of fresh vitreous body is transparent, and hence, the vitreous body is considered a uniform tissue. Many studies performed to date have suggested that hyaluronic acid, which has a coil shape, is uniformly distributed of scattered light intensities and dynamics from bovine vitreous body in vitro, subjected to the changes in the external conditions. These studies will promote better understanding of the function and the mechanism of diseases of the vitreous body.The phase equilibrium property and struc … More tural and dynamical properties of bovine vitreous body was studied by macroscopic observation of swelling behavior and dynamic light scattering under various conditions. It was found that the vitreous body collapses into a compact state isotropically or anisotropically depending on the external conditions. The vitreous body collapses while maintaining the shape when the pH (< 4) and the concentration of calcium ions (e 1 mol/L) are changed, whereas it collapses along the orbital axis in a mixed solvent of methanol and water. From observations of the dynamics of light scattered by the vitreous body, intensity autocorrelation functions that revealed two independent diffusion coefficients were obtained. The diffusion coefficients were found to be statistically independent of position within a focal depth range of 1-1.5 mm. Divergent behavior in the measured total scattered light intensities and diffusion coefficients was observed as the concentration of calcium ion approached the critical threshold, 1 mol/L. Namely, a slowing down of the dynamic modes accompanied by increased "static" scattered intensities was observed. The divergent behavior in the scattered light intensities and diffusion coefficients was reversible. This is indicative of the occurrence of a phase transition upon calcium ion concentration.Polyvinylalcohol (PVA) hydrogel cross-linked by gamma irradiation was assessed as a possible vitreous substitute. From a series of experiments, rise of intraocular pressure and inflammatory changes in the vitreous cavity after operation were observed in some cases. Crab-eating macaques were used for this experiment. PVA gels were injected into vitreous cavity after vitrectomy and followed clinically by opthalmoscopy, tonometry, fundus photography, electroretinogram (ERG), chemotaxis, and flare cell meter. Histopathologic examination by light and electron microscopy was performed after 3 months. As a result, there were no significant changes in ophthalmoscopic findings. No abnormal rising of intraocular pressure (IOP) was recognized. ERG did not show meaningful amplitude weakness. From the photon counting of flare cell meter, significant break of blood-aqueous barrier and blood-retinal barrier was not observed. Histopathologic examination revealed that all layers of the retina were intact and no loss of tissue was evident. However, in PVA gel-injected eyes, some vacuolations of the inner retina were found in some specimens. To conclude, PVA gel was well tolerated in these experiments. The gel with a network similar to the vitreous body showed the best biocompatibility, though it is necessary to investigate the biocompatibility for the long-term. PVA gel is a good candidate for a vitreous substitute. Less