Retinal phosphenes and discrete dark noises in rods: A new biophysical framework

Spontaneous rhodopsin activation produces discrete noises indistinguishable from single-photon responses. However, there is a serious discrepancy between the apparent energy barrier of thermal events compared with that of the photon-driven process. Current estimates of the activation energies of discrete dark noises in vertebrate rod and cone pigments are 40–50 kcal/mol for activation by photon and 20–25 kcal/mol for activation by heat. To reconcile this discrepancy, it was assumed that thermal activation and photon activation of rhodopsin follow different molecular mechanisms. The most convincing hypothesis for a separate low-energy thermal pathway is that the discrete dark noises of rods arise in a small subpopulation of rhodopsins, where the Schiff base linking the chromophore to the protein part has been deprotonated.According to Narici et al.’ experiments (2009, Radiation Measurements), phosphene perception in space travel is due to the ionizing radiation-induced free radicals that generate chemiluminescent photons from lipid peroxidation. These photons are absorbed by the photoreceptors chromophores, which modify the rhodopsin molecules (bleaching) and start the photo-transduction cascade resulting in the perception of phosphenes.Here, we point out that not only retinal phosphenes but also the discrete dark noise of rods can be due to the natural redox related (free radical) bioluminescent photons in the retina. In other words, under regulated conditions, lipid peroxidation is a natural process in cells and also in retinal membranes. Since the natural lipid peroxidation is one of the main sources of bioluminescent photons and the photoreceptors have the highest oxygen demand and polyunsaturated fatty acid (PUFA) concentration, there is a continuous, low level bioluminescent photon emission in the retina without any external photonic stimulation. During photopic or scotopic vision, evanescent bioluminescent photon emission is negligible. In contrast, in dark-adapted retinal cells this evanescent bioluminescent photon emission is not negligible. Therefore, our hypothesis is that the discrete dark noise of rods can be due to these bioluminescent photons.     

人眼视网膜成像自适应光学系统设计

设计一套基于液晶空间光调制器的人眼视网膜成像自适应光学系统,以获得高分辨率视网膜图像,并且使该系统实现体积小,功耗低,成本低等优点.采用夏克-哈特曼探测器和基于硅基板上的液晶器件分别作为波前探测器和波前校正器.系统采用双对准光源以主观方式来使人眼对准,近红外光探测成像以减小对人眼的刺激.使人眼对有限距离对焦,以减小离焦对成像的影响,使该系统既可用于正常眼,又可用于近视眼.用ZEMAX软件对系统进行了模拟分析,认为该系统可获得高于3 μm的视网膜分辨率,该系统设计是合理可行的.     

人眼视网膜成像液晶自适应光学系统的优化设计

针对已有的人眼视网膜成像液晶自适应光学系统的不足,提出了新的优化设计方案.新设计的系统能对不同视度下的人眼进行高分辨率成像.新系统还采用了瞳孔监控装置和成像区域快速精确定位装置,并且采用了改进的消杂散光方法,能够使探测准确度和定位准确度得到保证.研究证明,该系统新的设计方案操作方便、灵活,便于推广使用.     

Influence of DFT-calculated electron correlation on energies and geometries of retinals and of retinal derivatives related to the bacteriorhodopsin and rhodopsin chromophores

DFT-calculations were performed on retinal in the all-trans, 1, 11-cis-12-s-cis, 2, and 11-cis-12-s-trans configuration, 3, and on the corresponding N-methyl Schiff base and protonated N-methyl Schiff base derivatives; for the latter, the corresponding 6-s-trans conformations and the 6-s-trans-13-cis-14-s-trans isomer which play a role in the bacteriorhodopsin photocycle were also studied. All geometries were fully optimized using the Becke- three-parameter Lee-Yang-Parr method in conjunction with the 6-31G^** basis set (B3LYP/6-31G^**). The stabilities in order of increasing energy are 1, 3 and 2 regardless of the type of substitution of the end group. While the energy of 3 relative to 1 is almost constant (5 ± 0.2 kcal mol⁻¹), the relative energy of 2 depends somewhat on the nature of the functional group: it is highest in the protonated Schiff base derivative 2-SBH + with its steric congestion along the C12-C13 bond. Comparison with results previously obtained on the basis of RHF/6-31G^** ab initio calculations reveals that the B3LYP method is more biased towards π-electron delocalization. This is indicated by the reduced degree of double bond fixation along the chromophore and also in the increased tendency towards planarization as manifest, e.g. by the change of the C5-C6-C7-C8 dihedral angle between the cyclohexene ring and the open chain double bond system.     

Ocular integrity following manganese labeling of the visual system for MRI

Injection of manganese into the eye will enhance the contrast of visual system neuronal pathways imaged by MRI (MEMRI). The present study was undertaken to determine the effect of a range of MnCl₂ doses upon the integrity of various ocular structures. Anesthetized mice received ocular anterior chamber injections of 50–500 nmol of MnCl₂. One week later, the eyes were fixed, embedded in paraffin, sectioned, and stained with hematoxylin and eosin. Additional animals received 50 nmol of MnCl₂ injected into the anterior chamber and were later imaged using T1-weighted 7 T MRI. Following 500 and 300 nmol MnCl₂, the corneal stroma and endothelium were degenerated, the anterior chamber contained a dense fibrin matrix with extensive inflammatory cell infiltration, a plaque often formed on the anterior lens, and significant retinal degeneration was observed. Following 100 nmol MnCl₂, retinal preservation of ocular structures was significantly better than at higher doses. In addition, there was no difference from vehicle control retina in cell counts within the ganglion cell layer, or in the width of the inner nuclear layer or outer nuclear layer. Also, there was no difference in the thickness of the inner plexiform layer. However, there was thinning of the peripheral outer plexiform layer, as well as in the outer segment layer. Visual system elements labeled in MRI of mice that received 100 nmol MnCl₂ included the retina, optic nerve, lateral geniculate nucleus, and superior colliculus. The preservation of ganglion cell layer cell counts and inner plexiform layer thickness following 100 nmol MnCl₂ suggests there was negligible injury to RGCs following this dose. These results support using 100 nmol MnCl₂ in mouse eyes for in vivo assessment of the integrity of RGC projections to target neurons in the brain.     

紫膜菌紫质的拉曼光谱测试

菌紫质是一种可进行光信息存储与能量转换的生物膜蛋白分子。在光化学循环中 ,它包含的视黄醛产生快速的全反——— 1 3顺式异构化并去质子 ,然后又重新质子化并在反应循环终了转为全反式构型。了解菌紫质的分子构造及光化学反应机制是很有意义的事 ,但由于菌紫质是紫色膜蛋白 ,加之光反应时的荧光问题 ,用普通拉曼技术获得菌紫质的特征峰有一定困难。一般都用时间分辨付里叶变换红外光谱来进行它的测试工作。文本采用传统拉曼技术 ,分别用 5 3 2、785和 1 0 64nm波长激光作激发光源 ,测试了菌紫质的拉曼光谱 ,并得到了菌紫质的大部分特征拉曼谱带。     

Laser applications and system considerations in ocular imaging

We review laser applications for primarily in‐vivo ocular imaging techniques, describing their constraints based on biological tissue properties, safety, and the performance of the imaging system. We discuss the need for cost‐effective sources with practical wavelength‐tuning capabilities for spectral studies. Techniques to probe the pathological changes of layers beneath the highly scattering retina and diagnose the onset of various eye diseases are described. The recent development of several optical‐coherence‐tomography‐based systems for functional ocular imaging is reviewed, as well as linear and nonlinear ocular‐imaging techniques performed with ultrafast lasers, emphasizing recent source developments and methods to enhance imaging contrast.     

Analysis of Purkinje images as an effective method for estimation of intraocular lens implant location in the eyeball

The implantation of an artificial intraocular lens (IOL) into a capsular bag in place of an extracted natural, but nontransparent lens is a standard therapy method in the case of cataract. Any decentration or tilt of the IOL can cause a deterioration of the retinal image quality, thus decreasing the vision quality. The analysis of the relative position of Purkinje images being a reflection of the point light source from the refracting surfaces of the eyeball determines the location of IOL inside the eye and thus enables to state its wrong or correct location. The paper describes the Purkinje experimental setup consisting of an illuminator (several infrared LEDs arranged in a circle), an imaging telecentric lens and image recording CCD camera and reports details of the system calibration The usefulness of the experimental setup has been proven both in laboratory conditions using artificial model of the eyeball and in measurements on human subjects. Simulations of the retinal image with different decentrations or tilts are shown.