角膜接触透镜材料的研究进展

综述了接触透镜材料的研究进展,接触透镜从材料方面主要分为硬镜和软镜;介绍了各种透镜材料的成分、性能,并对其优缺点进行评定.聚甲基丙烯酸甲酯(PMMA)是最初的接触透镜材料,随后研制出透气性硬镜材料(RGP)以保持佩戴角膜健康.为改善佩戴舒适性,广泛研究水凝胶类软接触透镜材料,主要有聚甲基丙烯酸β-羟乙酯(HEMA)、聚乙烯吡咯烷酮(PVP)和聚乙烯醇(PVA)等材料;为提高软镜的透氧性等性能,目前研究的热点是高透氧性软接触透镜材料,主要以有机硅、有机氟等大分子单体合成水凝胶材料,以及生物改性的软镜材料.     

Investigation of the polarization optics of the living human cornea and lens with purkinje images

We present what to our knowledge is a new method for assessing the polarization optics of the cornea and lens, by examining the state of polarization of the first, second, and fourth Purkinje images. When linearly polarized light is incident on the cornea at 70 degrees to the line of gaze along the horizontal meridian, and then traverses the cornea, or the cornea and the lens, the emergent light is elliptically polarized. The degree of ellipticity varies widely between subjects. The results indicate that both the cornea and the lens may be optically active and to our knowledge are the first to suggest that the cornea may exhibit circular birefringence.     

角膜接触镜材料的应用和研究进展

综述了各种透明高分子材料在角膜接触镜领域的应用及其特性,指出了角膜接触镜材料存在的问题,指明了角膜接触镜材料的发展趋势.     

LLDPE的紫外辐照改性及增韧PA66

通过紫外辐照在线性低密度聚乙烯(LLDPE) 的分子链上引入C=O、C —O 和—OH 含氧基团, 其含量随辐照时间延长而增加。紫外辐照后, LLDPE 的晶型和晶面间距未发生变化, 但是其熔融温度和结晶度下降。与LLDPE/ 尼龙66 (PA66) 复合材料相比, 辐照LLDPE/ PA66 复合材料的分散性和相容性得到显著改善, 两相之间的界面粘结力明显提高。随辐照时间延长, 辐照LLDPE/ PA66 复合材料的拉伸强度、弯曲强度和缺口冲击强度提高, 在辐照24 h 时达到最高值, 分别比LLDPE/ PA66 复合材料提高了20 %、13 %和330 % , 辐照LLDPE 表现出较好的增韧作用。      

Nonlinear optical behavior of ocular tissue during laser irradiation

A pump (cw Ho-YAG laser) and probe (He-Ne laser) system was used to study the dynamics of the optical behavior of ocular tissue during laser heating. The nonlinear optical behavior of porcine corneal and vitreous-humor tissue was characterized in vitro by means of measurements of the radial profile of a He-Ne laser beam transmitted through the tissue. Temperature gradients in the tissue created by the absorption of pump radiation caused the probe beam to diverge. For constant laser power, the rate of divergence was made dependent on the spot size of the pump beam. The profile of the transmitted probe beam returned to its original magnitude and shape after the tissue was permitted to cool. This reversible change in optical behavior was attributed to the formation of a negative lens owing to thermally induced local gradients in the refractive index of the tissue.     

Morphological transition of gold nanostructures induced by continuous ultraviolet irradiation

Gold nanoparticles were synthesized through a continuous UV irradiation method using citric acid as a reducer and protective agent. After a period of continuous UV irradiation, the nanoparticles transformed into two-dimensional (2D) nanonetworks, porous nanoplates and compact nanoplates with hexagonal, triangular or truncated triangular pores through a self-assembly process which was dependent on the citric acid concentration. Selected area electron diffraction (SAED) patterns indicated that both the nanonetworks and the porous nanoplates were single crystalline. The influence of citric acid concentration and irradiation time on the morphological transition of Au nanostructures was investigated. The process of morphological transition was presumably discussed.     

Aging of the human lens: changes in lens shape at zero-diopter accommodation

Scheimpflug photographs of the zero-diopter-accommodated anterior segments of 100 human subjects, aged 18 to 70 yr and evenly spaced over this range, were digitized and analyzed to characterize lens and lens nucleus shape as a function of age by the Hough transform and other image analysis methods. Anterior and posterior lens surface curves exhibit a decrease in radius of curvature with increasing age, in qualitative but not quantitative agreement with the earlier observations of Brown [Exp. Eye Res. 19, 175 (1974)]. In contrast, the shape of the lens nuclear boundaries changes little with age. Overall lens volume at zero diopters increases with age, but the volume of the lens nucleus remains unchanged. The lens center of mass moves anteriorly with increasing age, as does the central clear region of the lens. Although these data sets were found to be more variable than those of Brown, the complementary variability of other factors, such as anterior chamber depth, for each subject leads to a very high statistical correlation between lens shape and lens location relative to the cornea. This supports the finding of previous work that image formation on the retina for a given individual results from the multifactorial balancing of related factors.     

Contribution of the cornea and internal surfaces to the change of ocular aberrations with age.

We studied the age dependence of the relative contributions of the aberrations of the cornea and the internal ocular surfaces to the total aberrations of the eye. We measured the wave-front aberration of the eye with a Hartmann-Shack sensor and the aberrations of the anterior corneal surface from the elevation data provided by a corneal topography system. The aberrations of the internal surfaces were obtained by direct subtraction of the ocular and corneal wave-front data. Measurements were obtained for normal healthy subjects with ages ranging from 20 to 70 years. The magnitude of the RMS wave-front aberration (excluding defocus and astigmatism) of the eye increases more than threefold within the age range considered. However, the aberrations of the anterior corneal surface increase only slightly with age. In most of the younger subjects, total ocular aberrations are lower than corneal aberrations, while in the older subjects the reverse condition occurs. Astigmatism, coma, and spherical aberration of the cornea are larger than in the complete eye in younger subjects, whereas the contrary is true for the older subjects. The internal ocular surfaces compensate, at least in part, for the aberrations associated with the cornea in most younger subjects, but this compensation is not present in the older subjects. These results suggest that the degradation of the ocular optics with age can be explained largely by the loss of the balance between the aberrations of the corneal and the internal surfaces.     

Nanolubrication: patterned lubricating films using ultraviolet (UV) irradiation on hard disks

Nanolubrication is emerging to be the key technical barrier in many devices. One of the key attributes for successful device lubrication is self-sustainability using only several molecular layers. For single molecular species lubrication, one desires bonding strength and molecular mobility to repair the contact by diffusing back to the contact. One way to achieve this is the use of mask to shield the surface with a patterned surface texture, put a monolayer on the surface and induce bonding. Then re-deposit mobile molecules on the surface to bring the thickness back to the desired thickness. This paper describes the use of long wavelength UV irradiation (320-390 nm) to induce bonding of a perfluoropolyether (PFPE) on CN(x) disks for magnetic hard disk application. This allows the use of irradiation to control the degree of bonding on CN(x) coatings. The effect of induced bonding based on this wavelength was studied by comparing 100% mobile PFPE, 100% bonded PFPE, and a mixture of mobile and bonded PFPE in a series of laboratory tests. Using a lateral force microscope, a diamond-tipped atomic force microscope, and a ball-on-inclined plane apparatus, the friction and wear characteristics of these three cases were obtained. Results suggested that the mixed PFPE has the highest shear rupture strength.     

Allotropic phase transformations induced by ultraviolet power laser irradiation of graphite

Optically induced allotropic phase transformations of carbon were studied. Under irradiation with a laser beam of 337.1 nm wavelength, at an energy density of 1.9 mJ per 0.1 mm², graphite transformed into -carbin, and amorphous carbon-film transformed into rhombohedral graphite with no evidence of high-temperature effects. The transformations differ from the changes occurring due to heating alone. We suggest that the results could be explained by the one-photon excitation and recombination of electrons.     

Minimizing the exposure of airborne pathogens by upper-room ultraviolet germicidal irradiation: an experimental and numerical study

There has been increasing interest in the use of upper-room ultraviolet germicidal irradiation (UVGI) because of its proven effectiveness in disinfecting airborne pathogens. An improved drift flux mathematical model is developed for optimizing the design of indoor upper-room UVGI systems by predicting the distribution and inactivation of bioaerosols in a ventilation room equipped with a UVGI system. The model takes into account several bacteria removal mechanisms such as convection, turbulent diffusion, deposition and UV inactivation. Before applying the model, the natural die-off rate and susceptibility constants of bioaerosols were measured experimentally. Two bacteria aerosols, Escherichia coli and Serratia marcescens, were tested for this purpose. It was found out that the general decay trend of the bioaerosol concentration predicted by the numerical model agrees well with the experimental measurements. The modelling results agree better with experimental observations for the case when the UVGI inactivation mechanism dominates at the upper-room region than for the case without UVGI. The numerical results also illustrate that the spatial distribution of airborne bacteria was influenced by both air-flow pattern and irradiance distribution. In addition to predicting the local variation of concentration, the model assesses the overall performance of an upper-room UVGI system. This model has great potential for optimizing the design of indoor an upper-room UVGI systems.     

Aging of the human lens: changes in lens shape upon accommodation and with accommodative loss.

Accommodation in the human eye occurs through controlled changes in crystalline lens shape, thickness, and refractive surface placement relative to the cornea. The changes in lens curvatures, whether surface or internal, have been characterized as a function of accommodation and subject age by use of quantitative analysis of Scheimpflug slit-lamp photographic images. Radii of curvature of the major lens refractive surfaces--the external and nuclear boundaries--decrease linearly with increasing accommodation in all eyes that are capable of accommodation. The rates at which they change with accommodation are age dependent, decreasing steadily toward zero with increased age. For the curves visible in each lens half, arising from boundaries between adjacent zones of discontinuity, radius of curvature and location are linearly related over the entire accommodative range for a given lens and over the age range for the population. The slope of this relationship changes with both accommodation and age, decreasing linearly in both cases. The relationship between these geometric changes and the loss of accommodative amplitude is discussed.     

Evaluation of phase, microstructure and composition of human dentine after Er,Cr:YSGG laser irradiation

This study aims to evaluate the composition, micro-structure and inorganic phase alternations of human dentine irradiated by Er,Cr:YSGG laser with water cooling spray system. X-ray diffraction (XRD) analysis indicated that the main inorganic phase of dentine before and after laser irradiation were all Hydroxyapatite (HA) structure, approximately 30 nm in size. No significant changes occurred in the average particle size after irradiation in four energy densities (6.18 J/cm2, 8.04 J/cm2, 9.89 J/cm2, 11.1 J/cm2). Atomic force microscope (AFM) phase image and the energy-dispersive spectroscope (EDS) analysis, however, demonstrated that the thermal effects of Er,Cr:YSGG laser with water-cooling spray system on the dentin surface was intense enough to induce notable decrease of the organic matter. Both scanning electron microscopy (SEM) and AFM analysis showed that the irradiated dentine presented rough surface morphology. The surface is clean and dentinal tubules are completely open. The ablation rate of both peri- and intertubular dentine increased at higher energy densities but no significant changes of gross appearance took place. Chemical analysis reveals that laser photothermal effect would decrease significantly the organic content of superficial dentinal layer. We conclude that the Er,Cr:YSGG laser, as a new type clinic laser, would not significantly influence the inorganic phase structure of the surface dentine layer, however, thermal ablation was occurred in organic component. Moreover, the rough ablated surface as well as the opened dentinal tubules induced by irradiation, might be advantageous to the infiltration of the adhesive materials, thus the adhesion of dental restoration could be enhanced. Further studies should focus on the correlation between bond strength and Er,Cr:YSGG lased dentine.     

Numerical implementation of generalized Coddington equations for ophthalmic lens design

A method for general implementation in any software platform of the generalized Coddington equations is presented, developed, and validated within a Matlab environment. The ophthalmic lens design strategy is presented thoroughly, and the basic concepts of generalized ray tracing are introduced. The methodology for ray tracing is shown to include two inter-related processes. Firstly, finite ray tracing is used to provide the main direction of propagation of the considered ray at the incidence point of interest. Afterwards, generalized ray tracing provides the principal curvatures of the local wavefront at that point, and its orientation after being refracted by the lens. The curvature values of the local wavefront are interpreted as the sagital and tangential powers of the lens at the point of interest. The proposed approach is validated using a double-check of the calculated lens performance in the spherical lens case: while finite ray tracing is validated using a commercial ray tracing software, generalized ray tracing is validated using a software application for ophthalmic lens design based on the classical version of Coddington equations. Equations of the complete tracing process are developed in detail for the case of generic astigmatic ophthalmic lenses as an example. Three-dimensional representation of the sagital and tangential powers of the ophthalmic lens at all directions of gaze then becomes possible, and results are presented for lenses with different geometries.