准分子激光眼屈光手术中的一种过渡区模型

提出了一种在准分子激光眼屈光手术中过渡区模型的构造方法.首先设计一种修边函数,然后提取光学区边界的切削深度,并将其扩展到整个过渡区,最后通过修边函数和过渡区上扩展切削深度的乘积得到过渡区模型.再将该模型进行计算机仿真研究和临床研究.临床上统计了8名患者16只眼睛接受该模型指导的激光手术情况:术前平均裸眼视力为0.09±0.04,术后第1天平均裸眼视力为1.06±0.24,之后视力逐渐升高,在术后一个月时平均裸眼视力为1.42±0.36,裸眼视力最小值为1.0.仿真结果,特别是临床结果表明:过渡区模型实现了光学区与非切削区之间光滑平坦地过渡.采用参数化控制的模型,特别适用于光学区直径和过渡区宽度经常调整的情况,对各种眼屈光不正情况均适用;在光学区直径确定后,过渡区宽度的改变不影响光学区的切削深度;模型有较强的通用性,适用于传统仅矫正屈光不正(近视、远视、散光)的光学区模型,也适用于波前像差引导的激光眼屈光手术.利用过渡区模型可提高手术后患眼的视觉质量.     

激光视力矫正术的应用研究

人眼屈光不正是眼科常见疾病，可用眼外科术(角膜屈光性手术)改变角膜曲率来矫正。即使角膜曲率变平或变陡，或使整个角膜表面变成正圆球形，改变其屈光力，从而矫治近视、远视和散光。目前临床应用的激光视力矫正术(Laser Vision Correction)有下列几种方法。     

波前像差引导的角膜切削模型及实现技术的研究

对波前像差概念和表示方法做了必要的叙述,深入研究了波前像差引导的角膜个性化切削模型,推出了角膜手术区域中角膜修正量的基本公式,给出了实现个性化像差矫正手术的软硬件框图.采用该模型引导的扫描频率为120Hz,光斑直径为0.9mm的准分子激光眼科治疗机做PMMA试验,对比传统的屈光不正矫正模型,在手术区域直径为6.5mm条件下,给出了近视、远视、近视散光各种情况下手术的最大切削深度和切削时间.试验结果表明,各种情况下角膜最大切削深度基本相同,波前像差矫正切削模型的切削时间稍大,PMMA板切削效果良好.     

激光眼屈光外科术：回顾与现状

眼角膜屈光外科术是为了修正角膜前表面曲率，从而达到校正近视、远视和散光的目的。空气·泪层的内面为一强折射层，较小的曲率变化就可以引起较大的屈光能力变化。激光和角膜组织的完美作用性使得激光能在眼屈光外科中成功地应用，已为临床应用开发了许多系统。本文对激光眼屈光外科术的临床和研究状况作一个综述。     

基于人眼光学模型建立的角膜模型

考虑角膜面型的非球面特性,应用光学设计软件Zemax,从光学成像角度提出了结合人眼光学模型的角膜双二次曲面模型的建立方法;结合国人正视眼和近视眼的有关实测数据和分析结果,以人眼的波像差为评价函数,对初始模型眼进行优化,给出了符合我国人眼特点的正视眼和近视眼模型中的角膜模型.讨论了矫正近视的矫正眼模型中的角膜理想模型和可用于角膜屈光手术中的切削模型,切削深度的最大值在角膜中心处,约26.5μm.结果表明:基于人眼光学模型的角膜双二次曲面模型,符合角膜的面型特点,适合临床实际应用,可为波像差引导的个性化角膜切削方案提供更适用的数字化模型.     

基于人眼光学模型的角膜模型的研究

位于眼球最前端的角膜是人眼光学系统的主要屈光元件之一,建立角膜模型具有重要的研究和临床意义。基于角膜面型的非球面特性,应用光学设计软件Zemax,从光学成像角度,提出了结合人眼光学模型的角膜双二次曲面模型的建立,并结合国人正视眼和近视眼的有关实测数据和分析结果,以人眼的波像差为评价函数,通过对初始模型眼的优化,给出了符合我国人眼特点的正视眼和近视眼模型中的角膜模型,讨论了矫正近视的矫正眼模型中的角膜理想模型和可用于角膜屈光手术中的切削模型。基于人眼光学模型的角膜双二次曲面模型也可为波像差引导的个性化角膜切削方案提供一个更适于实际应用的数字化模型。     

六角棱镜调制电脑验光仪对散光眼模型检测精度分析

针对传统电脑验光仪调焦速度慢,聚焦误差大的缺陷,对现有验光仪六角棱镜的成像系统进行优化。通过光学仿真软件分析和对比发现六角棱镜调制的验光仪在散光度和散光轴位的测量误差（柱镜示值平均误差CYL=0.8m-1,轴位示值平均误差AX=3.73°）均明显大于普通圆环调制的验光仪（CYL=0.2m-1,AX=1.75°）。因此,采用圆环代替六角棱镜调制可以增加检测的精度。另外,对六棱镜分光法设计的验光仪的设计和检验需要特别注意其柱镜度和柱镜轴位的检测评价,避免造成验光误差。     

基于眼模型的数字眼底相机设计

本文基于Gullstrand-Le Grand眼光学模型设计了一个视场角为30°免散瞳手持式的数字眼底相机,在综合考虑人眼本身和外部系统的像差后,实现了全视场200万像素的高清晰眼底成像;引入眼模型辅助设计,解决了人眼自身的色差问题,从而适用于白光照明。同时,为避免角膜中心曲率大的区域反射引入杂散光,专门设计了环形光阑和共轴照明相结合的照明系统。结果显示,该相机系统成像分辨率高于120lp/mm,场曲值小于0.86mm,畸变仅为7.2%,并且具有较大调焦能力,对-10D至7D屈光度人眼普遍适用。     

Toric人工晶状体植入术一年后旋转稳定性及影响因素

目的 :观察Toric人工晶状体植入术1年后旋转稳定性,探讨影响Toric人工晶状体旋转稳定性的相关因素。方法 :选择2013年3月至2017年6月接受超声乳化白内障吸除联合Toric人工晶状体植入的305例(392眼)患者,对其1年随访资料进行回顾性分析。分析患者人工晶状体植入1年后旋转情况,应用Pearson相关性分析、多元线性回归分析,总结影响Toric人工晶状体植入术1年后旋转稳定性的相关因素。结果:术后1年患眼平均残余散光度为(-0.85±0.18)D,其中94例残余散光度为0 D,残余散光度≤1.00 D者共占71.94%。患眼术后1年人工晶状体旋转度为(4.21±0.95)°,除8例未发生旋转外,其余患者人工晶状体均发生旋转,旋转度> 5°者占26.02%。Pearson相关性分析结果,术后1年患眼残余散光度与Toric人工晶状体旋转度呈正相关(r=0.629,P <0.05)。多元线性回归分析结果,眼轴长度、前囊膜混浊分级是影响Toric人工晶状体植入术1年后旋转稳定性的独立因素(P <0.05)。结论 :Toric人工晶状体植入术1年后旋转稳定性尚可,但术前眼轴长度、术后前囊膜混浊分级可对人工晶状体稳定性造成一定影响,应予以重视,以降低人工晶状体旋转对术后残余散光的不良影响。     

虹膜拉钩在白内障伴晶状体半脱位超声乳化术中作用

目的 :分析虹膜拉钩在白内障伴晶状体半脱位超声乳化术中作用,探讨提高超声乳化术临床效果及安全性方法。方法 :2014年9月—2015年9月我科单眼白内障伴晶状体半脱位行虹膜拉钩辅助白内障超声乳化术患者35例。比较患者手术前后视力、角膜散光、角膜内皮细胞、晶体伪调节力变化,观察其并发症发生情况。结果 :患者术后裸眼视力、最佳矫正视力均显著提高,差异有统计学意义(P<0.05)。其术后角膜散光、角膜内皮细胞、晶体伪调节力均未见明显变化,差异无统计学意义(P>0.05)。35例患者术中未出现囊膜撕裂、眼内明显出血,术后并发症发生率为25.8%,次随访人工晶体均位置居中。结论 :虹膜拉钩能够有效维持白内障伴晶状体半脱位超声乳化术中囊袋的完整性及术后人工晶体的稳定性,在保证手术安全性、促进患者视力恢复方面具有价值。     

基于双经度模型的鱼眼图像畸变矫正方法

针对鱼眼镜头拍摄图片桶形畸变大的问题,提出了一种基于双经度图像畸变矫正算法,以改善其视觉效果。首先,在未知镜头视角大小且鱼眼图像非圆形的情况下,利用鱼眼图像特征求得球面中心及其半径,并对半径大小做优化处理以减弱极点畸变;在此基础上采用双经度模型方法,通过正交投影策略将鱼眼图像映射到球面上,转化为球面横向经度和纵向经度坐标,从而投射为以横向、纵向双经度坐标为基础的正方形平面图像,实现图像的快速、精确变换。最后,利用2个实例验证了该文所提算法的有效性和可行性。     

一种非接触式R-test测量仪球心坐标计算方法

R-test测量仪是用于五轴数控机床转动轴结构误差测量的专用设备,其通过测量球相对测量坐标系的位置变化进行误差辨识。在测量坐标系中,测量球球心坐标计算的准确性和稳定性是保证测量精度的重要前提。为进行测量球球心坐标的精确计算,构建了非接触式R-test测量仪的结构模型并建立了球心坐标计算方程组。以球心坐标计算方程组为基础,简化得到用于球心坐标求解的非线性方程组并构建其目标函数,然后采用差分进化算法提高球心坐标求解的精度。最后,在GF Mikron UCP800五轴机床上进行对比实验,将测量球球心坐标的计算结果与机床实际坐标进行对比,验证所提出球心坐标计算方法的精度和可靠性。     

Ultrastructural and three‐dimensional study of post‐LASIK ectasia cornea

INTRODUCTION: Post‐laser in situ keratomileusis (LASIK) corneal ectasia is a serious late postoperative complication. Here, we report the ultrastructural features of the post‐LASIK cornea of two patients. METHODS: Two normal corneas (age 24 and 37 years old) and two post‐LASIK ectaic corneas from two patients (A and B) were studied. The “patient A” (age 27 years) underwent penetrating keratoplasty and “patient B” (age 31 years) underwent deep‐anterior lamellar keratoplasty. The excised corneas were processed for light and electron microscopy. A total of 120 images for three‐dimensional (3D) reconstruction were taken by using the software “Recorder” and using a bottom mounted camera “Quemesa” attached to a JOEL 1400 transmission electron microscope. The 3D images were constructed using “Visual Kai” software. RESULTS: In the post‐LASIK cornea, the hemidesmosomes, the basement membrane, and Bowman”s layer were abnormal. The stromal lamellae were thin and disorganized. The collagen fibrils (CFs) diameter and interfibrillar spacing had decreased. Aggregated microfibrils were present in the Bowman's layer and all parts of the stroma. A large number of microfilaments were present at the detachment end of the flap and residual stroma. The 3D images showed the presence of collagen microfibrils and proteoglycans (PGs) within the CF of the normal and post‐LASIK cornea. The collagen microfibrils and PGs within the CFs had degenerated in the post‐LASIK cornea. CONCLUSION: Collagen microfibrils and PGs within the CFs were degenerated, leading to the degeneration of CFs, followed by the disorganization of lamellae in post‐LASIK cornea. The CFs diameter and interfibrillar spacing decreased. Microsc. Res. Tech. 77:91–98, 2014. © 2013 Wiley Periodicals, Inc.     

A novel type compact five-coordinate measuring machine with laser and CCD compound probe

In this paper, a novel type compact five-coordinate measuring machine with laser and CCD compound probe, which consists of three translational axes and two rotational axes, was designed and built. The compound probe is employed and the measurement mathematical model is established. An improved genetic algorithm is applied to solve the unknown parameters of the model. Hence, by means of this model, the 3D surface data of the tested object can be transformed into the same reference coordinate system. Quasi-Newton method is introduced and in charge of processing tested surface data. Based on the variety of tested object, such as plane, sphere, cylinder etc. the corresponding optimization objective function and initial condition are set properly to achieve the solution of characteristic parameters. Especially, in this work, an evaluation function method based on the “roundness” information of the through-hole image is proposed to detect the diameter and spatial location of hole, which particularly fits for inspecting those thin and small through-holes drilled at the soft and easy-deformed objects. Consequently, the measurement puzzle of spatial angle between two thin and through-holes is easily solved. The experiments show that the measurement repeatability of this machine is within 1.6 μm. Meanwhile, the experiments illustrate the validity and feasibility for through-holes measurement.     

Measurement of lens aberrations by means of image displacements in beam-tilt series

Electron microscope image aberrations are determined by means of the beam tilt/image displacement method with respect to the precision required to obtain a resolution of 1 A. The method simultaneously yields all image aberrations to the fourth order and it is independent of the material used for the procedure. The experimental procedure using amorphous carbon is described and errors in measuring beam-tilt angles, magnifications and image displacements can be kept sufficiently small to achieve the required accuracy. The method is applied to determine aberration constants of a CM300 FEG/UT microscope with correction of the three-fold astigmatism. The coefficient of spherical aberration and the modulus of the three-fold astigmatism were measured to 0.60 (+/- 0.02) mm and 150 (+/- 50) nm, respectively. The beam tilt/image displacement procedure is also computer simulated using an amorphous model structure yielding the same values for the lens aberrations which are used for imaging. However, a coefficient of spherical aberration of 0.67 mm is obtained by applying the focus variation/diffractogram analysis on the same model.     

光电经纬仪脱靶量和坐标动态修正

提出了目前采用的脱靶量修正模型的适用条件,采用坐标变换推导经纬仪脱靶量修正公式,获得与球面三角学相一致的推导结果,并在此基础上推导出成像系统无照准轴平行约束条件的通用脱靶量合成公式。采用光学系统的物方焦点作为摄像机系统的投影中心,推导出投影中心与经纬仪回转中心不重合条件下摄像机投影中心在测量坐标系中的坐标值。经测量设备的实际验证,该修正方法突破了现有修正模型的局限性,适用于多传感器经纬仪成像系统     

Free vibration of a class of solids with cavities

The Ritz method is used to obtain an eigenvalue equation for the free vibration of a class of solids. Each solid is modelled by means of a segment which is described in terms of Cartesian coordinates and is bounded by the yz, zx and xy orthogonal coordinate planes as well as by two curved surfaces which are defined by polynomial expressions in the coordinates x, y and z. Simple algebraic polynomials which satisfy the boundary conditions at the five surfaces of the segment are used as trial functions. By exploiting symmetry, the range of problems which can be treated is substantially broadened and includes a variety of problems of significant interest in structural analysis, such as thick or very thick shells with various shaped cavities. In order to demonstrate the accuracy of the approach, natural frequencies are given for a sphere with a spherical cavity (a thick spherical shell) as calculated by using the present analysis and by using an exact formulation. The versatility of the approach is then demonstrated by the treatment of several other hollow solids of differing geometry, including a thick cylinder with end plates, a cubic box, a cube with a spherical cavity and a cylinder with a conical inclusion.     

应用坐标变换动态修正光电经纬仪脱靶量

分析了目前采用的脱靶量修正模型的适用条件,采用坐标变换法推导出经纬仪脱靶量修正公式,获得了与球面三角学相一致的推导结果,并在此基础上推导出成像系统无照准轴平行约束条件的通用脱靶量合成公式.采用光学系统的物方焦点作为摄像机系统的投影中心,推导出投影中心与经纬仪回转中心不重合条件下摄像机投影中心在测量坐标系中的坐标值.经测量设备的实际验证表明,该修正方法突破了现有修正模型的局限性,适用于多传感器经纬仪成像系统.对于水平不平行度为6.13°,物方焦点到固联中心的距离为0.247 m的成像系统,脱靶量合成修正误差＜16.0"(高低角为65°);投影中心位置误差＜0.04 m.     

Zur konstruktion der sphärischen wendekurve

It is a well-known result of instantaneous spherical kinematics that the locus of those points of the moving sphere, whose paths have a vanishing geodesic curvature, is a curve w on a cubic cone Ω with vertex in the center O of the sphere. In this paper we give a simple construction of the inflection curve w using the following theorem: The intersecting curve l of the inflection cone Ω with a sphere κ, which is centered on the pole-axis p and contains the point O, lies on a cylinder of revolution. This cylinder contains the inflection circle of that planar motion in the tangent plane τ of κ in the pole P = p ∩ κ (P ≠ O), whose relationship between the points and centers of curvature of their paths is induced in τ by the spherical motion. Furthermore we use this result to draw some geometrical conclusions on the set of the ∞¹ inflection curves belonging to a given canonical frame. In a special case the inflection curve is a spherical trochoid.