排序方式: 共有17条查询结果,搜索用时 390 毫秒
1.
2.
《Contact lens & anterior eye》2019,42(4):462-466
PurposeTo describe a simple method to quantify scleral contact lens decentration using over-topography captured with a Placido ring videokeratoscope, and its repeatability.MethodsScleral lens over-topography (E300 videokeratoscope, Medmont) was measured on 10 healthy participants following 15 min of lens settling (16.5 mm total diameter ICD miniscleral, Capricornia). Horizontal and vertical lens decentration was quantified from the translation of the front optic zone relative to the pupil centre derived from ellipses manually fitted to tangential power over-topography maps using both a standard and normalised dioptric scale. Intrasession (different maps captured within the same measurement session), intraobserver (identical maps analysed by the same observer), and intertechqniue (standard or normalised tangential power scales) repeatability were calculated.ResultsThe mean lens decentration was 0.62 ± 0.18 mm temporally and 0.91 ± 0.33 mm inferiorly. Lens decentration derived from tangential topography maps with a standard power scale were more repeatable (95% limits of agreement for intraobserver repeatability ± 0.07 mm and intrasession repeatability ± 0.15 mm) than measurements derived from normalised maps (95% limits of agreement for intraobserver repeatability ± 0.11 mm and intrasession repeatability ± 0.20 mm).ConclusionsScleral lens decentration can be reliably quantified using tangential power maps with a standard (fixed) scale captured during over-topography without the need for customised instrumentation or image analysis software. This method has a range of potential applications in research and clinical practice. 相似文献
3.
针对加热炉采用的蜂窝蓄热体出现的破损问题,利用数值模拟技术,对蓄热烧嘴内部气体流动状况进行了冷态数值模拟实验研究。研究结果表明,在蓄热和放热过程中烧嘴内部存在明显的速度偏心现象,该问题是导致蓄热效率下降和蓄热体损坏的主要原因 相似文献
4.
刀具偏置的校正是超精密车削的首要任务,对提高超精密车削效率及精度具有非常重要的意义。传统的刀具偏置校正方法由于缺乏理论指导,存在校正效率低、精度低的缺点,即使利用国外进口软件进行辅助校正,也存在一些问题。对超精密车削中金刚石刀具偏置造成的车削误差展开理论分析,在理论分析的基础上,给出提高刀具偏置校正精度及效率的原则,提出一种新的刀具偏置校正方法——泰曼格林干涉仪在线检测法,并用实验证明其准确性。 相似文献
5.
为使铅网水平电池发挥最佳性能,对拉丝工序使用的设备、工艺参数进行了规范。结合实际生产经验,总结了拉丝设备操作规程和过程控制要点,分析了该工序存在的安全隐患和质量缺陷,表述了比较完整的处理方法。 相似文献
6.
Stephen J. Vincent David Alonso-Caneiro Michael J. Collins 《Contact lens & anterior eye》2018,41(2):162-168
Purpose
To examine the time course of the reduction in central corneal clearance and horizontal and vertical lens translation (decentration) during miniscleral contact lens wear and the theoretical influence upon the optics of the post-lens tear layer.Methods
Repeated high-resolution OCT images were captured over an 8 h period of miniscleral contact lens wear (using a rotationally symmetric 16.5 mm diameter lens) in 15 young, healthy participants with normal corneae. Central corneal clearance and lens decentration were derived from OCT images using semi-automated image processing techniques.Results
Central corneal clearance decreased exponentially over time, reducing by 76 ± 8 μm over 8 h. Fifty percent of this reduction occurred within 45 min of lens wear and seventy-five percent within 2 h, with thinning of the post-lens tear layer plateauing 4 h after lens insertion. Lens translation exhibited a similar pattern of change (0.18 ± 0.04 mm temporal and 0.20 ± 0.09 mm inferior decentration) stabilising 1.5–2 h after insertion. The change in the lens fit over time resulted in a small reduction in the power of the post-lens tear layer (?0.12 ± 0.01 D) and induced a prismatic effect of 0.01 ± 0.16 Δ base out and 0.50 ± 0.19 Δ base down relative to the pupil centre.Conclusions
For the miniscleral contact lens studied, horizontal and vertical lens decentration followed an exponential decay over 8 h that plateaued approximately 2 h after lens insertion, while central post-lens tear layer thinning plateaued after 4 h of lens wear. 相似文献7.
光学中心偏测量对光学系统的检验和装校起着重要的作用,光轴拟合则是对中心偏测量数据的优化过程。提出了一种光轴拟合的新方法。该方法具有一些特点:原理上更科学,符合光学测量的实际;数学模型简单,易于编程实现;可以响应一些特殊的测量要求。该方法已经用于对多组实测数据进行优化,达到了预期的优化效果。 相似文献
8.
反射式光学系统中心偏的测量 总被引:1,自引:0,他引:1
通过分析反射式光学系统的特点,在现有透射式光学系统中心偏测量仪的基础上,提出了适合该系统中心偏测量的方法,分析了球心像的观察条件,并推导出反射系统中心偏的计算公式,从而形成了一个完善的反射式光学系统中心偏测量体系。该方法能获得与透射系统中心偏测量相同的精度,操作方法也基本相同。 相似文献
9.
10.
Web2.0网站的特点与社区化模式 总被引:3,自引:0,他引:3
分析了Web2.0网站的基本特点及其采用的新技术,介绍了Web2.0网站的去中心化概念和社区化模式趋势,并在此基础上进一步分析了网络社区中心重构的运行机制和一系列的社区化模式.通过理论和统计数据双重分析得出,传统的Web1.0站点向Web2.0的转变和社区化进程,已经逐渐成为网络发展的主流趋势. 相似文献