2 # 大 中 小 发表于 2007-9-30 14:19 只看该作者 在开始检查以前，应先询问病史，检查外眼时，可借助自然光线作一般视诊检查，再利用集合光线（斜照法）检查。 眼底检查在暗室进行。 必要时进一步作特殊检查。 第一节 视功能检查 一、中心视力检查 中心视力简称视力（vision），即视敏度（visual acuity），是指黄斑部中心凹的视力功能，也就是眼分辨得出小目标物的能力。 视力的好坏是衡量眼机能是否正常的尺度，也是分析病情的重要依据。 视角原理：测量视力是用视力表上的字形作为标准，每个字形的构造都是根据视角来计算的。 视角是指由目标物两端发出的两条光线射向内节 点（此节 点位于晶体后部，射入眼内光线通过节 点，不发生屈折）时相交所夹的角。 视网膜能辨认某一物体（或更具体地说区分两个点）时，必须在眼内形成一定的视角。 正常眼能辨别最小物体（或区分最近的两个点）的视角叫最小视角，大多数正常眼的最小视角为一分角。 实验证明，正常人在0.5～1分视角下看清物体时，其在视网膜上的物象约等于0.002～0.004毫米，大致相当于锥体的直径。 由此推知，分辨两个点在视网膜上单独存在的主要条件是两个感光单位（锥体）的兴奋，而在这两个锥体间至少要被一个不兴奋的锥体所隔开。 如果点的象落在邻近两个锥体时，这个象就会重合而不能分辨了（图2-1） 图2-1 一分视角 根据上述原理，各种视力表的标记都是一分视角的五倍（五分视角）作为面积而制成的。 规定线条的宽度、缺口与大小都是一分视角。 如国际标准视力表及标准对数视力表上“E”形字的线条宽度和线条间距，Landolt氏视力表上“C”形字的线条与缺口大小都为一分角。 视力表上的大小标记是在五分视角下，依据距离眼的远近分别制定的，如国际标准视力表上端最大标记（0.1行）是在五分视角下，50米距离制定的，第十行标记（1.0行）是在五分视角下，五米距离制定的，其他各行也都在五分视角下依不同距离而制定的（图2-2）。 （一）远视力检查法 1. 安装视力表的注意事项 (1)表面须清洁平整。 (2)表的高度以表上1.0视力（对数视力表上5.0）的标记与被检查的眼等高为准。 图2-2 视力表E字与五分视角的关系 (3)表上必须有适当、均匀、固定不变的照明度，一般为400～1000Lux，且必须避免由侧方照来的光线，及直接照射到被检者眼部的光线。 阴晴不定的自然光线亦不适宜，以免引起不准确的检查结果。
类别: 夜间视力范围
· 波动光学 wave optics
类别: 夜晚视觉光学
April 17 Lemma, Proposition, Theorem and Corollary There is no technical distinction between a lemma, a proposition, and a theorem. A lemma is a proven statement, typically named a lemma to distinguish it as a truth used as a stepping stone to a larger result rather than an important statement in and of itself. Of course, some of the most powerful statements in mathematics are known as lemmas, including Zorn's Lemma, Bezout's Lemma, Gauss' Lemma, Fatou's lemma, etc. , so one clearly can't get too much simply by reading into a proposition's name. Even less well-defined is the distinction between a proposition and a theorem. Many authors choose to name results only one or the other, or use both more or less interchangeably. A partially standard set of nomenclature is to use the term proposition to denote a significant result that is still shy of deserving a proper name. In contrast, a theorem under this format would represent a major result, and would often be named in relation to mathematicians who worked on or solved the problem in question. The greek word "lemma" itself means "anything which is received, such as a gift, profit, or a bribe. " According to, the plural 'Lemmas' is commonly used. The correct greek plural of lemma, however, is lemmata. The greek "Theoria" means "view, or vision" and is clearly linguistically related to the word "theatre". The apparent relation is that a theorem is a mathematical fact which you see to be true (and can now show others!) . A somewhat more distinct concept (though still subject to author discretion) is that of a corollary, which is a result that can be considered an immediate consequence of a previous theorem (typically, the preceding theorem in the text).
类别: 廉价的夜视护目镜
van vincent gogh night starry painting
类别: 亚特兰大俱乐部夜视
