Harris W F
Department of Optometry, Rand Afrikaans University, Johannesburg, South Africa.
Optom Vis Sci. 1993 Aug;70(8):666-7. doi: 10.1097/00006324-199308000-00014.
Twelve years ago Keating pointed out that dioptric powers existed which could not be represented by the familiar three parameters sphere, cylinder, and axis. They are the equivalent powers of optical systems (including many eyes) with separated obliquely crossing astigmatic elements. Four parameters are required to represent such powers, and all four are unfamiliar to most clinicians and researchers. This note shows that it is, in fact, possible to transform the four parameters so that the three familiar parameters are retained and only one (called asymmetry) remains unfamiliar. The consequence is that it is always possible to represent a power by means of sphere, cylinder, axis, and asymmetry. Powers commonly used in practice all have asymmetry equal to zero which is why only the first three are usually necessary. Powers, however, do exist, and are of potential interest in optometry, for which asymmetry is not zero and cannot be omitted from the representation. Two numerical examples are given, including Keating's model eye.
十二年前，基廷指出存在一些屈光力，无法用常见的三个参数——球镜度、柱镜度和轴位来表示。它们是具有斜交散光成分的分离光学系统（包括许多眼睛）的等效屈光力。表示这种屈光力需要四个参数，而大多数临床医生和研究人员对这四个参数都不熟悉。本笔记表明，实际上可以对这四个参数进行变换，以便保留三个熟悉的参数，只留下一个（称为不对称性）不熟悉的参数。结果是，总是可以通过球镜度、柱镜度、轴位和不对称性来表示一种屈光力。实际中常用的屈光力其不对称性都等于零，这就是为什么通常只需要前三个参数的原因。然而，确实存在不对称性不为零且在表示中不能省略的屈光力，并且它们在验光中可能具有潜在的研究价值。给出了两个数值示例，包括基廷的模型眼。
