| 单词 |
astigmatism |
| 释义 |
astigmatism|əˈstɪgmətɪz(ə)m|
[f. as prec. + -ism.]
1. a. A structural defect in the eye (see quot.), which prevents the rays of light from being brought to a common focus on the retina.
1849G. B. Airy in Trans. Camb. Philos. Soc. VIII. 361 Twenty years ago, I had the honour of submitting to this Society a statement of the effects of a mal-formation in my own left eye. The nature of the effect was this: that the rays of light coming from a luminous point and falling upon the whole surface of the pupil do not converge to a point at any position within the eye, but converge in such a manner as to pass through two lines at right angles to each other, (a geometrical phenomenon, to which the term astigmatism was very happily affixed by the present Master of Trinity College [Whewell]). 1862J. Laurence in Med. Times 1 Nov. 474/1 Correction both of the astigmatism and the ametropia. 1878Foster Phys. iii. ii. 411 The cause of astigmatism is..unequal curvature of the cornea.
b. Optics. A similar defect in a lens.
1859Parkinson Optics iv. 48 When a pencil of rays is reflected or refracted at the surface of a medium, the reflected or refracted rays will not, in general, pass accurately through one point. This peculiarity is sometimes called astigmatism. 1892J. T. Taylor Optics Photogr. xxiii, Astigmatism is a serious fault for a lens to possess in any marked degree.
2. fig.
1934G. Bottomley in Ess. & Stud. XIX. 142 This mental astigmatism..was not noticed while the fires of great genius flamed high. |
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