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Webster 1913 Edition
Astigmatism
A-stig′ma-tism
,Noun.
[Gr.
ἀ
priv. + [GREEK], [GREEK], a prick of a pointed instrument, a spot, fr. [GREEK] to prick: cf. F. astigmatisme
.] (Med. & Opt.)
A defect of the eye or of a lens, in consequence of which the rays derived from one point are not brought to a single focal point, thus causing imperfect images or indistinctness of vision.
☞ The term is applied especially to the defect causing images of lines having a certain direction to be indistinct, or imperfectly seen, while those of lines transverse to the former are distinct, or clearly seen.