Hypertext Webster Gateway: "astigmatism"
From Webster's Revised Unabridged Dictionary (1913) (web1913)
Astigmatism \A*stig"ma*tism\, n. [Gr. 'a priv. + ?, ?, a prick
of a pointed instrument, a spot, fr. ? 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.
Note: 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.
From WordNet (r) 1.7 (wn)
astigmatism
n 1: (ophthalmology) impaired eyesight resulting usually from
irregular conformation of the cornea [syn: {astigmia}]
2: (optics) defect in an optical system in which light rays
from a single point fail to converge in a single focal
point [syn: {astigmia}] [ant: {stigmatism}]
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