Astigmatism and Cataracts

Astigmatism

An optical system with astigmatism is one where rays that propagate in two perpendicular planes have different foci.

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}]

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. [1913 Webster] 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. [1913 Webster]

Ametropia \Am`e*tro"pi*a\, n. [Gr. ? irregular + ?, ?, eye.] (Med.) a visual impairment resulting from faulty refraction of light rays in the eye. Subtypes include {myopia} {astigmatism} and {hyperopia}. -- {Am`e*trop"ic}, a. [1913 Webster +PJC]

Cataracts

A cataract is a clouding of the lens inside the eye which leads to a decrease in vision. It is the most common cause of blindness and is conventionally treated with surgery.

Additional data for cataracts may be on the way.

Data Sources:

  • astigmatism: WordNet (r) 2.0
  • astigmatism: The Collaborative International Dictionary of English v.0.44
  • astigmatism: The Collaborative International Dictionary of English v.0.44

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