irregular astigmatism


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astigmatism

 [ah-stig´mah-tizm]
an error of refraction in which a ray of light is not sharply focused on the retina, but is spread over a more or less diffuse area; it is due to differences in curvature in the refractive surfaces (cornea and lens) of the eye. adj., adj astigmat´ic. Its exact cause is not known; some common types of astigmatism seem to run in families and may be inherited. Probably everyone has some astigmatism, since it is rare to find perfectly shaped curves in the cornea and lens, but the defect is rarely serious. If the refractive error is troublesome, corrective lenses may be needed.
compound astigmatism that in which both principal meridians are either hyperopic (compound hyperopic astigmatism, with rays coming into focus behind the retina) or myopic (compound myopic astigmatism, with rays coming into focus in front of the retina).
corneal astigmatism that due to the presence of abnormal curvatures on the anterior or posterior surface of the cornea.
hypermetropic astigmatism hyperopic astigmatism.
hyperopic astigmatism that in which the light rays are brought to a focus behind the retina.
irregular astigmatism that in which the curvature varies in different parts of the same meridian or in which refraction in successive meridians differs irregularly.
lenticular astigmatism astigmatism due to defect of the crystalline lens.
mixed astigmatism that in which one principal meridian is hyperopic and the other myopic.
myopic astigmatism that in which the light rays are brought to a focus in front of the retina.
regular astigmatism that in which the refraction changes gradually in power from one principal meridian of the eye to the other, the two meridians always being at right angles; this condition is further classified as being against the rule when the meridian of greatest refractive power tends toward the horizontal, with the rule when it tends toward the vertical, and oblique when it lies 45 degrees from the horizontal and vertical.

ir·reg·u·lar a·stig·ma·tism

astigmatism in which different parts of the same meridian have different degrees of curvature.

ir·reg·u·lar a·stig·ma·tism

(ir-reg'yū-lăr ă-stig'mă-tizm)
Astigmatism in which different parts of the same meridian have different degrees of curvature.
References in periodicals archive ?
Once patients achieve a good visual outcome eg after intracorneal ring implants or reduction of irregular astigmatism following topography guided surface ablation, the cornea may be treated with CXL in order to prevent any further deterioration.
High degrees of irregular astigmatism typically accompany this graft, which requires correction with a rigid lens; however fitting contact lenses can be particularly difficult because corneal lenses tend to centre over the steepest part of the cornea.
We were extremely delighted with the results of those patients in the final group with irregular astigmatism because all patients had a significant improvement in their uncorrected and best spectacle corrected visual acuity.
Mixed astigmatism or irregular astigmatism describes the unequal curvature of the cornea in which one principal meridian is myopic and the other is hyperopic.
1,2) An increase in myopia, irregular astigmatism, higher order ocular aberrations and corneal scarring can lead to reduced visual acuity (VA).
Irregular astigmatism is a topic of rising importance in ophthalmology.