regular astigmatism


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Related to regular astigmatism: myopic astigmatism, hyperopic astigmatism

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.

reg·u·lar a·stig·ma·tism

astigmatism in which the curvature in each meridian is equal throughout its course, and the meridians of greatest and least curvature are at right angles to each other.

reg·u·lar a·stig·ma·tism

(reg'yū-lăr ă-stig'mă-tizm)
Ocular condition in which the curvature in each meridian is equal throughout its course, and the meridians of greatest and least curvature are at right angles to each other.
References in periodicals archive ?
The symmetric matrix includes regular astigmatism. The nonzero entries in the antisymmetric matrix indicate that the principal meridians of the lens surface are not perpendicular.
Table-1: Type of regular astigmatism with relation to age (pLess than 0.002).
Laser refractive surgery remains the treatment of choice in patients with astigmatism of less than 6D who are not yet presbyopic, providing patients fulfil the standard safety criteria for laser vision correction such as a normal corneal topography (regular astigmatism) and an adequate tear film.
The corneal topographic parameters studied included the average corneal power (CP), regular astigmatism (RA), spherical aberration (SA), and higher-order aberration (HOA).
Early in the disease, soft toric lenses may be adequate to correct myopia and regular astigmatism. As the disease progresses, rigid gas permeable (RGP) lenses are used.