astigmatism

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Related to myopic astigmatism: hyperopic astigmatism

astigmatism

(əstĭg`mətĭz'əm), type of faulty vision caused by a nonuniform curvature in the refractive surfaces—usually the cornea, less frequently the lens—of the eye. As a result, light rays do not all come to a single focal point on the retina. Instead, some focus on the retina while others focus in front of or behind it. The condition may be congenital, or it may result from disease or injury; it can occur in addition to nearsightednessnearsightedness
or myopia,
defect of vision in which far objects appear blurred but near objects are seen clearly. Because the eyeball is too long or the refractive power of the eye's lens is too strong, the image is focused in front of the retina rather than upon it.
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 or farsightednessfarsightedness
or hyperopia,
condition in which far objects can be seen easily but there is difficulty in near vision. It is caused by a defect of refraction in which the image is focused behind the retina of the eye rather than upon it, either because the eyeball is
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. The spherical lenses used to correct nearsightedness and farsightedness must be specially adapted to correct the out-of-focus plane of vision of the astigmatic eye. When the patient observes a pattern of straight lines placed at various angles, those running in one direction appear sharp while those in other directions (particularly at right angles to the sharp lines) appear blurred. A special cylindrical lens is placed in the out-of-focus axis to correct the condition. In many cases contact lenses are the most effective means of correcting astigmatism.
Astigmatism: astigmatism due to concave mirrorclick for a larger image
Astigmatism: astigmatism due to concave mirror

astigmatism

(ă-stig -nă-tiz-ăm) An aberration of a lens or mirror system that occurs when light falls obliquely on the system and is focused not as a single point image but as two perpendicular and separated lines. In the reflecting system shown in the illustration rays from points A and B on the mirror converge to the vertical line image ab; rays from C and D converge to the horizontal line image cd. The pencil of reflected rays, elliptical in cross section, cannot produce a sharp image anywhere along its path; the plane of optimum focus occurs between ab and cd where the pencil has its smallest cross section. Astigmatism is not as severe an aberration as coma.

astigmatism

[ə′stig·mə‚tiz·əm]
(electronics)
In an electron-beam tube, a focus defect in which electrons in different axial planes come to focus at different points.
(medicine)
A defect of vision due to irregular curvatures of the refractive surfaces of the eye so that focal points of light are distorted.
(optics)
The failure of an optical system, such as a lens or a mirror, to image a point as a single point; the system images the point on two line segments separated by an interval.

astigmatism

, astigmia
1. a defect of a lens resulting in the formation of distorted images; caused by the curvature of the lens being different in different planes
2. faulty vision resulting from defective curvature of the cornea or lens of the eye
References in periodicals archive ?
33%), followed by myopic astigmatism (30%), hypermetropia (15%), hypermetropic astigmatism (5%), and mixed astigmatism in (6.
Wavetront-optimized vetsus waveftont-guided LAS1K for myopic astigmatism with the ALLEGRETTO WAVE: three-month results of a prospective FDA trial.
Katsanevaki, evaluated the efficacy and safety of Epi-LASIK for the treatment of low myopia and myopic astigmatism, using the Norwood EyeCare Epikeratome in 95 eyes of 65 patients ("Epi-LASIK: Clinical Results of an Advanced Surface-Ablation Procedure").
Management indicated in narrow Palpebral fissure is levator muscle Resection and spectacles for high myopic Astigmatism.
A 39-year-old woman underwent successful Wavelight femtosecond LASIK in each eye for treatment of compound myopic astigmatism in both eyes.
Methods: Total 33 eyes of 21 consecutive patients who underwent implantation of TICL for the correction of moderate to high myopic astigmatism were recorded and a minimum follow-up of six months was performed.
The myopic astigmatism data, which is preliminary, included 211 eyes of 194 patients with an average correction of -5.
14, 1997--VISX, Incorporated (NASDAQ/NMS:VISX) announced today that it has received an approvable letter from the Food and Drug Administration for its excimer laser systems to treat low to moderate nearsightedness with myopic astigmatism.
High myopic astigmatism causing poor vision may have accentuated/or caused esodeviation in early childhood which developed over several years into strabismus fixus.
Raymond Stein, Beacon's Medical Consultant was presented, highlighting the fact that 97 percent of patients with myopic astigmatism (preoperative spherical equivalent up to -5.