mixed 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.

mixed a·stig·ma·tism

astigmatism in which one meridian is hyperopic whereas the one at right angle to it is myopic.

mix·ed a·stig·ma·tism

(mikst ă-stig'mă-tizm)
A vision defect in which one meridian is hyperopic while the one at a right angle to it is myopic.

mixed astigmatism

Astigmatism in which one meridian is myopic and the other hyperopic.
See also: astigmatism
References in periodicals archive ?
Regression formulas were obtained to calculate the [K.sub.DHC] from the [K.sub.pop average 1] and the [K.sub.pop average 2] for the four groups of eyes (high myopic, low myopic, hyperopic and eyes with mixed astigmatism) (Figures 1, 2).
It did not happen in hyperopic eyes or with mixed astigmatism. We found a correlation of [K.sub.pop average 1] and [K.sub.pop average 2] with that obtained by [K.sub.DHC].
In hyperopic eyes and with mixed astigmatism, the results were less conclusive, since no clear advantage was found when using the MPP on the [Km.sub.pop] or the Sim[K.sub.pop] regarding their errors compared to the [K.sub.DHC] (Table 3).
of cases Percentage Astigmatism 150 42.37 Simple hypermetropic astigmatism 56 37.33 Compound hypermetropic astigmatism 14 9.33 Simple myopic astigmatism 50 33.33 Compound myopic astigmatism 22 14.66 Mixed astigmatism 8 5.33 Hypermetropia 76 21.46 Presbyopia 60 16.94 Myopia 44 12.42 Mixed 24 6.77 Table 7: Amount of diaptoric power in various type of astigmatism in headache (n = 150) Type of Astigmatism Astigmatism Astigmatism astigmatism (A) up to 1 D 1.25-2 D >2 D No.
Myopia, was found to be the most frequent refractive error in young adults (43.33%), followed by myopic astigmatism (30%), hypermetropia (15%), hypermetropic astigmatism (5%), and mixed astigmatism in (6.67%).