Astigmatism eye

Astigmatism eye - combination in one eye different refraction or different degrees of one of refraction.
Astigmatism eye to the retina does not create a clear image of the examined subject. There are corneal astigmatism (irregular curvature of the cornea and the lens (irregular shape of the lens), right and wrong. Correct astigmatism eye (the same interpretation in the course of one Meridian) is more often congenital. In the eye with the correct astigmatism there are two major mutually perpendicular Meridian: the most and least refractive. Depending on the combination of clinical refraction (see refraction of the eye) in the main meridians there are simple (nearsighted or farsighted) astigmatism eye, complex and mixed. Irregular astigmatism eyes (different refraction in the course of the same Meridian) occurs when the scars and corneal opacities.
astigmatismAstigmatism eye a small extent (up to 0.5 dioptres) occurs frequently and have no significant impact on the vision. Astigmatism eye more degrees always significantly reduces the severity of view.
Define astigmatism eye using subjective and objective methods of research. To identify astigmatism eye subjective method in the study of visual acuity (see) in the test frame before the investigational eye put an opaque shield with a narrow slit; rotating it, pick up this state of cracks, which achieved the highest visual acuity. Using spherical corrective glasses determine the refraction of this Meridian. Turning the plate with a crack 90, determine visual acuity and refraction of another home Meridian. The difference in refraction main meridians will show the degree of astigmatism eye. Objective methods for determining astigmatism eye are skiaskopia (see) and ophthalmometry (see). Correction of astigmatism eye is positive or negative cylindrical lenses.
In propisi points with cylindrical lenses indicate the position of the axis of glass in degrees (from 0 to 180 degrees; Fig.).

Astigmatism eye (from the Greek. negative prefix a -, and stigma - point) - a combination in one eye different refraction or different degrees of refractive errors of one kind, in connection with which the rays emanating from any point of the space, do not give after refraction them in the optical system of the eye focal point of the image on the retina. Astigmatism eye usually due to an irregular curvature of the cornea, much less commonly, the wrong shape of the lens; it is possible to combine in one eye astigmatism cornea and the lens. Almost matters mainly corneal astigmatism.
Distinguish right and wrong astigmatism eye. If improperly each Meridian cornea at different sites have different curvatures and refractive power. Such A., usually purchased and is caused by haze, Robovie changes, changing the shape of the cornea when the so-called keratoconus (see the cornea, Staphyloma cornea).
When properly A., different meridians of the cornea are different curvatures and refractive power, but the same throughout. Correct, A. usually congenital not change during the lifetime may be inherited; sometimes develops after operations on the eyeball [cataract extraction (see)]. The image of a point in astigmatic eye has an oval shape, circle or line depending on the provisions of the retina in relation to the light beam.
In the eye with the correct astigmatism has two main meridians is one with the largest refracting force, the other - with the least; these meridians is always perpendicular to each other. The difference in the refractive power of the main meridians, expressed in diopters, characterizes the degree of astigmatism eye. Correct, A. small extent (up to 0,5 D) is common, visual acuity is not affected (the so-called physiological astigmatism eye); A. G. higher degrees significantly reduces the severity of view.
Depending on the refractive main meridians eyes distinguish the following types of astigmatism: a simple - in-one main Meridian emmetropia, in another myopia or hyperopia; complex - both meridians myopia or hyperopia, but different degrees; mixed in one Meridian myopia, in another farsightedness.
A. G. determine the subjective method in the study of visual acuity using a special flap with a narrow slit and selection of suitable glasses (see visual Acuity) and objective - special devices (ophthalmometer, Refractometer), and through skiaskopia (see).
For vision correction with proper A. G. prescribe glasses with cylindrical lenses (see Points). When A. incorrect, such spectacles little to improve vision and shown (for example, keratoconus) the appointment of contact lenses.