ASTIGMATISM

A B B D E F G And K L M N O U R C T Y P X C H W E I

Astigmatism - visual distortion of the image due to the different refractive power of individual elements of the eye as an optical system. If astigmatism is not generated on the retina a clear image of the subject. There are wrong and correct astigmatism. Wrong astigmatism is usually acquired (scarring or corneal opacity). In this form of pathology of individual sections of the cornea have a different refractive power, whereby the visual image on the retina of the eye is characterized by varying degrees of clarity. The correct astigmatism caused by the deviation of the eyes in the field of corneal spherical (for example, conical and ellipsoidal). In this main meridians of the cornea (.. M with mutually perpendicular axes drawn through the eye pupil centers, one of which is characterized by the greatest, and the other - the lowest refractive power) have deviations from a strictly vertical or strictly horizontal position, remaining mutually perpendicular. Depending on the combination of clinical refraction in the principal meridians emit simple (nearsightedness or farsightedness), complex and mixed types of astigmatism.

Astigmatism small extent (up to 0.5 diopters) is common and has no significant effect on vision. Astigmatism big powers always significantly reduces visual acuity.

Determine astigmatism using subjective and objective methods. To detect astigmatism subjective method in the study of visual acuity in the trial frame in front of the studied eye put an opaque plate with a narrow slit; rotating it, pick a slot position, at which the highest visual acuity. With the help of corrective glasses determine the refraction of the meridian. Turning plate with a gap of 90 °, and define the visual acuity refraction other principal meridian. The difference in refraction of the principal meridians shows the degree of astigmatism. Objective methods for determining astigmatism are skiascopy, Oftalmometres and refractometry.

Astigmatism correction is performed by positive or negative cylindrical glasses. The cylindrical prescription glasses with glass panes axis indicates the position in degrees (from 0 to 180 °).