Astigmatism refers to the fact that the eye has different refractive power at different meridians, i.e., the refractive surface of the refractive system of the eye has an astigmatic surface, usually from the cornea and the lens. The so-called astigmatic surface is a concept opposed to the sphere. If from a sphere, this part forms a spherical surface. At the center of this sphere is the midpoint, connecting its edges, forming different lines called meridians. Each meridian has the same radius of curvature. If a portion is cut from an ellipsoidal sphere, this portion forms a face with each meridian having a different radius of curvature. The radius of curvature of one of the meridians is the largest, and the radius of curvature of the meridian perpendicular to the other is the smallest, such a surface is called astigmatic surface. A meridian refractive force is the smallest, the axis of the astigmatism surface.
Causes of astigmatism.
Astigmatism in the eye comes primarily from genetics and development, and is not generally related to acquired eye use.
In infants, the eye is developing and astigmatism is generally unstable, but after 2 years of age, when the eye is close to maturity, the astigmatism will not change much and may remain with the eye for life.
Types of astigmatism.
As a result of astigmatism, parallel rays of light entering the eye cannot form a focal point, but instead form lines that are parallel to each other and at a certain distance, called focal lines. According to the position of the two focal lines in relation to the retina, astigmatism can be divided into the following categories.
1, simple myopic astigmatism: if a focal line is located in front of the retina, the other focal line is located on the retina. Such as glasses prescription: -2.00DC × 90° (here DC indicates corrective column lens, the value after × indicates the axis of column lens).
2, simple hyperopia astigmatism: if a focal line is located on the retina, the other focal line is located behind the retina. If the glasses prescription is: +2.00DC×90.
3, compound myopic astigmatism: if two focal lines are located in front of the retina, glasses prescription such as -2.00DS-2.00DC×180.
4, compound hyperopic astigmatism: if two focal lines are located behind the retina;, the other focal line is located on the retina. If the glasses prescription is: +2.00DS+2.00DC×90.
5, mixed astigmatism: if one focal line is located in front of the retina, the other focal line is located behind the retina. If the prescription of glasses is: -1.00DS+2.00DC×90.
Regular astigmatism and irregular astigmatism.
The above astigmatism are all different meridians with different diopters, and the points on a meridian have the same diopters, so collectively they are called regular astigmatism. If the refractive power differs between points on the same meridian, it is called irregular astigmatism.
Performance.
The patient likes to squint to see things. There may also be visual fatigue. Higher degrees of astigmatism in infancy and early childhood prevent the retina of the eye from forming a clear image, which affects the child’s visual development and will likely lead to amblyopia.
Examination.
Astigmatism must be determined by optometry to determine the exact prescription and axial direction.
Correction.
There is currently no treatment for astigmatism, and vision can be corrected by wearing column or spherical column lenses.
Astigmatism of high magnitude in infancy and early childhood must be corrected as soon as possible, not only to give the child clear vision, but also to prevent the occurrence of amblyopia.
The treatment of amblyopia caused by astigmatism in early childhood must also be based on the prescription of glasses to correct astigmatism.
In addition to frame glasses, hard contact lenses can also be worn. If the prescription is low, soft contact lenses may also be worn.
For irregular astigmatism, which cannot be corrected by frames and soft contact lenses, hard contact lenses must be used for correction.