Astigmatism - a refractive error that cannot be ignored

After many children go to the hospital for an eye test, the doctor will tell them whether they have astigmatism. Everyone may be familiar with myopia, but many people are confused about what astigmatism is. Today I will take you to understand "astigmatism".

Astigmatism literally means that light is scattered and cannot be focused. Why is the light scattered? Because our eyes are not a perfect optical system. Astigmatism is like a rugby ball. It has a large curvature (radian) in some directions and a small curvature in other directions. This means that the refractive power of the eye is different in different directions. This will cause the astigmatism eye to see objects clearly in some directions but not in others. After the light passes through the eye, it cannot be well focused on the retina into one point. Secondly, if ≥2 points are formed, the light is "scattered".

Causes of astigmatism: 1. Congenital factors: Most astigmatism is congenital and is caused by the shape of the eyeball itself, especially in children with small palpebral fissures, because the eyelids cover part of the cornea, resulting in inconsistent development of the various parts of the cornea. Congenital astigmatism is generally relatively stable, and the degree does not change much with age. 2. Bad eye habits: squinting, rubbing eyes frequently, reading in bed, etc. will all lead to increased astigmatism. 3. Pathological factors: such as ptosis, dermoid tumors, corneal opacities, corneal ulcers, pterygium, etc. can all cause astigmatism. Keratoconus, which should be especially vigilant here, will show a rapid increase in myopia and astigmatism in the early stages of the disease. Once this situation is encountered clinically, further examination must be carried out to clarify the diagnosis, so as to achieve early detection and early treatment.

Astigmatism classification:

1. According to the regularity of astigmatism, it is divided into regular astigmatism and irregular astigmatism. Regular astigmatism means that the difference between the direction of maximum curvature and the direction of minimum curvature is equal to 90 degrees; irregular astigmatism means that the difference between the direction of maximum curvature and the direction of minimum curvature is not equal to 90 degrees, and the curvatures in different directions are different, and no mutually perpendicular directions can be found. It is more common in patients with pathological diseases such as keratoconus, corneal scars, corneal ulcers and lens opacities.

2. According to the refractive component of the eyeball, it is divided into: (1) Anterior corneal astigmatism: astigmatism caused by inconsistent curvature of the anterior corneal surface; (2) Posterior corneal astigmatism: astigmatism caused by inconsistent curvature of the posterior corneal surface. Generally, the posterior corneal astigmatism is small, but when pathological changes occur in the cornea, a larger posterior surface astigmatism may also occur; (3) Lens astigmatism: caused by different curvatures of different areas of the lens or inconsistent refractive indices. Lens astigmatism is generally against-the-rule astigmatism; (4) Others: For example, if the macular area is not on the visual axis, a slight amount of oblique axis astigmatism will be generated.

3. According to the direction of astigmatism, it is divided into: (1) with-rule astigmatism: when the astigmatism is expressed by a negative cylinder, its direction is within ±30° horizontally, that is, between 0-30° or between 150-180°; (2) against-rule astigmatism: when the astigmatism is expressed by a negative cylinder, its direction is within ±30° vertically, that is, between 60-120°; (3) oblique axis astigmatism: when the astigmatism is expressed by a negative cylinder, its direction is between 30-60° or between 120-150°.

Astigmatism treatment: Astigmatism in children and adolescents cannot be treated, and vision can only be corrected by wearing glasses. Different correction methods are selected according to the type of astigmatism. For example, regular astigmatism can be treated with frame glasses or contact lenses, while irregular astigmatism can only be treated with hard gas-permeable corneal contact lenses. The greater the astigmatism, the greater the impact on visual quality. After the age of 18, if the astigmatism caused by some pathological changes on the cornea is excluded, refractive surgery can generally be used to treat astigmatism.

Prevention of astigmatism: Congenital astigmatism is mainly caused by the refractive system of the eye, such as the cornea, lens and other structural factors, and is generally impossible to prevent. However, avoiding squinting, rubbing eyes, eye injuries, etc., and paying attention to eye hygiene and developing good eye habits can effectively prevent the occurrence and development of acquired astigmatism. (Lv Tianbin, deputy chief physician of the Optometry Center of Henan Provincial Eye Hospital)