astigmatism, like myopia and hyperopia, is a type of refractive error. In simple terms, the eyeball of astigmatism is not a perfectly spherical shape but a flat oval shape, so the refractive power of the eyeball varies along different meridians. When parallel light rays pass through the eyeball and are refracted, they cannot converge at one point, thus failing to form a clear image. This refractive state is called astigmatism. Astigmatism cannot form a clear image through accommodation or by moving objects away. Only by wearing appropriate cylindrical lenses can a clear image be formed on the retina. Astigmatism can be caused by the cornea or the lens. The former is called corneal astigmatism (the most common), and the latter is called intraocular astigmatism.
Astigmatism is mostly congenital, but it also has a certain hereditary nature, especially when parents have a high degree of astigmatism. There are also those caused by eye trauma or eye diseases. For instance, keratoconus, peripheral corneal degenerative changes or scars left after corneal inflammation. In addition, astigmatism can also occur after cataract surgery or when an eyelid mass compresses the eyeball. Mild astigmatism below 50 degrees is considered physiological and is caused by frequent compression of the upper and lower eyelids. With the increase of age, this physiological astigmatism has a tendency to increase slightly.
(1)Astigmatism can be classified into two major categories: regular astigmatism and irregular astigmatism. Regular astigmatism can be further classified into regular astigmatism, counter-astigmatism and oblique astigmatism. Irregular astigmatism has no discernible pattern and is often caused by corneal diseases, lens diseases or eye surgeries.
(2) Typical symptoms
1) Decreased vision and blurred vision: In cases of astigmatism, what people perceive is not only blurriness but more obviously double vision symptoms, that is, seeing one point as many points. Vision decline is closely related to the degree and type of astigmatism. People with mild astigmatism usually have normal vision. However, those with moderate to high astigmatism or oblique astigmatism have poor distant and near vision. Astigmatism has a greater impact on vision than regular astigmatism. If not corrected in time, it can lead to amblyopia.
2) Visual fatigue: The blurred images on the retina need to be constantly fine-tuned, and the vision is distorted. Therefore, people with astigmatism, especially those with hyperopic astigmatism, are prone to visual fatigue. It is manifested as eye pain, tearing, headache (especially obvious in the forehead area), double vision, and inability to work at close range for a long time. 3) Compensatory head position and squinting for vision: People with highly asymmetrical astigmatism in both eyes often tilt their heads to see more clearly. After astigmatism correction, the condition can be restored. Sometimes, in order to get a larger retinal image, children often bring objects closer, just like children with myopia. People with high astigmatism often squint when looking at both distant and nearby targets, creating a pinhole and slit effect to improve their vision. Looking through pinholes or fissures can reduce the impact of astigmatism on vision.
(3) The diagnosis, treatment and prognosis of astigmatism can be determined through refraction or corneal topography examination. For children, wearing cylindrical lenses for optical correction is the main treatment for astigmatism, including frame glasses and contact lenses. For astigmatism, its degree is generally relatively stable or slightly increases with age, and a decrease in degree is less common. If there is a significant increase in astigmatism, it is necessary to consider whether other eye problems have occurred, such as keratoconus or lens dislocation.
