What is astigmatism?
Many people will have doubts, what exactly is astigmatism? Astigmatism is a kind of refractive abnormality of the eye, which is related to the curvature of the cornea. After the parallel light enters the eye, because the eyeballs have different refractive powers on different meridians, they cannot be concentrated at one point (focus), and a clear object image cannot be formed. This situation is called astigmatism. Astigmatism eyes can not form a clear image by adjusting the distance between the target and the eye. Only by wearing a suitable cylindrical lens can a clear image be formed on the retina.
Astigmatism is so common that almost all of us have astigmatism to some extent. Some common symptoms may be signs of astigmatism, such as:
• Eye fatigue or discomfort
• Squint to see near or far images
• Difficulty viewing printed text
Why is there astigmatism?
The main cause of astigmatism is changes in the curvature of the cornea of the eye. The normal cornea is not only smooth and transparent, but also a complete hemispherical shape. Its main function is to concentrate the light so that the light enters the pupil and reaches the retina at the fundus to form a focal point, and then reflects to the brain so that people can clearly see the outside world.
Therefore, when the curvature of the hemispherical cornea changes, just like an unevenly ground lens, when the surface is uneven and irregular, the external light cannot focus on the retina, but diffuse in all directions. The brain's understanding of external objects is blurred, which creates astigmatism. This kind of astigmatism is medically called irregular astigmatism. Because the corneal curvature changes too much, it is difficult to correct with glasses.
Types of astigmatism
There are three main classifications of astigmatism, which are defined by the main meridian (the meridian with the steepest and flattest eye).
1. Myopic astigmatism: The main meridian of the eye is myopia (myopia + astigmatism).
2. Hyperopia astigmatism: Hyperopia (hyperopia + astigmatism) on the main meridian.
3. Mixed astigmatism: nearsightedness and hyperopia in the main meridian (astigmatism is the main refractive error).
Problems caused by astigmatism
• Loss of vision: the degree of which varies greatly due to the nature of astigmatism, the height of the refractive power and the direction of the eye axis. Astigmatism belonging to the physiological range usually has no effect on the near and far vision. High degree of astigmatism is mostly due to the combination of linear amblyopia or other abnormalities, the vision loss is obvious, and it is difficult to obtain good corrected vision.
• Astigmatism: In order to improve visual acuity, patients with mild astigmatism often use methods such as changing adjustment, squinting, and torticollis for self-correction. Constant adjustment tension can easily cause asthenopia.
• Since the curvature of the meridians of the cornea and the lens are inconsistent in size, the difference between the horizontal and vertical meridians is usually the largest.
• Due to corneal lens disease, such as keratoconus, corneal cloud photo, early senile cataract, etc.