Does astigmatism mean “unfocused vision”?

As usual, Dr. Jingcai promises that this is pure popular science, no deception, no selling, please feel free to read:

To understand what astigmatism is, you must first understand the basic structure of the eyeball. You can read Dr. Jingcai's other article "Small Eyeball, Big Knowledge" in detail. Here we briefly review the necessary parts:

What we call the black eyeball is actually the color of the iris. In front of the iris, there is a transparent structure that is often difficult to detect when looking at the eyeball from the front. It is the cornea. As shown in the left side of the picture below, when looking from the front, we can only see the blue eyeball (the color of the iris of foreigners) and the pupil (the round hole in the middle of the iris). Where is the cornea? On the right side of the picture below, when we "cut open" the same eye from the side, the cornea is obvious.

After the review, let's look at the definition of astigmatism: astigmatism is a kind of "refractive error", which means that the refractive power of the eyeball is different on different meridians. After being refracted by the eye's refractive system, parallel light rays can no longer form an intersection on the retina, but form two focal lines, ultimately forming an unclear image on the retina.

Any factor that causes different refractive powers on different meridians of the eye may cause astigmatism, but the most common one is caused by the cornea - this is why Dr. Jingcai takes you to review the previous content.

The surface of a normal person's cornea is close to a sphere, and the refractive power in each meridian direction is consistent, as shown in the following figure:

However, in an astigmatic cornea, the refractive power is inconsistent on different meridians, and the surface of the cornea is no longer approximately spherical, but becomes irregular, for example, it becomes approximately an "ellipsoid" - you can imagine the surface of an egg in different positions, which is roughly what it means.

The comparison between normal eye and astigmatism eye is shown in the figure below:

The main symptom of astigmatism is blurred vision, both near and far. Moreover, astigmatism can coexist with other refractive errors such as myopia or hyperopia.

Can astigmatism be corrected? In most cases, it can. Depending on the type of astigmatism, the doctor will choose frame glasses, corneal contact lenses, etc. for the patient to correct vision;

Will astigmatism affect myopic teenagers and children wearing orthokeratology lenses? Yes, but it depends on the doctor's evaluation after examination. Some orthokeratology lens brands have "toric lenses" specifically for myopia + astigmatism.

The above is Dr. Jingcai’s simple popular science explanation about astigmatism. If you find it helpful, you are welcome to share it with more parents. Thank you.

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About Dr. Jingcai: The creators of Dr. Jingcai's popular science content all have a professional background in ophthalmology, a master's degree or above, and are former ophthalmologists. For some popular science content with a higher degree of professionalism, we will also invite working ophthalmologists and optometry experts to review and check it, striving to be responsible for the accuracy of the content and avoid misleading readers.