10 questions and 10 answers to help you understand astigmatism

Author: Wang Mengyu: The Sixth People's Hospital Affiliated to Shanghai Jiao Tong University School of Medicine

Reviewer: Wu Qiang, Chief Physician, Shanghai Sixth People's Hospital, School of Medicine, Shanghai Jiao Tong University

1.What is astigmatism?

Simply put, myopia means "seeing things clearly at close range but blurry things at a distance"; astigmatism means "seeing things unclearly at close range or at a distance", and seeing things with double images. In fact, astigmatism is a type of refractive error, which is mainly related to the curvature of the cornea. Ideally, a normal person's eyeball is like a round "football", the curvature of the cornea is the same in all directions, and the astigmatism of the eye is small or close to 0. However, some people's eyeballs are like flat "rugby balls", and the curvature of the cornea in all directions is different, some are larger, and some are smaller. The light entering the eye cannot be focused into one point, so a clear image of the object cannot be formed, and the imaging will produce double images, etc. This situation is astigmatism.

Figure 1 Copyright image, no permission to reprint

2.What are the symptoms and manifestations of astigmatism?

The most common symptoms of astigmatism are decreased vision and blurred vision. In order to see objects clearly, people with astigmatism will use the eye's adjustment power as much as possible, which will cause eye muscle tension and lead to visual fatigue. If visual fatigue is not taken seriously, its degree will worsen and the visual quality will be seriously reduced, such as increased double vision and glare. Tilting the head and squinting are habitual actions of many people with astigmatism to try to adjust their vision, which can usually be controlled in time after wearing glasses. Squinting is to improve vision to a certain extent through the pinhole effect and slit effect in physics.

3.How to test astigmatism yourself?

Astigmatism can be self-tested using an astigmatism chart/solid line disk. People who wear glasses need to take off their glasses first; cover the left and right eyes in turn, and distinguish the distribution and color depth of the dotted lines in the picture. If there is no obvious difference in the depth of the lines in each direction, it means that the eyes have no astigmatism or the degree of astigmatism is very mild; if the solid line in a certain direction, such as 12 o'clock-6 o'clock, is the darkest, it indicates the direction of your astigmatism. Of course, this is only a preliminary self-test. If you want to know the exact degree of astigmatism, you need to go to a professional ophthalmology hospital for a medical optometry examination.

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4. How to understand your astigmatism degree?

On the optometry form, R (or OD) and L (or OS) represent the right eye and left eye respectively; S (or DS) refers to the spherical power, with a positive sign for hyperopia and a negative sign for myopia; C (or DC) refers to the cylindrical power, which indicates astigmatism, with a positive sign for hyperopic astigmatism and a negative sign for myopic astigmatism; the axis position represents the direction of astigmatism. Each eye is automatically measured 3 times, and the optometry result in the last row is the average of the 3 times.

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5.Is astigmatism hereditary?

According to relevant studies, astigmatism is hereditary to a certain extent, especially when both parents have high astigmatism (when the astigmatism is above 150 degrees). Moreover, most astigmatism is congenital. Astigmatism in infants and young children is related to the development and degree of compression of the eyeball in the mother's belly during the fetal period. For example, children with umbilical cords around their necks often have congenital high astigmatism. Among children under 2 years old, more than 50% have astigmatism, mostly 100 to 200 degrees; among children aged 2 to 4 years old, 30% to 40% have astigmatism, between 100 and 200 degrees. Generally speaking, the degree of astigmatism will become less and less with age. Therefore, it is a normal physiological phenomenon for children to have a certain amount of astigmatism, but astigmatism that exceeds a certain limit needs treatment, such as 1-year-old children with astigmatism ≥ 250 degrees, 2-year-old children with astigmatism ≥ 200 degrees, and 4-year-old children with astigmatism ≥ 150 degrees, then medical treatment is required. From birth to 6 years old is a critical period for visual development. Regular check-ups should be conducted to pay attention to changes in children's astigmatism.

6. I am an adult, why is my astigmatism still increasing?

People often complain: My astigmatism was 100 degrees last year, but it's 200 degrees this year! Why does the degree of astigmatism in adults keep increasing? In fact, the degree of astigmatism changes throughout life, regardless of whether you are an adult or not. There may be several reasons:

(1) Not wearing glasses with the right degree.

(2) Caused by bad habits: The astigmatism of children in their teens and twenties is "squeezed", that is, the shape of the cornea changes. The eyelids of young people are relatively "tight". Most people have less tension in the upper and lower eyelids than in the left and right eyelids, and the eyeball is like a horizontal "football". In addition, bad habits such as squinting or sleeping prone can also squeeze the cornea for a long time, squeezing the round "football" into a horizontal "football". The flatter the football, the higher the astigmatism.

(3) Keratoconus: If the degree of astigmatism of a young person increases year by year and the annual increase is more than 50 degrees, a corneal topography examination is needed to rule out the possibility of keratoconus (an eye disease in which the cornea is dilated, the central part becomes thinner and protrudes forward, and the shape is cone-shaped). This is especially true when the direction of astigmatism is oblique (the axis of astigmatism in the eye examination form is 30°-60° or 120°-150°), that is, the corneal shape is tilted like a "rugby ball", which requires more attention.

7. Are videos of astigmatism recovery training reliable?

As mentioned before, the degree of astigmatism is related to the shape of the cornea. To correct astigmatism, you need to wear glasses or change the shape of the cornea. Therefore, the astigmatism recovery training video is actually useless and is just a "placebo". Instead of watching videos, you might as well look far away more and watch less electronic products!

8.Does astigmatism need to be corrected?

Astigmatism of ≤75 degrees is low astigmatism, and astigmatism of >75 degrees is medium to high astigmatism. Low astigmatism does not affect vision and does not need to be corrected; however, medium to high astigmatism can cause double vision, blurriness, eye pain, and even symptoms of visual fatigue such as dizziness and nausea, which require correction. Physiological astigmatism is about 50 degrees, which not only hardly affects the clarity of vision, but also has certain benefits, such as increasing the depth of field, that is, a stronger sense of three-dimensionality. Therefore, most experts believe that the goal of correcting astigmatism is to control the astigmatism within 75 degrees, and there is no need to correct it to 0 degrees.

9.How to correct astigmatism scientifically?

Astigmatism is a higher degree in a certain direction, so the correction method is the same as myopia, including wearing frame glasses, corneal contact lenses [soft contact lenses, hard contact lenses (such as RGP and orthokeratology lenses/OK lenses)] and surgical treatment. Wearing glasses will not reduce the degree of astigmatism, but it can keep the astigmatism level stable. However, if the right glasses are not worn correctly, the astigmatism may continue to increase, especially for children in their growth period.

10How to choose astigmatism correction surgery?

(1) Myopia surgery: There are two main types of mainstream myopia surgery, one is laser myopia surgery, and the other is ICL lens implantation myopia surgery. The former includes all-femtosecond laser surgery, which improves vision and visual quality by shaping the cornea. It has the characteristics of small incision, small trauma, and fast recovery. The best correction range is myopia within 1000 degrees and astigmatism within 600 degrees; the latter corrects vision by implanting ICL lenses into the eye, which can correct myopia within 1800 degrees and astigmatism within 600 degrees. No matter which surgical method is chosen, it is safe and effective.

(2) Patients with cataracts: Cataract extraction combined with astigmatic intraocular lens implantation can be selected. This is to improve vision and visual quality by implanting an astigmatic lens into the eye. Currently, the field of intraocular lenses is developing rapidly. Under the guidance of a doctor, you can choose high-end lenses that can solve cataracts, presbyopia, myopia/hyperopia and astigmatism problems at the same time.