Astigmatism

Astigmatism is the phenomenon of blurred or double vision in certain directions. If left untreated, severe astigmatism not only makes it difficult and inconvenient to see, but can also cause eye fatigue, headaches, and stiff in the shoulders as the eyes try to focus.

This article describes following topics.

・Types and causes of astigmatism
・How to check for astigmatism
・Methods to correct astigmatism optically or surgically

Some types of astigmatism can be corrected with spectacles or contact lenses, so if you notice that you may have astigmatism, you should see an ophthalmologist as soon as possible.

Astigmatism is a condition in which the blur isn’t uniform but instead spreads in one direction.
Normally, a single focal point is formed on the retina, which is called emmetropia. Astigmatism, on the other hand, causes blur to spread in a certain direction, resulting in the following symptoms:

Objects appear blurred or as though they have a shadow of the same image.

The human eye isn’t perfectly spherical, and most people have some degree of astigmatism.
If the degree of astigmatism is low, the degree of blur is insignificant and often not noticed by the patient and can be left untreated. If the degree of astigmatism is high, this can cause significant blurring and warrants correction,

The cornea and crystalline lens refract incoming light and focus it to a single point. This lens enables the eye to see an image in focus.
When a patient develops astigmatism the cornea and lens becoming, disrupting incoming, resulting in blurred or double vision. Astigmatism can be sub-divided into two types: regular astigmatism and irregular astigmatism.

Regular Astigmatism

In regular astigmatism, the cornea or crystalline lens is distorted in one direction.
When the cornea or crystalline lens form oval shape like a rugby-ball, there is a flat curve in one direction and steep curve in the other direction, resulting in two focal lines as shown in the figure above.
Astigmatism changes the images we see depending on whether the cornea or crystalline lens has a flat curve in the vertical, horizontal, or oblique direction. A characteristic symptom of regular astigmatism is that even if lines are clearly visible at a certain direction, lines that intersect in orthogonal direction are difficult to see.

With-the-rule astigmatism

This is caused when the meridian showing the strongest refraction is vertical. The image appears crushed vertically and vertical lines are clearly visible, but horizontal lines appear blurred. It’s the most common type of astigmatism, although it depends on the age of the patient.

Against-the-rule astigmatism

This is caused when the meridian showing the strongest refraction is horizontal. The image appears crushed horizontally, Against- the- rule astigmatism is the opposite of with-the-rule astigmatism, in which horizontal lines are clearly visible but vertical lines are difficult to see. The number of people who develop against-the-rule astigmatism increases with age.

Oblique astigmatism

A condition in which the axis of cornea or lens is oblique in shape. Certain oblique lines are easier to see, while lines oriented diagonally are difficult to see.
It’s also characterized by a tendency for objects to have a shadow which in some cases may be described by patients as double vision.

Irregular Astigmatism

Irregular astigmatism describes a condition in which the corneal surface is irregularly distorted, or the crystalline lens is distorted which prevents images from being properly focused.
When one eye with irregular astigmatism looks at an object, see an image with multiple layers of blur.
It’s caused by damage to the cornea or partial hardening of the lens during the early stages of cataracts.

If the degree of astigmatism is mild, there are almost no subjective symptoms. With higher level of astigmatism, objects appear distorted or blurred.

＜Astigmatism may be present if any of the following are true>:

• The lights of oncoming cars appear blurred
• Tend to squint when trying to see
• The moon or stars appear to have a shadow
• Lights in the nightscape appear to blur
• Difficulty reading text on a computer or smartphone
• Tend to feel eye fatigue. -have headaches and/or tension in the shoulders
• Difficulty in distinguishing letters such as “V” and “W” or “3” and “8
• Clock hands appear to double.
• Blurred letters on traffic signals and signs are difficult to read.

It’s important to note that if a young child has high levels of astigmatism, it may lead to amblyopia. It’s easy to detect that by observing your child is squinting, glaring more than others, or having difficulty seeing the scale on a ruler.

Amblyopia: A condition in which the desired level of vision cannot be obtained even with correction. It is often recoverable with early treatment.

Check the following radial diagram by looking at with one eye.

Although the figure is uniform, if you feel that the density or thickness of the lines differs depending on the direction, you may have astigmatism.
However, the above diagram is only for a simplified examination. Even if the thickness of the lines does not appear uniform, it’s difficult to determine if you have astigmatism by yourself, so it’s better to visit an ophthalmologist for a detailed examination.
The astigmatism test performed by an ophthalmologist, the state of the corneal curve and the shape of the cornea are analyzed to confirm whether the patient has regular or irregular astigmatism.

If the astigmatism is mild, the effect on vision will be minimal. If you don’t feel inconvenienced by your vision in your daily life, you don’t need to take any special treatment. If you find it difficult to see, you can correct it with spectacles lenses that correct your astigmatism or contact lenses.
However, there are different methods of dealing with regular astigmatism and irregular astigmatism.

Regular Astigmatism

The oblate curve of the eye is offset by wearing spectacles that create a curve in the opposite direction to the curve of the cornea. Regular astigmatism can be corrected with hard contact lenses, soft contact lenses or spectacles.
It’s important to note that if the method of correction method is not correct, eye fatigue and discomfort may occur. Please have an examination with an ophthalmologist and receive a prescription for spectacles or other eyewear suitable for you.

Corneal ectasia

Irregular corneal astigmatism is caused by an uneven surface of the cornea and is corrected using hard contact lenses instead of spectacles.
Hard lenses, which are made of hard material, don’t deform to follow the shape of the cornea. Therefore, tears that enter between the lens and the cornea cover the surface irregularities and function as a lens. This is called a lacrimal lens.
It’s important to be aware that this type of astigmatism cannot be corrected with spectacles or soft contact lenses. If the astigmatism cannot be corrected even with hard contact lenses, surgery may be performed.

Lenticular irregular astigmatism (Irregular astigmatism of the crystalline lens)

When the crystalline lens is unevenly distorted, it’s called irregular Lenticular astigmatism. While some cases are congenital, acquired lens distortion is caused by aging.
It cannot be corrected with spectacles or contact lenses, and in advanced cases, surgery to reconstruct the lens is required.

If the level of astigmatism correction isn’t appropriate, it can cause irritation and reduce concentration. People with astigmatism are sometimes reluctant to wear glasses, and this may be because the astigmatism isn’t being properly corrected
In young children, if severe astigmatism is present, it’s best to fully correct this. A careful refraction will reveal some degree of astigmatism in almost everyone.
Even if astigmatism is found to be present, the extent to which it should be corrected is determined on a case-by-case basis. It’s best to consult with the ophthalmologist who examined you.

Can astigmatism and myopia occur at the same time?

It’s not uncommon for people to have astigmatism and myopia at the same time. myopia (near sightedness), hyperopia (far sightedness), and astigmatism are all caused by refractive errors, and a condition called “myopic astigmatism” or “hyperopic astigmatism” can also occur. Myopic astigmatism is a combination of myopia, which causes blurring of distant objects, and astigmatism, which causes blurred or shadows in the vision.

Internal link: Why does myopia occur? How the eye and vision work and the relationship between heredity and environment

What happens when you have astigmatism?

Astigmatism is a condition in which the image is out of focus, making it difficult to see as it looks blurry or appears to have shadow. When astigmatism is combined with myopia or hyperopia, it becomes even more difficult to see.

Severe astigmatism can cause eye strain, tense shoulders, and headaches, so it’s recommended that you consult an ophthalmologist to see if you should use spectacles or contact lenses to correct it.

Can astigmatism be corrected with spectacles?

Regular astigmatism can be corrected with cylindrical spectacle lenses or contact lenses. A correction that distorts the eye in the opposite direction to the curve of the eye is appropriate. However, in case of Corneal ectasia, an uneven corneal surface, this should be corrected with hard contact lenses instead of spectacles.