What Causes Astigmatism? Here’s Why It Occurs

injured eye

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  • Genetics is also said to be a factor, as astigmatism can run in families. The development of an infant can also play a role, as it appears to be more common among premature or low-birthweight infants
  • Astigmatism usually occurs when the surface of the cornea becomes damaged. Another risk factor is if anything persistently presses on the corneal surface, such as a large lump on the eyelid, pushing it out of shape

Astigmatism is not an eye disease.1 It is not something you can get from a bug, and it is not transmissible.2 Rather, this common eyesight problem is called a refractive error. This means that your eye has difficulty with bending of light (also called refraction). Refractive errors are responsible for reduced eyesight level, also known as visual acuity.

Refraction is done by the eye in order to focus it. This means that if you have a refractive error, your eye isn’t able to properly focus light on the retina. In the case of astigmatism, this occurs because there is an abnormality in the shape of the eyeball.3

Your Eyeball’s Shape Plays a Part in Astigmatism

In people with a normal eyeball, the shape usually resembles a perfectly round ball.4 The cornea is smooth and curved equally in all directions. This allows light that enter the eye to bend evenly – it is focused on all planes and directions equally. This gives you a clear view.

However, people with astigmatism have corneas with front surfaces that are curved more in one direction compared to others. This means that the eyeball is shaped more like a football or rugby ball, or even the back of a spoon. As a result, the light gets bent more in one direction than others. Hence, it seems as if you’re looking into a distorted or wavy mirror. This occurs because the eye is unable to focus light rays towards one point.

People with corneal surfaces that have a high degree of variation in the curvature makes the refraction severely impaired. This means that at any given time, only a proportion of the rays are properly focused, so the image is consistently blurred. In these cases, wearing corrective lenses is necessary to allow light rays to focus better.5

What Causes Your Cornea’s Irregular Shape?

The exact cause of astigmatism is unknown; however, there are certain factors that are believed to play a role. It’s said that in most people, the irregularity in the cornea is already present at birth, although it is possible to also develop later in life.

Genetics is also said to be a factor, as astigmatism can run in families. The development of an infant can also play a role, as it appears to be more common among premature or low-birthweight infants. This may be because the cornea did not have sufficient time to properly develop in the womb. Other factors that may lead to astigmatism include:

  • An eye injury
  • Scar on the eye
  • Eye operation

Astigmatism usually occurs when the surface of the cornea becomes damaged. Another risk factor is if anything persistently presses on the corneal surface, such as a large lump on the eyelid, pushing it out of shape.

Certain genetic problems that affect the cornea’s structure may also come with astigmatism, such as Down’s syndrome. One in 5 people with this condition have significant astigmatism. Corneal disorders that develop throughout life may also lead to this refraction error, the most common of which is keratoconus, which comes with nearsightedness, corneal scarring and severe astigmatism.6

MORE ABOUT ASTIGMATISM

Astigmatism: Introduction

What Is Astigmatism?

Astigmatism Symptoms

Astigmatism Causes

Astigmatism Test

Types of Astigmatism

Astigmatism Treatment

Contact Lenses For Astigmatism

Astigmatism Prevention

Astigmatism FAQ



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