Astigmatism: what is it, what does it look like, causes, symptoms and genetics

What is astigmatism?

Sometimes, the front part of the eye is not completely round; it's a little squished.

When the eye is more oval-shaped, it causes astigmatism, making things look blurry or distorted.

This uneven shape can happen as a natural part of how the eye grows, or it can be influenced by genetics. When this happens, we call it astigmatism.

There are two kinds of astigmatism: "against-the-rule" and "with-the-rule."

"Against-the-rule" means the squished part of the eye is like a rugby ball lying on its side.

"With-the-rule" means it's more like a rugby ball standing upright. "With-the-rule" astigmatism is what we most commonly see in our patients.

What causes astigmatism?

Astigmatism is typically caused by irregularities in the shape of the eye, especially in the cornea (the clear front part of the eye) or, less commonly, in the lens inside the eye. There are a number of things that can cause this to happen:

• A family history of astigmatism can increase the likelihood of developing this eye condition. If your parents or other close relatives have astigmatism, you might be more likely to have it too.
• Sometimes, as the eye grows, it can take on a slightly irregular shape, leading to astigmatism. This can be a natural part of eye development.
• Injuries to the eye or certain eye surgeries can also result in changes to the shape of the cornea, potentially causing astigmatism.
• It can also be caused by keratoconus is an uncommon condition where the cornea gradually becomes thinner and takes on a more conical shape, leading to astigmatism.
• Some people are simply born with a cornea that is not perfectly spherical, which can lead to astigmatism without any specific cause.

How common is astigmatism?

Astigmatism occurs in about 1 in 3 of all people.

The rate of astigmatism significantly increases from 14.3% in the under 15-year-old age group to 67.2% in the age group of over 65-years old.

What are the symptoms and what does vision look like with astigmatism?

• Blurred or distorted vision: Both nearby and distant objects appear blurry or distorted. Images may be stretched or skewed.
• Difficulty seeing at night: Astigmatism can cause glare, halos, or difficulty seeing in low-light conditions, such as when driving at night.
• Eyestrain: Astigmatism may lead to eye discomfort, fatigue, or strain, especially after extended periods of reading, computer use, or other close-up tasks.
• Headaches: Frequent headaches, particularly around the eyes or forehead, can be a symptom of uncorrected astigmatism, as the eyes work harder to focus.
• Squinting: Squinting is a common instinct to try to bring objects into focus. If you find yourself squinting often, it may be an indication of astigmatism.
• Double vision: Astigmatism can cause double vision, where you see two overlapping images of the same object.
• Difficulty with contact lenses: If you wear contact lenses, difficulty in achieving a comfortable fit or consistent vision may be related to astigmatism.

How to tell if you have astigmatism

If you’ve noticed any of the above symptoms, it’s a good idea to book an eye test. A definitive astigmatism diagnosis should be made by an Optometrist during a comprehensive eye exam.

Is astigmatism hereditary?

Astigmatism can be hereditary, meaning it can run in families. If your parents or close relatives have astigmatism, you may have a higher risk of developing it yourself. This is because the shape and structure of the eye, including the curvature of the cornea and lens, are influenced by genetics.

However, while genetics can play a role in the development of astigmatism, it's not the sole factor. Even if there is a family history of astigmatism, it doesn't guarantee that you will have it, and people without a family history of astigmatism can still develop this condition.

Regular eye exams are essential to detect and manage astigmatism and other vision issues, especially if there is a family history of eye problems.

Read more about the links between family history and eye health

Can astigmatism cause blindness?

Astigmatism by itself does not typically cause blindness. It can cause blurry or distorted vision, but it doesn't usually lead to complete loss of vision or blindness.