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Have you ever gone to the optometrist for an eye test and been told that your eyes are shaped like footballs?
Or maybe you’ve noticed that your vision is getting blurry or harder to focus?
You may be one of the 40% of people in the world who have astigmatism.
What is the cause of astigmatism?
The eye acts like a camera, capturing light through the front surface (cornea) and focusing it onto a “film” at the back of the eye (retina).
In order to obtain a clear image, the eyeball and all of its surfaces (cornea, lens, and retina) must meet certain size and shape specifications.
Otherwise, vision may appear blurry and out of focus, known as “refractive error.”
Astigmatism (uh-STIG-muh-tiz-um) is a refractive error in which one or more of the eye’s surfaces are uneven and/or rounded. It is roughly divided into two types: regular and irregular.
Regular astigmatism is the most common. It usually comes from changes in the shape of the cornea. It’s not round, but oval, like a football or an egg. We don’t fully understand why some people develop periodic astigmatism, but part of it is genetics.
Irregular astigmatism is rare. This occurs when part of the cornea is no longer smooth (due to scarring or growth on the cornea), or its shape changes unevenly or asymmetrically.
Eye diseases such as keratoconus (where the cornea weakens and becomes conical in shape over time) can cause irregular astigmatism.
If the cornea is no longer round or smooth, light entering the eye will scatter onto the retina. This may cause blurred or distorted vision, decreased sensitivity to contrast, shadows, or double vision, and increased sensitivity to bright light.
Is astigmatism a new condition?
1727, Sir Isaac Newton The first describes the physics of how an irregular surface affects the focus of light passing through it.
Later in 1800 Thomas YoungA scientist with astigmatism described in a lecture how it affects his vision.
About the author
Flora Hui is a Research Fellow at the Australian Center for Eye Research and an Honorary Research Fellow at the Department of Surgery (Ophthalmology) at the University of Melbourne. Angelina Duan is an Optometry Research Scientist at CSIRO.
This article is reproduced from dialogue Licensed under Creative Commons. read Original article.
In 1825, astronomer Sir George Airy, who also suffered from astigmatism, discovered that he could see better when he tilted his glasses at a certain angle. He became the first to recommend the use of cylindrical lenses to correct astigmatism. These are still in use today.
The name “astigmatism” was the last to appear, coined by William Whewell in 1846. The name is derived from the Greek: “a-” (“without”) and “stigma” (“mark/spot”), which literally means “without point” and refers to the lack of a single, clear focus of vision.
How is astigmatism measured?
Optometrists typically detect and measure regular astigmatism during an optometry procedure, when they place different lenses in front of the eye to determine the eyeglass prescription.
Because irregular astigmatism may involve very small rough patches or masses, it is best seen with specialized imaging such as corneal topography. This creates a 3-dimensional map showing local bumps and irregularities on the cornea.
I have astigmatism, what do I need to know?
Astigmatism can appear at any age but becomes more common as we age.
Over time, you may develop astigmatism, and the degree of it may change.
Symptoms of astigmatism
NHS
The main symptoms of astigmatism are:
- blurred vision
- Headache
- Eyestrain – you may notice this after concentrating for long periods of time, such as when using a computer
Astigmatism often occurs along with nearsightedness or farsightedness.
With mild astigmatism, you may not notice any problems with your vision. As astigmatism increases, your vision becomes less clear. This may cause vision loss, eye strain, or fatigue.
You may need astigmatism correction to see easily and clearly. The purpose of correcting astigmatism is to compensate for the different curvature of the cornea to ensure that light entering the eye is correctly focused on the retina.
To correct conventional astigmatism, cylindrical lenses compensate for every curvature in the “football.” Cylindrical lenses are prescribed for eyeglasses or contact lenses.
Astigmatism can also be corrected with laser eye surgery.
Orthokeratology (ortho-k) may also be used. This involves wearing specialized rigid clothing contact lenses overnight. These hard contact lenses temporarily reshape the cornea, allowing the wearer to go without glasses during the day.
In order to control irregular astigmatism, it is also important to treat the underlying disease that causes the astigmatism. But typically, hard contact lenses are needed to achieve clear vision during the day because they can be placed on the surface of the eye to compensate for localized uneven patches in a way that glasses or soft contact lenses cannot.
Surgery such as corneal transplantation is sometimes required as a last resort to replace a damaged, misshapen cornea and control irregular astigmatism.
Should I worry about my child having astigmatism?
In children, if enough astigmatism is present to cause blurred or distorted vision, it can affect their learning and development in the classroom and in sports.
Untreated astigmatism is not dangerous, but high levels of astigmatism in young children may cause other vision problems, such as “eye rolls” or “lazy eyes.”
But don’t worry, regular eye exams with a pediatric (and adult) optometrist can allow for early detection and management when needed.