Astigmatism

Causes of astigmatism

Astigmatism can result from a cornea or lens that is distorted in shape, or a scar on the cornea.

Normally, the curvature of the cornea is spherical, so it has the same radius of curvature in every direction, and its refractive power is the same. All the light rays coming from objects enter the eye via the cornea through the pupil, and the eye lens focuses the light so that it lands on the retina.

In the astigmatic eye, the cornea is irregular, so its curvature is not spherical but toric (like the side of a ring doughnut). The horizontal and vertical radii are not equal. This means that the refractive power of the eye is different in different directions. Light rays coming from objects in the field of vision will not “land” at a single point, which means that, with astigmatism, vision will be distorted and more out of focus in some directions than others.

Objects, letters, and numbers may be out of focus horizontally, vertically, or both at once.

A less common variant of astigmatism is called irregular astigmatism. This may be caused by a scar on the cornea. Irregular astigmatism causes light to be scattered in a specific, irregular direction.

Astigmatism is thought to be genetic. Contrary to popular myth, it is not caused by reading in dim light or sitting too close to the television.

The curvature of your lens is susceptible to change, meaning your astigmatism can either improve or worsen over time.

Types of astigmatism

Astigmatism is often associated with short-sightedness (myopia) or farsightedness (hyperopia) or even both.

Myopic astigmatism

Just like with myopia, the light that enters the eye falls in front of the retina, rather than on the retina. With myopic astigmatism, the light rays fall or converge at different points in front of the retina

Hypermetropic astigmatism

The different points where the light rays converge are behind the retina, resulting in blurred or distorted vision.

Mixed astigmatism

If the light rays fall both in front of and behind the retina, it is called mixed astigmatism.

Astigmatism in children

It is important to detect and treat astigmatism in children as they are still learning how the world is supposed to look, and their brains are developing the ability to process the signals from their eyes. If their brains receive blurred images rather than clear ones, this could have an impact on the development of the visual processing ability. An indication of astigmatism might be your child being reluctant to do close-up activities such as painting or reading.

It can be difficult to notice astigmatism in children, as they may not have the ability to describe the problems they’re experiencing. If you have any concerns, have their eyes tested.

Treatment for astigmatism

There are many treatments for astigmatism, including glasses, contact lenses and laser eye surgery.

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