What is astigmatism?
Astigmatism is a common condition in which the cornea or lens has an irregular shape. This causes light entering the eye to be split across multiple zones, resulting in blurred vision for both near and distant objects.
What causes astigmatism?
Astigmatism is part of a group of eye conditions known as refractive errors. Other conditions in this group include: myopia, hyperopia, and presbyopia.
The condition can be described as corneal or lenticular. Corneal astigmatism is the more common of the two, and simply means that your cornea does not have a perfectly curved shape. Similarly, if your lens has an irregular curvature, this is referred to as lenticular astigmatism.
While there are many different causes of astigmatism, it is most commonly hereditary. It tends to run in families; you are born with it and it develops over time. Almost everyone has some degree of astigmatism, but mild cases may not require any treatment.
What are the symptoms of astigmatism?
It often occurs alongside myopia (short-sightedness) or hyperopia (long-sightedness); the most common symptom is blurred vision, but you may also experience:
- Headaches
- A need to squint (to focus on text or objects)
- Eye strain (particularly when you need to focus for extended periods)
If you experience any of the symptoms listed, consult your optician, as they may be related to another condition.
Regular astigmatism versus irregular astigmatism
There are two types of astigmatism. If it is confined to just one area of the cornea or lens, regular astigmatism can usually be corrected fairly easily. It is more common than irregular astigmatism, which occurs when the cornea is uneven across multiple areas, and is typically caused by an eye injury or keratoconus.
How is astigmatism treated?
Regular astigmatism can be corrected with glasses or contact lenses, and in some cases through laser eye surgery. Lenses work by bending light rays (to compensate for the underlying refractive error), allowing images to be correctly projected onto the retina. Soft contact lenses used for astigmatism, called toric lenses, are designed to realign your contact lenses with each blink, giving you clear and stable vision.
Irregular astigmatism can only be corrected with rigid gas-permeable (RGP) contact lenses. These are thicker than soft lenses and their rigidity provides a more rounded shape over the cornea, allowing light entering the eye to be focused correctly.
Contact lenses that correct astigmatism are generally referred to as “toric” lenses and have the following specifications:
- Spherical lens power, either positive or negative, indicating whether you are short-sighted or long-sighted. It is possible to not be short-sighted or long-sighted but still have astigmatism, in which case the spherical power reading on your prescription will be zero (+0.00).
- Cylinder: a measurement indicating how flat or irregular your cornea is.
- Axis: where on your cornea the astigmatism is located.
Your prescription will typically look something like this: -1.00 (sphere) / -1.25 (cylinder) x 90 (axis)
How to check for astigmatism
We have created a test so you can see through the eyes of someone with astigmatism and someone without, but please remember that this cannot replace a visit to an optician and should not be used as a diagnostic tool.
