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 split into 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.
This condition can be described as corneal or lenticular. The corneal type is the more common of the two, and simply means that your cornea does not have a perfect curvature. Similarly, if your lens has an irregular curvature, it is called 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 with age. 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
- Feel the need to squint (to focus on text or objects)
- Suffer from eye fatigue (especially when you need to focus for extended periods)
If you experience any of the symptoms listed, consult your optician, as it could be related to another condition.
Regular vs irregular astigmatism
There are two types of astigmatism. If it is limited to just one area of the cornea or lens, regular astigmatism can usually be corrected quite easily. It is more common than irregular astigmatism, which occurs when the cornea is uneven across multiple zones, and is usually 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. The lenses work by bending light rays (to compensate for the underlying refractive error), allowing images to be properly 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) lenses. They are thicker than soft lenses and their rigidity provides a more rounded shape over the cornea, allowing light entering the eye to focus correctly.
Contact lenses that correct astigmatism are generally called “toric” and have the following specifications:
- Positive or negative spherical lens, indicating whether you are short-sighted or long-sighted. It is possible to be neither short-sighted nor long-sighted but still have astigmatism, in which case the spherical lens 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 normally look something like this: -1.00 (spherical lens) / -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.
