What is astigmatism?
In order to see perfectly clearly, any object we look at needs to be uniformly in focus at the back of the eye. Astigmatism usually occurs when either the cornea or crystalline lens of the eye (or in some cases both) are not the ideal spherical ‘football’ shape, but more like the pointed end of a rugby ball. This means the eye focuses light at two separate points on the retina, which is the light-sensitive layer at the back of the eye, this can cause blur and distortion in the vision.
Astigmatism is common and easy to work around your lifestyle. Most people with astigmatism wear glasses or contact lenses. See your optician to find the best option for you.
What are the symptoms of astigmatism?
Most glasses wearers will have some form of astigmatism. In more developed cases, or without treatment, symptoms could also include:
- Having to squint to see clearly
- Eye strain or tiredness when focusing on prolonged tasks - like when you’re reading a book or a computer screen
What causes astigmatism?
Astigmatism is usually something you’re born with and is also more common in premature or low birth weight babies. Astigmatism can sometimes develop later on in life and may occur following trauma or surgery to the eye.
It’s not clear why it happens if you are born with it, but it’s most likely linked to your genetics and tends to be hereditary. Astigmatism is commonly found in conjunction with long or short-sighted prescriptions, mild levels of astigmatism are very common as very few eyes are perfectly spherical.
More significant astigmatism is often seen if you suffer from an eye condition known as keratoconus which causes your cornea to get progressively thinner and more irregular in shape. This then leads to a more irregular focus with your eyes and results in astigmatism that can develop rapidly as the eye shape changes as the condition progresses.
Lots of children are born with astigmatism, but as they grow and their eyes change shape, it can improve with age. If astigmatism is in one eye only it may cause a lazy eye (amblyopia), a condition that often occurs in children as a result of one eye not seeing as clearly as the other during the development of the child’s vision. It’s important to get your child’s eyes tested to ensure that they can see okay, especially prior to starting school.
Astigmatism could also develop after:
- An eye injury
- Eye surgery
- An eye disease
During your eye test your optometrist will speak to you about any concerns you have about your eyesight and will review the outcome of your pre-test exams.
One of these will be the results of the autorefractor test which measures the shape and focus of your eyes while you focus on a point of light. In looking for refractive errors, the autorefractor notes whether the reflected light coming from the eye is focused differently in one direction to the other, which could indicate astigmatism.
Your optometrist will perform both subjective and objective tests to check your vision and eye health. One of the objective tests used to help detect astigmatism will be a small, handheld instrument called a retinoscope which is used to shine a beam of light into your eye. The optometrist uses the instrument to test how the light beam moves once it enters the eye and is reflected back towards them. The type of reaction shows if astigmatism is present and in what quantity.
Another test used by the optometrist to check for astigmatism will be the Jackson cross cylinder test, which relies on your answers. During this subjective test, the optometrist will show you two choices of lens on a number of occasions and ask which one makes some dots or a letter look the clearest of the two. Both will appear slightly blurry, but this is a way of fine-tuning the power needed to correct the astigmatism.
What is the difference between myopia and astigmatism?
The main difference between myopia (short-sightedness) and astigmatism is that they are two different refractive errors. Astigmatism causes blurred vision at any distance, whereas myopia causes far away objects to appear out of focus.
Glasses are a simple solution to astigmatism, and can be customised based on your prescription. For instance, if your astigmatism symptoms are more severe in one eye than the other, your glasses can accommodate for this.
If you have astigmatism, your optician can prescribe you a special type of soft contact lenses called toric lenses (lentes tóricas). They can bend light more in one direction than the other, which makes them ideal for people with astigmatism. Find out more about contact lenses here.
Laser eye surgery
Laser eye surgery is a more permanent treatment for astigmatism. The surgeon uses a special laser to change the shape of your cornea and correct the refractive error within the eye.