What is Astigmatism?

What is the main cause of astigmatism?

To kick things off, astigmatism is extremely common.

It's a refractive defect where light is not correctly focused inside your eye to create a good point of focus.

The main cause of astigmatism is due to an uneven curvature in the cornea or sometimes in the lens of the eye.

These irregularities are distinguished by an asymmetry in the cornea or the crystalline lens. As opposed to being spherically symmetrical, one side is more curved than the other.

This means the eye is shaped more like a rugby ball than say a football and effects how light is refracted (bent) towards the retina within the eye.

Here's an illustration of what this means.

Astigmatism is considered as a genetic trait inherited from your parents.

Astigmatism in children and adults accounts for 47% of the UK population. It is a very common condition and is typically more predominant in one eye than the other.

Comparatively, other bodily characteristics such as the ears and nose are equally as likely to be asymmetric.

When you think about it, this makes this unevenness seem pretty normal...

Astigmatism symptoms

The symptoms of astigmatism typically include;

• Blurry or distorted vision at various distances.
• Squinting to read.
• Difficulty seeing at night.
• Eye strain.
• Headaches

Astigmatism test

During your eye test, your optometrist will go through a series of ocular assessments.

The primary test for astigmatism (retinoscopy) is also used for detecting near-sightedness and far-sightedness. To assess this, a series of lenses are separately introduced using what is called a phoropter.

This instrument contains a carousel of optical lenses which are placed over your eyes in front of a bright light. As the light is shone into your eye through the various phoropter-lenses, the optometrist can establish if you have any refractive defects in your eye-lens or cornea.

Progressing through the phoropter-lenses, you’re able to verbally describe which dioptre of lens gives you the best visual focus. Looking at the eye test chart at the opposite side of the examination room, this process of elimination defines your prescription lenses, if indeed you require them.

How do glasses correct astigmatism?

On your prescription paper, you'll see two neighbouring sections called CYL and AXIS for each eye. Together, these corresponding values use dioptric power, tilted at a specific angle to compensate for your astigmatism.

Here's a breakdown.

The terms CYL denotes your required cylindrical correction in your lenses to correct your misshapen cornea. This is measured in dioptres so the higher the CYL, the more astigmatic your eye is.

E.g. +2.25, -0.50 or +1.75 

Directly after, you'll see a corresponding box called AXIS. This is measured as an angle which compensates for the asymmetry in your cornea. Depending on your specific astigmatism, this angle can be anywhere within 180 degrees.

Eg: 090, 120, 010

Astigmatism may be present in just one or both of your eyes. If you have a cylindrical power for either eye, you will always see a follow AXIS value.

If your prescription doesn't state any cylindrical power, you won't have any AXIS angle and therefore do not have astigmatism in that eye.

If you'd like a better understanding of your prescription paper, we've made a handy guide which you can see here.

Can astigmatism be cured?

Astigmatism can be rectified in three different ways.

This can be done via contact lenses, prescription glasses or refractive surgery.

Your lifestyle and personal preference will play a role in how you’d like to correct your astigmatism. Generally, prescription glasses are the most popular solution as they are less difficult to wear than contact lenses and less costly than refractive surgery.

Astigmatism shouldn’t necessarily be viewed as ‘curable’ as asymmetry is present is many other bodily aspects. This refractive issue is a structural defect and shouldn’t be considered as a disease or transmittable condition.

Good quality eyeglasses are by far the simplest solution for an astigmatism cure.

How do things look with astigmatism?

The side effects of astigmatism effects your ability to correctly focus the light that enters your eye.

As the light passes through your cornea, it becomes distorted from improper refraction. This scatters the light before it reaches the retina at the back of your eye which creates an imperfect retinal signal.

This signal is then passed on to the brain giving a poor interpretation of what is in front of you.

As seen in the illustration above, the light is entering the eye and becoming fragmented. Depending on what you are looking at and at what distance, this fragmentation results in blurred vision, making it difficult to focus properly.

Astigmatism glasses are a good way to resolve this issue by correcting this refractive defect. Lenses with a CYL and relative AXIS will compensate for the asymmetry in your cornea.

Image credit: Lucy Brook for Cereal Magazine | Margaret Howell

What causes astigmatism to worsen?

Unfortunately, astigmatism is known to change throughout your life and can deteriorate with age.

Unusual injuries to the eye such as blunt trauma or the disease keratoconus are known to induce or worsen astigmatism. These are generally the only external circumstances that can make this eye condition worse.

There are various myths that surround astigmatism, one of which concerns whether or not wearing your glasses can have a negative effect. This myth is simply not true and has no detrimental influence at all.  

Other myths include squinting too often or reading in poorly lit environments. Neither of these can cause astigmatism to worsen and are more likely to be a cause of eyestrain or headaches.