Astigmatism – Vision, causes and correction
Astigmatism is an oval-shaped deformation of the cornea that distorts images along a specific axis. Depending on the degree of astigmatism, vision is more or less blurred, both at a distance and up close. It can be present from birth (congenital) or develop later in life (keratoconus). Astigmatism can be corrected with glasses, contact lenses, laser surgery, and during cataract surgery using a toric intraocular lens implant .
What is astigmatism?
Astigmatism is an imperfection in the curvature of the cornea or lens of your eye.
It may be helpful to imagine that the normal eye is shaped like a football.
In the case of astigmatism, it is more like the shape of a rugby ball (egg-shaped or oval).
Depending on the direction of the distortion, astigmatism can be classified as:
Direct – Or to the rule, when the steepest curve is vertical, the ball being lying on its side.
Indirect – Or inverse, when the steepest curve is horizontal, like an upright rugby ball.
In cases of astigmatism, images focus in front of and/or behind the retina.
Objects appear blurry both from a distance and up close.
What is vision like with astigmatism?
The cornea and lens are normally curved equally in all axes.
When your cornea or lens has a deformed shape, you suffer from astigmatism.
Your vision is therefore blurry or distorted both near and far, as if you were looking in a distorting mirror. You may appear too tall, too short, too wide, or too thin.
Astigmatism and other refractive errors
Astigmatism can be associated with other refractive errors, such as
Myopia
Hyperopia
Presbyopia
Impact of astigmatism
Adults with significant astigmatism may find that their vision is not as good as it should be without glasses.
Children with astigmatism are often unaware they have it and are unlikely to complain. However, uncorrected astigmatism can negatively impact their academic performance, which is why vision screening is conducted in preschool and again in primary school.
Causes of astigmatism
Astigmatism is very common. Doctors don't know why the shape of the cornea or lens differs from person to person.
However, it is proven that the probability of developing astigmatism is hereditary.
Astigmatism can also develop after an eye disease (keratoconus), an eye injury, or surgery.
It is a myth that astigmatism can develop or worsen by reading in dim light or sitting very close to the television.
Symptoms of astigmatism
Symptoms suggestive of astigmatism include:
Blurred vision or areas of distorted vision.
Eye strain.
Headaches.
Squinting to try to see clearly (pinhole).
If you are experiencing these symptoms, you don't necessarily have astigmatism. You should consult your ophthalmologist. A complete eye examination will determine the cause of your symptoms.
Diagnosis of astigmatism
There are several solutions for correcting astigmatism. Glasses and soft contact lenses are the most common. Discussing this with your ophthalmologist will help you choose the correction best suited to your visual needs.
Glasses and soft contact lenses
In the case of low power, the correction is referred to as "resting".
Wearing it is recommended primarily for close vision and prolonged work.
The goal is to reduce accommodation efforts from the beginning of the day, in order to limit the symptoms of visual fatigue (asthenopia) at the end of the day.
Wear your glasses first thing in the morning when you start working.
Rigid and scleral lenses
Rigid gas permeable (RGP) and scleral lenses were once the only contact lenses for astigmatism. This is no longer entirely the case.
However, if you suffer from severe astigmatism, rigid lenses may be a better option to smooth out the astigmatism.
These are the lenses to be used as a first-line treatment to correct irregular astigmatism in the context of keratoconus or pellucid marginal degeneration.
The cornea can be reshaped to correct astigmatism. This is called refractive surgery. The techniques most often used are laser surgery, with LASIK, PRK, and SMILE giving excellent results.
When laser surgery is not indicated because the cornea is too thin or too fragile, surgery by implant placement (phake implant or lens operation) with a toric implant may sometimes be indicated.
Complications of astigmatism
Some astigmatisms are neither direct nor inverse, but irregular. This means that the cornea has a herniation due to fragility. The two forms of irregular astigmatism are:
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Keratoconus – primarily affecting young patients who rub their eyes
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Pellucid marginal degeneration – affecting older patients, with no identifiable triggering factors.