Astigmatism: what is it?
Astigmatism is an abnormality of the cornea. In the event of astigmatism, the cornea (= superficial membrane of the eye) is rather oval instead of being of very round shape. We are talking about a cornea shaped like a “rugby ball”. Consequently, the light rays do not converge on one and the same point of the retina, which produces a distorted image and therefore blurred vision both near and far. Vision becomes imprecise at all distances.
Astigmatism is very common. If this visual defect is weak, sight may not be affected. In this case, astigmatism does not require correction with glasses or contact lenses. It is considered weak between 0 and 1 diopter and strong above 2 diopters.
Astigmatism can occur from birth. Later, it may be associated with other refractive errors such as myopia or hyperopia. Astigmatism can also appear following keratoconus, a degenerative disease that usually appears in adolescence and during which the cornea takes a cone shape, which causes severe astigmatism and reduced visual acuity. Note that astigmatism is not temporary and can get worse over time.
People with astigmatism can confuse certain letters such as H, M and N or even E and B. Astigmatism must therefore be identified as early as possible and in particular, before learning to read.
Although corneal astigmatism is the most common, there is internal astigmatism where the deformation does not affect the cornea but the lens located inside the eye. If the two deformations are associated, we then speak of total astigmatism.
Astigmatism is very common. More than 15 million French people are said to be astigmatic. A study 1 conducted in the United States to describe the prevalence of refractive errors suggested that more than 30% of participants suffered from astigmatism. The prevalence would be the same in Canada.
The diagnosis of astigmatism is made by an ophthalmologist or optometrist. The latter checks vision, near and far, then using a refractometer, measures the radii of curvature of the cornea which will confirm the presence of astigmatism.
Astigmatism usually occurs from birth. The causes of its appearance at this time are unknown. Sometimes, a cataract surgery for example, or a corneal transplant can damage and deform it and thus cause astigmatism. An infection or injury to the eye can also be responsible.
Astigmatism can cause amblyopia, i.e. decreased vision in one of the two eyes caused by an abnormality in visual development during childhood (e.g. strabismus, congenital cataract, etc.) .
Symptoms and people at risk of astigmatism
Symptoms of astigmatism
A slight astigmatism has no repercussions on the vision. Low astigmatism and good eyesight are thus compatible.
For more severe astigmatisms, the main symptoms are:
- Blurry, imprecise, distorted vision;
- Headaches ;
- A need to squint;
- Discomfort in the presence of strong light;
- Eye fatigue.
People at risk
Men are as affected as women by astigmatism. The risk of having this visual defect is not linked to the presence of astigmatism in his parents. There are therefore no people who are more at risk of having astigmatism than others.
Prevention and medical treatment of astigmatism
Prevention of astigmatism
Astigmatism cannot be prevented. On the other hand, it is always useful to protect your eyes from the sun with sunglasses with an appropriate protection factor, or during a risky activity that could cause an injury to the cornea with the wearing of protective glasses when DIY, for example.
Astigmatism medical treatments
Low astigmatism does not require correction. For astigmatism that causes discomfort in vision, a correction should be considered.
This correction involves wearing glasses with adapted lenses or contact lenses.
In France, the ophthalmologist will prescribe glasses or lenses adapted to correct your vision. Note that in Quebec, the optometrist is also authorized, and that in France, the optician can renew the optical equipment after a visual examination with a prescription valid for 3 years, under certain conditions.
Surgery can also be considered. Refractive surgery, which is most often done with laser, “flattens” the cornea. This operation changes the shape of the cornea and makes it rounder.
Our doctor’s opinion on astigmatism
Astigmatism is very common and does not always affect vision. However, it should not be taken lightly as its consequences can be significant. Indeed, an astigmatic child may encounter difficulties in learning to read since he may have a tendency to confuse certain numbers and certain letters. His academic performance may be affected by this visual defect. The latter must therefore be taken into account and dealt with effectively. Screening, especially in young children, is very important.