What is Astigmatism
Astigmatism is an abnormality of the cornea. In case of astigmatism, the cornea (= superficial membrane of the eye) is rather oval instead of being of round shape. We are talking about a cornea shaped like a “rugby ball”. Therefore, the light rays do not converge on one and the same point of the retina which produces a distorted image and therefore, a blurred vision of near and far. The vision becomes inaccurate at all distances.
Astigmatism is very common. If this visual defect is low, the view may not be affected. In this case, astigmatism does not require correction with glasses or 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 disorders such as myopia or hyperopia. Astigmatism can also occur following a keratoconus, a degenerative disease that usually appears in adolescence and during which the cornea takes a cone-shaped shape, which causes significant astigmatism and decreased visual acuity. It should be noted that astigmatism is not temporary and may get worse over time.
Astigmatic people may confuse certain letters such as H, M and N or 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 an internal astigmatism where the deformity does not affect the cornea but the lens inside the eye. If both deformations are associated, then we speak of total astigmatism.
Prevalence of Astigmatism
Astigmatism is very common. More than 15 million French people are astigmatic. A study 1 conducted in the United States to describe the prevalence of refractive disorders suggested that more than 30% of participants had astigmatism. The prevalence would be the same in Canada.
Diagnostic of Astigmatism
The diagnosis of astigmatism is made by an ophthalmologist or optometrist. The latter verifies the vision, from near and far, then with the help of a refractometer, measures the radii of curvature of the cornea which will confirm the presence of astigmatism.
Causes of Astigmatism
Astigmatism usually occurs from birth. The causes of its appearance at this time are unknown. Sometimes, for example, a cataract surgery, or a corneal transplant can damage and deform it and cause astigmatism. An infection or injury to the eye may also be responsible.
Complications of Astigmatism
Astigmatism can cause amblyopia, that is, decreased vision in one of the eyes caused by an abnormal visual development during childhood (eg strabismus, congenital cataract, etc.). .
Symptoms of Astigmatism
A slight astigmatism has no effect on vision. Low astigmatism and good eyesight are thus compatible.
For larger astigmatisms, the main symptoms are:
- Blurred vision, imprecise, distorted;
- Headaches ;
- A need to squint;
- Discomfort in the presence of strong light;
- Eye fatigue
People at risk
Men are affected as much as women by astigmatism. The risk of having this visual defect is not related to the presence of astigmatism in his parents. So there are no people who are more likely to have astigmatism than others.
Prevention of Astigmatism
We cannot prevent astigmatism. On the other hand, it is always useful to protect one’s eyes from the sun with sunglasses with a suitable protection factor, or during a risky activity that could cause a corneal injury with the wearing of protective glasses during DIY, for example.
Medical Treatments for Astigmatism
Low astigmatism does not require correction. For astigmatism that causes discomfort in vision, a correction should be considered.
This correction involves wearing glasses with suitable lenses or contact lenses.
In France, the ophthalmologist will prescribe glasses or lenses adapted to correct your vision. In Quebec, the optometrist is also authorized, and in France, the optician can renew the optical equipment after a visual examination with a prescription valid for 3 years, under certain conditions.
Surgical operation may also be considered. Refractive surgery, which is most often done by laser, “flattens out” the cornea. This operation changes the shape of the cornea and makes it more round.