Astigmatism is a defect in vision due to the shape of the cornea or lens.
Normally, the cornea and lens are smooth and rounded with equal curvature in all directions, so they can focus the rays of light on the retina and the back of the eye.
However, if the cornea and lens are not smooth and rounded with an equal curvature in all directions, the rays of light converge to different points.
Astigmatism can also be defined as an optical aberration, that is, imperfection of the eye that causes the distortion of the images.
A person may be born with astigmatism and may have other refractive errors at the same time: myopia or farsightedness .
Adults with astigmatism realize that sight is not as good as it should be, but children who have these symptoms may not be aware of the disease and can barely complain of blurred or distorted vision.
Non-correct astigmatism can affect a child’s performance in school and in sports.
What is an eye meridian?
To indicate the degree of curvature of a sphere (for example, the planet earth), the term meridian is used, that is, a line representing the intersection between a plane and the surface of the sphere.
Usually the curvature of the cornea is greater vertically than horizontally, whereas in the lens it is the opposite.
The two curves compensate, but in astigmatism the meridians of the cornea have a more pronounced difference and the lens can not correct this defect.
Classification of astigmatism
1. Corneal astigmatism means that the cornea has an irregular shape.
2. Lenticular astigmatism means that the patient has a change in the shape of the lens.
3. Physiological astigmatism has a value of approximately 0.5 diopters (unit of measure of the convergence of a lens) that sometimes can reach 1 diopter, but does not have an impact on the quality of the view.
Types of astigmatism according to the angle formed between the meridians
- Regular Astigmatism
When the two main meridians are perpendicular to each other.
Most cases of astigmatism are regular.
There are three subtypes:
1. In favor of the rule or direct where the most curved meridian is that vertical;
2. Against rule or indirect in which the vertical meridian is more curved of that horizontal;
3. Oblique astigmatism where the axes are neither vertical nor horizontal.
- Irregular Astigmatism
When the two main meridians are not perpendicular to each other.
The curvature of the meridians is uneven.
It can be caused by trauma , disease or degeneration.
Usually, irregular astigmatism is not correctable to 20/20.
Classification based on the location of the foci compared to the retina
In this case, the focus (the point where light rays converge) is located on a line rather than a point.
When one focus is located on the retina and the other is not in the retina.
This type is divided into:
- Simple myopic astigmatism
When one focus is in front of the retina and the other is focused on the retina.
- Simple hypermetrope astigmatism
When one focus is behind the retina and the other is in the retina. In this case, closer vision is more difficult.
astigmatism Astigmatism is done when the patient also suffers from another refractive defect.
This type is divided into:
- Compound myopic astigmatism
When the two outbreaks are in front of the retina.
- Astigmatism hypermetrope compound
When the two foci are focused behind the retina. Ipertropical astigmatism causes blurred vision at close range.
When one focus is in front of the retina and the other is behind the retina.
Classification based on the symmetry of the two eyes
- Symmetric astigmatism
The main meridians or axes of the two eyes are symmetrical (for example, both eyes are according to rule or against rule, see regular astigmatism).
The sum of the axes of the two eyes is equal to about 180 °.
- Asymmetrical astigmatism
The principal meridians or axes of the two eyes are not symmetrical (for example, one eye is according to the rule while the other eye is against it)
The sum of the axes of the two eyes is not equal to 180 °.
What are the causes of astigmatism?
The cause of astigmatism is unknown:
- Many experts believe that it is present at birth , so it may be genetic.
- In some cases, astigmatism develops following an eye injury or eye surgery .
- Among other causes, a rare disease called keratoconuscan cause astigmatism.
In keratoconus the cornea has a progressive thinning and assumes a shape more similar to a cone, this translates to astigmatism.
- People with diabetes often develop lenticular astigmatism because elevated blood sugar levels can lead to change in the shape of the lens.
The process usually develops slowly.
When blood glucose levels are reduced with treatment, even the shape of the lens returns to normal.
- According to the blood group diet , the cause of astigmatism is a diet that includes milk and dairy products.
- According to natural medicine and hygiene , vision does not depend on eye size, in fact, the quality of photography is not dependent on the size of a camera. The lens or lens can change the thickness and curvature very quickly. Everyone has eyes of different shape and size, but that does not detract from vision. So if the muscles, ligaments and nerves that alter the shape of the lens work well, glasses are not needed.
Symptoms of astigmatism
Those who suffer from astigmatism may experience some or all of the following symptoms:
- Distorted or blurred images from near or far;
- Strabismus ,
- Pain in the eyes ;
- Fatigue or eye eye strain because the patient often beats the cilia to try to see better.
Does astigmatism regress or worsen over time? When does it stabilize?
The evolution of astigmatism is not easily predictable.
If the patient wears glasses, the eye adapts and becomes accustomed, then there should not be major changes in vision.
According to the Bates Method and Hygienism, astigmatism can regress in one week with:
1. Specific exercises to be performed regularly, at least 15 minutes a day,
2. Natural diet, simple and with the right food combinations.
Is there any complication?
Astigmatism in one eye can cause amblyopia (lazy eye). The affected eye does not learn to see why the brain ignores the signs of the eye.
Diagnosis of astigmatism
The first visit of the optician to find out if the child has astigmatism should be done between 3 and 5 years of age.
Astigmatism can be diagnosed through a thorough eye examination.
The ophthalmologist performs the tests to measure:
- The focusing of light,
- To determine the corrective power of optical lenses, necessary to compensate for vision defect.
Tests and exams for astigmatism
Visual acuity test – the patient should read the letters on a distance chart.
The test measures the visual acuity that is written as a fraction, for example, 5/10.
This test is performed by placing an optotype (plaque with letters of different sizes) on the wall and holding the patient 3 meters away.
The number on the right indicates the smallest line of letters you can read.
A healthy person should reach a value of 10/10, a blind person has a visual acuity of 0/10.
A surveyor is the main instrument used to measure the curvature of the cornea.
By focusing a circle of light on the cornea and measuring its reflection, we can determine the exact curvature of the surface of the cornea.
This measure is particularly critical in determining the appropriate measure for contact lenses.
A more sophisticated procedure called corneal or corneal opiography can be done in some cases to give greater detail of the shape of the cornea.
Refraction – Using an instrument called a phoropter, your optometrist places a series of lenses in front of your eyes and measures the focus of light.
The operation is performed using an instrument called a retinoscope that automatically evaluates the focusing power of the eye.
The power must be adapted according to the patient’s responses to determine the lenses that allow clearer vision.
Using the information obtained from these exams, your ophthalmologist can determine if you are suffering from astigmatism.
These results together with the other tests allow the optician to determine the power of the corrective lenses required by the patient.