Astigmatism is a refractive error of the eye caused by the shape of the cornea or lens.
Normally, the cornea and lens are smooth and rounded and have equal curvature in all directions. Thus, it is possible that the light rays meet at the focal point on the retina and the back of the eye.
However, if the cornea or lens are not smooth and uniformly rounded, the light rays converge at different points.
Astigmatism can also be referred to as optical aberration, i.e. aberrations that cause a distorted image.
Physiological astigmatism is about 0.5 diopters (unit of measurement for the refractive power of the lens), sometimes it can reach up to 1 diopter, but this has no effect on vision.
People can be born with astigmatism and at the same time may have other refractive errors: nearsightedness or farsightedness.
Adults with astigmatism know that their visual acuity is not as good as it should be. However, children who have these symptoms are not necessarily aware of this condition and rarely complain of blurred or distorted vision.
Uncorrected astigmatism can affect the child’s performance in school and sports.
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What is an eye meridian?
To indicate the degree of curvature of a sphere (for example, the Earth), the meridian represents a line representing the intersection between a plane and the surface of the sphere.
In general, the curvature of the cornea is greater in the vertical direction than in the horizontal direction, while in the lens it is the other way around.
The two curves compensate each other, but in astigmatism, the meridians of the cornea are more pronounced and the lens cannot correct this defect.
Classification of astigmatism
1. Corneal astigmatism means that the cornea has an irregular shape (astigmatism).
2. Lens astigmatism means that the shape of the lens is disturbed.
Types of astigmatism due 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 subspecies:
- According to the rule or directly, in which the more curved meridian is the vertical;
- Against the rule or indirectly, where the more curved meridian is the horizontal;
- Oblique astigmatism, in which 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 not uniform.
This can be caused by trauma, illness or degeneration.
Irregular astigmatism is often not correctable until 20/20.
Classification according to the position of the focal lines with respect to the retina
Simple astigmatism (astigmatism simplex) In this case, the focus (point where the parallel light rays converge)
is on a line, rather than on a single point.
One focal line is in the retinal plane, the other is not.
It can be further subdivided into:
- Simple myopic astigmatism (astigmatism myopicus simplex)
When one focal line is in front of the retina and the other on the retina.
- Simple transparent astigmatism (astigmatism hyperopicus simplex)
When one focal line is behind the retina and the other is on the retina. In this case, close vision is difficult.
Composite astigmatism (astigmatism compositus)
One speaks of compound astigmatism when there is another refractive error (nearsightedness or farsightedness).
A further subdivision is made into:
- Compound myopic astigmatism (astigmatism myopicus compositus)
When both focal lines are in front of the retina.
- Compound transparent astigmatism (astigmatism
hyperopicus compositus)
When the two focal lines are behind the retina.
Mixed astigmatism (astigmatism
mixuts)
When one focus is in front of the retina and the other behind the retina.
Classification according to symmetry of the eyes
Symmetrical astigmatism
The main meridians or axes of the two eyes are symmetrical (for example, both eyes are according to the rule or against the rule, see regular astigmatism).
The sum of the axes of both eyes corresponds to about 180°.
Asymmetric astigmatism
The main meridians or axes of the two eyes are not symmetrical (for example, one eye is after the rule while the other eye is against the rule).
The sum of the axes of both eyes does not correspond to 180°.
What are the causes of astigmatism?
The cause of astigmatism is unknown:
- Many experts assume that it has existed since birth, so it can be genetic.
- In some cases, astigmatism develops after an eye injury or after eye surgery.
- Among the causes is a rare condition called keratoconus, which can cause astigmatism.
In keratoconus, the cornea becomes progressively thinner and takes the shape of a cone. This leads to astigmatism. - People with diabetes often develop lenticular astigmatism because the elevated blood sugar levels can lead to changes in lens shape.
The process usually progresses slowly.
If blood sugar decreases during therapy, the lens also returns to its normal shape. - According to the blood group diet, the cause of astigmatism is a diet that includes milk and dairy products.
- According to natural medicine and hygienism, vision does not depend on the size of the eye, just as the quality of a photo has nothing to do with the size of the camera. The lens can change its thickness and curvature very quickly. Everyone has a different eye shape and eye size, but this does not affect their vision. So if the muscles, ligaments and nerves that change the shape of the lens are working well, glasses are not needed.
Symptoms of astigmatism
Those who suffer from astigmatism may have some or all of the following symptoms:
- Distorted or blurry images from near and far
- Strabismus
- Eyestrain
- Fatigue or asthenopia, as you blink more often to see better
Does astigmatism regress or worsen over time? When does stabilization occur?
The development of astigmatism is difficult to predict.
If the patient uses glasses, the eye gets used to them and adapts, so there should be no major changes in vision.
According to the Bates method and hygienism, astigmatism can regress within a week by the following measures:
- Special exercises to be performed regularly for at least 15 minutes a day.
- Natural, simple nutrition with the right food combinations.
Are there complications of astigmatism?
Astigmatism of just one eye can lead to amblyopia (weak vision). The affected eye does not learn to see because the brain ignores the impulses of this eye.
Diagnosis of astigmatism
The first ophthalmological examination of the child should be done between the ages of 3 and 5 to determine whether the child suffers from astigmatism.
Astigmatism can be detected during a comprehensive eye examination.
The ophthalmologist conducts examinations:
- to measure astigmatism,
- to measure the light focus,
- to determine the corrective performance of the optical lenses required to compensate for the visual defect.
Tests and examinations for asigmatism
Visual acuity test – the patient must read letters on a distant blackboard.
The test measures visual acuity, which is given as a fractional number, for example 5/10.
This test is performed using an eye chart positioned on the wall, on which letters (optotypes) of different sizes are depicted; the patient keeps a distance of 3 meters.
The number on the right indicates the series of the smallest letter that can be read.
A healthy person should reach a value of 10/10, a blind person has a visual acuity of 0/10.
Keratometry
An ophthalmometer (or keratometer) is an instrument used to measure corneal curvature.
A circle of light is focused on the cornea and by measuring the reflection, the exact curvature of the corneal surface can be determined.
This measurement is especially important when determining the correct measure for contact lenses.
A more demanding procedure is the so-called corneal topography. It can be done in some cases to determine the corneal shape more accurately.
Refraction – using a so-called phoropter, the optician places a series of lenses in front of the eyes and measures the focus of the light.
The examination procedure is performed by using a retinoscope, which automatically evaluates the performance of the eye focus.
Performance should be adjusted to the patient’s responses to determine the lenses that allow for better vision.
With the help of the information obtained from the tests, the ophthalmologist can determine whether astigmatism is present.
This result, in conjunction with other test results, allows the ophthalmologist to determine the strength of the visual aids required for the patient.
