Ophthalmology

Astigmatism

Synonyms in a broader sense

Medical: astigmatism

Clarity, pointlessness

English: Astigmatism

definition

Astigmatism (astigmatism) refers to a visual disorder that is caused by an increased (less often a decreased) corneal curvature. Incident light rays cannot be bundled in one point and round objects, for example a sphere, are depicted and perceived as rods.

Detecting astigmatism

What are the symptoms of astigmatism?

In general, astuteness leads to general visual blurring at all distances. People with sight vision sometimes try to improve the depth of field by squinting their eyes. In addition, headaches can be a sign of astigmatism because the eye is constantly trying to compensate for the blurred vision by changing the focus (accommodation).

Read more on the topic: Astigmatism symptoms, eye pain, corneal dystrophy

How can you test a skin curvature?

A slight astigmatism is not a problem and is often not even noticed by those affected. Typical symptoms are only noticeable when they are more pronounced: everything is seen blurred and blurred, and glasses do not bring any improvement. In this case one should consult an ophthalmologist. He can use various means to determine whether there is an astigmatism.

Often the ophthalmologist or optician diagnoses an existing astigmatism during the normal visual acuity determination (Eye test) firmly.
In an objective eyeglass determination, the automatic refractometer provides the first useful values.During the subjective eyeglass determination, the optician can then determine the exact diopter values using classic test glasses or a modern phoropter and indicate the exact axis position of the corneal curvature.

The so-called ophthalmometer plays another important role in the diagnosis of astigmatism. This is able to determine the corneal curvature. To do this, the ophthalmologist measures the direction of curvature of the eye in each of the planes and then calculates its refractive power from these values. The result is given in diopters. The axis in which the curvature lies is specified in angular minutes.

The following tests provide an initial assessment of a possible corneal curvature:

In the first test, four circles are shown, each of which is hatched evenly in a different direction. It is checked whether the parallel lines in the circles in all four images can be seen clearly from a distance of approx. 30-40 cm.
The second test is what is known as the astigmatism sun gear. Here it is checked whether the rays running outwards can all be seen clearly.

How is astigmatism diagnosed?

The diagnosis can be made by the ophthalmologist (specialist in ophthalmology) using various auxiliary devices. Severe astigmatism / astigmatism can be diagnosed with the so-called Placido disk.
This is a disk on which concentric circles are drawn alternately in black and white. There is a small hole in the middle that the doctor can see through. In this way, the doctor approaches the patient's eye so closely that the disc is reflected on the patient's cornea.
With normal (spherical) cornea the circles appear round (concentric), with regular astigmatism oval and with irregular astigmatism irregularly distorted.

The strength of astigmatism is measured with an ophthalmometer. This makes it possible to measure the different radii of the corneal axes (vertical, horizontal) and thus determine the refractive power.
The principle of the ophthalmometer is the generation and observation of two luminous figures that are brought into congruence on the patient's cornea. Since you know the measuring distance to the patient and the distance between the two figures on the device, you can determine the radius of curvature of the cornea.
The total astigmatism can be measured with a retinoscopy or refractometer.
As with nearsightedness and farsightedness, the strength of the astigmatism is given in diopters.
This is the reciprocal of the focal length (distance between the optical apparatus and the focal point). With a focal length of 2m you would have a refractive power of 0.5 diopters (1 / 2m). In addition, the axis in which the curvature lies in degrees is given.

Treat an astigmatism

How is astigmatism treated?

Regular astigmatism is usually treated with glasses or dimensionally stable contact lenses.
The lenses are ground cylinder glasses that are precisely tailored to the patient's asthma. In adulthood, this may take a little getting used to and lead to headaches. This problem can initially be tackled with weaker lenses, in which the strength is gradually increased up to the optimal visual acuity setting.

The irregular corneal curvature cannot be treated with glasses. If the cornea is smooth and without scars, hard contact lenses can be used.
Another option is corneal transplantation (Keratoplasty). To do this, a donor must be found, from whose cornea a disc is then cut out and transplanted into the patient's cornea.

Lately astuteness has also been treated with an eye laser, the so-called excimer laser. The excimer laser is a cold light laser that only minimally penetrates the cornea. This is a very gentle procedure in which the adjacent tissue / eye is hardly injured. So much tissue is then removed from the regions of the cornea where the corneal curvature exists, until a normal refraction ratio also prevails at these points. Not every form of astigmatism is suitable for laser surgery. The decision as to whether laser therapy makes sense is the responsibility of the attending specialist in ophthalmology.

For more information, see: Laser therapy for astigmatism

Can astigmatism be treated with lasers?

Quite a few of those affected by astigmatism feel that their everyday life is severely impaired by the constant wearing of glasses or contact lenses. Laser treatment with a so-called excimer laser then offers the opportunity to go through life again without glasses.
These lasers make it possible to ablate the cornea to such an extent that the curvatures and protrusions are removed and the optimal roundness of the cornea can be restored. Even if the affected person's cornea is naturally very thin, it can only be removed to a small extent.
While nearsightedness and farsightedness are easy to correct, the correction of astigmatism is limited early on and a curvature can only be reliably restored up to -4.00dpt.

The operation is usually done on an outpatient basis, which means you don't have to be admitted to the hospital as an inpatient. During the procedure, the patient is awake and only the eye is anesthetized. The procedure is not painful and patients only feel pressure for a short time when the laser is put on.
In most surgical centers, both eyes are treated in one session, which means you don't have to wait several days between treatments for both eyes. Only if the cornea is very crooked in one eye, two sessions may be necessary.
During the operation, the cornea is cut open and unfolded in a ring shape and processed with the laser and smoothed until there are almost no more curvatures. After this correction, the opened corneal part is folded back onto the eye and the operation is ended.
In over 90% of patients, this procedure leads to an enormous improvement in vision with a maximum deviation of 50% from the target value. After the operation, many patients complain of dry eyes, a foreign body sensation or a glare at night. However, these effects usually disappear within the first few months after the operation. Watery and burning eyes have usually disappeared the day after the operation and only last longer in patients with chronically dry eyes and can be treated well with wetting drops. Blindness is not one of the risks of laser treatment, as treatment is not carried out in the eye itself, but only at the anterior interface. After a week of healing, the eye is again able to master difficult tasks such as swimming, flying and diving. The ability to work is given again the next day and those affected do not fall out with several days of illness.

The person concerned bears the costs of a laser treatment himself. There is currently no reimbursement by the statutory health insurance companies. In the case of private policyholders, there are significant differences between the individual insurance carriers and a decision is made on a reimbursement in individual cases.

How does the treatment with contact lenses differ?

For many glasses wearers, sooner or later the question arises of the possibility of replacing the often annoying glasses with contact lenses, at least temporarily. Just like with farsighted or short-sighted patients, this is usually no longer a problem these days. In the case of very strong deformations of the cornea or irregular deformations (= irregular corneal curvature), the contact lens may even be the better treatment method compared to glasses.

A lens that is often used is the toric lens. This is offered as a soft and dimensionally stable (= hard) variant. Soft lenses can only be used with less curvature, as they are too unstable for higher values and cannot hold their shape sufficiently. The rigid, rigid lenses must then be used here. These are made individually for each patient and, unlike soft lenses, are not immediately available in multiple packs in opticians' shops. The toric lens is cylindrical and has different refractive powers in two mutually perpendicular directions, thus compensating for the curvature of the cornea.

In contrast to the lenses for nearsighted and farsighted people, the lenses have a few important differences in the case of astigmatism. The lens with astigmatism must not rotate in the eye like the lenses of nearsighted and farsighted people, since the toric lens has different refractions for certain points of the corneal curvature.
In order to ensure that the different refractive powers are now correctly distributed over the eye and no longer shift or rotate, the lenses of the various manufacturers are weighted differently in order to be able to guarantee stability with every movement. This is achieved, for example, by a small ballast on the lower edge of the lens. An ophthalmologist or optician should decide which type of contact lens is best for the individual affected. This first measures the refractive power of the eye, which is responsible for nearsightedness or farsightedness, before it then measures the curvature of the cornea and determines the corneal curvature. Here, too, all variants are available, from daily, monthly and annual lenses to long-lasting, dimensionally stable lenses. Soft lenses are only suitable for a lesser degree of astigmatism. Lenses are also commercially available which, in addition to the astigmatism, also compensate for nearsightedness or farsightedness.

Preventing astigmatism

What are the causes of astigmatism?

A distinction is made between regular astigmatism and irregular corneal curvature.

Regular astuteness can be divided into two groups:

the astigmatism according to the rule (Astigmatism rectus) and
the astigmatism against the rule (Inverse astigmatism).

With astigmatism according to the rule, the refraction of the longitudinal axis (vertical) is stronger. The permanent pressure of the upper eyelid is probably the cause.

With astigmatism against the rule it is the other way around and the horizontal axis refracts the light more strongly. The first form is much more common than the second form.

There are also further differentiated forms of astigmatism / astigmatism, which are classified according to the strength of the refractive power:
If the refractive power is stronger than normal, it is a myopic (nearsighted) astigmatism (see: Myopia), if the refractive power is weaker it is a hypermetropic (farsighted) astigmatism (see: Farsightedness). Mixed forms can of course also occur.

The irregular astigmatism / vision results from a very irregular curvature of the cornea. This is the case, for example, with corneal scars or keratoconus (malformation of the cornea with a conical protrusion of the center of the cornea).

Curvature of the cornea

What is the prognosis for astigmatism?

The prognosis for regular astigmatism is very good, as it usually does not change. Once properly treated, it stays that way.

The irregular astigmatism, on the other hand, can increase over time. Regular check-ups are therefore essential. Blurred vision and headaches can be signs of a further flare-up in astuteness. The headache arises from the unsuccessful attempt by the eye to focus the image.

One has astuteness or one does not have it. This is why there is no prophylaxis. Astigmatism should be treated at an early age, and parents who are known to have astigmatism should have their children's eyes examined at an early stage.

Further questions about astigmatism

How are the measured values of a corneal curvature obtained?

The corneal curvature values are given in cylinders. It indicates how pronounced the corneal curvature is. In the glasses passport that every wearer of glasses gets from his optician, this is with the abbreviation Cyl. or cyl. specified. As with nearsightedness or farsightedness, this value is also given in dioptres. The abbreviation for this is dpt. The value is specified here in steps of 0.25. The smallest possible value is 0.25 D, whereby values up to 0.5 D are considered normal, i.e. do not necessarily count as worthy of treatment.
In addition to this value - i.e. the strength of the curvature - the optician needs information about where on the cornea the curvature is, i.e. where the cylinder must be installed in the glass. To express this value, an optician uses the so-called axis position (abbreviation: A or Ach). It can also be found in the glasses pass. The number indicates a number of degrees that describes where the curvature is in the circle if the cornea is imagined as a circle. Here 0 ° means that the corneal curvature lies vertically in a circle, 90 ° means a horizontal position. The values here are between 0 ° and 180 °.

All these values are determined and documented by the optician or ophthalmologist during the eye test. Every optician can use this information to produce the right glass or contact lens with the specified values.

Read more on the topic: Corneal curvature values

How does astigmatism affect children?

Since astigmatism is usually congenital and does not improve in the course of life, it is extremely advisable to see even small children at an ophthalmologist at an early age.

Read more about this: Astigmatism in children

A latent astigmatism is usually not even noticed in everyday life in children, since the brain is quite able to compensate for the visual defects of one eye with the help of the other.

The first indications of a visual defect in children are, for example, a conspicuously clumsy movement pattern and behavior. If the child stumbles over the doorstep frequently or if the building block towers keep falling over because they are simply stacked crookedly and crookedly, this can indicate that the child is not perceiving the surroundings 100% correctly.
In principle, the same methods are used to diagnose astigmastism in children as in adults.

Glasses are the preferred choice for correcting astigmatism in young children.
Usually special glasses made of break-proof plastic and the soft nose bridge are used. These baby goggles also don't have classic temples, but an elastic rubber band (comparable to ski goggles).
From the age of five it is then possible to offer contact lenses. The child's cooperation is of course a prerequisite.
After completion of the physical development, i.e. roughly from the 18th birthday, laser treatment on the eye can be considered.

It may also be necessary to cover one of the two eyes with special child-friendly plasters. This would be the case if a visual defect has already been compensated for by the brain and there is a "good" and a "bad" eye. By masking the better-seeing eye, the brain is forced to use and train the originally poorer eye.

In the first two years of life, the child's brain is still very changeable. If an existing ametropia is corrected in good time, missing nerve tracts can develop without any problems and no long-term consequential damage is to be expected. It is therefore absolutely advisable to consult an ophthalmologist as early as infancy.