Astigmatism

Synonyms in a broader sense

Medical: Astigmatism Astigmatism, Pointlessness

Definition

Astigmatism (astigmatism) is a visual disorder caused by an increased (or more rarely a decreased) astigmatism. Incident light rays cannot be bundled in one point, and round objects, for example a sphere, are imaged and perceived as rod-shaped. In general, the astigmatism leads to a general visual blur at all distances.

Astigmatic people sometimes try to improve the depth of field by squeezing their eyes together. Headaches can also be a sign of astigmatism because the eye is constantly trying to compensate for the visual blur by changing the focus (accommodation). Corneal dystrophyA slight astigmatism is not a problem and is often not even noticed by those affected.

Typical symptoms only become apparent when the condition is more pronounced: everything is seen blurred and blurred, and even glasses do not bring any improvement. In this case you should consult an ophthalmologist. He or she can determine whether astigmatism is present by various means.

Often the ophthalmologist or optician will detect an existing astigmatism during the normal visual acuity test. In an objective eyeglass determination, the autorefractometer 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 axial position of the astigmatism.

The so-called ophthalmometer plays another important role in the diagnosis of astigmatism. This is able to determine the astigmatism. 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 given in angular minutes. The following tests offer a first assessment of a possible corneal curvature:

  • In the first test, four circles are shown, each of which is equally hatched in a different direction.

    It is tested whether the parallel lines in the circles in all four illustrations can be recognized sharply from a distance of approx. 30-40 cm.

  • The second test is the so-called astigmatism sun wheel. Here it is tested whether the rays running outwards are all seen sharply.

The diagnosis can be made by the ophthalmologist (specialist in ophthalmology) using various aids.

A severe astigmatism astigmatism can be diagnosed with the so-called placido disc. This is a disc on which concentric circles are drawn alternately in black and white. There is a small hole in the middle through which the doctor can see.

This allows the doctor to approach the patient’s eye until the disc is reflected on the patient’s cornea. With a normal (spherical) cornea, the circles appear round (concentric), with a regular astigmatism oval, and with an irregular astigmatism irregularly distorted. The strength of astigmatism is measured with the 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 creation and observation of two luminous figures which are brought into alignment on the patient’s cornea. Since the measuring distance to the patient and the distance between the two figures on the device are known, the radius of curvature of the cornea can be determined.

The total astigmatism can be measured with the skiascopy or refractometer. As with myopia and hyperopia, the degree of astigmatism is indicated in diopters. This is the reciprocal of the focal length (distance of optical apparatus to the focal point).

Thus, with a focal length of 2m, one would have a refractive power of 0.5 diopters (12m). In addition, the axis of the curvature is given in degrees. Regular astigmatism is usually treated with glasses or dimensionally stable contact lenses.

The lenses are cut cylindrical lenses that are precisely adjusted to the patient’s astigmatism. In adulthood, this may take some getting used to at first and lead to headaches.This problem can initially be tackled with weaker lenses, with which the strength is gradually increased until the optimum visual acuity is achieved. However, irregular astigmatism cannot be treated with glasses.

If the cornea is smooth and without scars, hard contact lenses can be used. Another possibility is corneal transplantation (keratoplasty). This involves finding a donor from whose cornea a slice is cut out and transplanted into the patient’s cornea.

Recently, astigmatism is also treated with an eye laser, the so-called excimer laser. The excimer laser is a cold-light laser that penetrates the cornea only minimally. This is a very gentle procedure that hardly damages the adjacent tissue of the eye.

As much tissue is then removed from the regions of the cornea where the astigmatism exists until a normal refraction ratio is achieved at these points. Not every form of astigmatism is suitable for laser surgery. The decision as to whether laser therapy is appropriate is the responsibility of the treating ophthalmologist.

Quite a few people affected by astigmatism feel severely impaired in their daily lives by the constant wearing of glasses or contact lenses. A laser treatment with a so-called excimer laser then offers the possibility to go through life without glasses again. These lasers make it possible to ablate the cornea to such an extent that the curvatures and protrusions are removed and the optimal rounding of the cornea can be restored.

Even if the cornea of the affected person is already very thin by nature, an ablation can only be performed to a small extent. While nearsightedness and farsightedness are easy to correct, there are limits to the correction of astigmatism at an early stage and a curvature can only be reliably restored to -4.00 dpt. The operation is usually performed on an outpatient basis, i.e. you do not have to be admitted to hospital as an inpatient.

During the operation the patient is awake and only the eye is anaesthetized. The procedure is not painful and the patients feel only a brief sensation of pressure when the laser is applied. In most surgery centers, both eyes are also treated in one session, which means there is no need to wait several days between treatments of both eyes.

Only if the cornea of one eye is severely curved, two sessions may be necessary. During the operation, the cornea is cut open in the shape of a ring and opened and processed with the laser, smoothing it until there is almost no curvature left. After this correction, the unfolded corneal part is folded back onto the eye and the operation is finished.

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 effect at night. However, these effects usually disappear within the first months after the operation.

Tearing and burning eyes usually disappear 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 performed in the eye itself, but only at the anterior interface. After a week of healing time, the eye is again able to master difficult tasks such as swimming, flying and diving.

The ability to work is restored the very next day and those affected do not have to be absent with several days of illness. The costs of a laser treatment are borne by the affected person himself. A reimbursement by the public health insurance companies does not exist so far.

With private policyholders there are considerable differences between the individual insurance companies and in individual cases a refund is decided upon. For many spectacle wearers, the question sooner or later arises as to whether it is possible to replace the often annoying glasses with contact lenses, at least temporarily. Just as with long-sighted or short-sighted patients, this is usually no longer a problem nowadays.

In case of very severe deformations of the cornea or irregular deformations (=irregular astigmatism), the contact lens may even be the better treatment method compared to glasses. A frequently used lens is the toric lens. This is offered as a soft and dimensionally stable (= hard) variant.Soft lenses can only be used with less curvature because they are too unstable for higher values and cannot hold the shape sufficiently.

This is where the dimensionally stable hard lenses must be used. These are made individually for each patient and are not available immediately in multiple packages like the soft lenses in opticians‘ stores. The toric lens is cylindrical and has different refractive powers in two perpendicular directions, thus compensating for astigmatism.

In contrast to the lenses for short- and long-sighted people, the lenses for astigmatism have a few important differences. The lens for astigmatism must not rotate in the eye like the lenses for short and long sighted people, because the toric lens has different refractions for certain points of astigmatism. In order to achieve that the different refractive powers are now correctly distributed on the eye and no longer shift and rotate, the lenses of the different manufacturers are weighted differently 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 suited to the individual concerned. The optician first measures the refractive power of the eye, which is responsible for short- or long-sightedness, before measuring the curvature of the cornea and determining the astigmatism.

Here, too, all variants are available, from daily, monthly and annual lenses to long wearable, dimensionally stable lenses. Soft lenses are only suitable for a lower degree of astigmatism. Lenses are also available in stores which, in addition to astigmatism, also compensate for short- or long-sightedness.

A distinction is made between regular astigmatism and irregular astigmatism. Regular astigmatism can be divided into two groups: In regular astigmatism, the refraction of the longitudinal axis (vertical) is stronger. The cause is probably the permanent pressure of the upper eyelid.

With astigmatism against the norm, it is the other way round and the horizontal axis refracts the light more strongly. The first form occurs much more frequently than the second form. In addition, there are further differentiated forms of astigmatismCorneal curvature, 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: nearsightedness); if the refractive power is weaker, it is a hypermetropic (farsighted) astigmatism (see: farsightedness).

Of course, mixed forms can also occur. Irregular astigmatism is caused by a very irregular curvature of the cornea. This is the case, for example, with corneal scars or keratoconus (malformation of the cornea, with conical protrusion of the corneal center).

  • The astigmatism of the cornea according to the rule (astigmatism rectus) and
  • The astigmatism against the rule (astigmatism inversus).

The prognosis for the regular astigmatism is very good, as it usually does not change. So once properly treated, it stays that way. The irregular astigmatism, on the other hand, can increase over time.

Therefore regular check-ups are essential. Blurred vision and headaches can be an indication of a further increase in astigmatism. Headaches are caused by the eye’s unsuccessful attempt to focus the image.

One either has astigmatism or one does not have it. Therefore, there is no prevention (prophylaxis). However, astigmatism should be treated at an early age, and especially parents with known astigmatism should have their children’s eyes examined at an early age.

The values of astigmatism are given in cylinders. It indicates how pronounced the astigmatism is. In the eyeglass passport, which every spectacle wearer receives from his optician, this is indicated with the abbreviation Cyl.

or Cyl. This value is also indicated in dioptres, as with short- or long-sightedness. The abbreviation for this is dpt.

The value is indicated here in 0. 25 steps step by step. The smallest possible value is therefore 0.

25 dpt, whereby values up to 0.5 dpt are considered normal, i.e. not necessarily worthy of treatment.In addition to this value – the strength of the curvature – the optician needs information about where on the cornea the curvature is located, i.e. where in the glass the cylinder has to be installed. To express this value, an optician uses the so-called axial position (abbreviation: A or Ach).

It can also be found in the spectacle passport. The number indicates a degree number, which describes where the curvature is located in the circle, if the cornea is imagined as a circle. 0° means that the corneal curvature is located vertically in the 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. Based on this information, every optician can now produce the appropriate lens or contact lens with the specified values.

Since astigmatism is usually congenital and does not improve over the course of a lifetime, it is highly advisable to present even small children to an optician at an early age. A latent astigmatism is usually not even noticeable in children’s everyday life, as the brain is quite capable of compensating for the visual defect in one eye with the help of the other. First indications of a visual defect in children are, for example, a conspicuously clumsy movement pattern and behavior.

If the child stumbles over the threshold of a door or if the building block towers keep falling over because they are simply stacked crookedly, this can indicate that the child does not perceive the environment 100% correctly. In principle, the same procedures as for adults are used to diagnose astigmastism in children. For small children, glasses are preferably used to correct astigmatism.

These are usually special glasses made of unbreakable plastic and the soft nasal bridge is used. Also, these baby glasses do not have classic temples, but an elastic rubber band (comparable to ski goggles). From the age of five years it is then possible to offer contact lenses.

The prerequisite is of course the cooperation of the child. After completion of the physical development, i.e. roughly from the age of 18, a laser treatment of the eye can be considered. It may also be necessary to mask one of the two eyes with special child-friendly plasters.

This would be the case if a visual defect has already been compensated by the brain and there is a “good” and a “bad” eye. By masking the better-sighted eye, the brain is to a certain extent forced to use and train the originally worse eye. In the first two years of life, the child’s brain is still very changeable.

If an existing defective vision is corrected in time, missing nerve tracts can still develop without problems and no long-term consequential damage is to be expected. Therefore, it is highly advisable to consult an ophthalmologist already in infancy. A latent astigmatism is usually not even noticeable in children’s everyday life, as the brain is quite capable of compensating for the visual defect in one eye with the help of the other.

First indications of a visual defect in children are, for example, a conspicuously clumsy movement pattern and behavior. If the child stumbles over the threshold of a door or if the building block towers keep falling over because they are simply stacked crookedly, this can indicate that the child does not perceive the environment 100% correctly. In principle, the same procedures as for adults are used to diagnose astigmastism in children.

For small children, glasses are preferably used to correct astigmatism. These are usually special glasses made of unbreakable plastic and the soft nasal bridge is used. Also, these baby glasses do not have classic temples, but an elastic rubber band (comparable to ski goggles).

From the age of five years it is then possible to offer contact lenses. The prerequisite is of course the cooperation of the child. After completion of the physical development, i.e. roughly from the age of 18, a laser treatment of the eye can be considered.

It may also be necessary to mask one of the two eyes with special child-friendly plasters. This would be the case if a visual defect has already been compensated by the brain and there is a “good” and a “bad” eye. By masking the better-sighted eye, the brain is to a certain extent forced to use and train the originally worse eye.In the first two years of life, the child’s brain is still very changeable.

If an existing defective vision is corrected in time, missing nerve tracts can still develop without problems and no long-term consequential damage is to be expected. Therefore, it is highly advisable to consult an ophthalmologist already in infancy.