The eye is an optical system, comparable to a camera. Like a camera, the eye also consists of several refractive media (in particular the cornea and the lens).
These deflect incident light (e.g. an image) so that they meet at a focal point on the retina. Usually at the point of sharpest vision. The amount of deflection is called refraction, the so-called diopter.
If the incident rays of light are incorrectly projected onto the retina, the image becomes blurred and is referred to as defective vision.
Illustration of short-sightedness and long-sightedness through deformed eyeballs
The types of defective vision can be divided into
Your spectacle pass provides information about the type of defective vision you have.
This is what the abbreviations on your spectacle pass mean:
R: Values for the right eye
L: values for the left eye
sph (sphere): describes your short-sightedness or long-sightedness in diopters (dpt).
Negative values mean short-sightedness. In the spectacle pass above, it is -3.75 dpt for the right eye. Long-sightedness is given in positive values, e.g. + 1.5 dpt.
cyl (cylinder): describes your corneal curvature in diopters, in the above example -1.0 dpt for the right eye. The sign is irrelevant for you.
ach (axis): indicates the axial position of your corneal curvature in degrees. In our example, the corneal curvature on the right eye has a direction of 90°.
add (addition): shows the value of presbyopia as soon as it occurs. The value +2.75 dpt is added to the spherical correction.
In addition to spectacle and contact lens correction, there are three laser correction procedures for correcting defective vision that change the refractive power of the cornea: LASIK, LASEK and PRK.
Thanks to precise laser technology, many visual defects can be corrected easily, safely and permanently.
The procedures differ in the microsurgical corrections that change the refractive power.
The following procedures are possible:
The ophthalmologist can find out which procedure is suitable for your eye through a detailed preliminary refractive examination.
Information on short-sightedness
Short-sightedness (myopia) is one of the most common visual defects alongside long-sightedness and astigmatism. The technical term myopia is derived from the Greek: Myops means as much as blinking face, because in fact people often squint their eyes when they are short-sighted. Myopia means that objects in the distance can only be seen blurred.
In most cases, short-sightedness is caused by an eyeball that is too long. This can be inherited, but can also be caused by being born too early. In most cases, it develops in the first three decades of life. Experts also refer to it as axial myopia.
Visual acuity correction for short-sightedness @ ZZMC /AdobeStock
Another form of this type is refractive myopia. In this case, the refractive power of the cornea or lens is too high. Refractive myopia is also not uncommon in cataracts with a very cloudy cornea.
It is unclear whether external factors such as sunlight, intensive screen work or reading in poor light cause the disease.
Only rarely are both eyes affected to the same extent, and in most patients one eye sees worse than the other. It often occurs in conjunction with astigmatism.
Symptoms of short-sightedness
A clear symptom is blurred vision in the distance. This is particularly noticeable at night at the beginning. However, patients can see objects close up as normal.
Diagnosis and treatment of short-sightedness
A simple eye test by an ophthalmologist or optician provides information on whether myopia is present. The refraction measurement then determines the exact degree of visual impairment. This is indicated with negative diopter values, such as -2.
The treatments are all aimed at correcting the refractive error. This means that the focal point of the incident light rays is no longer in front of the retina, but behind it.
This refractive error is usually corrected with glasses. However, younger people are more likely to opt for contact lenses or laser therapy. Mostly for cosmetic reasons. Unfortunately, health insurance companies only cover the costs in exceptional cases.
Laser surgery is becoming increasingly popular. However, as with any operation, complications can occur. The patient may also need a visual aid after the operation. Laser surgery is not suitable for all short-sighted patients. However, special examinations quickly provide clarity.
If you decide to wear contact lenses, you should opt for hard lenses. Although they take longer to get used to, they are much better tolerated.
A distinction is made not only between soft and hard lenses, but also between daily, monthly and annual lenses. No matter which type of contact lens you choose: Hygiene should be a top priority.
A new type of lens is the night lens, which you only wear at night and can manage without aids during the day.
Preventing short-sightedness
You can hardly prevent it. However, you should have your eyes checked regularly.
Patients who suffer from short-sightedness are more susceptible to damage to the cornea. This is particularly true for contact lens wearers. They should make sure they have their retina checked regularly.
Eye training cannot remedy or prevent short-sightedness.
Information on long-sightedness
In the case of long-sightedness (hyperopia), experts distinguish between axial and refractive hyperopia. In contrast to short-sightedness, those affected can see sharply at greater distances, but can only see objects close up out of focus.
Axial hyperopia is the most common form of long-sightedness. In this case, the eye and therefore the distance between the cornea and retina is too short.
In refractive hyperopia, on the other hand, the refractive power of the lens is not sufficient for sharp vision.
In both forms, the focal point of the incident rays lies behind the retina. If the axis is shortened by just one millimeter, this already causes a change of +3 diopters. In most cases, axial hyperopia is present from birth.
Farsightedness can also affect children and adolescents, although they can usually compensate for the visual impairment quite well. However, the extra strain on the eyes can lead to side effects such as eye pain or headaches.
With increasing age, long-sightedness often develops and occurs either alone or in combination with presbyopia. Almost all people over the age of 45 suffer from long-sightedness. They need appropriate visual aids. However, it does not usually worsen with increasing age. Only presbyopia usually sets in earlier in patients with long-sightedness.
Symptoms of long-sightedness
The symptoms of long-sightedness are usually more severe in older people than in children and adolescents. They can no longer see close objects clearly, which is noticeable when reading magazines and books, for example.
As the eye strains more with farsightedness, those affected usually have eye pain and headaches and tire quickly.
Diagnosis and treatment of long-sightedness
In order to diagnose this defective vision, the optician or doctor must first determine the refractive power of the eye. This examination quickly reveals the number of diopters the patient needs. In the case of farsightedness, the diopter is always positive (e.g. +1.5).
The treatment methods are all aimed at correcting existing refractive errors. Both glasses and contact lenses are frequently used.
However,contact lenses often lead to burning or dry eyes and require very good care. However, contact lenses and suitable care products are associated with costs.
For patients who suffer from both long-sightedness and short-sightedness, so-called varifocals are suitable . The lenses are divided into different areas. When looking through the lower half, they correct long-sightedness. Myopia through the upper half
In the past, patients who suffered from multiple visual impairments needed the right glasses for each impairment. This is now a thing of the past thanks to varifocals.
Long-sightedness can also often be corrected by laser surgery. However, surgery for long-sightedness is often not as successful as for short-sightedness. The risks and side effects are equally low. Corneal scars and over- or undercorrection of farsightedness are the most common surgical risks.
The operation is possible for patients with up to four diopters. An artificial lens can be implanted if the diopters are higher. This procedure is very popular and can be performed on an outpatient basis in doctors' surgeries.
The cost of LASIK surgery is around 1,000 to 3,000 euros per eye. As this is a purely cosmetic procedure, health insurance companies only pay for this operation in exceptional cases.
Prevention of long-sightedness
It is not possible to prevent this vision defect. However, it is important to correct farsightedness in children in good time to prevent them from squinting inwards.
Information on astigmatism of the eyes
Astigmatism, also known as astigmatism, is similar to short-sightedness and long-sightedness and is a less common visual defect. It can affect one or both eyes.
Patients with astigmatism may have blurred vision both near and far. The name "astigmatism" comes from the fact that those affected perceive a point as a blurred line or rod.
In those affected, the curvature of the cornea deviates from its natural shape. A normal cornea is evenly curved (similar to a sphere). Corneal curvature leads to areas of the cornea that are curved to varying degrees, which has a negative effect on refractive power.
A distinction is made between regular and irregular astigmatism. In most cases, astigmatism is congenital, although scars after corneal injuries are also a possible cause.
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Healthy eye (top) and eye with astigmatism (bottom). Due to the abnormal curvature, the light is distorted and not projected correctly onto the focal point. The image appears blurred
Symptoms of astigmatism
Those affected usually do not notice a slight curvature of the cornea.
Blurred vision is often accompanied by eye pain and headaches caused by eye strain.
Diagnosis and treatment
The ophthalmometer can be used to precisely determine the curvature and the radius of curvature in each plane. The diopter value also indicates the severity of the deformity.
A regular corneal curvature can be corrected with the help of glasses or dimensionally stable contact lenses. If the cornea is severely damaged, corneal replacement surgery is necessary.
Laser surgery can correct the condition in many cases. However, the prognosis for success is more difficult the more severely the cornea is curved.
If the angle between the maximum and minimum refractive planes of the cornea is greater than 90°, glasses will no longer help. In this case, special contact lenses or a corneal transplant can be considered.
Prevention
Astigmatism is a visual defect that cannot be prevented. Parents should have their children examined by an ophthalmologist as early as possible in order to rule out any future visual defects.
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