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Nearsightedness (myopia) - eye test, causes
myopia (also "myopia") is an ametropia of the eye. The widespread form "myopia simplex" is not considered a disease, but a physiological change in the body. Myopic people have Difficulties, distant things clearly visible: the further away from the eye, the more blurred they look. First, an online eye test that can check if you are nearsighted. The task is to recognize the opening in the ring (so-called Landolt ring) from a distance of approx. 50 cm and to click on the corresponding circle.
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Online eye test with Snellen hook
The previous eye test has the disadvantage that the standardized Landolt rings are not shown properly on most displays. Therefore, in the following an alternative eye test, in which so-called Snellen hooks can be recognized. Here, too, the task is to recognize the direction in which the hook is open - one could also say the direction in which the "E" is pointing.
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Cause of myopia
Myopia is a Image errors: the refraction of light through the cornea and the lens of the eye is too strong, so that the focal point lies in front of the retina. But only if the focal point is mapped exactly on the fovea, the place of sharpest vision, can we see clearly. Put simply: the cause of nearsightedness is an eyeball that is too long - measured by the refractive power of the dioptric apparatus (light-refracting parts of the eye).
Brief description of vision: The environment reflects light that falls through the cornea into the eye. Due to the curvature of Cornea and Eye lens the light is broken. Normally, the light beam would be refracted in such a way that it is focused on the back of the retina in as small a point as possible. In myopic people, the focal point is in front of the retina. The image is somewhat scattered on the retina - this is precisely what results in a blurred visual impression.
There are two possible causes of myopia.
- For one thing, the eyeball can be too long. As a result, the image in front of the retina is focused and then scattered, which means that it is "out of focus" on the retina. This is called "Axial myopia".
- On the other hand, the eyeball can also have a normal length - however, the refractive power of the dioptric apparatus is too strong. This then also has the effect that the image focus is in front of the retina. This form of myopia is called "Refractive myopia"(also" refractive myopia ").
- If the cornea is the cause of the change in refraction, one also speaks of "Curvature myopia"
- If the lens of the eye has an altered refractive power, one also speaks of "Lens myopia".
If the refractive power of the dioptric apparatus is normal, but the eyeball itself has grown too long in the course of growth, it is called one Axial myopia.
If the length of the eyeball is normal, but the power of the dioptric apparatus is too strong (due to the curvature of the cornea and / or lens of the eye), it is called a Refractive myopia.
Myopia leads to a blurred image. Men do not recognize things that are far away. These include, for example, car license plates, street signs, people, etc. Since one can easily deform the eye for a short time with the help of muscle strength, one often subconsciously tries to compensate for myopia. In the long run, however, this is a burden that often causes headaches.
Ultimately, however, the visual impression depends very much on the degree of myopia. Because the focal point can be very close in front of the retina, but it can also be quite far away.
Classification of myopia
Depending on when the myopia develops, there are four types of myopia:
- Myopia has been present since birth (usually Degenerative myopia).
- Myopia, which usually develops between the ages of 10-12 (mostly Myopia simplex). The deterioration, that is, the continuous increase in myopia, usually ends at around 22-25 years of age, in rare cases only at around 27 years of age, according to the growth process.
- Myopia, which only begins to develop from the age of 20.
- In rare cases, myopia does not develop until the age of about 40 years.
With regard to the degree of visual impairment, a distinction is made between two types of myopia:
- The Myopia simplex is the most common form of myopia. It is likely that it is both genetic and can be intensified by external influences (for example, if you are very busy in close proximity). Since myopia simplex is only up to approx. -6 D and therefore the visual impairment is rather "moderate", it is not considered a "disease", but a physiological deformation. This is particularly relevant for the health insurances: they only pay for glasses as a correction of myopia up to the age of 18 years. Afterwards you are responsible for correcting your own poor eyesight.
- The Degenerative myopia (also called malignant myopia), on the other hand, is an eye disease. The degree of myopia is usually significantly higher than -6 dpt. The cause is usually a congenital deformation of the back of the eye. Degenerative myopia is also referred to as a real visual impairment.
The refractive power of the "dioptric apparatus" (cornea and lens) is approx. 60 diopters in the normal state. If you are nearsighted, the strength of your nearsightedness is given in diopters, namely the value you need to regain normal refractive power.
In rare cases, later years develop myopia. Despite its widespread use, the question of the extent to which myopia is inherited is still largely unanswered.
Temporary myopia can also occur in women during pregnancy and breastfeeding. This can be up to one diopter. These "Maternity myopia"but goes back a few weeks after weaning at the latest.
How do you notice myopia?
A congenital myopia can only be recognized when the toddler begins to respond to visual stimuli. Since with nearsightedness you can only not see what is far away, parents can try to observe different reactions of the children.
The School myopia can develop insidiously. It usually begins with puberty, around 10-12 years of age. The youngsters usually don't even notice at the beginning. It is only when they are around 15-16 years old that they realize that they can no longer read things properly on the blackboard at school. A clear indication to visit an optician or ophthalmologist and do an exact eye test.
Diagnosing myopia - difficult to spot at first
One ability of the eye makes it difficult to diagnose myopia: the Accommodation. Accommodation (from Latin: adapt) means the dynamic adaptation of the refractive power of the eye. Roughly simplified, the eye can do that Curvature of the lens actively change, which changes the refractive power of the lens. In short: it is not that easy to recognize myopia in the early stages.
Street signs or texts on television are good indicators of nearsightedness. If you can no longer see it properly, you should check your own vision.
Ultimately, there are two professional groups that can reliably diagnose myopia: Ophthalmologists and optician. And even better, you can accurately measure the strength of myopia. This in turn is the basis for the right choice of correction: glasses, contact lenses or eye lasers (more on this below).
Cure or correct myopia?
Myopia cannot be "cured". How the eye grows is specified in the genetic information (DNA). However, there are various ways of correcting this poor vision - depending on how severe the nearsightedness is. There are basically two ways of being able to see sharply again as a nearsighted person: with a corrective lens (visual aid) in front of it or with an operative change in the cornea (eye operation).
"Cure" myopia with pinhole glasses?
Another possibility is often advertised - often with a false promise: the possibility of "curing" myopia with the help of raster glasses or pinhole glasses, often in connection with so-called "eye training". Thereby glasses are used, which are supposed to increase the accommodation ability of the eye. This is to correct the aberration caused by deformation of the eyeball with the help of your own eye muscles. With very low diopter values, this is also possible for a short time. However, if these grid glasses are used for too long, there is a risk of permanent squinting.
Behind this is often a fear of wearing glasses for a long time. Many worry that doing so will make them unattractive. Others shy away from practical restrictions, e.g. when doing sports. Ultimately, one can only say: there are suitable visual aids for almost every application. And many faces only become interesting through glasses. Strictly speaking, glasses are fashion accessories - and the big fashion labels have long recognized this and almost all have their own glasses collections.
Laser eyes for nearsightedness
For some time now, there has been an alternative to visual aids for nearsighted people between the ages of 25 and 45: that Laser eye surgery. This is part of the cornea permanently worn away. This changes the refractive power of the cornea so that the focal point is exactly on the retina again.
In principle, the cornea is ablated in the middle, resulting in a concave curvature. However, laser eye surgery is not suitable for everyone. The first requirement is that the Growth process completed have to be. Otherwise, there might be a further deterioration in the refractive power after the laser eye surgery, which can then no longer be corrected with an operation.
Second, the Cornea a certain thickness have - which in turn depends on the strength of the correction. If the cornea has grown normally, it is possible to compensate for up to -6 diopters. However, if the cornea is thinner than average, you would have to remove too much. The cornea would then become unstable.
Thirdly, laser eye surgery is of course a must surgical interventionwhich is comparable to a cosmetic operation. Many medical ethicists have concerns about removing what is basically healthy and functional tissue. You have to remember: the cornea can heal, but it will never regain its original thickness. As with any operation, there is also a residual risk of blemishes or painful infections.
The basic sequence of such an eye laser correction is illustrated in the following graphic.
The surface of the cornea is first cut open in a ring and set aside as a so-called flap. Then the middle layer of the cornea is removed. Then the flap is closed again. This procedure enables a good healing and regeneration process. While with the conventional LASIK procedure the flap is cut with the help of a sharp blade, with Femto-LASIK this is done by a laser.
The costs of an eye laser correction are usually not covered by health insurance. Depending on the procedure, you have to calculate between 1000 and 3000 euros per eye. With bargain offers, especially at foreign clinics, the risk that something does not go as desired is greater.
Glasses for correcting nearsightedness
Most people correct myopia with the help of a lens attached to them. You can wear these either as glasses or as a contact lens. To compensate for myopia, they are concave Spectacle lenses required, which scatters the light beam a little before it hits the eye.
In the course of the centuries, and especially in the course of the last few decades, the technology has developed enormously, so that today almost any ametropia can be optimally corrected with a lens placed in front of it.
Nearsighted and presbyopic? Varifocals
Especially for nearsighted people, who develop presbyopia over the years, had the problem that they always needed two glasses: one for distance vision (against nearsightedness) and one for near vision (against presbyopia) ). There is now a solution for this: varifocals. Similar to bifocal glasses, they correct two ametropia - but with a stepless lens.
Contact lenses to correct myopia
As an alternative to glasses, the lens can also be worn directly in the eye on the cornea: this is a contact lens. It swims in the tear fluid that covers the cornea anyway.
Contact lenses for correcting nearsightedness can be purchased in different types: as dimensionally stable annual lenses, as monthly or weekly lenses - or just as soft daily lenses (e.g. for sports).
The same applies to contact lenses as to laser eye surgery: not every eye is suitable for this. It depends on the nature of the cornea and, above all, on the production of tear fluid. If this is not sufficiently formed and the surface of the cornea becomes too dry for the lens to adhere, it can become painful. For most people, however, this is not a problem. Only a visit to the ophthalmologist or optician can bring certainty.
Diopter as a unit of measurement
If you get glasses as a nearsighted person, then the refractive power of the lens, which is necessary to compensate for the nearsightedness, is given in diopters. For example, it is said that to compensate for a myopic eye you need a lens with a refractive power of minus 3 diopters, or -3 dpt for short. The Diopter measurement unit (Abbreviation: dpt) was introduced in 1872 by the French ophthalmologist Ferdinand Monoyer and is still considered today as the unit for describing the refractive power of an optical lens.
- Mild nearsightedness is myopia of −3.00 D or less.
- Moderate nearsightedness is myopia between −3.00 and −6.00 dpt.
- Severe nearsightedness (also: myopia magna) is an ametropia of −6.00 dpt or more. About 18% of nearsighted people develop severe myopia.
Difference in diopter and vision (visual acuity)
When assessing ametropia, however, another aspect also plays a central role. The so-called visual acuity, which can also be referred to as image sharpness or visual acuity. How well you can see, i.e. how well you can see small details, also depends on the resolution of the retina. Millions of small light sensory cells are arranged there. The density of sensory cells is greatest in the fovea, the place of sharpest vision. This is exactly why you can see things that are shown here particularly well and sharply. However, the degree of density differs from person to person. Some have a particularly large number of sensory cells, they have a very high resolution and thus a high visual acuity. Others have fewer sensory cells (this is also hereditary). In these people, the visual acuity is rather low.
With an eye test - more precisely with a refraction (precise measurement of the refractive error), you not only measure which dioptric value you need to correct an aberration, but also how high the resolution is. Since both are not (!) Related to each other - refractive power of the cornea and lens and density of the sensory cells - one cannot convert diopter values one to one. The corresponding conversion tables are therefore based on an average visual acuity, which, however, can vary in individual cases. See: Visual acuity and diopters - difference and conversion
The glasses pass
If you need a visual aid, the values that have been determined are entered in a glasses passport. In the case of nearsightedness, the lens must be concave, i.e. have a slight scatter, i.e. have a negative diopter value - one also speaks of "minus lenses".
It is not uncommon for the values for the two eyes to differ. For example, someone needs a lens against myopia of -2.5 dpt on their left eye and one with -3.0 dpt on their right eye (that's how it is with me :-).
The values for the lenses for correcting myopia are entered in the Sphere field. For people who also have astigmatism (an aberration of the corneal, colloquially also called astigmatism), the values cylinder (Cyl) and the axis (A), i.e. the direction of the deviation, are required. Specifically for multifocal glasses (e.g. varifocal glasses) is the specification of the addition (Add), with which one specifies the difference between distance vision and near vision.The pupil distance is also a very important piece of information (this is particularly important if you do not order the glasses from an optician, but online): if the optimal point of view is not exactly in front of the pupil, the visual impression can be inharmonious in the long run.
The Snellen eye test
The above online eye test can only give an approximate impression of your eyesight. Alternatively, you can print out an eye test and do it at home. Here is the eye test that the Dutch ophthalmologist Herman Snellen first presented to the public in 1862:
Manual: Pick up a pen and pad. Sit in front of your monitor at a distance of approx. 100 cm. Look at the picture above. Write down line by line on your pad. More information about this test. If you are unsure, you will find an eye test to print out here. However, you will only get certainty about myopia from an ophthalmologist or optician.
The Landolt eye test
What if someone doesn't know any letters? That was a significant problem in the 19th century. This is why the Swiss ophthalmologist Edmund Landolt developed an alternative eye test to determine myopia a few years later, which in principle is still valid today. It is based on the so-called Landolt ring, a visual symbol (icon). This ring is open on one side - it is precisely this side that should be recognized and named as the test object.
Video illustrating myopia
Finally, a short video that summarizes the topic of myopia once again: it is crucial that the focus is in front of the retina through a change in the eye, so that only a diffuse image is displayed on the fovea, the place of sharp vision. The further away things are, the more blurred they appear. The following video illustrates this again:
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