How bad is 20 100 eyesight
The eyesight is actually called visual acuity or visual acuity.
This term refers to the resolution of the eye. So how big a letter has to be, for example, so that we can recognize it. We achieve optimal eyesight when our eyes are in focus. In about half of the people this is the case by itself, then no glasses are necessary. However, around 50% of Germans need glasses to achieve optimal focus. At least for certain distances (see ametropia below).
But even if the eye is optimally focused (with or without glasses), eyesight is limited. Letters from z. B. 1 mm size, we can usually just about 40 cm. But nobody can see a 1 mm letter on the top of the church tower. Our ability to resolve (eyesight) is limited. The measure of eyesight is often given as a percentage. The average person starts life with a vision of around 100%. Other spellings are: 1,0 or 20/20. Visual acuity varies from person to person and, with optimal glasses, is usually between 160% (1.6) and 70% (0.7) in the healthy eye.
You can usually pass the driver's license eye test with an eyesight of 70% without any problems. Eyesight can be decreased by two factors:
- The eye is not optimally focused. This can be compensated for with optimal glasses. (see ametropia)
- There is a congenital or suffered eye disease.
So do it regularly
an eye test from your optician.
If your eyesight cannot be fully restored there with glasses, you will have to be examined by an ophthalmologist. Also have preventive examinations at the ophthalmologist. Children up to 14 years of age should also have the eye test carried out directly by the ophthalmologist. A preventive medical check-up for children is sometimes carried out by the pediatrician as part of the "U-examinations". Since the children's eye can only develop optimally if there is no ametropia, you should ask your doctor specifically about an eye test on your child.
Case 1: nearsightedness (myopia)
Myopia is easy to describe.
The name says it all: you can see well briefly (i.e. at close range). Objects further away appear blurry. The corresponding concave lens compensates for this.
The measure of the lens is negative for nearsightedness. e.g. -3.25 dpt. The reciprocal of this number indicates the distance in meters [m] from which one can no longer see clearly without glasses.
In our example, 1: 3.25 = 0.307 m. In this example, the unclear area begins about 30 cm from the eye. Myopia can (like all other ametropia) be compensated for in the short term by squinting your eyes.
From this squeezing comes the Greek name myopia. Why are you nearsighted? There is also a simple answer to this: the eye is too long in relation to its refractive power.
The sharp image of distant things is not created on the back of the eye (retina) but in front of it.
Therefore, myopia often increase in the growth phase of humans. Myopia often increase up to the age of about 30 and then remain constant for a long time. Unfortunately this is not always the case.
Case 2: Presbyopia ("presbyopia")
Far-sightedness is actually the opposite of myopia, but it's not that easy to explain. In fact, its effects are not the opposite of myopia. Therefore we save the farsightedness for case 3!
And now we come to presbyopia, also known under the uncomfortable term “presbyopia”. This "ametropia" overtakes everyone and is therefore quite normal! The term "ametropia" is particularly misplaced here. The effects are the exact opposite of those of myopia. Everything that is further away appears clear. The closer an object is, the more indistinct it becomes. Those who do not wear glasses notice the effects of presbyopia when they are 45 years old on average. At first it is sufficient to hold the cell phone further away, then the arms become too short and it says: "Help, I can no longer read."
But why is it that with increasing age you can no longer read without glasses?
The human eye lens is highly flexible at birth. One can increase the refractive power of the eye through this flexibility. When looking up close (as with the autofocus of a photo camera), the necessary close-up adjustment is automatically made. Unfortunately, this flexibility is decreasing, a gradual “remodeling process” that already begins in childhood. At the age of 15 you can still look into your partner's eyes while kissing. At 30 years of age, this already appears blurred from this extremely close distance. At around 45 years of age, the adjustment option is then limited to a distance of around 40 cm. 40 cm is a distance in which we like to read and work, which is why the difficulties for “non-glasses wearers” start at this age. Your optician can help. Reading glasses or the close-up effect of varifocal glasses (multifocal glasses) usually have a "plus effect" e.g. +3.25 dpt. If you accidentally look into the distance through this strength, which is intended for close up, you will see blurred. In our example, everything from 1: 3.25 = 0.307 m is blurred, i.e. from a distance of approx. 30 cm. With myopia (case 1) it is the case that you can no longer read with the previous glasses and you have to take off the glasses to see clearly up close. This can be remedied by new glasses from your optician, e.g. varifocals. What it looks like with farsighted people can be found under case 3.
Case 3: farsightedness (hyperopia)
The farsightedness is Not the opposite of myopia, hence it became in Clarity renamed.
At a young age, those with a clear view are usually able to compensate for the ametropia and, depending on their strength, can see clearly at all distances. Excellent! So you don't need glasses ?! Attention! Especially with children this is a dangerous fallacy! If you have a clear view, you can already use the flexibility of the lens for wide viewing when looking into the distance. But nature intended this flexibility for close viewing. It would be OK to use this opportunity to look far if we only had one eye. But since we have two eyes, the close look also involves a swiveling movement. This means that if you have a clear view, you often look slightly inward (without glasses). That would lead to double vision. One eye is then often "switched off" without further ado so that one does not see twice. In children, this can lead to irreversible visual impairment in one eye. So always wear the glasses! Anyone who only becomes clear as an adult can suffer from headache and eye pain. The problems with reading (case 2) can start earlier, not just at the age of 45. Many easy overviews are therefore only recognized in connection with presbyopia (reading problems) between the ages of 30 and 45 years.
Why is it clear?
The reason is then again the opposite of myopia. The eye is too short in relation to its refractive power. Therefore, clarity tends to decrease with growth. The measure of the corresponding lens is a positive number. e.g. +3.25 dpt.
Case 4: Astigmatism "astigmatism"
Now that sounds really like an eye disease. But it is only a small deviation from the norm. Almost no eye is spherical. Let's imagine the eye as a ball. Only in this rare case one does not have an astigmatism. If you sit on this ball, the ball becomes an ellipsoid ("an egg"). The curvature is not the same in all directions, and so is the refractive power of the eye. The glasses values then no longer look as simple as in the examples above +3.25 dpt or - 3.25 dpt. There is another value that describes how much the eye is flattened. Such a value looks like this, for example:
sph: - 3.25 cyl: -1.0 A 75 °
The degree of myopia in this example is on average: -3.75 dpt.
The degree of corneal curvature is indicated by the cylinder (cyl or zyl) (in the example cyl -1.0 D). The deviation of the eye from the spherical shape creates here two different degrees of myopia. On the one hand -3.25 dpt and on the other hand (sph + cyl) -4.25 dpt. The third number (A 75 °) indicates the direction of rotation in which the eye (or the cornea) is slightly flattened.
The dangerous sounding corneal curvature is therefore a completely harmless thing that can be compensated for without any problems with the right glasses. If you do not wear the right glasses, you will see blurred (at all distances). In addition, e.g. circles on the fundus are shown as ellipses. The visual impression is therefore distorted, depending on the degree of astigmatism. Slight distortions are compensated by the brain, but with higher corneal curvatures this factor is also noticeable as a disturbance.
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