Myopia: Description
Myopia is a congenital or acquired visual defect of the eye. People who are short-sighted can usually still see well up close, while objects in the distance appear blurred (the opposite is true for long-sighted people). A short-sighted person therefore does not generally have poorer vision. At close range, they may even be superior to someone with normal vision.
The degree of defective vision is measured in diopters (dpt). Someone with a negative reading is short-sighted, and the higher the number after the minus, the more so. A measured value of -12 dpt, for example, describes a high degree of myopia, i.e. severe short-sightedness.
Strictly speaking, short-sightedness is usually not a disease at all. Up to a visual defect of minus six diopters, it is only considered an anomaly, i.e. a deviation from the average value. Pathological (abnormal) myopia is only present with more severe defective vision.
How common is short-sightedness?
Myopia simplex and myopia maligna
Experts distinguish between myopia simplex (simple myopia) and myopia maligna (malignant myopia):
Myopia simplex is also known as school myopia. It begins during the school years, usually around the age of ten to twelve. It can worsen in the following years and then usually remains stable from the age of 20 to 25. Most people affected by this form of short-sightedness achieve dioptres of -6 dpt at most. In a small proportion, myopia worsens to -12 dpt and only stabilizes by the age of 30.
Myopia maligna, on the other hand, also progresses in later adulthood. It therefore has real disease value. Consequential damage can also occur, such as tissue damage with the formation of small scars or holes in the retina, which can also lead to retinal detachment. Glaucoma can also occur – as can staphyloma (bulging of the sclera).
Short-sightedness in children
Children of short-sighted parents are more likely to suffer from short-sightedness than children of parents with normal vision. This suggests that short-sightedness also has a hereditary component.
The ophthalmologist can discuss with you whether glasses or contact lenses are suitable as a visual aid for your child. Correctly adjusted glasses do not make the eyes worse.
Special glasses are available to delay the progression of short-sightedness in children. They cannot reverse the defective vision, but studies have shown that they slow down the progression of short-sightedness by around 60 percent.
Short-sightedness: symptoms
Short-sighted eyes are adjusted to near vision and sometimes even see more clearly in this range than people with normal vision. However, short-sighted people cannot focus their eyes on an object in the distance. It therefore appears blurred. The distance at which a short-sighted person can see well depends on their visual acuity: Affected people with a dioptre of -1 dpt can see objects up to one meter away in focus, while people with -12 dpt can only see objects at a distance of around eight centimetres.
Short-sightedness can cause other symptoms in addition to impaired distance vision: In the course of life, the vitreous humor in the eye liquefies. This often happens more quickly with short-sightedness than with normal eyesight. If streaks float around in the vitreous body, those affected can see shadows in their field of vision.
Short-sightedness: causes and risk factors
In people with defective vision, the refractive power of the eye does not match the distance of the retina.
How a healthy eye works
For a better understanding, the eye can be compared to a camera: Here, the lens corresponds to the cornea and the lens. The retina can be compared to a film. Incident rays of light are refracted by the cornea and lens and focused at one point. A sharp image is created at this point. In order for us to perceive it, this point must lie on the retinal plane.
In order to see both near and distant objects clearly, the eyes must change their refractive power (accommodation). To do this, the shape of the crystalline lens, which is responsible for refracting light rays, is changed using muscle power: If the lens of the eye is stretched, it becomes flatter – its refractive power decreases. It can then see distant objects clearly. In contrast, a less tightly stretched, i.e. more spherical lens has a greater refractive power – close objects can now be imaged sharply.
What goes wrong with short-sightedness
There can be various reasons for the disproportion between refractive power and axial length in myopia:
- The most common cause is axial myopia. In this case, the eyeball is longer than in people with normal vision and the retina is therefore further away from the cornea and lens. An eyeball that is only one millimeter longer can cause short-sightedness of -3 dpt.
- In the rare case of refractive myopia, the eyeball is of normal length, but the refractive power of the cornea and lens is too strong (for example, because the radius of the cornea is unusually small or the refractive power of the lens is altered due to diabetes or a cataract).
Risk factors for short-sightedness
There are some diseases that cause myopia more frequently. This is the case with diabetes mellitus, for example, when blood sugar levels are poorly controlled. When blood sugar levels normalize, myopia can disappear again.
A form of cataract (so-called nuclear cataract) can also promote short-sightedness. It occurs more frequently in older people: even before they notice the clouding of the lens, they can sometimes suddenly read again without reading glasses. Cataracts can temporarily improve near vision due to the myopia that also occurs, but distance vision deteriorates.
Children born prematurely are also more prone to myopia.
In some cases, myopia is the result of an accident in which the lens fibers have become loose or torn.
Short-sightedness: examinations and diagnosis
If you have the feeling that you are short-sighted, you should make an appointment with an ophthalmologist.
Medical history
The doctor will first ask you about your medical history (anamnesis). He may ask the following questions, among others:
- When did you notice a deterioration in your vision?
- Did it occur suddenly or gradually?
- When does the visual impairment affect you the most?
- How does the visual impairment manifest itself (e.g. as blurred vision or color vision impairment)?
- When was the last time your eyes were examined?
- Do you suffer from other diseases such as diabetes?
- Are there other people in your family who are short-sighted?
- Are there any hereditary diseases in your family?
Ophthalmologic examinations
The doctor will look into your eyes with a bright light and a magnifying glass. He will also use a device to measure the refractive power of each eye. To do this, he asks you to look at a distant object (often a colored cross) in the device.
Sometimes it is necessary to dilate the eyes with special eye drops before the examination. Afterwards, your vision will be very blurred for a while and you will therefore not be allowed to drive for a few hours.
A comprehensive eye examination also includes other methods. To check your spatial vision, for example, the ophthalmologist will show you cards in which an object appears to protrude from the card. You will also have to indicate whether you perceive a box pattern as straight or curved. To rule out color vision deficiency, you will need to recognize numbers or patterns of different colored dots.
As short-sightedness sometimes leads to increased intraocular pressure, the doctor will advise you to take a corresponding measurement.
As short-sightedness can cause other eye changes, those affected should be examined by their ophthalmologist about once a year.
Short-sightedness: treatment
Various methods can be used to improve short-sightedness. Spectacles or contact lenses compensate for the defective vision. Surgery can even cure short-sightedness in certain cases. If several methods are combined, even severe myopia can often be treated well.
Glasses for short-sightedness
Up to a visual acuity of -8 dpt, glasses are the most common visual aid. They offer several advantages:
- If myopia changes, glasses can be readjusted at any time. This treatment is therefore particularly suitable for children whose eyeballs change as they grow.
- Glasses are also suitable for people who need a different setting for reading than for distance vision. With varifocals, both needs can be met in one lens.
- Glasses are very gentle on the eye.
Contact lenses for short-sightedness
Contact lenses are an alternative to glasses for many short-sighted people. They are small transparent lenses made of soft or hard plastic. An ophthalmologist can determine which type of contact lens is suitable for you personally.
he advantages of contact lenses are
- Contact lenses are invisible.
- Unlike glasses, they cannot fog up.
- As they are placed directly on the eye, they correct visual acuity across the entire field of vision – one reason why athletes in particular prefer to wear contact lenses rather than glasses.
- In the case of pronounced short-sightedness, contact lenses do not reduce the image – unlike the strong minus lenses of glasses. This effect is relevant from a visual acuity of -3 dpt.
Contact lenses require good hygiene. They must be cleaned regularly to prevent eye infections. In addition, contact lenses should not be worn indefinitely. Under a contact lens, the eye is less well supplied with oxygen. Some people’s eyes become irritated (e.g. after wearing them for too long, if there is dust in the air or if the air is dry from heating) – they become red and painful.
Contact lenses for the night (orthokeratology)
For certain forms of short-sightedness, special rigid (hard) contact lenses can be worn at night. They exert a certain force on the cornea so that the cornea flattens out after a while. This compensates for short-sightedness, even during the day. However, the effect diminishes over the course of the day, meaning that you may have to insert lenses or wear glasses later in the day.
These special lenses for the night can be an alternative for short-sighted people who cannot tolerate contact lenses during the day due to dust or irritants, for example.
Surgical correction of short-sightedness
There are also surgical treatment methods for short-sightedness:
Corrective lenses implanted in the eye can compensate for short-sightedness. This procedure is usually only used in cases of severe short-sightedness, as it can restrict the eyes’ ability to accommodate – i.e. their ability to adapt from near to far vision and vice versa.
In some cases of short-sightedness, the patient’s own lens is replaced with an artificial lens. The operation is then similar to cataract surgery.
Each of these operations carries certain risks, which the doctor should discuss in detail with the patient beforehand. Cortisone drops after the operation are intended to prevent the formation of scars that restrict vision. If exposed nerve endings are damaged during the operation, pain is possible.
Chances of success of an operation
Whether myopia can really be cured by surgery varies from person to person. It is also not possible to predict with one hundred percent certainty what the result will be before the operation. The patient may still be dependent on a visual aid after the operation. If vision deteriorates after the operation or if presbyopia occurs, visual aids will also be necessary.
Short-sightedness: eye training helpful?
Myopia: progression and prognosis
Short-sightedness often develops in childhood. It can both improve and worsen as the child grows. In most cases, however, myopia hardly changes after the age of 20.
With increasing age, the eyes are generally less able to accommodate. The ability of the lenses to optimally adjust to distance and near vision begins to decline from around the age of 25. From the age of 40, many people eventually become presbyopic and need reading glasses.
As short-sightedness can promote other eye diseases, the eyes should be examined regularly by an ophthalmologist.
