Glasses
and Carola Felchner, science journalistValeria Dahm is a freelance writer in the medical department. She studied medicine at the Technical University of Munich. It is particularly important to her to give the curious reader an insight into the exciting subject area of medicine and at the same time to maintain the content.
More about the expertsCarola Felchner is a freelance writer in the medical department and a certified training and nutrition advisor. She worked for various specialist magazines and online portals before becoming a freelance journalist in 2015. Before starting her internship, she studied translation and interpreting in Kempten and Munich.
More about the experts All content is checked by medical journalists.Glasses (more precisely: corrective glasses) are optical aids that correct ametropia such as nearsightedness or farsightedness. In addition, glasses can protect the eyes from external influences such as UV light (sunglasses) or sparks and dust (safety glasses). Read here which glasses are available, how the different types of models work and what risks and inconveniences you have to expect with glasses.
What are glasses?
Glasses consist of a frame and two glasses. The glasses frame rests on the so-called bridge of the nose and with two temples on the side of the head behind the ears. Eyeglass frames can be made of plastics, metals, wood and other materials such as titanium or horn. Shape and color also vary considerably - glasses are now often considered a fashion accessory.
Traditionally, spectacle lenses are made of mineral glass. In the meantime, however, plastic has overtaken glass. Because glass is more scratch-resistant and easier to care for, but heavier and less break-proof than plastic.
There are different types of glasses, each with different (main) tasks. Prescription glasses (corrective glasses) are used, for example, to correct the ametropia of the eye using the refractive power in the glass. This is done by means of diopters adjusted to the respective eyesight of the wearer.
Eyesight
Eyesight describes the ability of the eye to see things and contours clearly. The functional principle behind it is similar to that of a camera: the eye can focus on a point by muscles stretching or compressing the lens behind the cornea (accommodation). This change in the shape of the lens is accompanied by a change in the refraction of light, i.e. the shape of the lens is adapted in such a way that the light passing through is refracted in an optimal way - the focused object is sharply imaged on the retina.
If the lens can no longer change its shape (sufficiently), this process no longer works properly - the person concerned is ametropic.
Diopters
Diopters are a unit of measurement that describes the strength with which a spectacle lens refracts light. The higher the number of diopters, the more pronounced the ametropia is.
When do you need glasses?
Glasses are visual aids that are intended to correct ametropia of the eye:
Nearsightedness (myopia)
In myopia, the eyeball is too long or the refractive power of the eye is too strong. As a result, light rays falling into the eye - despite the deformation of the lens to adjust the refractive power - are not bundled on but in front of the retina. This makes objects that are far away appear blurred. Glasses compensate for this with so-called diverging lenses (minus lenses).
Farsightedness (hyperopia)
In farsightedness (hyperopia), the eyeball is too short or the refractive power is too weak. The incident light rays are therefore not bundled up, but behind the retina. As a result, those affected can only see objects that are close by in a blurred manner. Glasses with so-called converging lenses (plus lenses) are the right correction aids here.
Astigmatism
In astigmatism, the cornea - rarely the lens - is not evenly curved. This is why one speaks of astigmatism. The consequence of this is that the incident light rays do not hit the retina in the form of a point, but in a line. The optician uses so-called cylinder glasses for correction.
As for farsighted and nearsighted people, there are also special contact lenses as an alternative to glasses for people with astigmatism.
What types of glasses are there?
There are different types of glasses that can be differentiated depending on the lens or intended use. Among other things, there are:
- Glasses for people with long, long and short sighted eyes
- Glasses for people who do not see well in the distance or up close and who do not want to constantly change their visual aid (bi- / trifocal and varifocals)
- Glasses for people who only need visual aids to read, drive a car or use a computer (reading / monitor glasses).
In addition, there are glasses that are specially tailored to the needs of children or athletes.
Children's glasses
Like glasses for adults, children's glasses correct ametropia. In addition to nearsightedness, farsightedness and astuteness, this often includes squinting (strabismus) in children. In addition, children's glasses prevent so-called weak eyesight (amblyopia). In the case of people with impaired vision, visual acuity is impaired by a developmental disorder of the visual system (eye, optic nerve, brain): The two eyes send such different images to the brain that the brain cannot combine the information into a uniform visual impression.
If a child is cross-eyed or ametropic in the first six years of life, the brain will not receive the stimuli it needs to train and develop binocular vision without appropriate vision correction.
Signs of vision problems in children
As children often do not notice their poor eyesight, you should talk to your doctor about children's glasses if you notice any of the following symptoms in your child:
- headache
- rapid eye fatigue
- frequent winking or blinking
- Clumsiness playing or accessing
The eye doctor can check your child's eyesight with various age-appropriate tests. For example, the so-called masking test can be used to detect strabismus in infants:
To do this, the child should first fix an object with both eyes. For children who cannot speak yet, this can be achieved with colored or luminous objects. Now the doctor first covers one, then the other eye of the child with a plastic disc. If it is a question of the healthy eye, the cross-eyed one will give up its squint position and jump into the fixation position (saccade), because a cross-eyed person only fixes objects with one eye.
Children's glasses: what to consider when choosing
As useful as children's glasses are for ametropia and strabismus, they can also involve risks. One thing may be that they do not (correctly) compensate for the ametropia (nearsightedness, strabismus, etc.). Then there is the risk of developing impaired vision. In addition, glasses can press on the nose or behind the ears if the size or shape has not been optimally selected.
When choosing the frame for children's glasses, the child should also be able to say what they like (provided they are not too small for it). Then they will be more willing to consistently wear the children's glasses.
Shatterproof materials such as plastic have proven their worth for children's glasses. Glasses for toddlers should also be as light as possible and not slip while playing.
Sports glasses
Sports glasses are primarily used to protect the eyes from environmental influences during sports and other outdoor activities. Examples:
- Skiing, hiking, sailing & Co .: Strong UV radiation can cloud the lens (cataract) as well as permanently damage the cornea and retina. This is particularly dangerous when snow and water reflect the light. Sports sunglasses provide protection here.
- Swimming: Swimming goggles protect the eyes from chlorine and water as well as the germs they contain.
- Cycling: If you are fast on your racing bike or mountain bike, there is airflow. And that can dry out the eyes because there is not enough tear fluid left to wet the conjunctiva and cornea. On the one hand, this worsens visibility and thus also safety on the bike. On the other hand, it can result in infections and inflammations and even scarring of the cornea. Cycling goggles protect against this - as well as against the penetration of foreign bodies (such as mosquitoes or dust) into the eye.
There are now prescription sports glasses for people who wear glasses.Then those concerned do not have to wear contact lenses under conventional sports glasses. The ametropia is corrected directly by the prescription sports glasses. There are various models for this, for example sports glasses lenses with ground-in correction or a clip that the athlete clamps behind the lenses of normal sports glasses.
Sports glasses: what to consider when choosing
Sports glasses can pose a risk if the model does not fit the intended use and / or the head shape of the wearer. For example, an incorrectly chosen lens tint can restrict the view, a frame that is too small can cause drafts in the eyes or the lenses can fog up as soon as the athlete begins to sweat. It is therefore important to ensure that sports glasses do not impair sharp vision in any way.
Possible risks are also:
- Pressure points on the nose or behind the ears if the sports glasses do not fit properly
- Eye injuries when glasses and frames are not stable enough and break while exercising
- Radiation damage to the eye if the UV protection of the glasses is insufficient
That is why you should always choose your sports glasses depending on their later use. When buying, make sure that the sports glasses are as light and comfortable as possible to wear and that they fit correctly. The glasses must not slip during jerky movements, but they must not press either. Lenses and frames should be made of a break-proof material. The glasses should offer sufficient UV protection.
Get advice from an optician when buying sports glasses. If you need prescription sports glasses, your optician should do an eye test with you and adjust the lenses to your individual requirements.
Varifocals
The questions "What are varifocals?" One could answer flatly: glasses for all visual situations. To be more precise: the task and function of varifocals is to combine different vision solutions in one and the same lens. The wearer can see clearly at different distances without having to change glasses.
In contrast to multifocal glasses such as bi- or trifocal glasses (two- or trifocal lenses), in which the different areas of vision are separated from one another by a recognizable line in the lens, the transition between the different areas of vision is fluid with varifocals. This means that there are no so-called image jumps at the edges when the wearer raises or lowers their gaze.
Complex structure
A pair of glasses with varifocal lenses smoothly corrects the vision close up (up to 0.5 m), into the distance (from 2 m) and also for the intermediate area, so that the wearer can always see clearly. The structure of the lenses is correspondingly complex: In the lower visual area of the varifocals the lens has a different curvature than in the areas above. At the bottom, varifocal glasses improve the close-up view (e.g. for reading), at the top the distance view and in the intermediate area the view in the area between half a meter and two meters (e.g. for reading the raised display board at the train station).
In addition to the normal varifocals, there are also special versions for drivers or for working on a computer screen.
Types of progressive lenses
There are differences in progressive lenses. So exist:
- Simple varifocals: relatively small areas of vision, less visual comfort, longer getting used to
- Universal varifocal lenses: sufficiently large areas of vision, good comfort and good tolerance
- Individual progressive lenses: Made to measure, offer maximum visual comfort and the highest image quality
Regardless of which lens variant you choose: In order for the smooth vision correction transition to work with varifocals, the lenses in the frame must be large enough that the surfaces are sufficiently large for the individual visual areas. You should also be able to see well around the edges of your glasses. With less high-quality lenses, varifocals often blur the field of vision outdoors.
Another quality feature is the transition from local to television. With cheap glasses it is sometimes not fluid, but abrupt.
Cost of varifocals
How expensive varifocals are depends on the quality of the frame and lens. In any case, it has more to book than glasses with conventional corrective lenses, because the manufacture of progressive lenses is significantly more complex.
It is not advisable to use very cheap glasses that cost around 30 euros. Their areas of vision are usually much too small, and the transitions are bumpy. Progressive lenses can only be referred to as “high quality” from around 100 to 200 euros - with such lenses, the “change of vision” is smooth and immediate, and the wearer quickly gets used to the visual aid.
Disadvantages of varifocal glasses
As practical as they may be, varifocals also have disadvantages. For example, gliding vision is limited to the middle glass area. If you look to the side, you have to follow your gaze, sometimes with your head, so that you stay in the correct correction zone. Accordingly, varifocals are not suitable for people who also have to see clearly in the lateral area, for example draftsmen.
Even people who have to work overhead (e.g. car mechanics) are better off with single vision glasses because they look overhead "the other way round". So you would need the area for close vision at the top and the area for distant vision at the bottom.
Which glasses do i need?
If you notice that your eyesight is deteriorating for the first time, you should see an ophthalmologist. This also applies if you suddenly see double or flashes of light. The ophthalmologist will examine you in detail to see if the ametropia can be corrected with glasses.
Both an ophthalmologist and a master optician are allowed to issue glasses on prescription. Both are qualified to measure and prescribe the required glasses strength.
At the beginning, your doctor or optician will usually check your visual acuity with the help of typical eye charts. To do this, you sit at a certain distance from these boards and have to read numbers or letters in different sizes - with both eyes at the same time and also with each eye individually.
Then the specialist determines the objective refraction, i.e. the refractive power of your eyes, with what is known as an automatic refractometer, without your having to help. To do this, it projects an image onto your retina, which the automatic refractometer uses to determine which additional refractive power is required to bring the image into focus.
For subjective refraction, look through special glasses (photoropter), in which the doctor or optician swaps glasses with different refractive powers until you can see clearly.
The specialist documents all examination values in a glasses pass.
What are the risks of glasses?
At first, your new glasses can give you headaches and a feeling of dizziness, because the brain first has to get used to the changed visual conditions. If you do not notice any improvement, even though you are consistently wearing the glasses, it may be due to the wrong strength of the glasses. It can then be necessary and helpful to have your eyesight checked again and, if necessary, to change your glasses.
If the glasses frame does not fit properly, you can also get pressure marks on your nose and / or behind your ears from glasses.
What do I have to consider with glasses?
Glasses improve your eyesight. If you can see blurred despite glasses, an examination by an ophthalmologist or optician will clarify the situation. If necessary, you have to have your glasses lenses adjusted. Since the eye changes with age, an eye test is also required regularly (i.e. every one to two years) to determine its refractive power.
Anti-reflective glasses cause additional costs, but prevent annoying reflections and increase safety in traffic or at work.
Special glasses for PC or screen work are required if normal glasses impair vision or cause discomfort (such as headaches).
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