Edge filter glasses can help people with special visual impairments to perceive contrasts better and protect them from intense light.
In this article you will learn more about the different edge filters and what you should consider when buying or testing them. But what are edge filter glasses actually?
Edge filters are eyeglass lenses with a special tint that filter out and block harmful wavelengths, primarily the blue and violet portions of the light spectrum. The eyes and thus the sensitive retina are protected from the high-energy short-wave blue light.
This allows you to achieve restful and high-contrast visual comfort. Normal sunglasses reduce visible light relatively evenly across the entire spectrum. With an edge filter, a portion of the light is cut off at a precisely defined point and the short-wave light below this edge is absorbed.
While normal sunglasses that reduce the glare of light relatively evenly across the wavelengths are sufficient for most people, eyes with vision impairments often lack the necessary adaptability. Especially when it comes to situations in which bright light switches to less brightness and back. The general glare sensitivity often plays a role in the following diseases:
- Macular degeneration
- Retinitis Pigmentosa
- Diabetic retinopathy
Edge filters do not work the same for every person. It is always necessary to test individually how a person reacts to edge filter glasses. In general, however, it can be said that it makes sense to try edge filter glasses for the following complaints.
- High sensitivity to light (in migraine, headache)
- With increased sensitivity to glare
- With reduced contrast vision
What Do Edge Filter Glasses Do?
Edge filter glasses reduce the light entering the eye by filtering out a portion of the perceptible light between 400 nm and 780 nm. This can achieve a reduction in glare. This is due to the fact that different wavelengths are refracted differently in the eye. Blue light is refracted particularly strongly. When this can no longer enter the eye due to the edge filter, the glare is reduced.
The different refraction of light is also known as The Dispersion in the eye. In the picture below you can see that the short wavelength blue light is refracted more than the long wavelength red light. In such a case sensitivity to brightness is very likely. Each eye refracts the light a bit differently. This is why some people benefit more form edge filter glasses.
The picture below illustrates what an edge filter in the glasses does. Behind the edge filter lens less light enters the eye. The image on the retina then delivers an image with better contrasts because the disturbing lower wavelengths are blocked out.
What Edge Filters Are Available for Glasses?
Edge filter glasses come in a wide variety of tints, ranging from bright yellow to dark reddish brown. There are edge filters in combination with polarization and also without.
The important thing is that a trained optician can listen to your exact needs and give you the opportunity to try out different edge filters in your glasses. You should then be able to test them directly in the situations in which you have problems seeing.
Manufacturers often have similar edge filters with manufacturer’s own designations.
Some companies designate their filter types according to the point in the spectrum where the 100 percent absorption of the edge filter is reached. This includes Corning, for example. Zeiss, on the other hand, defines its products according to the average transmission. The filters therefore look practically the same, although they have different designations. The same applies to the effect.
However, not always. More on this under the point Experiences with edge filters.
Edge Filter Glasses Experience
In my personal experience, if you have a well-functioning edge filter, it pays to stick with just that. Even if the transmission curves are extremely similar, some wearers of edge filter glasses do not like a special residual reflex on the lenses, which is related to the antireflection coating.
Some are blue others are greener. Most customers do not care about these little things. However, it does matter if you are dealing with particularly sensitive eyes. That is why I like to show such differences within the consultation.
If there are problems outside in bright light then the customer should be able to gain direct experience with the edge filters outside. How are bumps or curbs to be seen now? Such questions are important and should be asked several times with different filters. The optimum filter can then be found. As a rule, customers quickly have a favorite with which they have had the best experience.
To give customers a first impression, clip ons with the different edge filters are very practical. These can be quickly put on the glasses and exchanged. These are also available for purchase and are usually cheaper compared to the production of an edge filter in which the strength of the glasses is built directly into the lens.
The disadvantage of a filter, however, are increased reflections on the lens surface. These are always present and can be irritating depending on the angle of view and light illumination. Therefore, I prefer to have the edge filter made directly with the customer’s prescription. This reduces the reflections and also looks aesthetically better. The disadvantage is, of course, that you are bound to one edge filter per pair of prescription glasses. If you need several edge filters, this can quickly become more expensive.
Which Edge Filter to Choose When You Are Very Sensitive to Brightness?
In case you are very sensitive too brightness edge filter which block more light with a darker tint are the first things to try. Eschenbach for example has the very dark wP85 edge Filters with absorb between are a combination of edge filter and a tint with 85% absorption of the light.
The advantage with this variant is that it is suitable for use in road traffic. Many glasses are with stronger filtering effects are not suitable for use in road traffic.
Because of color distortion, stronger edge filters of 511 nm, for example, are only conditionally roadworthy, i.e. permitted for daytime driving. With even stronger filter effects from 527 nm, there is often no longer any permission by law to use them in road traffic. The 400 and 450 nm edge filters, on the other hand, are fully roadworthy. Your optician can give you more detailed information regarding the country in which you live,
But the edge filter with the darkest tint is not automatically the best. Try it out outside when the sun is shining and compare different ones. Your optician can also combine some edge filters with polarization technology which also helps reducing bright glare. For polarized edge filters I like to show products from Eschenbach.
What Do Edge Filter Glasses Cost?
Prices for edge filters vary from 80$ per lens up to 250$ per lens for single vision designs. Depending on what manufacturer the optician uses and what coating is used the price may vary.
Since edge filters are often needed for medical reasons it is possible that your health insurance will pay for part or all of the glasses. Here subsidies are always different depending on the tariff. For this reason, you should send the cost estimate from your optician to your insurance company for further information.