Technological triggers of heterophoria

22.10.2020

What triggers heterophoria

In the previous article What is heterophoria? it was explained, that you may not notice you have heterophoria nor any trouble stemming from it throughout your whole life. The trouble comes only when your already strained visual system is pushed beyond its compensation capabilities.

In my case I can still use the older technology that I have used in the past with no issues.

I still use my old laptop for longer periods of reading, writing and watching movies. Doing this on new technology would be either uncomfortable and unnecessarily straining, or downright painful. And we are talking about the case when I have done two years of very successful visual therapy already and use proper glasses.

It's therefore clear that new technology is behaving differently than the old one. However not all of it does so, and not all of it does so in the same way in each case. Isn't that confusing, you say? Well you are not alone. So let us look at the so far known causes of why sometimes your eyes and head hurt right away, sometimes after an hour, and sometimes only after your computer or smart phone automatically updated itself.


LED light

LED light has been mentioned for some time now as problematic for your eye health. It is true that in recent times it has replaced almost all alternatives, especially when it comes to the backlighting of computers, smart phones, TVs and other displays. There is also a recently published article about the harmful effects of LEDs, which you can read here.

LED light has two problems - the amount of blue light emitted and the way in which the light flickers. The harmful effects of blue light have been discussed a lot, however from my personal experience no software to lessen the blue spectrum, nor any blue light blocking glasses have ever helped me in any way. The pain was still the same even when I was using completely red glasses and used software to shift the screen to complete orange. Some people have reported success with this approach, so it is up to everyone to try it on their own. It is likely that blue light is only a part of the problem, so getting rid of it won't fix the issue completely. It still stands however that it is an important factor worth exploring.

The flickering of LEDs has by now been confirmed to play a role. When compared to classical light sources, LED lights have no afterglow. When you turn the LED on, it is immediately at its full power, and when you turn it off, its immediately dark. When you use alternating current, which powers all household lights, the LED becomes a stroboscope. This flickering might not be obvious at first sight, but your brain can notice it and will try to adjust your eye movement to it. So if you for example read a printed text illuminated by this light, your eyes may try to refocus, find their place on the page and fixate the gaze every time the phase dark-light happens. If you are using both of your eyes and they already barely work they way they are supposed to, it might be the last straw to push them beyond their capabilities. You can find LED lights on the market claiming to be flicker and blue light free, however I would prefer to personally check these myself first, before trusting the claims of the manufacturer.


PWM

PWM was first discussed and still is as a proven cause of issues. It is a way in which display brightness is regulated in LED backlit displays. Unless you connect LEDs in more complicated ways, there is no way to smoothly regulate their intensity. LED light can either be on or off. However your smart phone and computer display can be darkened anyway, so how is that possible?

To regulate the brightness of LED lights a thing called PWM - Pulse Width Modulation is being used. It simply means that LEDs are made to flicker with a changeable frequency, which can make them appear darker. However compared to older types of backlighting, the LEDs flicker in the same stroboscopic way like an LED bulb. Same problems therefore emerge - loss of solid eye fixation and repeated attempts to fixate your gaze. This way your whole visual system tires significantly even if your eyes are completely healthy. In that case it's just going to take a lot longer.

Some manufacturers have noticed this issue and started to use higher frequencies of flicker when regulating backlighting of displays. The idea is that the flicker should not be noticeable at higher frequencies. However to check your display flicker frequency you have to rely on reviewer tests (or test yourself), as the manufacturers do not state any information on the flicker themselves. The so called flicker-free monitors should be taken with a grain of salt, as when properly measured, some still do flicker.

Another problem here is that even if you really have a very high frequency LED flicker, an interference with other factors may happen (that are listed below), which can make the overall flicker frequency drop back to dangerous levels again.


Font smoothing and anti-aliasing

Just like other people with similar issues as mine, at some point I have noticed that even when I get a screen that claims to be flicker free and I lowered the blue light to minimum, the issues still did not disappear.

It's important to realize that when you do something on a computer, most of the time you might be reading or fixating your gaze on letters. Even when watching movies a lot of people use subtitles, therefore they read while watching most of the time. The issue with font anti-aliasing and smoothening lies in the fact that in order to have prettier looking fonts, their edges are "blurred". This is usually done in a way where the pixels or even sub pixels at the edge of the font are either darkened or flicker, therefore creating the illusion of a smoother gradient between the edge of the letter and the background.

As you may know from your own experience, focusing your eyes on something that is blurred is more difficult than on something that is sharp. When talking about flickering of edges of letters, the same that was mentioned earlier applies - fixating your gaze on anything that flickers is difficult and exhausting. If some issues with your eyes are already present, then it might be downright impossible. It will not take long then for problems to arise.

Some operating systems already offer an option to alter or turn off font smoothing. Unfortunately in most situations not completely and not in the scale that would be necessary. Unfortunately some forms of rendering are programmed in a way that if you happened to turn off font smoothing completely, everything would look horrible. For this reason the creators try to avoid such option. Another issue is that this function is often run by applications themselves inside of their interface. So you can turn off font smoothing in your operating system, but another app might turn it on again when started. Solution of this problem would require communication between vast numbers of application creators and programmers.

This can answer however why some people complain that one program, app or even internet browser trigger headaches, and others don't.


Dithering

Just like in the case of font smoothing and anti-aliasing, dithering is run by software (applications, programs, OS) and is also a form of flicker. There surely was a case when you have seen an image with very bad color banding. What dithering does is it makes sure that this banding seems invisible and therefore the color gradient looks smoother. "Seems" is however an important word here, because the smoothness is achieved by flickering the pixels near the harsh edges of color transition. This way the illusion of another color is achieved, that fills the gap in the gradients.

This is also done in case of black and white rendering, so turning your screen colors off unfortunately doesn't help much in this case.

The problem with dithering is that when it's turned off, the display will be revealed as not being able to show as many colors as advertised. From millions of colors all of a sudden you only have couple tens of thousands.

The picture will also get significantly degraded when dithering is turned off. Many modern operation systems and applications are not made for this limited color range, so they will look a lot worse than in the past, when a small color range was standard and programmers considered it when developing software.

Measuring dithering is very difficult, as the flicker doesn't happen on all parts of the screen, but most likely only where smoother gradients are needed at the time. Some people online have shared videos of flickering pixels near color gradients taken through a microscope and it was confirmed, that the devices that flicker the least cause fewer or no issues.

We have conducted similar tests with some friends from the CVUT tech university using a microscope and a camera. Some theories were confirmed by our findings, but more testing with a larger amount of devices is needed.


Combination of all factors

So what if all these factors get combined? The problem with a technological solution to this problem lies in the fact that it is very difficult to separate one factor from another. If you have a severe headache, all factors can be at play at once. If you only have mild issues, maybe only one or two factors may play role in that case.

PWM and flicker can be measured by an oscilloscope and this way you can make sure that this factor is eliminated. You can also get one of the many programs that allow you to control the brightness of your screen in alternative ways than by using PWM (I use IRIS). Blue light however is still a largely unexplored phenomena and it's unclear whether the special glasses or apps really decrease it in the way that is necessary. Font smoothing and anti-aliasing can be switched off, but you can never be sure if it's switched off for good. Unless you try to always inspect your device with a microscope and a high-speed camera. In case of dithering the same applies, except that apart from one program that was online for some time and that is probably not working anymore, you cannot switch it off at all.

In times of automatic updates like these, the software that can alter these factors needs to be updated all the time, otherwise newer versions of Windows, MacOS and other operating systems will render them obsolete.

For example on the forum ledstrain.org many people have complained about an auto update on Windows 10. In the version 1511 it was usable, in the following it wasn't. Was it some new form of font-smoothing, dithering or some other way of image rendering not known so far, that this update brought with it and that made it unusable? Unfortunately nobody knows.

This issue was also discussed with Intel Company for 4 long years. After much information provided by all the people affected and some official testing, the results were inconclusive. You can read the summary here.

It has to be said that according to the report from the tests, there was no testing of font-smoothing, dithering or possible interference of backlight flicker with image rendering. In these areas such testing would have been most useful and could probably yield some results.

So is a technological solution to this problem possible? At this moment I believe it isn't, at least not if you're trying to solve this on your own. There are too many factors (and not even all might be known so far) and their removal would require vast communication between the creators of computer hardware and programmers of software and applications. Such effort could probably be only enforced by some elaborate legal action.

If you happen to be amongst those unlucky enough to suffer from heterophoria and are negatively affected by modern technology, I recommend focusing your efforts on visual therapy. At least until this issue is more known and with that hopefully more possible solutions come to light.

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If you would like to discuss this matter in person, feel free to book a consulting session with me. I will also be grateful for any donation to help me run this blog and my future research in this field.

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