It might sound somewhat strange, but one thing affecting migraines could be the "accommodation strain" of the eyes, especially in people over 40, when the "presbyopia" starts to affect. (Apologies for taking the thread off topic.)
From this age and increasingly onwards, the lens of the eye becomes less and less flexible. The ciliary muscle (controls the accommodation process of the eye) has to work harder to make the lens change its refraction to see objects up close (reading). As
the ciliary muscle is linked directly to the ciliary ganglion and further to the autonomic nervous system, "overworking" the muscle (reading a lot, looking at computer screens, doing close work, etc) can cause migraines and headaches.
So, wearing appropriate reading glasses could alleviate migraine symptoms.
Most people have hyperopic eyes, meaning the eyeball is "too short". They say that the eyes have been designed by nature to be like this. Hyperopia enables the eye to see better in dark conditions: so called "night myopia" phenomenon.
In night myopia, the eye becomes somewhat nearsighted in dim light.
If the eye was perfectly "round" (emmetropic eye), when looking to the distance, the ciliary muscle would not have to constrict, it would be in a relaxed state. In daylight, the vision would be 20/20. But when the light dims, "night myopia" would start to affect, and objects in the distance would become blurry. Due to night myopia and the changes it causes in the lens, objects in the distance are focussed in front of the retina in the round/ emmetropic eye, hence the blurriness.
With the too short (hyperopic) eye, the ciliary muscle has to constrict when looking in the distance (and even more so when looking at objects up close). However, the too short eye would not be affected by night myopia: as the focussing point for objects in the distance moves forward within the eye, and as the eye is "too short", it manages keep the focus on the retina and see clearly far.
This type of eye was understandably at an advantage during paleolithic times. During modern times though, with all the reading and computer/ smartphone work, it is at a disadvantage, especially when the lens starts to become less flexible with age. The ciliary muscle becomes "strained" and in susceptible people headaches, migraines and other autonomic nervous system ailments can ensue. Simple reading glasses (in the "plus" direction) could help.
It is a complicated and simple concept at the same time!
Here is some further information (unfortunately the pictures don't seem to work at the moment):
kaisuviikari.com
(Ophthalmogist Kaisu Viikari had loads of migraine patients flocking to her practice, and she was able to "cure" their migraines and headaches by only prescribing them approriate glasses. She describes the process in her books.)
Accommodation spasm of the eye: major ramifications
On the other side of the coin, the accommodation strain can become a "cramp" and cause a "pseudomyopia" of the lens of the eye (aka school myopia). This cramp could be released and vision restored by using plus glasses for reading. If minus glasses are prescribed as is usually done, the person sees clearly in the distance, but the young malleable eye can grow in anatomical length, causing irreversible, true myopia.
Even in older years when the eye has become irreversibly myopic, the worsening of the myopia can be stopped by wearing glasses that have "plus additions". People can experience improvement of vision at that stage too, if there has been pseudomyopia involved in the "total" myopia (total myopia = pseudomyopia of the lens + anatomical true myopia).
And of course, headaches and migraines and other autonomic nervous system originated symptoms could improve.
