At least a couple times a month I have a patient describe a visual episode that goes something like this:
"I was working on my computer this morning when I started getting these patchy little blind spots in my vision. The blind spots started more central and had these flickering little zig-zag borders around them. Over time they expanded and finally left my vision after about 20 minutes. I didn't get a headache."
Of course the symptoms can vary. Sometimes these individuals are experiecing this for the first time and are understandably very concerned, and in other cases they might just offhandedly mention that this happens a few times a year.
In either case, once we rule out other possibilities (such as retinal detachments or vascular problems), we will diagnose this as an ocular or ophthalmic migraine.
Allaboutvision.com has a great summary of ophthalmic migraines and I recommend you read their article to learn more about this strange phenomenon.
What I want to talk about here is these unusual zig-zag disturbances that can be seen when experiencing this type of migraine. While in optometry school I learned that these disturbances are called fortification scotomas, where "scotoma" (Greek for "darkness") means blind spot. I never gave much thought to the "fortification" part until a few years later when I was reading a textbook that stated "fortification" refers to the appearance of 16th century French forts.
This intrigued me.
It seems that medieval fortresses were usually rounded structures that were place on high hilltops. This worked well as the soldiers defending the fortess could loose their arrows and watch them sail towards their distant invaders. From the perspective of an invader, well, it was really difficult to attack the strongholds with arrows raining down on you.
Then, the cannonballs came.
By the 17th century technology had evolved to the point where manueverable cannons and gunpowder became the invader's weapons of choice. When this started to happen, the old fortresses with their rounded stone walls didn't fare so well.
In response, military engineers began to rethink the way fortifications were designed. In particular, a Frenchman named Sébastien le Prestre de Vauban designed forts that were better suited for the new modes of warfare. Vauban started his career directing sieges in Louis XIV's army and, after attacking a lot of fortifications, learned a thing or two about what makes a fort vulnerable.
"Knowing how he would attack a stronghold, his solution was to build "star-shaped" forts with straight-sided moats, lined with walls built of local materials (mainly brick in the north). He left no “blind spots” where an attacker could hide. His defenders could fire on the enemy with cannon mounted behind thick walls on the ramparts; and rake the moats with handguns fired through slits in the walls."