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Evan Hazard: A non-threatening visual quirk

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Evan Hazard: A non-threatening visual quirk
Bemidji Minnesota P.O. Box 455 56619

The first time, it was daytime and I was alone. I don’t recall if it was indoors or out, or the season, and I neglected to write anything down. There was nothing else odd happening that I could relate it to. Also, it was well before 2010, because I often talked with Elaine about it.

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It went like this. Something flickered to my right. But when I glanced there, it moved; I could not look directly at it. This meant:  First, it was going on somewhere in my visual system, not “out there.”

It was in the same part of my visual field no matter where I looked. It has also occurred in the dark in bed, more evidence that it happens within my visual system.

Second, I could not see it clearly, since we have high definition only at the macula (or fovea) of each retina, with their high concentration of cone cells. (You first learned that in high school biology, or freshman college biology).

So here was this flickering, indistinct pattern of black and white off to the right, growing larger and more obvious.

It did not move away from its original position, it just took up more room. It never reached my macula, so I never saw it clearly. Then it slowly faded away.

The whole show lasted 20-30 minutes. When I described it, Elaine said it was an ocular migraine. But so far I’ve never had migraine headaches, with or without the ocular bit.

From my own experience, what else have I learned?  Well, I’m unsure how long they’ve been happening. In a visually busy environment, especially if I were concentrating on a task, flickering to one side might have gone unnoticed. I’ve noticed them rarely, two-to-four times a year.

There’s not yet been any pain involved. They’ve been rare enough that I’d never thought to ask about them during an annual eye checkup.

Initially, I also did not know how they began. But, sometime in ‘12 or ‘13, a small grayish spot appeared off to my right or left. It stayed put, but gradually grew, and there was a telltale black and white flickering. So that’s how they start, and in several minutes, they’re full sized.

The patterns vary and are hard to describe. They are light and dark, sort of geometric but distorted, sometimes like a chessboard twisted badly out of shape, sometimes like uneven zebra stripes. And they flicker.

The latest episode stimulated me to write. Mid-morning Wednesday, March 19, 2014, I was working on the laptop. I’d been typing only a short while when I began having trouble focusing on the words.

Something was messing with the detailed focus at my macula. (I dread the possibility of developing macular degeneration, so was leery.)  But wait: a little gray spot there was growing.

And it had a little moving pattern in it. I was having an ocular migraine, and it looked to be in the maculae of both eyes.

Not being able to work, I decided to nap, and fell asleep as the pattern enlarged and did its thing. (Could I have folded two weeks worth of laundry?  Of course I could, but such things seldom occur to me.)

However, there are questions. Are they in one eye or both?  Do they occur in the retina or back in the occipital lobes where visual input is interpreted?  Human neural anatomy makes the first hard to answer. Vertebrate optical nerves cross at the optic chiasma, on the underside of the brain. In some vertebrates, all the neurons from the right eye go to the left occipital lobe, and all those from the left go right.  

In “higher” primates (monkeys, apes, and people), neurons from the inner halves of each retina cross, going to the opposite occipital lobes. However, those from the outer halves turn and continue to the lobe on the same side. So our right side’s info all goes to the left occipital lobe and our left side’s info all goes right. Thus, the info of both eyes that view the right visual field will be processed on the left side of the brain, and vice versa. So we cannot tell if one or both eyes are involved. Shutting your eyes won’t help, since the pattern is internal. If ocular migraines originate in the occipital lobes, however, we will perceive them as originating in both eyes.

A Web search? Good luck. A dozen plus sites all admit that we know neither what causes ocular migraines nor migraine headaches, and most note that the two may or may not go together. Some say they occur in one eye, some say both. Some say they move across the visual field. Mine don’t. One animation shows them originating in the center of the visual field and radiating outward. Most of mine originate laterally. Some say they originate in retinas, some say occipital lobes. Welcome to an area of active research. For me at least, it is so far an innocuous quirk. To learn more than you want about this go to: <http://physrev.physiology.org/content/81/4/1393>

EVAN HAZARD, a retired BSU biology professor, also writes “Northland Stargazing” the fourth Friday of each month.

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