In a normal/healthy human being, the optical axes of the eyeballs involuntarily converge on whatever object is being stared at:
-If you are gazing upon a distant landscape, your eyeball axes are almost parallel.
-If you are staring at a bee six inches from your face, your eyeball axes both point at it, and you appear (to an outside observer) to be cross-eyed.
Some people are able to voluntarily cross their eyes so the axes converge at a point very close to their face. I can converge my own eyes to a point about an inch from the bridge of my nose (though I can’t focus that close).
A few rare people are able to voluntarily diverge their eyeballs in a horizontal plane: left eye gazes leftward, right eye gazes rightward. I can’t do this.
Question #1: are there documented cases of people who can diverge their eyeballs vertically? That is, one eyeball looks downward while the other looks upward?
Question #2: The discussion so far has been about tilt/pan control (for aviation enthusiasts, pitch/yaw). Are there documented cases of people who have voluntary roll control over their eyeballs? This would be harder for a casual observer to identify, but could be confirmed by close observation of the iris for signs of rotation. But is it even possible? Do we have muscles that control eyeball roll, or are there fixed ligaments that lock in the rotational orientation of the eyeball early in our lives?
Maybe you’re thinking of Marty Feldman, who suffered from Grave’s disease and strabismus - but I don’t think he was able to voluntarily diverge his eyes.
Looking at the musculature and attachment points involved, I can’t see that we even have the apparatus to *rotate *our eyes at all, let alone do it voluntarily. I am not a biologist, nor am I an eye-muscle-doctor, so I could be wrong on that.
As for up-down divergence, I’m going to guess that if it can be done at all, it’s going to be limited to those people who can already diverge horizontally, which is a pretty small sample.
Now, whether or not you can “teach” a regular joe to diverge their eyes (either horizontally or vertically), that I don’t know. I know the muscles and nerves are available to do it, just that they don’t normally work that way. As a related point, the treatment for lazy eye involves covering the “good” eye to force the lazy one to get with the program, and that treatment does work, so it stands to reason that additional muscular activity could be taught if you were serious enough about doing it.
You can watch your eyes roll by looking at them up close to a mirror while tilting your head side to side. Your “tracking system” will attempt to keep your eyes at a fixed orientation relative to the world, which requires rolling them. The range of motion is limited, but there it is.
Two of the six eye muscles move the eye left/right. The other four are used in combination for up/down and rotation. Interesting feature: one muscle runs through a pulley to achieve its direction of action.
Resurrecting this 7-year-old thread to share this video, in which the host discusses in detail the ability (and necessity) of eyeball roll control, and includes some dramatic footage of his own eyeballs exhibiting rather dramatic extremes of roll movement.
I’ve realized in recent years that when rolling my head left/right, I can in fact feel my eyeballs repeatedly rolling and then snapping back to level (WRT my head). Kind of a disconcerting sensation.
I was going to amaze everybody by announcing eyeball roll and telling everybody to look in the mirror during head tilting. Alas, the race is to the swift.
All the same, I have a question about this. They don’t roll all that far. So, why isn’t it noticeable to me when I tilt my head too far and reach the limit of rotation? I don’t mean a banging noise when the studs in my eyeballs slam into the mechanical stops welded into my head. I mean, why doesn’t it get suddenly harder to make sense of things? As far as I can tell, reading, walking, facial recognition, manipulating tools with my hands, and whatever else I can remember, all seem to work best when level and gradually get a little harder the more I tilt. It isn’t perfect up to some amount of tilt, and then lousy afterwards.
I remember the scene below from Scary Movie 2. I can’t find out if this weird eye movement was done with CGI or if David Cross can actually move his eyes like that. But it seems to be what is being talked about, since the eyes did their rotations opposite to each other with one looking up and the other looking down.
Maybe not what you are looking for, but I noticed that if I turn my head from side to very rapidly I’m able to remain focused on an object in front of my face. However, if I hold my head still and try to look from side to side using only my eyes, they can’t move as fast.
Surely its the same muscles moving in the same way, right?
I don’t remember if it was in the above Steve Mould video (I didn’t rewatch it) or a different Steve Mould Video or someone else altogether (Smarter Every Day?), but that’s probably related to how you can’t move your eyes side to side smoothly unless you’re tracking something.
I accidentally taught my eyes to diverge when I was in my teens, about 50 years ago. In the beginning it was such a not-a-big-deal that I don’t think I even mentioned it to anyone.
But in the past 20-30 years or so, I have notice that when I’m tired, they often drift apart on their own. The two images do overlap, and you’d think the result would be confusing, but my left eye is quite dominant (I’m also left-handed BTW) and the image from the right eye is so easily ignored that I usually don’t realize that the eyes have drifted until someone points it out to me.
And they DO point it out to me. My family is mildly uncomfortable at the sight, and people who don’t know me so well get mildly freaked out. One eye (usually the left) is looking straight at them, while the other is way off to the side. (Children, course, think it’s uber-cool, so for them, I point my left eye to the left, and my right eye to the right.)
When the eyes are drifting, they are usually NOT perfectly level verticalwise. But the difference is very minor. For example, right now looking at my monitor, the left-right are off by about 6 inches, but vertically maybe a hal-inch. (I really ought to express that in degrees or radians, but I’m way too lazy to figure that out.)
This woman can hold one eye in a fixed position while moving the other around, diverging both horizontally and vertically at the same time. I have only ever seen her move the other around in a circular motion though so not sure if she can move one straight up and the other straight down. She can do it with either the left or right eye.
From “Invasion of the Body Snatchers,” I assumed this was movie magic. Not independent movement, but kinda weird.
Potentially related: some time ago I heard this way to perform a test. Stretch your arms in front of you. Put your hands together out in front of your face a couple feet; with your thumbs and index fingers, make a rough “diamond window” for you to look through. Focus on something in the distance…5 feet away is probably enough, but center it in the diamond. Squeeze one eyelid shut; still see it? Then squeeze the other; is it there? Now you know which of your eyes is dominant.
If I ever thought about it, I would have guessed the eyes average stimuli or share the visual field somehow. But you’ll see the thing in the “diamond” disappears (or mostly does) for the non-dominant eye. Is that independent operation?
In moments of extreme excitement: Ermahgerd, Lurchbernales!
