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Are you asking in a broad sense how does vision work? Or are you asking how does the brain process and differentiate the information it receives from having two eyes? Or something else? I feel like this question could be interpreted and answered in a lot of different ways, so I just want to clarify what you're actually asking before I attempt to answer.

You have a master eye. If you hold your thumb up at arms stretch, both eyes open , and line it up with a small object in the room; now close one eye. If you thumb is still in line then you have just closed the subordinate eye. Try it again, this time close the other eye and the thumb will appear to move.

Unless it is inconvenient (something in the way for example) , the brain utilises the master primarily and the other image is used to judge distance, it can be used to confirm detail at closer range (reading).

When I used to shoot pistols, I would have competitions with myself by using both a left hand and a right hand pistol; I would make a point of sighting the shot using my right eye to shoot with the right hand and the left eye to shoot with the left. You might find you can consciously choose which eye is acting as the master; ambidextrous people (me) find this easier than most, or so I understand; we use both sides of our brain more readily. There is a saying , "ambidextrous is using both hands equally badly"; luckily, nobody told Leonardo da Vinci or Michelangelo.

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Is it weird if my dominant eye and dominant hand are not on the same side?

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Hmmmm, never heard of or tried this before.

Didn’t work for me.

If I put my thumb up in front of the object and try to focus both eyes on the object, I see two thumbs, if I focus on my thumb there are two objects about equidistant on each side of my thumb. My thumb moves when I close either eye, although slightly less with the right eye.

I am partially ambidextrose - slight right hand dominance but use both hands for similar tasks and can easily "train" the left hand to be about as effective as the right on anything, like writing, where I’ve developed a more pronounced right-handed preference.

Maybe it’s because I’m moderately near sighted? 😋

The two retinas are tied/linked together in the brain. Are they tied 1:1, so that each retinal point corresponds to the same retinal point in the other eye? I.e., each retinal point from one eye shares the same binocular neuron with its counterpoint in the other eye?

No, it's just a little less common than having same side dominance for eye and hand.

https://pubmed.ncbi.nlm.nih.gov/15513026/

>in a population with 9.25% left-handedness and 36.53% left-eyedness, 34.43% of right-handers and 57.14% of left-handers are left-eyed.

So 5.29% are left eye + left hand dominant and 59.50% are right eye + right eye dominant, meaning there's concordance in 64.79% of people. The remaining 35.21% have different dominant sides for eye and hand (31.25% left eye + right hand, 3.96% right eye + left hand).

> You might find you can consciously choose which eye is acting as the master; ambidextrous people (me) find this easier than most, or so I understand; we use both sides of our brain more readily.

Well, it's different with vision. Both eyes use both sides of the brain. More specifically, each side of the brain is responsible for one side of the visual field in each eye.

The striate cortex is the part of the brain that processes visual inputs from the right and left optic nerve via the lateral geniculate nucleus in the thalamus. Essentially the brain can handle and blend both of these inputs and actually relies on it for holding visual spatial memory and depth perception.

another version is make a triangle with your fingers. With both eyes open, line up on a distant object.

Without moving, close one eye and then the other.

Your dominant eye will still have the object centered. Your subordinate eye will cause the "window" of your fingers to move.

It can also change.

I was right-eye dominant, but developed a cataract in my right eye and even after getting an IOL I am left-eye dominant now.

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I learned of this recently and have tried dozens of times in different locations. No matter which I eye close and which method I use, the thing I'm looking at appears to move. I always assumed this was true for everyone, not having heard of dominant eyes before a few weeks ago.

I don't know about how the brain is wired, but from a simple optics/geometry perspective, I think we can reason that your "tied 1:1 ..." suggestion is unlikely.

In any given scene, the two eyes don't see exactly the same thing, owing to the different viewpoints. We experience "stereo-disparity", and the principal effect of that is that the relative horizontal alignment (in the two eye) of different points in the scene depends on their depth.

I would argue (I can't prove) that we perceive a range of depths "instantaneously" without having to scan the eye-divergence to bring each conceivable depth into alignment (to meet some 1:1 mapping).

Similarly, if you were to look off-axis (like 30 degrees to the left or right) at something quite close (e.g. 20 cm away), the images will be noticeably different sizes on the two retinas (provable from basic geometry), so again a "1:1 mapping" isn't helpful - and in reality we can still fuse a 3D image in the brain.

I've spent a lot of time in the past creating 3D autostereograms and thinking about stereoscopic depth perception - and depth reconstruction from an image-pair. It's not trivial.

At some level the brain must be 'correlating' the two images with a range of possible horizontal-offsets (dependent on relative depth), and some small finite vertical tolerance too (to allow for optical distortions and misalignments). I think I read about tests (or maybe did my own tests 20+ years ago) showing that the human brain can stereo-fuse (and perceive different depths) even if the image presented to the left and right differ in size/magnification by up to about 10%.

Also this video is quite interesting https://www.youtube.com/watch?v=DkaJ6iK2CJc The ability to barrel-roll the eye (to a limited extent) is likely part of human "optical image stabilisation" !

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