why can’t we move our eyes outwards in opposite directions?
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Because there’s never a need to do so. Parallel is the most we need to see things far away, and cross-eyed lets us see things really close.
Humans evolved to be predators, our eyes are forward facing and able to focus on prey. We are not prey, where our eyes are split and always scanning for danger.
I’ve read the answers here and they all make sense but I’m going to phrase it slightly differently. Our eyes are independent, controlled by separate muscles, connected by separate nerves. Each eye is capable of looking around, can one learn to control them independently…?
To use a computer analogy, can one learn to access the lower level “point left eye” and “point right eye” functions instead of always relying on the “look at thing” higher level function?
NAD but if you were looking towards your peripheral vision/left and right at the same time, you wouldn’t see what was in front of you and might walk into it.
There would be no need to. We use both eyes to gauge distance and reference the whole environment. We wouldn’t be assessing our left and right at the same time that’s what peripheral vision is for, and I believe I had an anatomy instructor tell me women have better peripheral vision. Which makes sense to me as more than one child around requires eyes in the back of your head if you want them to survive!
Biology perspective – eyes are not lone wolves. Think of two ox yoked together. They can’t go in separate directions because they will pull themselves apart. Eye muscles and nerves work the same way.
Image generation perspective – you don’t see each image from each eye separately. The images combine in the brain to make the image you see therefore they must look in the same direction or you will see double. People who don’t have both eyes pointing in the same direction either shut the image from one eye off, alternate the images from each eye or they get headaches etc if seeing both images.
Non ELI5 answer – the visual system has an extremely complex but well thought out design / evolution.
Eyes need to be in perfect alignment ie light from the target object of focus must land at the central, most light / detail sensitive tissue at the back of each eye simultaneously. Equally each eye has a blind spot and the way they work, move together counters the blind spot in the other eye.
All of this light information is converted to an electrical signal when hitting the tissue at the back of the eye. This only remains on its own individual nerve pathway for a short distance before the signals are combined and split differently and then sent to the brain.
Here the signals are separated based on type (detail or gross) and area of the eye the light touched and go through a complex processing mechanism in your brain.
The output of this mechanism is what you actually ‘see’. This arrangement allows for things such as depth perception etc. different organisms will have different setups based on need / priority. Humans have great central detail and colour vision and effectively a great overall visual balance for a variety of situations.
Further the reason your eyes can come together is because when you change the distance of fixation the eyes need to come together to maintain a single image. Ie when they are they furthest apart you are looking the furthest away and they come together as you fixate closer.
As someone who spent many years in visual therapy because my eyes DO NOT move together- your brain makes images using both eyes together at the same time. So if you were to move your eyes in seperate directions like a rabbit, your brain is still trying to make one image but it’s getting different sensory data.
On a more realistic scale this looks like one eye not moving as fast as the other or it’s positioning on your head is a little above or below the other so the eyes are seeing from two seperate point of views which can cause blurred or double vision.
Also having two eyes positioned the way human eyes are positioned gives us our depth of field. While someone with only one seeing eye can have depth of field, it’s because their brain has learned how to do this versus being able to anatomically do it with the two inputs( both eyes)
I imagine rabbits have fine depth of field but they have a blind spot in the center of their vision (like us but bigger)
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