# One eye good, two eyes better, three eyes...?
**URL:** https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045
**Category:** Factual Questions
**Created:** [July 14, 2023, 7:56pm UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045 "2023-07-14T19:56:09Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@Czarcasm](https://boards.straightdope.com/u/Czarcasm)
#### Post date: [July 14, 2023, 7:56pm UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045/1 "2023-07-14T19:56:09Z")
Having one eye allows you to see, and having two eyes gives you depth perception. What would having three eyes, equidistant to each other, add to the equation, and is there a way to simulate this to find out?
---
### Author:  [@susan](https://boards.straightdope.com/u/susan)
#### Post date: [July 14, 2023, 8:14pm UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045/2 "2023-07-14T20:14:30Z")
Better visual range?
[ ](https://www.youtube.com/watch?v=C9gIIkUBOoo)
---
### Author:  [@ParallelLines](https://boards.straightdope.com/u/ParallelLines)
#### Post date: [July 14, 2023, 8:16pm UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045/3 "2023-07-14T20:16:59Z")
I think it would be worthwhile to consider that it does appear (to a degree) in the historical record.
[Parietal Eye - an overview | ScienceDirect Topics](https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/parietal-eye#:~:text=The%20parietal%20eye%20is%20also,%5D%2C%20and%20order%20Rhynchocephalia)).
So for the modern lizards that have a semi-vestigal option, it may work for hormone creation and thermo-regulation.
For a human? Personally, if I had a third eye, or was engineering one, I’d want it to be more like a [pit organ](https://en.wikipedia.org/wiki/Infrared_sensing_in_snakes) in a snake - we’ve got pretty good (color even!) vision as it is, but being able to ‘see’ via other frequencies other than the narrow band of visible light we use, could be quite useful.
---
### Author:  [@Elmer\_J.Fudd](https://boards.straightdope.com/u/Elmer_J.Fudd)
#### Post date: [July 14, 2023, 8:19pm UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045/4 "2023-07-14T20:19:31Z")
The eye in the middle could be utilized for monocular near sight (for reading and such), leaving the outside eyes entirely devoted to distance.
---
### Author:  [@Czarcasm](https://boards.straightdope.com/u/Czarcasm)
#### Post date: [July 14, 2023, 8:19pm UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045/5 "2023-07-14T20:19:37Z")
I am talking about a standard third eye, just like the other two,
---
### Author:  [@ASL\_v2.0](https://boards.straightdope.com/u/ASL_v2.0)
#### Post date: [July 14, 2023, 8:21pm UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045/6 "2023-07-14T20:21:41Z")
> [@susan](#):
>
> Better visual range?
Yep. Two eyes (binocular vision) aids in discerning depth/distance. I can’t imagine a third eye would have any greater benefit beyond wider range of vision and/or greater redundancy, but at the cost of having one more costly organ (and something else to get poked in, I suppose).
---
### Author:  [@TriPolar](https://boards.straightdope.com/u/TriPolar)
#### Post date: [July 14, 2023, 8:36pm UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045/7 "2023-07-14T20:36:42Z")
In a number of sports the third eye could allow an athlete to more easily pick up the trajectory of a moving object like a tennis ball or baseball, as well as picking up deviations from it’s initial path caused by aerodynamics.
It might be tested with a camera placed on a person’s forehead and feeding a tactile imaging device in the hand or some other location on the body. It would take some time for a subject to get used to it. I’d start with testing it in coordination with a single natural eye to see if depth perception is possible.
---
### Author:  [@Dr\_Paprika](https://boards.straightdope.com/u/Dr_Paprika)
#### Post date: [July 14, 2023, 8:48pm UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045/8 "2023-07-14T20:48:38Z")
It might increase your visual field and peripheral vision. Maybe it helps your chakras. Or help you see the future, especially if already a raven.
> **[What Would Happen If Humans Had Three Eyes? - Grunge](https://www.grunge.com/1025905/what-would-happen-if-humans-had-three-eyes/)**
>
> Evolution may have given Homo sapiens two eyes, but over the millennia, philosophers, mystics and clerics have longed for the development of a third.
---
### Author:  [@FlikTheBlue](https://boards.straightdope.com/u/FlikTheBlue)
#### Post date: [July 14, 2023, 9:05pm UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045/9 "2023-07-14T21:05:35Z")
Depends on what positioning we’re considering. A triangle with the third eye in the middle of the forehead? One towards the front of each temple with the third one at the back of the head? The former probably won’t do much or anything. The latter would sacrifice depth perception for greater field of view.
---
### Author:  [@burpo\_the\_wonder\_mutt](https://boards.straightdope.com/u/burpo_the_wonder_mutt)
#### Post date: [July 14, 2023, 9:09pm UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045/10 "2023-07-14T21:09:04Z")
If I were a musician, I’d want the third eye blind.
---
### Author:  [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)
#### Post date: [July 14, 2023, 9:09pm UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045/11 "2023-07-14T21:09:17Z")
My thought is that it would improve depth perception. Right now the eye parallax is only in the horizontal frame. A third eye would give us a vertical parallax as well.
---
### Author:  [@Cervaise](https://boards.straightdope.com/u/Cervaise)
#### Post date: [July 14, 2023, 9:16pm UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045/12 "2023-07-14T21:16:12Z")
> [@Czarcasm](#):
>
> equidistant to each other
This for me is key. You can define equidistant a couple of different ways.
Eye placement is commonly considered shorthand for distinguishing predator and prey. It’s a generalization with exceptions, but still illustrative of the concept:
[ ](https://azretina.sites.arizona.edu/sites/azretina.sites.arizona.edu/files/inline-images/main-qimg-48f66eef6060c56217d4db3bad6c846c.jpg)
So imagine three equidistant eyes all the way around. Take the head on the right, push the two eyes slightly together with a bit more overlap, and add a third smack in the middle rear.
Wouldn’t that be useful?
---
### Author:  [@gnoitall](https://boards.straightdope.com/u/gnoitall)
#### Post date: [July 14, 2023, 9:20pm UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045/13 "2023-07-14T21:20:45Z")
A third eye in the back of the head is standard equipment for the parents of naughty but gullible children.
---
### Author:  [@md-2000](https://boards.straightdope.com/u/md-2000)
#### Post date: [July 14, 2023, 9:38pm UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045/14 "2023-07-14T21:38:07Z")
> [@Cervaise](#):
>
> Eye placement is commonly considered shorthand for distinguishing predator and prey. It’s a generalization with exceptions, but still illustrative of the concept:
I assume that’s because the predator has to track and catch a moving target, while prey are chewing on plants which normally don’t have as much ability to evade capture…
---
### Author:  [@kenobi\_65](https://boards.straightdope.com/u/kenobi_65)
#### Post date: [July 14, 2023, 9:41pm UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045/15 "2023-07-14T21:41:39Z")
> [@md-2000](#):
>
> while prey are chewing on plants which normally don’t have as much ability to evade capture…
And, having their eyes on the sides of their heads gives prey animals a wider field of vision, giving them a better chance to spot threats.
---
### Author:  [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)
#### Post date: [July 14, 2023, 10:59pm UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045/16 "2023-07-14T22:59:05Z")
> [@Saint\_Cad](#):
>
> My thought is that it would improve depth perception. Right now the eye parallax is only in the horizontal frame. A third eye would give us a vertical parallax as well.
Parallax is greatly overrated. At ranges out to about 10 feet it provides a decent clue as to distance. Beyond that it’s not really used in the human visual system. The noise of how precisely eyes can align and how accurately they process the image overwhelms the signal of “eyes turned in 0.001 degrees” or whatever
Vertical parallax doesn’t really add anything; what’s going on internally is the eyes aim inboard slightly to focus at the same spot on the target, then compare the backgrounds, aspects, etc.
If you really wanted to do something useful with parallax, you’d want to increase the baseline. Two eyes on stalks that were 2 _feet_ apart would give much greater precision up close and a much greater range where parallax was more signal than noise versus the human standard design with 2+" between the eyes.
As various folks have said, the real value of a third eye would be to extend either the spectral range of visual sense, or the spatial range by mounting it elsewhere pointing in a different direction.
ISTM the current eyes could be augmented with more spectral range as easily as a third eye could be installed. So spectral isn’t the real use case for a third eye.
But seeing out the back of you head is not gonna happen without a sensor = eye back there pointing rearwards. Or maybe two aimed prey-style mounted behind the ears pointing at, say 4 o’clock & 8 o’clock with some overlap at 6’oclock and some small overlap at 10 and 2 with your existing eyes. These could be, much as your real eyes’ peripheral vision works, mostly motion detectors with limited acuity = image forming ability.
The idea upthread of an up-close “reading eye” that doesn’t become far-sighted with age would be handy too. Especially in the modern world.
---
### Author:  [@susan](https://boards.straightdope.com/u/susan)
#### Post date: [July 14, 2023, 11:33pm UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045/17 "2023-07-14T23:33:35Z")
Let us not forget “It May Look Like a Walnut,” where Laura grew eyes in the back of her head.
> **[It May Look Like a Walnut (1963)](https://www.imdb.com/title/tt0559769/mediaviewer/rm123329792/?ref_=tt_md_1)**
>
> Mary Tyler Moore and Dick Van Dyke in The Dick Van Dyke Show (1961)
On YouTube at 20:29.
---
### Author:  [@The\_Other\_Waldo\_Pepper](https://boards.straightdope.com/u/The_Other_Waldo_Pepper)
#### Post date: [July 14, 2023, 11:59pm UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045/18 "2023-07-14T23:59:15Z")
[ ](https://pbs.twimg.com/media/FnmTEW2XwAAszRC.jpg)
_“With one eye, you can see in two dimensions … there is no depth perception! With two, you see in three dimensions! With my three eyes, I see in four dimensions … and the fourth dimension is time!”_
---
### Author:  [@Moriarty](https://boards.straightdope.com/u/Moriarty)
#### Post date: [July 15, 2023, 12:05am UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045/19 "2023-07-15T00:05:57Z")
“If the doors of perception were cleansed every thing would appear to man as it is, Infinite.”
- William Blake
---
### Author:  [@Ponderoid](https://boards.straightdope.com/u/Ponderoid)
#### Post date: [July 15, 2023, 12:10am UTC](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045/20 "2023-07-15T00:10:27Z")
> Two eyes on a face
> Are usually enough
> But triops has got
> One that looks up
> And one that looks around
> And one to keep an eye
> On the other pair of guys
> Triops has three eyes
[ ](https://www.youtube.com/watch?v=zgIaSURBSDI)
[Next page](https://boards.straightdope.com/t/one-eye-good-two-eyes-better-three-eyes/987045.md?page=2)