3
$\begingroup$

is it possible to have multiple retinas, would there be advantages to this? Or would it just not work at all? I have a diagram (a shitty one) and more explanation if needed

Edit: sorry for the confusion I’m new here my main goal here is to have a combined human and jumping spider eye I want to do this with an “eye in an eye approach” here’s a diagram sorry it looks like an 8 year old made it enter image description here

$\endgroup$
7
  • $\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$
    – Community Bot
    Apr 15 at 4:50
  • 1
    $\begingroup$ The more details you can provide the better. Please upload your diagram, no matter how... unrefined. $\endgroup$
    – Monty Wild
    Apr 15 at 4:56
  • 2
    $\begingroup$ I like that the close options for questions include "needs more focus" and "needs more detail or clarity". What do you mean by "Multiple retinas"? stacked? side by side? something else? what distinguishes tywo retinas side-by-side but touching with a common blood supply and connected to the same optic nerve from a single retina? etc etc. $\endgroup$ Apr 15 at 9:37
  • $\begingroup$ (also, you should probably talk about the kind of eye you're thinking of, as not all eyes are quite the same). $\endgroup$ Apr 15 at 9:37
  • 1
    $\begingroup$ Related: compound eyes, such as those of the flies (though I don't think they qualify has having multiple retinas, but I'm not specialist). $\endgroup$
    – jcaron
    Apr 15 at 13:24

4 Answers 4

7
$\begingroup$

The main problem with having multiple retinas is that the eye optics can focus the image on a single point, point which, thanks to saccades, defines a plane.

Having multiple stacked retinas will result in only one of them being in the focal plane and producing a sharp image.

Having multiple retinas sharing the same plane will result in each retina having a lower capturing area, lowering the sensitivity of the eye with respect to the same eye with a single retina occupying the same total surface.

This without counting the added complexity of having multiple optical nerves going between the same two point.

$\endgroup$
4
  • 3
    $\begingroup$ Multiple stacked retinas would have one in the focal plane at a time. It might still be useful if the retinas were optimized for different conditions. Say, low light versus bright light $\endgroup$
    – No Name
    Apr 15 at 13:43
  • $\begingroup$ @NoName the problem with that is each retina is still capturing light and preventing it reaching the layer below, removing random parts and blurring your image $\endgroup$
    – John
    Apr 18 at 20:41
  • $\begingroup$ @John Vertebrate retinas are backwards - they are behind the blood vessels and nerves they need to work, which is why the optic nerve punches through them - and work just fine. Yes, they're inefficient, and there's a ton of post processing, but if the retinas themselves are the right way round, they only have to do the processing once, and might even get away with less $\endgroup$
    – No Name
    Apr 18 at 23:58
  • $\begingroup$ except unlike blood vessels and nerves, cones and rods are designed to capture light, they are far more opaque . and they will cause far more distortion. $\endgroup$
    – John
    Apr 19 at 20:50
2
$\begingroup$

The principal eyes of jumping spiders are organized with a tiered or layered retina. Is this what you meant by multiple retinas? The layered architecture appears to provide better spatial resolution and another mechanism for depth perception besides bicameral:

The principal eyes of jumping spiders have a unique retina with four tiered photoreceptor layers, on each of which light of different wavelengths is focused by a lens with appreciable chromatic aberration. We found that all photoreceptors in both the deepest and second-deepest layers contain a green-sensitive visual pigment, although green light is only focused on the deepest layer. This mismatch indicates that the second-deepest layer always receives defocused images, which contain depth information of the scene in optical theory. Behavioral experiments revealed that depth perception in the spider was affected by the wavelength of the illuminating light, which affects the amount of defocus in the images resulting from chromatic aberration. Therefore, we propose a depth perception mechanism based on how much the retinal image is defocused.

$\endgroup$
1
  • $\begingroup$ It's amazing that you mentioned jumping spiders, lol that's exactly what I was going for $\endgroup$ Apr 18 at 20:33
1
$\begingroup$

Optics are complicated. The argument about lenses is only true if you neglect the photon dispersion, i.e. the 'prism' effect that media have on light. In reality the focal length is different depending on the wavelength of light, but in everyday life our eyes' lenses are good enough that we don't really notice it.

1

However, suppose life went a different way, and we evolved to use very large eyes with Fresnel zone plates to focus light - specially shaped patterns of concentric rings, to focus light. The focal length $f$ is given by

$$f \simeq 2 r \Delta r / \lambda $$

where $\Delta r$ is the outermost ring's thickness, $r$ is its radius, and $\lambda$ is the wavelength of light. "Redder" light focusses closer to the surface than "bluer" light - stratifying the different photoreceptor cells spatially. Note that $\lambda$ changes by a factor of 2 between red and blue light, so this difference in $f$ is very large.

Supposing that we keep the same red, green, blue trifecta of light - a consequence of this eye structure would be the breakdown of the colour wheel - we only have the colour "purple" because our red receptors are also stimulated by blue light, but colour-stratified creatures would experience this colour cross-pollination very differently.

$\endgroup$
1
  • $\begingroup$ (1) Achromatic and apochromatic lenses do exist. (2) The lenses of our eyes are actually atrocious as lenses, about the quality of a toy camera. It is our brains who do the heavy lifting in postprocessing as it were. (3) Stacked photographic sensors are a real thing and they have no problem reproducing purple. (But they are not widely used because their advantages are overwhelmed by their technical problems.) $\endgroup$
    – AlexP
    Apr 15 at 14:45
0
$\begingroup$

It is absolutely possible to have multiple retina, there are fish with multiple retina, barreleyed fish, they allow the fish to see in multiple different directions at once. but you need a very specific shaped eye.

enter image description here

Overlapping retina however are completely pointless

It just makes each worse at resolving images AND more fragile. What you have drawn cannot even exist, the inner retina lacks a blood supply and a nerve connection.

source

$\endgroup$
1
  • $\begingroup$ FUCKKKKK i need to add that don't I $\endgroup$ Apr 18 at 21:48

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .