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So in real life there is glasses that use photochromic lens to adapt to the light intensity enter image description here

Would it be biologically possible to have a species that use a photochromic material instead of an iris to control light intensity?

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    $\begingroup$ (1) You probably mean a photochromic material in addition to an iris. The iris serves as a diaphragm, which limits the passage of light to the center of the optical system, where distorsion and aberrations are within acceptable limits. (2) Many humans use artificial eye coverings with such photochromic materials; so that the answer is trivially yes, there is at least one species which uses this mechanism to control the intensity of light. $\endgroup$
    – AlexP
    Jan 17, 2023 at 15:13
  • $\begingroup$ I think biology will have an easier time making tearducts that synthesize dark/light-obscuring microparticulates that dispense and cover the eye in response to excessive light, or dark nictitating membranes, than trying to make a photochromic lens. $\endgroup$
    – Lemming
    Jan 17, 2023 at 16:11
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    $\begingroup$ Could also go the route of making the fluid inside the eye more opaque in response to light(ocular melanin production/tanning?) but that's not really darkening the lense now is it $\endgroup$
    – Lemming
    Jan 17, 2023 at 16:18
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    $\begingroup$ Hello @Arzack1112, welcome to Worldbuilding. The answer to this question is trivially, "yes." However, from an evolutionary standpoint, nature tends to take the path of least resistance. It may not seem that way, but generally speaking, whatever complexity you observe, nature took the simplest path to get there. If there's a simpler solution, it's unlikely to use this solution. Nictating membranes would be the most likely solution. However, the solution meets suspension of disbelief. Do you have a problem to solve? As-is, I'm not really sure what you're asking from a worldbuilding POV. $\endgroup$
    – JBH
    Jan 17, 2023 at 18:04
  • $\begingroup$ note that size and shape of the iris have an effect on the optical system beyond the amount of light this is being used by several species to extract more information from the picture. $\endgroup$
    – bukwyrm
    Jun 21, 2023 at 7:03

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