The benefit of the inverted retina doesn’t scale with size. It decreases with size.
Amount of retina scales like r^2, while amount of eyeball to put neurons in scales like r^3. This means that the smaller you are, the harder it is to find space to put neurons, while the bigger you are, the easier it is. This is why humans have eyeballs full of not-so-functional vitreous humor, while the compound eyes of insects are packed full of optical neurons.
Yes, cephalopods also have eye problems. In fact, this places you in a bit of a bind—if evolution is so good at making humans near-optimal, why did evolution make octopus eyes so suboptimal?
The obvious thing to do is to just put the neurons that are currently in front of the retina in humans behind the retina instead. Or if you’re an octopus, the obvious thing to do is to put some pre-processing neurons behind the retina. But these changes are tricky to evolve as a series of small mutations (the octopus eye changes less so—maybe they have hidden advantages to their architecture). And they’re only metabolically cheap for large-eyed, large-bodied creatures—early vertebrates didn’t have all this free space that we do.
The benefit of the inverted retina doesn’t scale with size. It decreases with size
It’s the advantage of compression reduction that generally scales with size/resolution due to the frequency power spectrum of natural images.
The obvious thing to do is to just put the neurons that are currently in front of the retina in humans behind the retina instead.
Obvious perhaps, but also wrong, it has no ultimate advantage.
Yes, cephalopods also have eye problems. In fact, this places you in a bit of a bind—if evolution is so good at making humans near-optimal, why did evolution make octopus eyes so suboptimal?
Evidence for near-optimality of inverted retina is not directly evidence for sub-optimality of everted retina: it could just be that either design can overcome tradeoffs around the inversion/eversion design choice.
The benefit of the inverted retina doesn’t scale with size. It decreases with size.
Amount of retina scales like r^2, while amount of eyeball to put neurons in scales like r^3. This means that the smaller you are, the harder it is to find space to put neurons, while the bigger you are, the easier it is. This is why humans have eyeballs full of not-so-functional vitreous humor, while the compound eyes of insects are packed full of optical neurons.
Yes, cephalopods also have eye problems. In fact, this places you in a bit of a bind—if evolution is so good at making humans near-optimal, why did evolution make octopus eyes so suboptimal?
The obvious thing to do is to just put the neurons that are currently in front of the retina in humans behind the retina instead. Or if you’re an octopus, the obvious thing to do is to put some pre-processing neurons behind the retina. But these changes are tricky to evolve as a series of small mutations (the octopus eye changes less so—maybe they have hidden advantages to their architecture). And they’re only metabolically cheap for large-eyed, large-bodied creatures—early vertebrates didn’t have all this free space that we do.
It’s the advantage of compression reduction that generally scales with size/resolution due to the frequency power spectrum of natural images.
Obvious perhaps, but also wrong, it has no ultimate advantage.
Evidence for near-optimality of inverted retina is not directly evidence for sub-optimality of everted retina: it could just be that either design can overcome tradeoffs around the inversion/eversion design choice.