This week I learnt that, because different frequencies of light bend differently when they enter the eye, they have different focal points, some behind the retina, some infront and some bang on. Some animal eyes compensate by having concentric rings of different thickness in thier lens bringing the different wavelengths back into focus and so greater detail perception in the periphery of thier vision. In effect, varifocal lenses.
That system breaks down in very bright light when the iris becomes small and covers the concentric rings in the lens. And this is why some animals have a slit iris instead of a circular one, they can still close up but now there's the slits that allow light to enter the eye through the varifocal bits of lens.
View attachment 166762
Cropped in close from the above pic.
View attachment 166763