That just sounds like 'survival of the fittest'. No evolution here, just some puppies in the litter are stronger than others. If that's all evolution is I'm on board.
But if evolution makes claims such as, the gradual elongation of the eye sockets of some species of raptors provided telescopic vision, I have to jump ship.
Let's stick with the eye thing.
First of all, stereoscopic vision is determined by the position of the eyes relative to each other, not the shape of the eye socket. You need to eyes mounted next to each other so they give slightly different angles of the same thing. This is what provides the stereoscopic (3D) vision. When you see a 3D movie, two images are being projected onto the screen at once. The glasses you wear are polarized in different directions so that each lens lets only one of the images through. Each eye sees a different image, which your brain interprets as depth.
But as for the evolution of eyes, think about this.
Your skin is sensitive to infra-red radiation, which is part of the same spectrum as light. Our skin feels it as heat. I could blindfold you, but you would still be able to tell easily when a source of infra-red radiation was being directed at you, because you'd feel the heat from it. In fact, infra-red is used in heaters:
https://en.wikipedia.org/wiki/Infrared_heater
Now, lets say I put your hand on the table, palm up. If I shone IR radiation onto it, like from a special IR flashlight, you could tell when the IR was switched on and switched off. You could feel it as heat. But you couldn't tell which direction it was coming from. This is similar to the eyes we find in very primitive life forms, they are basically light sensitive cells on the surface of the body. This is similar to the eyes of the earthworm. They are only enough to tell it if it is in light or dark.
But now, imagine that you cup your hand. Now you can get some idea of which direction the IR radiation is coming from. If I hold the IR light above your elbow and aim the beam at your hand, then your fingertips will feel the heat but the palm of your hand will not. And if I move the light so it is out past your hand, then your fingers won't feel it (not the underside of them anyway, where they felt the heat before), but your palm will. So now, unlike before, you can tell which direction the IR light is coming from. This is similar to the eyes of planarians, a kind of flatworm.
The next stages are rather difficult to use your hand as an analogy. We started with simple light sensitive cells on the surface of the skin, and saw how this primitive eye was improved by indenting it into a bowl shape. Now imagine that it keeps indenting, getting deeper, and the opening gets narrower. Now, any light shining onto this eye will strike only a small part of the light sensitive surface, giving a greater accuracy in the direction of light. And this increased accuracy formed by having a smaller hole will start to form a crude image. It's the same principle as a pinhole camera. And as the eye begins to close up, it starts to fill with a jelly like material (which only needs one or two mutations - mucous is quite common, after all) which supports the shape of the eye. This is the type of eye that the chambered nautilus has.
Of course, this can be improved. A pinhole camera must have a small hole, which can cause problems when light levels are low. But opening the hole wider also gives worse eyesight because it can't form images as clearly. But if the jelly inside the eye begins to thicken, it can form a lens which helps to focus the image, thus allowing a clearer image to form, even with a wider hole. This is the kind of eye that is found in your average garden snail.
Further simple mutations can develop the lens (remember, each mutation doesn't have to create a perfect eye, it just needs to be a slight improvement over what came before), move the lens to a better position and change the lens's refractive index.
So we can end up with a complex eye, such as the eye of an octopus, having developed from simple light sensitive cells on the skin. Each change was tiny and required only slight mutations from what came before, but all the little changes added up to form a complex eye from a simple beginning. And each step can be found in animals alive today, each animal having developed the eyes it has to the degree it needs them. A worm, for example, with only simple eye spots, doesn't develop more advanced eyes because it simply doesn't need to. It needs only to tell light from dark, and developing more advanced eyes would mean a use of resources that it could use to better effect with something else. (It's the same reason why you'd need only a low resolution screen to see if someone is walking up the front path, but a much higher resolution screen to watch your blu ray collection on).
So, going back to your puppies analogy, if you accept that small changes in one generation can produce some that are slightly stronger, then you should also accept that small changes in one generation can turn a flat patch of light sensitive cells into a slightly indented one. And just as how a slightly stronger puppy has a slightly better chance of surviving long enough to reproduce, a slightly indented eyespot can give the individual possessing it a slightly better chance to reproduce. And over many generations, this happens again and again - animals in each population getting slightly better able to survive, whether it is puppies that are slightly stronger or worms with slightly better eyesight. The mechanism behind both of these is exactly the same - small changes per generation which give a slight benefit, which add up over many generations to create new species and more advanced body structures.
If you accept the puppies getting stronger, then you must also accept the eyes evolving.
