Anyway, we're doing optics. In class we discussed real images and virtual images. I won't go into too much detail but basically, what I became aware of is that for the eye to form an image, it must have a lens that focuses light onto a single point. This is because unfocused light cannot create a real image.

Without a lens, the light from a point on the object will be spread out onto a wide area. However, for an image to be created, the light from a specific point needs to converge (with a lens) onto a single point on the surface the image is being constructed on.

Our eye uses a converging lens in order to do this. Light from images goes through the lens, and the eye's lens automatically adjusts to focus the light from an object onto the retina.

As you can see, unless the light is completely focused, no actual image is formed. Or, should I say, the image becomes blurred.
Thus, without the lens in the eye, no image is formed. Without a lens the eye wouldn't be able to form an image. At all. Which then means there is no purpose in having a retina that can discern between colors, and no need for the brain to have the necessary facilities to discern an image from the cell's input, and thus vision wouldn't be anywhere near as advanced. "primitive" eyes without a lens in real life can only tell between light and dark.
An example of this kind of "primitive" eye is the jellyfish, which has a number of light-sensing organs that the jellyfish uses to determine which way is up. These organs can only sense light, and cannot form an image. Even if they had a lens, they wouldn't be able to create an image, because the jellyfish's nervous system is not capable of interpreting data from retinal cells. If the jellyfish were to have retinas covering its body, it still wouldn't be able to see, because not only would its brain be incapable of interpreting the results as an image (unless we assume it had that too) but the lack of a lens means that no image would be formed on the retinas.
So my question to those defending naturalistic evolution, I want to ask how it is possible for a complex system such as the human eye--which depends on multiple parts simultaneously working together in order to achieve its basic function--to evolve through natural selection? Don't tell me that I am arguing from incredulity. It is simple scientific fact that the eye would not work at all, even at a basic level, without a lens. The lens and the retina are both CRUCIAL parts and we have NO evidence that they evolved from an existing structure.