Answer:
I understand that you are asking for the steps that needed to take place to lead to the evolution of the human eye.
The evolution of the eye is an interesting research topic because it is a feature you can find in many different living organisms and in a wide range of structures.
The steps needed to lead to the evolution of the human eye (camera type eye) can be divided in 6 major stages:
1- The appereance of light sensitive cells (photoreceptor cells with opsin protein)
2- The appereance of pit eyes or "cup" shape eyes and nerve fibers (this new shape allowed directional differentiation).
3- The appereance of the "pinhole" eye (the light opening width was reduced and turned to be more efficient for directional differentiation and visual resolution)
4- The developpment of a transparent humour and an enclosed chamber (The reduction of the light opening let transparent fluids stay inside as a protection against infections and let an enclosed chamber to be formed; as a consequence, this kind of eyes could develop a higher refractive index, colour filtering, U.V. protection and even the possibility to work in or out of water).
5- The lens formation (this feature let light to be concentrated in one point or small area)
6- The iris and separate cornea developpement (the visual acuity was improved and the camera-type eye developped).
Step-by-step explanation:
All eyed animals, human beings included, share the genetic background for eye development. One of the common traits of eyed animals are the presence of opsins (light sensitive proteins) in photoreceptors cells that trigger nerve impulses. These cells are present in very basic organisms and they can act, even without a brain, like a sense aimed to identify the presence or the abscense of light in the environment.
The complex eye started with a patch of photoreceptors (eyepatches) that gradually formed a "cup" shape eye, giving the possibility of knowing the directions of the light. In fact, the "cup" shape allows to identify where the light is coming from, because of the angle that hits the photoreceptors layer. Then, this "cup" shape eye began to constrict and to form a "pinhole" eye, with a narrow opening for light. With this narrow opening, directional differentation and visual resolution improved, and at the same time, some protective layer began to form. Little by little, a closed chamber was formed with a transparent humour inside, that lead to multiple features like increasing reffractive index, colour filtering, U.V. protection, etc. Then, a mass of transparent cells developped into lens, made of multiple proteins, thet diversify and improved visual acuity. Finally, the cornea (transparent layer) and the iris (nontransparent layer) appeared, and let the camera-type eye develop.