Insane Similarity!
Though differing in their evolutionary pathways, the eyes of humans and octopuses are almost the same regarding structure and appearance. Both organisms have stereoscopic vision, even if they belong to totally unrelated classes, i.e., Vertebrata and Cephalopoda, respectively.
Convergent evolution has played a very important role in the development of complex life forms since the time of appearance of the first organisms. The features in organisms that perform the same functions, but have different evolutionary history are called analogous/convergent structures. This type of development of structures is also called homoplasy. For example, wings have the same functions for insects and birds, but there is no evolutionary similarity between them.
Read more at Buzzle: http://www.buzzle.com/articles/analogous-structures.html