The evolution of the eye has been a subject of significant study, as a distinctive example of an analogous organ present in a wide variety of taxa. Complex, image-forming eyes evolved independently some 50 to 100 times.
Complex eyes appear to have first evolved within a few million years, in the rapid burst of evolution known as the Cambrian explosion. There is no evidence of eyes before the Cambrian, but a wide range of diversity is evident in the Middle Cambrian Burgess shale, and the slightly older Emu Bay Shale. Eyes show a wide range of adaptations to meet the requirements of the organisms which bear them. Eyes vary in their visual acuity, the range of wavelengths they can detect, their sensitivity in low light levels, their ability to detect motion or resolve objects, and whether they can discriminate colours.
If you ever wondered how animals see the world, check out this video: