In the swamp were blind creatures. Blind because they were eyeless. If they swam too near the surface, birds would pick them off and eat them.
Due to a lack of nutrients one year some of the creatures developed thinner skin than the others. They didn't last long. Apart from the ones that developed thinner skin over the cerebral cortex. These were able to react, just about, to light. They swam away from it, not liking its unusual nature. They preferred the dark.
And those who swam deeper, away from the surface, away from the light, survived. Soon all the survivors had thinner skin over the cerebral cortex because these were the only ones left alive to breed.
Every now and again, in the cycle of nutrient rich/bad nutrient seasons, some creatures developed which had very thin skin over the cerebral cortex. Not only could they react to light but they could respond to the shadows on the surface of the swamp when a bird swooped. These creatures lived, bred and soon all the surviving creatures had very thin skin near their brains which reacted to light. The thinner the skin, the more eye-like it looked and the more eye-like it was the greater the chances of the creature's survival.
Over a period of time all the creatures in the swamp that lived and bred could 'see' in much the same way as we can.
Sadly a nearly-human tribe came along which found these 'eyes' a delicacy and soon the seeing swamp creatures were completely extinct. Life's a bitch. But if anyone ever uses that illustration again about the unlikeliness of watches having designers yet eyes falling together by accident I swear I'll poke their eyes out. Evolution takes a huge amount of time. Eye poking is instantaneous.