According to the movie Green Lantern
Millions of years ago, a group of beings called the Guardians of the Universe used the green essence of willpower to create an intergalactic police force called the Green Lantern Corps. They split the universe into 3600 sectors, with one Green Lantern per sector. One such Green Lantern, Abin Sur of Sector 2814, defeated the being Parallax and imprisoned him in the Lost Sector on the ruined planet Ryut.
In the movie we see, some alien astronauts crashed on Ryut and inform the base that they have crashed on Ryut and requests for help. During their walking, they fell into a pit and found Parallax. But despite being imprisoned, he took their lives, became strong and broke the prison.
It seems somewhat faulty. Did Abin Sur, the great Lantern, make such a fragile prison to hold an evil such as Parallax, so that it could easily be broken? And did Abin Sur not know that he can eat on lives by his eye? If he knew, why did not he make such a mechanism(like a cover in-front of his eyies or opaque jail), so that Parallax cannot take lives from a distance? Certainly he did not do it intentionally. And also we see, right after his flee from the prison, Parallax attacks Abin Sur and surprisingly, Abin Sur could not return a good fight, which is somehow not expected from him. Let it be taken that, Parallax became stronger feeding upon those astronomers lives. But how come he so easily vanquished Abin Sur?