The story goes something like this that for the protection of the world Lord Vishnu wanted to have in his possession a weapon which is all powerful. With this in mind he went on to commence the worship of Lord Shiva with a thousand flowers so as to get the sudarshana chakra as a boon from the Lord Almighty., This had been created by Lord Shiva for jalandhara samhara.
Therefore Maha Vishnu collected the required flowers and started the worship. of Lord Shiva , but during the worship, Lord Vishnu found that he fell short of one flower to thousand, and since he did not want to stop his prayer to Lord Shiva at any cost whatsoever, he did not hesitate a single moment , and went on to pluck out and offered one of this eyes as a substitute for the missing thousandth flower.
Lord Shiva was overwhelmed by this extreme devotion, and immediately gave the Sudarshan Chakra to Maha Vishnu, and thenceforth Maha Vishnu got the name "lotus eyed" (padmaksha) due to the devotion in offering the eye to make up for a lotus.