All SEAL candidates must first meet Navy entrance physical requirements for vision, which must be correctable and in a SEAL's case, no night blindness. There are additional requirements for officer candidates. I recommend if you really want to be a SEAL, get your eyesight fixed (if possible) before you come into the Navy, and come into the Navy with an approved SEAL contract.
As far as I can see, you are really interested in joining the army and be one of the Navy Seal. However, you should know that US Army forces require a lot of inborn qualities, including your physical conditions, and good eyesight is highly considered in the selection process. Perhaps you should consult a recruiter to see if you can receive some lasik surgery or do something to make it up.
It depends on how poor your eyesight. It is widely known that all seal candidates have to first meet Navy entrance physical requirements for vision, which should be correctable and in a seal's case, no color or night blindness. At the same time, the vision correction requirements can be found at the medical DQ list at Military.com. In general, there is few navy seal could allow to wear any corrective lenses.