Why? The number of mutations required is irrelevant, considering that at no point does the process demand that any of those mutations be useless independently, or appear one at a time or in any particular order. Plus, given how many times that eyes have evolved independently, there clearly are a large number of different mutation pathways that produce eyes.
Heck, even finding the fewest necessary mutations to produce an eye would be pointless, because evolution is a natural process very unlikely to proceed down the most efficient path possible.
However, if one is generous and defines an eye as "a spot on a body or cell that is specialized to respond to light", that would only take 1 mutation; one that causes a portion of the body/cell to be darker and more heavily pigmented than the rest of it, since that is all that would be necessary for that spot to feel light differently than the rest.