but, you can be sure that they can see alot further than you or I could, at the same depth/water clarity :D (probably even with a swim mask on, too :p )
You have to take into account two other factors : smell & their lateral line !! While Crappie are generally considered "sight feeders" ... in dingy/turbid water, these two factors come into play, and may overtake the need for "sight, from any distance". Also, even when they "can" see a bait ... smell and their lateral line still can be +/- factors.
... cp