For a character who can't see far away, I'd reduce spotting ranges (See terrain types in SRD), as well as increase penalties for range increments.
For a character who can't see up close it's more complicated. I would impose a -5 penalty on all skills relying on detailed observation, like appraising a gem, or crafting a sword, or picking a lock. With appropriate role-playing a near-sighted character could overcome some (though not all) of these penalties.