Isaiah 61:1: Captives or blind?

On a Septuagint e-mail distribution list, someone recently argued that the Septuagint plays on the letter ס in Isa 61:1, reading it עו instead, and changing the meaning from לאסורים "to the captives" to לעורים "to the blind". One alternate possibility struck me, however. It appears, at face value, we may have an instance of simple scribal error. עו in the Qumran scrolls is often written together so as to be almost indistinguishable from the letter ש. It is probably not a coincidence then, that the letter ש is a common alternative spelling for אשורים  = אסורים "captives". The extra א is a little more difficult to account for. If the MT is original, perhaps the א was omitted by quiescence לעורים < לאעורים. If the LXX is original, perhaps the MT text added the א as a secondary correction after misreading the עו as ש. Where this variant gets interesting is that the MT פקח-קוח is often understood as meaning "opening of the eyes." If this is the case, then עורים "blind" is clearly more contextually suitable than the vague metaphor of MT. On the other hand, if the meaning is not necessarily this specific but could apply to an opening of prisons, then MT's אסורים is probably original, as it more easily explains the LXX text. So in the end, the conclusion to this text-critical problem probably hangs on the choice of translation for the difficult פקח-קוח.