What are the blind eyes?
Rashi: They do not see His Gevurah, to put to heart to repent to Him.
Radak: Yisrael's eyes in Galus, due to afflictions.
Malbim: There is light, just their eyes are blind from seeing (i.e. they do not see) it.
Why does it say "Lehotzi mi'Masger Asir"?
Rashi #1: Via opening their eyes, prisoners will leave their incarceration.
Rashi #2: To inform them of Galus Bavel, which will come upon them; in the end, they will leave it.
Radak: You are incarcerated in Galus, in a jail, and sit in darkness.
Malbim: There are two groups of Yisrael in Galus. (a) Shevet Yehudah and Binyamin were scattered in the four directions. In many places they are incarcerated in the chains of poverty - "Lehotzi mi'Masger Asir" applies to them. (b) Refer to 42:7:3:1.
Why does it add "mi'Beis Kele Yoshevei Choshech"?
Malbim: The 10 tribes were exiled to Chalach and Chavor. Their place was hidden, and they resemble those who sit in darkness, in jail, and no one sees them.