Dear ilker,
Wa alaikumus salaam,
In my view, when the Qur’an talks about being ‘blind’ on earth, I find it ‘metaphorical’ (2:171) in the sense of spiritual destruction (2:18). This follows as a result of an individual’s own utter ‘disbelief - kufr’ (6:109) where one’s own faculties of discernment and assessing information are sealed (2:7) off their power (7:179) after willful denial and neglect (2:6, 2:10) of clear and manifest signs and information availed to them (6:110-111).
It should thus be noted that in the first place, such an individual knew for sure the truth with the signs (ayat) revealed but chose to deny (kadhb) them or not take heed.
As a recompense, such a person is similarly despised on that Day (84:10) [as opposed to the ‘right-hand’ bearer - 17:71], left helpless, suffering their fate, thus symbolically ‘blind’ (a'ma) with none or nothing to lend a hand out of their misery. Thus, the way they chose to ‘forget/shun’ the verses on earth, 'blindly,' is the way they shall be ‘forgotten’ (20:126) that Day, 'blind' (20:125).
As for the unveiling of the ‘seal’ (khatam) or ‘screen’ ('idhwa-a) out of ‘blindness,’ I see this informing us that what the deniers used to deny and ignore/shun of signs and promises on earth (18:101) shall plainly be brought in the open (18:100) for them to witness that Day (68:42-43). The ‘screen’ ('idhwa-aka) shall be 'removed' (fakashafna) and the willful capacity to shun shall as a result have no room to administer (50:19).
Hopefully that helps insha Allah.
Regards,
Athman.