Spoilers! A certain characters eyes

[Kotemon]

Well in a sense that she was struggling to maintain herself in the lifestream all this time. She also learned and gained new spells and senses. But the forbidden technique seem to have left her actually blinded, but not really. You see she can now see everything through aether form, but at a cost of her own lifeforce. Matoya was truly concerned considering the spell she used was very dangerous. We can also assume that her powerful spells also use some hint of her LF too. Talk about commitment.

So how is this similar to how the Garlians see aether via a white looking third eye, and if so then why can she still use magics.

[Morningstar1337]

So how is this similar to how the Garlians see aether via a white looking third eye, and if so then why can she still use magics.

Because for starters, the Garleans still have their normal sight.

As for the magic. I think the Garleans cannot use Aether like the other races because they do not have as much aether as the other races. They know how it works and how to artificlay produce it to power their machines, but they do not have enought for even a simple teleport spell

Thancred's case is similar, the trip thought the Lifesteam did drain him of all his aether to the point where he has as much as a Garlean and it is unlikely that he'll even regain that lost aether again.

Also I think Minfilia might have sabotaged the spell, causing it to spare Y'sholta's aether but take away her sight as the "toll" through the lifesteam.

[Ashkendor]

Also I think Minfilia might have sabotaged the spell, causing it to spare Y'sholta's aether but take away her sight as the "toll" through the lifesteam.

I don't really think Minfilia would know how to tamper with Y'shtola's magics in such a specific way. Y'shtola cast a forbidden spell out of desperation and attempting to mess with it at all could have completely unforeseeable (and disastrous) consequences.

Minfilia may have the Echo, but ultimately she's a bureaucrat, not a mage.