Although he didn't actively use magic, mana still filled Toz's body, and since his eyes were part of his body, they also enjoyed the benefits of being passively strengthened by mana. The mana vision, which had previously strained Toz's eyes and mind, could now be active for longer, thanks to his mana supporting his body.
Not only that, since the mana filling his body and supporting the mana vision was a mixture of his six elements, Toz had an easier time separating the elements in the air into those he didn't have access to and those he did have. His own mana supporting the mana vision also allowed him to more easily discern between all the elements since it seemed like the mana vision had become stronger.
Thanks to being able to separate the different elements more clearly, Toz realized that he could try and deduce where he was or what the circumstances outside the cell were. At least what they were or where he was when he was thrown into the cell and isolated within.
