This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
瞮 combines 目 (eye) with 徹 (or a related phonetic component). The exact historical development is uncertain, but it likely relates to clarity or brightness of vision.
The left side is 目 (eye), and the right side resembles the right part of 徹 (clear). Picture an eye that sees everything clearly, like a transparent lens.
For テツ, imagine a clear-eyed detective named Tetsu who sees through every mystery: Tetsu -> テツ.