blind, no pupil in the eye
瞍 centers on blindness, specifically the condition of having no visible pupil in the eye, which renders sight impossible.
瞍 combines 目 (eye) with 叟, which likely contributes the sound and may relate to an old or impaired state, together expressing blindness or lack of pupil.
The eye radical 目 on the left is paired with 叟, which looks like an old man with a cane. Imagine an old man whose eyes have no pupils, leaving him blind.
For ソウ, picture a blind person feeling their way along a wall, making a soft 'sou' sound as their hand slides: sou -> ソウ.