eyes diseased and dim
眵 describes eyes that are diseased and dim, with a focus on impaired vision or eye discharge.
眵 combines 目 (eye) with 多, which likely contributes a phonetic element. The exact historical development is uncertain.
The eye 目 on the left is paired with 多 (many), suggesting many problems in the eye, like discharge or dimness, leading to diseased eyes.
For シ, imagine a sick eye that needs a 'she' (シ) to care for it: she -> シ, and she helps clear the dim, diseased eye.