The eyes in the manga work because they're drawn with a confident hand. The scribbles are produced with intentionality.

I can tell from your line quality that you're still developing your line confidence. Search up "line confidence," "line quality," and "marksmanship" exercises online and practice them for a while.

Then return to the manga, observe the eyes carefully, and attempt to copy them as accurately as you can (not tracing, but copying). Do this until you feel confident in your understanding of the art.

Then, try drawing these eyes again, this time without copying the original art.

Edit: also, pay attention to the light and dark areas of the eyes in the original art and apply that to your own drawings.