It first started out as Kishimoto busy inking Itachi's MS. While working on it he had a mishap where the pen leaked too much ink, damaging the panel with a ink dripping down Itachi's eye.
Improvising, Kishimoto thought this looked kinda cool and didn't redraw the supposed screw up.
And that's why, Itachi's eye bleed.

Improvising, Kishimoto thought this looked kinda cool and didn't redraw the supposed screw up.
And that's why, Itachi's eye bleed.