I scratched my eyelid while applying mascara. It left what felt like an abrasion. I got prescribed antibiotics. Is this necessary for a eye scratch?

Yes. The surface cells of your cornea(epithelium) prevent most bacteria from gaining access to the deeper layers which can cause a serious infection. If you scratch off the epithelium there is the potential for infection so antibiotic eye drops are generally prescribed until the abrasion heals.