IME, I have learned at times that not doing anything, could actually be best for the injured fish. Sometimes, using meds to treat a fish can or may be causing more damage, than good.
I have had several fish in the past, get their eye(s) injured, scraped, bit, cloud-up and swell. Most of them all fully recovered. The only fish that didn't fully recover was a wolffish that lost his eye, only because i was careless enought not to have a heater cover/protector/sleeve on my heater?!!
In your case tho, if the scratch is as minute as you say it is... honestly, I wouldn't worry about it. Just be sure to keep the water conditions and quality up. Isolate the injured fish if you have to, and if using meds is totally necessary, don't use anything that's harsh. Adding a little aquarium salt and/or Melafix can go a long ways sometimes.

Good luck!