Certain treatments are ineffective for healing the eye. Hops, coriander, some other herbs. They may be used then on Shabbos. Eating hops can be done even when it is effective bc healthy ppl also eat hops.

Basting roast in ok. Even though it’s “fixing” the food, it’s still permitted the roast is edible without the it. This is comparable to the heter of putting clear wine or water in a strainer on Shabbos and it’s not borrer since it’s usable without further straining.

It’s forbidden to put vinegar on wound to reduce swelling bc it’s an act of healing. It’s permitted for most ppl to use wine bc it’s ineffective (unless one has sensitive skin) However, if the wound was on the top of the foot or the top of the hand it’s potentially a life threatening injury and it’s like an internal wound that one may desecrate Shabbos for.

Back when bathing was permitted on Shabbos, one could bathe on Shabbos in clean waters that healthy ppl bathe in, but not in waters that are only for medicinal purposes. It is only forbidden to linger in the water bc then it’s very discernible that ones doing an act of healing. For the Great Sea, there are purer parts where one may linger and dirtier parts where one may not linger.

There a dispute if seas of the world are considered מעיין or מקוה. The practical difference is whether it’s kosher to become pure if the waters are not still. Only a מעיין can purify with flowing waters but a מקוה can only purify still waters. R Meir says all seas all treated like מקוה. R Yehuda says only the Greats seas are like mikveh inland seas are like מעיין. R Yosi says all seas are treated like מעיין.

One can take “medicine” on Shabbos that is Foods healthy people eat. Any foods/drink only used by sick people is forbidden. It is permitted to drink them though to quench thirst.

One can’t eat eizovyon on Shabbos. It’s kind of hyssop that cures intestinal worms. One may eat pennyroyal that cures worms in the liver.