Yes you can. You can do that while creating a prescription or in the Settings area
In the Settings:
If you go to Settings, tap on Prescription (under Favorites)
You’ll see a list of meds you already set as your favorites
You can tap the Add button and a popup will appear
When Creating a Prescription:
Add the eye drops that aren’t in the database
Tap the Add to Favorites checkbox
Tap Create and now it will be in your Favorites list
Next time you create a prescription, you can just tap on Favorites and tap on the name of the drops you added.