Hello, I'm Dr Gary. I've been practicing veterinary medicine since 2007. I look forward to helping with your questions/ concerns.
This does sound like ear mites to me. The other potential cause would be an infection, but those don't usually go between cats. Ear mites can commonly be seen in all the cats in a house.
Personally, I don't use Ivermectin to treat. I use Milbemite drops in the ears. This is a one time drop that you use in the ears and it's very effective. I first clean out the brown debris and then I use the drops.
The other option is to use Revolution drops. This is a flea/ tick control med that I'll sometimes put a couple drops in each ear and it works very well.
I hope this helps, let me know if you have any other questions.
Thank you for your help Dr. Gary. If my vet won't help would it be advisable to use otc ear mite treatment? Is that as effective? If it is ear mites why does only one cat show symptoms. Cheshire has been showing symptoms for about a month but my other cat, Hatter, doesnt have any symptoms. Her ears are very clean and she doesn't itch her ears.
It sounds like Hatters are resolved. Not all cats will get them, but they can pass them around.
I would just talk to your vet and see if they can dispense Milbemite for you. That should take care of this and they shouldn't have an issue.