Horners Syndrome in Goldens

My almost 10 year old male golden retriever’s eye looks like this right now. It came on suddenly yesterday after playing rough with his brother. He is eating and drinking fine and doesn’t appear to have any discomfort or extra drool. The vet said it is Idiopathic Horners Syndrome and gave him some drops. The vet said it was probably brought on from him playing rough and having nerve damage in his neck. Apparently Goldens are more prone to this which I had no idea.

My question is for other dog parents whose Goldens have had this - how long did it take to heal? I feel so bad for him even though he’s his normal happy self and it’s not bothering him. I’m just curious on others heal times. The vet said it could be a couple months.