"Where did you get that ring?" asked the girls in my class. It's not often that a medical device, worn by a teacher, is considered cool by the students!
This ring is used to prevent "Swan Neck Deformity," a condition where the joint nearest the fingertip curves towards the palm and the joint closest to the palm bends away from it.
Your occupational therapist can make them. I had mine made by Marilyn of Cygnet Orthotics.
If you do get one of these rings, I have a word of caution. Take care when you are working with your hands - it can easily slip off your finger without your knowledge. I lost one of mine when I was at the mall, carrying a shopping bag. Miraculously, I found it in the parking lot!
Warning! If you are squeamish, do not watch the following Youtube video. It shows an extreme case of Swan Neck Deformity.