There are a number of reasons why your blind cat might walk in circles. One possibility is that he's trying to orient himself and figure out his surroundings. Another possibility is that he's uncomfortable or anxious and is walking around to try and calm himself down. If you think your cat might be walking in circles because he's blind, you can try to help him by providing a lot of stimulation in his environment (including lots of different textures and smells), helping him get accustomed to his surroundings, and providing plenty of positive reinforcement when he behaves in a way that you want him to.