Yes, most sunglasses, including the Oakley sunglasses, are designed to fit the average face width. Sunglasses should fit snugly on your face but if your face is narrow they may not fit correctly, then I think you have known the result: your Oakley sunglasses will slip down from your nose. Of course, there must be some ways to solve if there is some problem. The first and easiest way for you is that you can take your Oakley to the shop where you bought it, and the pros will help you make it fit you and your face. Then if you want to do it by yourself, following is some steps for you. First of all, you can insert a mini screwdriver into the screw hinges, which will tight the frame of the sunglasses. Meanwhile, you can adjust the nose pads of the sunglasses to make the sunglasses fit you better. The ways above will help you adjust your Oakley sunglasses to fit you. Good luck.
