Create an activity diagram and a set of detail use-case descriptions for the process of buying glasses from the viewpoint of the patient, but do not bother to identify the flow of events within each use case. The first step is to see an eye doctor who will give you a prescription.

Once you have a prescription, you go to a optical dispensary, where you select your frames and place the order for your glasses. Once the glasses have been made, you return to the store for a fitting and pay for the glasses.