Recall is the engine. A patient due in two years is a booking that happens almost automatically if the reminder goes out in the right month, and simply does not happen if it does not.
Dispensing carries on after the patient has gone. The lens order, the glazing, the fitting appointment and the collection are a small project, and the patient who has heard nothing for ten days assumes something went wrong.
Contact lens plans are subscriptions with a clinical obligation. Payment, delivery and an aftercare check that has to happen: missing the check is both a professional problem and the usual reason somebody cancels.
Clinical records outlive careers. Prescriptions, images and notes have to be retrievable years later by somebody who did not perform the examination, which is a records problem rather than a memory one.