Cal. Bus. & Prof. Code § 2559.1

On and after January 1, 1988, no individual may fit and adjust spectacle lenses unless the registration requirement of Section 2550 is complied with, and unless (1) the individual is a duly registered spectacle lens dispenser as provided in Section 2559.2 or (2) the individual performs the fitting and adjusting under the direct responsibility and supervision of a duly registered spectacle lens dispenser whose certificate of registration is then conspicuously and prominently displayed on the premises. A supervising registered dispenser shall be on the registered premises when an unregistered technician fits and adjusts spectacle lenses, allowing for usual and customary absences including illness and vacation.