(a) No optical glasses or kindred products or other instruments to aid vision that are produced or reproduced to personalized given formulas, or plano cosmetic contact lenses shall be sold at retail except under the direct supervision of a licensed optician and in a registered optical establishment, office or store. An optical establishment, office or store is defined as meaning one the owner of which has had issued to him an optical license selling permit.
(b) Notwithstanding the provisions of subsection (a) of this section, an optical establishment, office or store, registered with the Department of Public Health pursuant to section 20-151 , may remain open to the public during regular business hours without the supervision of a licensed optician for a period of time not to exceed four consecutive business days (1) in the event of reasonably unanticipated circumstances, including, but not limited to, the licensed optician's illness, injury, family emergency, or termination or resignation from the optical establishment, office or store; (2) if reasonable action is taken to have another licensed optician present at the establishment, office or store during regular business hours; and (3) the optical establishment, office or store posts clear and conspicuous signage that a licensed optician is not on site. The sign shall state: