Under Regulation 19 of the Optometrists and Opticians (Registration and Practising Certificates) Regulations, the Board may cancel the registration of a registered person if he has not renewed his PC for a continuous period of not less than 5 years, and that he has no address in Singapore which he could be contacted.

For practitioners who have received "Notice of Cancellation of Registration with OOB", please to this link for more details.