The certificate is valid for 2 years. In addition, drivers with specific medical conditions require more frequent certification:
Hypertension (high blood pressure) stable on treatment 1 year
Heart disease 1 year
Qualified under 391.64 the original diabetes and vision waiver program 1 year
New insulin and vision exemption program 1 year
Driving in exempt intra-city zone 1 year
Determination by examiner that condition requires more frequent monitoring, such as diabetes mellitus or sleep disorders.