Born in Calabar, Nigeria; Hannah had her basic medical training in Nigeria. Subsequently she received the Fellowship of the Royal College of Surgeons of Edinburgh in 1975. She is also a Fellow of the West African College of Surgeons.
In 1980 Hannah relocated to The Gambia with her family to work as the sole ophthalmologist, serving a population then of 800,000. She initiated the concept of comprehensive national eye care programming resulting in a fall in the prevalence of blindness from 0.7% to 0.4% between 1986-1996.
Hannah is internationally recognized as one of the founders of the VISION 2020 initiative and served as President of the International Agency for the Prevention of Blindness (IAPB) from 1999-2004. Hannah has also served as an advisor to the Prevention of Blindness programme of the World Health Organization (WHO), contributing to the focus on refractive error, low vision services and inclusive education. Active in research, she has authored over 60 publications with over 2000 citations and is a reviewer for journals.
On retirement in 2011, Hannah took on an adjunct professorship in international eye health in the University of Calabar, Nigeria.