Born in Calabar, Nigeria; Hannah received the Fellowship of the Royal College of Surgeons of Edinburgh in 1975 before relocating to The Gambia in 1980 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 recognised 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 Nigeria. She is also currently Trustee of the Moorfields Korle Bu Trust, member Scientific Advisory Board of the Queen Elizabeth Diamond Jubilee Trust, Global Advisory Board of Our Children’s Vision and chairs the Africa Research Vision Institute.