Sohan S Hayreh, professor of ophthalmology at the University of Iowa, was best known for his work on the vascular circulation of the visual system and vascular diseases of the eye and optic nerve. He made profound contributions to the understanding of vascular eye diseases and received many honours. Sohan Hayreh was born on 6 November 1927 in Littran, a small farming village in Punjab, India. With the encouragement of his parents, Surjit Singh, who was in the Army, and Balwant Kaur Hayreh née Kandola, a housewife, he completed elementary and high school and was admitted to King Edward Medical College in Lahore, India in 1946. Due to the Partition of India, he was forced to move to Punjab Medical College in Amristar, where he earned his MB BS in 1951 and his masters degree in 1959. As he began his surgical residency in January 1952, the financial stability of the people of India was uncertain as a result of Partition. He left his residency and served as a medical officer in the Indian Army Medical Corps. In 1955, Hayreh left his Army position and obtained a faculty position in the anatomy department of the new Government Medical College in Patiala, India. He did extensive research on the anatomy of the vasculature of the eye, optic nerve and orbit. This research was published in the *British Journal of Ophthalmology*. He wished to continue research on the pathogenesis of optic disc oedema in elevated intracranial pressure, however, funds were not available for continued research in India at that time. Hayreh applied for and was awarded the prestigious three-year Beit Memorial Research Fellowship for Medical Research in 1961. He moved to London and worked with Sir Stewart Duke-Elder at the Institute of Ophthalmology at the University of London until 1964. The research was the basis for his PhD from the University of London, awarded in 1965. In order to continue in British ophthalmology academia, Hayreh spent one year as a senior house officer at Birmingham and Midland Eye Hospital. He returned to the Institute of Ophthalmology and Moorfields Eye Hospital in London as a lecturer in clinical ophthalmology and research in 1965. In London, Hayreh extensively used the new technique of fluorescein fundus angiography in clinical and experimental research with the *in vivo* blood supply of the optic disc and glaucoma. In 1969, Hayreh passed the examinations for the fellowships of the Royal College of Surgeons of Edinburgh and the Royal College of Surgeons of England. That year he moved to the University of Edinburgh as a senior lecturer in ophthalmology and a consultant ophthalmologist to the Royal Infirmary of Edinburgh. At the university, he built his own research facility with a research grant from the Medical Research Council. In 1972, Hayreh sent a letter to Frederick C Blodi, head of the department of ophthalmology at the University of Iowa, to learn more about ophthalmology in America. He had met Blodi at European and British meetings. Blodi replied with an offer for Hayreh to join the department and in January 1973, Hayreh and his family moved to Iowa City. During his tenure in Iowa, Hayreh concentrated on ocular vascular disorders and optic nerve disorders (including glaucoma) in clinical practice and research. He also maintained interest in scleritis, episcleritis, uveitis and cataract. With research grants from the National Institutes of Health for clinical and experimental research, he was able to set up an ocular vascular experimental laboratory and an ocular vascular clinic for research and clinical projects. After prior work and friendship with Edward S Perkins at the Institute of Ophthalmology in London, Hayreh strongly recommended him to Blodi. In 1979, Perkins was invited to join the faculty as a professor. In recognition for his research, Hayreh was awarded the degree of doctor of science by the University of London in 1987. His research, ‘Ocular circulation in health and disease: optic nerve disorders’, was judged as a high standard and awarded Hayreh an authoritative place in ophthalmology. Hayreh assumed emeritus professor status at the University of Iowa in 1999. He died on 29 September 2022 in Maine at the age of 94 from complications of covid-19. He was survived by his wife, Shelagh, two sons, Davindar and Ravindar, and three grandchildren. Sohan S Hayreh continues to be recognized as a world authority on ocular and optic nerve circulation, vascular disorders of the eye, giant cell arteritis and other topics.