He was appointed an assistant in the Department of Physiology at University College London and practised medicine for several years in Finchley. He then became a clinical assistant at Moorfields Eye Hospital. In 1900 he received the MB London and the FRCS England. At Moorfields, he was promoted from clinical assistant and became, successively, curator and librarian and was then elected to the surgical staff in 1904. He became an ophthalmic surgeon at University College Hospital and continued as a surgeon there and at Moorfields until his retirement. He was also an ophthalmic surgeon for some years at the Hospital for Sick Children, Great Ormond Street. In ophthalmic pathology he became a world authority and produced numerous research articles and several books on eye diseases, ophthalmic optics. and ophthalmic circulation.
... His most popular work, which maintained an immense circulation all through his working life, was his Diseases of the Eye, an excellent, comprehensive and uniquely compact manual for students and practitioners which first appeared in 1907 and continually demanded new editions. But his first classical work was his monumental treatise The Pathology of the Eye, which appeared in four volumes (1904–8). As curator at Moorfields he had grounded himself well in pathology, and in this great work ophthalmic pathology was for the first time integrated into a self-contained discipline. ...[3]
Parsons served on various government committees dealing with vision tests, blindness prevention, and proper lighting in factories. During World War I he was a consultant ophthalmological surgeon with the rank of Colonel, Army Medical Service, for which he was awarded Commander of the Order of the British Empire (CBE) in the 1919 Birthday Honours. From 1928 to 1932 he was a member of the Medical Research Council.
... One of the band of great clinical leaders who retained for ophthalmology in this country at the end of the last and the beginning of the present century the proud position it inherited fifty years previously from Sir William Bowman—Nettleship, Doyne, Gunn, Collins, Fisher, Lawford, Paton, and others—he outstripped them all in intellectual brilliance and force of character. ... Alone among them he realized that advances in ophthalmology did not lie solely in the clinic or in the pathological laboratory, that a new age was emerging wherein clinical pictures were to be interpreted in terms of physiology, physics, and chemistry; and he had the energy and ability to follow out his convictions. ...[3]
