Whilst working with Royal Air Force casualties during World War II, Ridley noticed that when splinters of perspex from aircraft cockpit canopies became lodged in the eyes of wounded pilots, they did not trigger rejection, leading him to propose the use of artificial lenses in the eye to correct cases of cataracts.
He had a lens manufactured using an identical plastic – Perspex CQ made by ICI – and on 29 November 1949 at St Thomas' Hospital, Harold Ridley achieved the first implant of an intraocular lens, although it was not until 1950 that he left an artificial lens permanently in place in an eye. The first lens was manufactured by the Rayner company of Brighton & Hove, East Sussex, a company which continues to manufacture and market modern, small-incision versions of these lenses today.
In 1952 the first IOL implant was performed in the United States, a Ridley-Rayner lens implanted at the Wills Eye Hospital in Philadelphia.
Ridley went on to develop comprehensive programmes for cataract surgery with intraocular implants and pioneered this treatment in the face of prolonged strong opposition from the medical community. He worked hard to overcome complications, and had refined the technique by the late 1960s. With his pupil Peter Choyce he eventually achieved worldwide support for the technique, and the intraocular lens was finally approved as "safe and effective" and approved for use in the USA by the Food and Drug Administration in 1981. These first FDA approved lenses, (Choyce Mark VIII and Choyce Mark IX Anterior Chamber lenses) were manufactured by Rayner. Cataract extraction surgery with intracocular lens implantation is now the commonest type of eye surgery.
Ridley retired from NHS hospital service in 1971 and received many awards over the next 29 years. He was a Fellow of the Royal College of Surgeons and a Fellow of the Royal Society. In February 2000, Harold Ridley was knighted by HM Queen Elizabeth II at Buckingham Palace in London.