Sir (Nicholas) Harold (Lloyd) Ridley (10 July 1906, Kibworth Harcourt, Leicestershire – 25 May 2001, Salisbury, Wiltshire) was a British ophthalmologist who pioneered artificial intraocular lens transplant surgery for cataract patients.

He was educated at Charterhouse School, Pembroke College, Cambridge and St Thomas' Hospital, London, and worked as a surgeon at Moorfields Eye Hospital and St Thomas' Hospital in London, specialising in ophthalmology.

Whilst working with RAF 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, 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.

He 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 for use in the USA by the Food and Drug Administration in 1981. It is now the commonest type of eye surgery.

Harold Ridley also led important research into onchocerciasis. He was a Fellow of the Royal College of Surgeons and a Fellow of the Royal Society. In 2001 he received a knighthood for his services to medicine.