He was Assistant and subsequently Associate Professor of Ophthalmology under Morton F. Goldberg, MD at The University of Illinois Eye and Ear Infirmary and Abraham Lincoln School of Medicine in Chicago from 1971 to 1975.
He held the Pawek-Vallotton Chair of Biomedical Engineering and was Director of the Center or Research on Ocular Therapeutics and Biodevices until 2002.
During his Chairmanship of the Department of Ophthalmology in Charleston from 1988 to 1996 he successfully led the effort to raise $8.8 million to complete a three-floor expansion and general renovation of the Eye Institute.
His laboratory in Charleston (and at later sites: Salt Lake City, Sullivan's Island and Heidelberg) was an official Collaborating Center of the WHO Prevention of Blindness Programme.
His meeting with WHO Programme director Dr. Bjorn Thylefors of the Prevent Blindness Division, was instrumental in providing information to WHO on which type of IOL should be used in cataract surgery in developing countries[2] and Apple wrote on the subject in 1991.
He received the Senior Honor Award from the American Academy of Ophthalmology (AAO) in San Diego, CA.
He also taught us to be cautious with the latest innovation, and to study the long-term effects of each new IOL or gadget, before fully accepting it.In Salt Lake City during the 1980s, Apple started to study intraocular lenses (IOLs), including those explanted lenses which had been removed (explanted) from the eye, following complications.
His scientific papers on IOLs[10][11] attracted the interest of Harold Ridley, the British inventor of the intraocular lens.
Between 1999 and 2011 he had numerous bouts of pneumonia and was frequently hospitalised – most seriously with a cerebral vascular stroke two years after his move to Salt Lake City.
He liked to inform ophthalmologists that Johann Sebastian Bach died shortly after his health began to deteriorate as a result of a botched cataract surgery by an itinerant surgeon.
David reminded us that the first hostilities of the Civil War took place in Charleston, his home, with the Confederate bombardment of Fort Sumter.
He was pleased that his home was the model for one of the houses on Catfish Row, the stage setting for the American opera "Porgy and Bess."
Ann nurtured, maintained, and cared for him magnificently over the ensuing years as he dealt with the chronic pain and the terrible side effects of his surgery and anti-cancer treatments.
This method of sectioning the cadaver eye was initially developed by Kansatu Miyake MD and refined by David Apple.
Both Amon and Apple recognised in 2002 (through respectively a laboratory study on Centerflex minus power lenses and a clinical study of the regular power Centerflex lenses[17] ) that all modern single-piece, injectable IOLs in 2002 had a weakness (which Apple termed the "Achilles heel") at the haptic-optic junction: where there is no square edge and thus an incomplete barrier to PCO.