OKLAHOMA CITY (REUTERS) - A former third-grade teacher in Oklahoma was sentenced to 45 years in prison on Friday for taking lewd photos of her young students at the behest of a retired college professor.

Kimberly Crain pleaded guilty to 19 counts of sexual exploitation of a child under 12, possessing child pornography and lewd molestation, according to District Attorney Richard Smothermon.

Crain blamed much of her actions on retired Pennsylvania college professor Gary Doby, whom she described as an "online love interest" who urged her to provide him photos of her students at the grade school in McLoud, a small town 48.3km east of Oklahoma City.

Doby, 66, who had met Crain in the 1970s when he taught at Oklahoma Baptist University, was sentenced to life in prison in January.

In a letter to the court, Crain also cited depression, menopause and an inattentive husband for her actions.

Crain, 50, will not be eligible for parole until she is 87 because she must serve 85 per cent of her sentence, said Mr Smothermon.

"This literally shook the community to its core," Mr Smothermon said. "She was trusted and beloved by the community."