Leroy Hoeck, 97, a Washington pediatrician who helped solve one of the great medical mysteries of the postwar era, died May 25 at a retirement home in Salisbury, Md. He had arteriosclerotic cardiovascular disease.

Hoeck (pronounced Hake) was a staff member at the District of Columbia’s public hospital when he teamed up with a physician still in training to figure out why an unusual number of premature infants were becoming blind after prolonged stays in the newborn nursery. Their hunch that supplemental oxygen might be the cause turned out to be correct. But they had to prove it.

They did so in a randomized, controlled trial, the first in ophthalmology, that ran from 1951 to 1953 at Gallinger Municipal Hospital, the huge institution in Washington that was later renamed D.C. General.

That a pair of unknown researchers could show that a substance as beneficial as oxygen could cause a condition as devastating as blindness was so surprising that the pediatric medical establishment repeated the experiment on a huge scale to confirm the findings.

Nevertheless, the initial clinical trial at Gallinger was crucial to showing the importance of testing medical therapies — even those as seemingly beneficial as extra oxygen — with randomized trials.

“Doctors have to approach their patients, and what they think they know, with a certain amount of humility,” said Steven Goodman, a physician at Johns Hopkins University’s Bloomberg School of Public Health and an expert on the history of medical research. “This is one of the trials that taught us humility.”

Hoeck’s partner in the study, Arnall Patz, went on to become chairman of ophthalmology at Johns Hopkins Hospital and winner of the prestigious Lasker Award for his research on retrolental fibroplasia, as the eye damage was then called.

Hoeck, in contrast, became a private practitioner after he left Gallinger in 1954. He had an office in his home in the Prince George’s County, Md. He then joined two other pediatricians at an office in Clinton, Md. He retired in 1990.

His role in the pivotal oxygen trial is largely forgotten, although Patz has credited him with having the initial suspicion that oxygen was the culprit in the mysterious blindings.