Julie Fitzgerald had been worried about strange spots on her 2-year-old's eye, but she initially brushed them off.
But then she saw viral story on Facebook about how a white glow that appeared someone's eye in photos could signal cancer. So she decided to snap a photo of Avery.
And there it was, the white glow.
"I just had this gut feeling in my stomach that something was wrong with his eye," Fitzgerald told ABC News.
Doctors diagnosed Avery with retinoblastoma and said cancerous tumors covered 75 percent of his eye, she said. They had to removed it entirely, but they said they caught the cancer just in time, Fitzgerald said.
"If we did not get this eye out, the cancer would spread to his blood and to his brain," Fitzgerald said. "Our lives went from normal to cancer to a cancer survivor in three weeks. It turned out to be our worst nightmare but it saved our son's life."
Last month, Joanna Murphy caught the rare cancer after noticing a white glow in her daughter's eye. And Tara Taylor's Facebook friend noticed a glow in her daughter's eye, prompting the diagnosis of another rare eye disease.
"It is a medical emergency," said Dr. Richard Besser, ABC News chief health and medical editor. "You need to see your doctor right away. It may be retinoblastoma. But if you miss that sign, it is usually fatal."