BOSTON — The surgeon held a translucent white plastic eye socket in each hand. Gently moving them away from each other, Dr. John Meara showed the distance between Violet Pietrok’s eyes at birth. He slid the sockets closer to demonstrate their positions 19 months later, after he had operated on her.

Violet, now nearly 2, was born with a rare defect called a Tessier facial cleft. Her dark brown eyes were set so far apart, her mother says, that her vision was more like a bird of prey’s than a person’s. A large growth bloomed over her left eye. She had no cartilage in her nose. The bones that normally join to form the fetal face had not fused properly.

Her parents, Alicia Taylor and Matt Pietrok, sought out Dr. Meara at Boston Children’s Hospital, thousands of miles from their home in Oregon, because the plastic surgeon had performed four similar operations in the previous three years.

Before he operated on Violet, Dr. Meara wanted a more precise understanding of her bone structure than he could get from an image on a screen. So he asked his colleague Dr. Peter Weinstock to print him a three-dimensional model of Violet’s skull, based on magnetic resonance imaging pictures.