New insights into facial anthropometry in digital photographs using iris dependent calibration

Background: In facial and reconstructive surgery objective assessment of anatomy is crucial to evaluate surgical results. Photographic computer-assisted anthropometry substitutes clinical measurements. The constancy of the horizontal iris diameter (IDh) allows iris dependent calibration of photographs, replacing the need for a scale. Methods: We performed a prospective cohort study to assess the constancy of the IDh in children. Frontal and close-up digital photographs of the eyes were taken of 100 children aged 5-18 years. The IDh was measured twice; once with a scale positioned on the forehead (IDh*forehead) and once with a scale positioned next to the tragus (IDh*ear). Results: Our data confirms the constancy of the IDh in children from the age of 5, with a mean IDh*forehead of 11.22 ± 0.52 mm. We found no difference between gender and no variation with age. For structures that are not in the same coronal plane as the iris, an adjusted iris diameter is needed to compensate for the difference in distance from the camera. Conclusion: We confirm the reliability of iris dependent calibration in frontal photographs from the age of 5. This technique allows evaluation of a wide variety of pre-existing photographs that do not have a scale included, simplifies photographic conditions and facilitates long-term follow-up.

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