Objective: Developed an objective, stable horizontal reference plane that was not affected by craniofacial deformities or bad posture to serve as a foundation for determining head position during cephalometric analysis.

Materials and methods: The study recruited a total of 30 patients (M:F; 15:15) with the mean age of 24.3 years. The head position assessed in this study including: (1) the ortho-ophthalmic determinated head position; (2) the estimated head position. All lateral cephalometric recording was performed. The angles between the S–N and the horizontal lines through the four head position were measured.

Results: The ortho-ophthalmic determinated head position was fairly constant. And the variance of the ortho-ophthalmic determinated head position was still significantly less than the variance of intracranial reference planes to the horizontal. Through the correct procedure, cephalometric analysis based on the ortho-ophthalmic determinated head position therefore remains valid.

Conclusion: (1) The true horizontal line passing through the ortho-ophthalmic head position is an extremely reliable horizontal reference line. (2) The ortho-ophthalmic head position can serve as a reference for head position in radiographic cephalometry. (3) Long-term reproducibility of the ortho-ophthalmic head position remain to be explored in future studies.