To classify the severity of the condition, the interorbital distance is used. This is the distance measured between the two dacryon.
The dacryon is the junction of the lacrimal bone, the frontal process of the maxilla and the frontal bone.
Adults The average adult interorbital distance is 25 mm in women and 28 mm in men. When accounting for the soft tissue, the intercanthal distance as measured is typically 4-6 mm greater than the bony distance.
Tessier classified orbital hypertelorism based on the interorbital distance:
1st degree: 30-34 mm 2nd degree: 34-40 mm 3rd degree: >40 mm
Children In children the severity grading is based on age and gender matched norms.
Average interorbital distance (mm)
The classification of orbital hypertelorism is then defined be the deviation from the norm.
1st degree: 2 to 4 mm deviation 2nd degree: 4.1 to 8 mm deviation 3rd degree: > 8 mm deviation