Radiographic exophthalmometry is based on the simultaneous exposure of a radiograph and a photograph. The fixed reference point for both eyes is the tuberculum sellae, which is a midline structure. Eye position is correlated with skull size and race to provide a sensitive detection of exophthalmos. A statistically significant difference in the position of the eyes in US black and white people has been found to exist. No difference in the position of left or right eyes has been found in either US black or white people.