Ocular Translation Due to Gravitational Acceleration

In supine position, gravity causes enophthalmos: a 0.73 to 0.85 mm shift in anteroposterior eye position that is significant relative to intraorbital optic nerve length. When in lateral decubitus position, the higher (upward) eye shifts nasally and anteriorly, so its translation is oblique to the orbital axis. The lower (downward) tilted eye shifts temporally and anteriorly along the orbital axis. Thus, the lower eye translation elongates the nerve by about threefold more than for the upper eye. Gravity therefore has an effect on the human eye that should be considered when modeling the effect of eye rotation on the mechanical state of the optic nerve and other orbital tissues.