Space-occupying orbital lesions: can critical increases in intraorbital pressure be predicted clinically?

Thirteen cadaver orbits were studied to determine whether noninvasive clinical measurements of globe excursion could be used to predict intraorbital pressure. Intraorbital pressure measurements, exophthalmometry, and orbitonometry (which measures resistance to globe retrodisplacement) were performed at 1-ml increments to 12 ml of added orbital volume. Orbitonometry, performed with forces of 100, 200, and 300 g, yielded both E (global position) and Y (retrodisplacement) values. Plots of orbital pressure against percentage of excursion, a function of orbital retrodisplacement (that is, orbital pressure versus [(E0 - E300)/E0] x 100), for 131 paired values over all orbits yielded a function with low percentage of excursion values associated with high intraorbital pressures. This relationship reflected both the proptosis and the increased orbital tension produced by added volumes. Comparison of clinical orbitonometry data with such experimental data may allow predictions about which patients are threatened by critical intraorbital pressure levels and may benefit from orbital decompression surgery to preserve vision.