Direct orbital manometry in healthy patients

Purpose: To determine orbital tissue tension and orbital compartment compli ance in normal patients. Methods: An orbital manometer was designed to directly measure orbital tiss ue tension before, during, and after a 5-ml retrobulbar injection of anesth etic in patients undergoing ocular surgery. Tissue tension was recorded for 5 minutes after the injection. Orbital compliance was calculated as change in volume divided by change in pressure. Data were collected from 18 norma l orbits. Results: Resting orbital tissue tension was 4.0 +/- 1.5 mmHg (mean +/- stan dard deviation). After retrobulbar injection, orbital tissue tension rose t o 11.6 +/- 2.6 mmHg (p = 0.00000000009 compared with baseline). After 5 min utes, tissue tension declined to 6.6 +/- 1.9 mmHg (p = 0.00000001 compared with preinjection and p = 0.00002 compared with postinjection). Orbital com partment compliance was 0.74 +/- 0.31 ml/mmHg. No adverse events occurred. Conclusions: The authors' orbital manometer safely determined orbital tissu e tension and orbital compartment compliance in normal orbits. Retrobulbar injection causes consistent measurable changes in orbital tissue tension. D irectly assessing orbital dynamics in vivo may prove useful both as an adju nct in the clinical evaluation of patients with disorders resulting in an o rbital compartment syndrome as well as in assessing the risk of retrobulbar injection in orbits at greater risk for complications from this procedure.