Orbital compartment syndrome. Direct measurement of orbital tissue pressure: 1. Technique. Many disorders of the orbit produce an increase in intraorbital pressure, which may result in the development of an orbital compartment syndrome and visual loss. Traditionally, orbital tension is assessed clinically by indirect means based on retrodisplacement of the globe. The authors describe their experience with the "slit-catheter" technique for direct tissue pressure measurement as applied to the orbit. The preliminary results indicate that normal orbital pressure ranges from 3.0 to 6.0 mm Hg. In patients with Graves' orbitopathy the values ranged from 7.0 to 15.0 mm Hg. The results suggest that the technique may have many exciting possibilities as a clinical research tool in orbital disease, and its use will result in better understanding of orbital compartment syndromes. 