Graves' exophthalmos: Volumetric assessment of orbital expansion.

INTRODUCTION Graves' ophthalmopathy is characterized by an increase in the volume of orbital soft tissue contents and an associated increase in intraorbital pressure. Surgical expansion of bony orbital volume is therefore an effective method of treating moderate to severe exophthalmos. Numerous correlations between specific decompression procedures and reduction of proptosis have been made. The main emphasis of the majority of these studies, however, appears to be of a qualitative nature rather than quantitative. OBJECTIVES To quantitatively examine the consequences of surgical orbital decompression in the treatment of severe Graves' exophthalmos, with respect to changes in ocular globe projection and orbital soft tissue and bony volume. MATERIAL AND METHODS A series of three patients (five orbits) with severe exophthalmos were evaluated. All patients were operated on by a single surgeon using a standard technique of orbitozygmatic osteotomy in conjunction with three-wall orbital decompression and release of periorbita. Data obtained from standardized preoperative and three-month postoperative computed tomography scans were transferred to an offline computer workstation. Scalar and volumetric parameters were quantitatively analyzed to determine changes in globe projection in relation to intraorbital volume differences. RESULTS Following surgery, mean globe retrodisplacement from the lateral orbital rim and from the optic foramen were 6.7 mm and 3.3 mm, respectively. Osteotomy and decompression were effective in producing an 18.6% increase in bony orbital volume. However, the volume of intraorbital soft tissues increased substantially following surgery, with a 23.4% increase in orbital fat volume and a 12.2% increase in neurovascular tissue volume. CONCLUSIONS The degree of globe retrodisplacement achieved by surgical expansion of the bony orbital cavity in patients with Graves' ophthalmopathy may be less than anticipated, due to a post-operative increase in the intraorbital soft tissue volumes.