Intraocular Pressure Lowering Effect of Orbital Decompression is Related to Increased Venous Outflow in Graves Orbitopathy

Abstract

Purpose: To investigate the effects of combined orbital bone and fat decompression on intraocular pressure (IOP) and superior ophthalmic vein blood flow velocity (SOV-BFV), and their association with the clinical features of Graves orbitopathy (GO). Methods: During the 2002-2008 period, 72 eyes of 36 GO cases demonstrating moderate to severe orbitopathy were evaluated according to their clinical features as: cases with or without dysthyroid optic neuropathy (DON), and underwent orbital decompression. A control group comprised 40 eyes of 20 healthy subjects. In both groups, a full ophthalmic examination including IOP and Hertel measurements was performed, and SOV-BFV was analyzed with color Doppler imaging. Examinations were repeated after orbital decompression in GO patients. Results: All the cases demonstrated clinical features of inactive disease. Among the patients 24 of 72 eyes (33.3%) showed clinical features of DON. After surgery, the mean decrease in Hertel values was 6.2 +/- 1.8mm (p = 0.001). The mean decrease in IOP was 3.0 +/- 1.7mmHg (from 17.3 +/- 2.7 to 14.3 +/- 2.0mmHg) after orbital decompression where the post-operative values were comparable with the control group (12.9 +/- 1.4mmHg, p = 0.36). The mean increase in SOV-BFV achieved with decompression was 1.2 +/- 0.6 cm/s (from 4.8 +/- 1.7 to 6.0 +/- 1.8 cm/s) and post-operative SOV-BFV values were also comparable with the control group (6.6 +/- 1.3 cm/s, p = 0.26). The increase in SOV-BFV in cases with DON did not differ from cases without DON (p = 0.32), however, post-operative SOV-BFV of cases with DON was stil lower than cases without DON (p = 0.035). Conclusions: Combined orbital bone and fat decompression significantly reduced the IOP levels and increased the SOV-BFV in GO. This could be the confirmative finding of prediction that elevated IOP in GO is associated with increased episcleral venous pressure. The post-operative changes in IOP and SOV-BFV show differences regarding the clinical features of disease.