[Intraorbital pressure measured before, during, and after surgical decompression in Graves' orbitopathy].

PURPOSE

In Graves' orbitopathy, the volumetric increase of the oculomotor muscles and orbital fat leads to exophthalmia and a rise in orbital pressure. This rise in pressure may be implicated in the appearance of a compressive optic neuropathy. To investigate this increase in pressure and its variations accompanying surgical decompression, systematic measurements were taken before, during, and after every case of orbital decompression in Graves' disease.

RESULTS

The intraorbital pressure before the surgical procedure was 14.05 mmHg ± 9.19 for a normal value estimated in the literature at 4 mmHg ± 1.5 (statistically significant difference, P<0.0001). In the group presenting a compressive optic neuropathy (NO), the preoperative pressure was 26.8 mmHg ± 7.85 versus 9.8 mmHg ± 4.2 in the group without NO: the pressure was significantly higher in the group with NO (P<0.001). After orbital decompression (one to three walls depending on the severity of the exophthalmia), the pressure was measured at 4.3 mmHg ± 2.53 for the entire series: 6.4 mmHg ± 2.07 in the group with NO versus 3.6 mmHg ± 2.32 in the group without NO (significant difference, P<0.05). The total decrease in pressure induced by the surgery was 9.75 mmHg ± 7.55 and was significantly greater for the group with NO: reduction of 20.4 mmHg versus 6.2 mmHg for the group without NO (P<0.001). The reduction in pressure was greater after collapse of the first wall (floor) than after collapse of following walls for all groups (P<0.001). The maximum pressure observed during the intervention (caused by the instruments) was measured at 78.3 mmHg ± 23.47 without pupillary changes.

DISCUSSION

This study shows that the intraorbital pressure is increased in Graves' orbitopathy and more in serious forms with compressive optic neuropathy. Orbital decompression, as its name indicates, provides decompression and a return to a near-normal orbital pressure situation. Compressive optic neuropathy does not result only from the direct compression of the oculomotor muscles on the optic nerve, but also from an overall rise in the pressure level within the orbital cavity.

CONCLUSION

Intraorbital pressure is increased in Graves' orbitopathy, participating in the appearance of compressive optic neuropathy. Orbital decompression provides a significant reduction in intraorbital pressure.