Decrease in intraocular pressure after orbital decompression for thyroid orbitopathy

Purpose. To determine the effect of orbital decompression surgery (DS) on the intraocular pressure (IOP) in patients with thyroid orbitopathy (TO).Methods. The records of 23 eyes from 15 patients that underwent DS for TO at our institution between 1985 and 1994, were retrospectively analyzed. Applanation IOP in primary gaze from preop and postop visits were recorded and net change calculated. Surgical indications included optic nerve compression, diplopia, corneal exposure and disfiguring proptosis. All patients were maintained on essentially the same medications pre- and postop. Four eyes were excluded, 3 for lack of timely followup and 1 for chronic prednisone use preop that was not continued postop. Results. Mean preop (3 weeks) and postop (3 months) IOPs were 19.7 and 16.9 mm Hg, respectively. The mean difference in IOP was 2.7, which was statistically significant (p=.04, using a test that corrects for correlation between the two eyes of individual subjects). All 7 eyes with elevated preop IOPs (≥21) had normal postop IOPs (<21), with a mean drop of 6.1 mm Hg.The 7 eyes in the nerve compression subgroup had a mean drop of 3.9, as compared to a 2.2 mm Hg drop in the group without compression. Conclusions. Thyroid orbitopathy is a chronic disorder that may lead to orbital venous congestion, increased episcleral venous pressure (EVP), and therefore elevated IOP. DS decreases venous congestion, and hence would be expected to reduce EVP and IOP. The results of this analysis show that DS significantly reduces IOP, suggesting that EVP contributes to preop IOP in patients with TO. Patients with elevated preop IOP (≥21) and those with acute nerve compression may represent groups with larger IOP drops after DS.