The effect of mydriasis and filtration surgery on intraocular pressure in eyes with normal- tension glaucoma

Background:The effect of mydriasis on intraocular pressure (IOP) in normal tension glaucoma (NTG) eyes has not been investigated. In addition, although filtration surgery is a technique that can lower IOP under normal conditions and reduce IOP fluctuation, its effect on IOP after mydriasis is unknown. Against this background, we investigated the effect of mydriasis on IOP and of trabeculectomy on mydriasis-induced IOP fluctuations in the same patients with NTG.Methods:We identified data for NTG patients regularly monitored for more than 5 years before and after surgical periods. All patients were conservatively followed up as medical treatment and then underwent initial trabeculectomy with mitomycin C as the surgical treatment. The mean IOPs during episodes of mydriasis and non-mydriasis were calculated for each period. IOP fluctuation was defined as the IOP difference between the mydriatic and non-mydriatic states. For both periods, the mean IOP differences between the mydriatic and non-mydriatic eye were separately evaluated using the paired t-test or the Wilcoxon signed-rank test.Results:We included 23 eyes of 23 patients with NTG (mean age, 62.4 years). The follow-up periods were 5.7 years for medical treatment and 6.1 years after surgical treatment. The mean IOP of 14.3 mmHg decreased to 9.0 mmHg after surgery (P < 0.01). During medical treatment, the mean (± standard deviation) non-mydriatic and mydriatic IOPs were 14.2 ± 1.8 and 14.5 ± 1.8 mmHg, respectively. The IOP increased significantly after mydriasis (by 0.30 ± 0.11 mmHg, P = 0.009). After surgery, the mean non-mydriatic and mydriatic IOPs were 9.0 ± 2.5 and 9.1 ± 2.4 mmHg; the difference was 0.18 ± 0.16 mmHg (P = 0.28). Conclusions:We demonstrated for the first time that pharmacological mydriasis significantly increased IOP, but trabeculectomy could suppress not only IOP but also mydriasis-induced IOP fluctuations in patients with NTG.