The results of the is study demonstrated that Ex-Press surgery significantly decrease the IOP and the number of postoperative glaucoma medications in patients with glaucoma. After 3 years of follow-up, the mean postoperative IOP values were 11.3 mmHg in the POAG group and 11.6 mmHg in the PEX group. Regarding postoperative IOP, several studies of the results of EXP indicated that the patients' postoperative IOP was 13.2–14.7 mmHg after 3 years [1, 2, 4]. Our present patients' surgical outcomes included IOP values that are lower than those of the cited reports. One of the possible reasons for this discrepancy is that our patients' pre-operative IOP values were lower than those of the patients in the previous studies. Postoperative IOP values that are even lower than patient's low preoperative IOP values are needed. In the present study we excluded patients who underwent additional glaucoma surgery due to high postoperative IOP, and since we used data only from cases in which the surgery was successful, the postoperative IOP in our present patient series might be lower compared to those in earlier investigations.
It is well known that glaucoma filtration surgery decreases the eye's CED. The mechanisms of CED reduction after EXP surgery might involve several factors, such as the effects of MMC, inflammation, and the abnormal aqueous humor flow [9–11]. The mean CED survival ratio in the present POAG group was 93.3%, and that in the PEX group was significantly lower at 85.0%. In other words, the reduction ratio was 6.7% in the POAG group and 15.0% in the PEX group. The CED outcomes after Ex-Press surgery have been described; for example, Arimura et al. reported that at 2 years after Ex-Press surgery, the CED was decreased by 18.0% [8], and Omatsu et al. observed that at 2 years after Ex-Press surgery, the patients' CED had decreased by 2.5% [7]. A meta-analysis revealed that Ex-Press surgery the CED had decreased by 8.11% after 2 years [5]. One of the reasons for such a wide range of CED loss values in these studies (i.e., 2.5%, 8.11%, and 18.0%) is that both POAG and PEX patients were included in their analyses.
Aoyama et al. reported that at 3 years after patients with POAG underwent Ex-Press surgery, their mean CED had decreased by 5.4% [12]. Our present finding is comparable. An investigation by Lee et al. indicated that Ex-Press surgery decreased the CED of POAG patients by 10.0% over a 12-month period [6]. Although that investigation was limited to POAG patients, the results differ somewhat from ours. In an earlier study by our research group, we compared the CED loss between cornea insertion and trabecular meshwork insertion and observed that the mean CED-reduction ratio was 5.2% in trabecular meshwork insertion group and 15.1% in the corneal insertion group [13]. There is also a report indicating that peripheral anterior synechia (PAS) formation causes CED loss [14]. It is thus apparent that the causes of CED reduction are influenced by various factors.
As previous reports, the mean CED value fell significantly faster in the PEX group [15]. It is important to know how much Ex-Press surgery will reduce the CED of patients with pseudo-exfoliation glaucoma (PEX), which tends to reduce the CED even without Ex-Press surgery. Higashide et al. reported that at 2 years postsurgery, trabeculectomy decreased the CED by 4.8% in their POAG group and by 18.2% in their PEX group [16]. Although it is well known that PEX is a factor that reduces CED, the underlying causes are unknown. There was a report that cytokines are involved [17].
Our study has some limitations. We included patients who had undergone cataract surgery, TLO, or SLT [18–20], and these surgeries affect the CED loss. Soro-Martínez et al. observed that trabeculectomy with simultaneous cataract surgery caused more endothelial cell damage than trabeculectomy alone [21]. We measured the present patients' CED only once at each timepoints. In addition, the measurement of the CED at the central cornea was not at exactly the same site in all cases, and measurement error is thus likely. It is desirable to measure the CED several times and use the average value. The number of patients in this study might also be too small to precisely evaluate the CED loss.
In conclusion, Ex-Press surgery resulted in significantly lower IOP values and decreased the number of post-operative glaucoma medications for POAG and PEX patients similarly. The mean CED survival ratio was 93.3% in the patients with POAG and 85.0% in those with PEX. Ex-Press surgery decreased the CED significantly more quickly in the PEX patients compared to the POAG patients.