In the study, the results showed that the rate of recurrence of PAS postoperatively was high in both the viscoelastics-alone group and viscoelastics-iris repositor group, the location of both preoperative and postoperative PAS is mostly concentrated from the upper part to the nasal side. Cases with the use of iris repositor had higher rates of re-PAS and intraoperative haemorrhage than cases with the use of viscoelastics alone (P<0.05). However, there was no significant difference between the two groups in terms of the surgical success rate and IOP management.
The recurrence of PAS is quite common after Phaco-GSL according to previous studies and the results in the present study. However, the result showed that Phaco-GSL is still being considered to be effective in controlling IOP for patients with PACG[19, 20], and the progression of PAS was rapidly resolved after 6 months postoperatively. A study has shown that 83.3% of patients with CPACG suffered from re-PAS, but the success rates was 100% at 6 months follow-up postoperatively[21]. Another study showed that the success rate after Phaco-GSL at 5-year follow-up was 85.9% (IOP<21 mmHg)[22]. Our previous study also found that 68.4% of eyes suffered from different degrees of synechial angle closure, but the complete success rate was 97.4% at the 18-month follow-up[8]. Besides, In the present study, re-PAS happened in 10 eyes (62.5%) in viscoelastics-alone group and 14 eyes (87.5%) in viscoelastics-repositor group throughout the whole follow-up period. Although the rate of re-PAS was high, the range of synechial angle closure at final follow-up was significantly much smaller than the baseline in both the groups (P<0.05). Moreover, most of the cases with re-PAS had a good control of IOP, and the complete success rates were 85.0% and respectively 89.5% at 3-year follow-up. In addition, our results also showed that the rate of re-PAS was already quite significant at 1-month postoperatively, especially in the viscoelastics-repositor group (71%, 12/17). And the range of synechial angle closure in the viscoelastics-repositor group rapidly progress within 6 months postoperatively, but such progression was rapidly resolved beyond the 6-month postoperative period. The results is in agreement with a recent study, which showed that PAS recurred very early postoperatively and all large-scale re-PAS (≥ 90°) occurred within 1 week after surgery[23]. These results suggested that PAS recurred very early postoperatively. But even when PAS recurred, the subsequent situation of most cases tended to be stable without significant progression. And it also indicated that it is important to identify when will PAS recur as if the problem is severe the patient can be receiving a timely treatment to avoid the progression of glaucoma.
For the formation of adhesive angle closure, the "inflammatory response" at the root of the iris might be a quite important reason especially after surgery. Some studies quantitatively assessed the intraocular infammation in eyes with CPACG, APAC, and normal eyes, and found that the mean fare value and mean cell counts were highest in APAC eyes, followed by PACG and normal eyes respectively[24, 25]. It noted that the influence of inflammation may be critical for the progression of the PAS. In addition, the result in our study showed that the viscoelastics-repositor group had a larger range of re-PAS (P<0.05) and higher rates of re-PAS (P=0.033) at the same location which were separated intraoperatively, and a significantly higher rate of recurrence of PAS happened within 1-month follow-up than cases with the use of viscoelastics alone (P<0.001). This suggested that even if the PAS is fully resolved using iris repositor, the chance of re-PAS is still high at early stage postoperatively. Moreover, a significantly higher rate of intraoperative haemorrhage was found in the viscoelastics-repositor group than the viscoelastics-alone group (42% vs 10%, P=0.022). These differences in the surgical outcomes between two groups may be accounted for the difference in the severity of the PAS preoperatively. The cases in the viscoelastics-repostior group had a significantly larger range of synechial angle closure preoperatively than those in viscoelastics-alone group (222.6° ± 61.9° vs 157.6° ± 85.9°, P=0.012), and the extent of postoperative PAS is positvely siginificant correlation with that of the preoperative PAS. Besides, the possible reason that accounts for the higher rate of re-PAS in viscoelastic-repositor group may as well be the mechanical damage on both iris and trabecular meshwork induced by the iris repositor. This may especially be true for eyes with long-term elevated IOP that leads to a widespread atrophy of the iris and therefore become more vulnerable to damage. Such damage may lead to the aggravation of postoperative inflammatory response, and then the iris tissue may prone to adhere onto the trabecular meshwork again. Therefore, it also suggested that the progression of PAS is most likely related to the degree of inflammatory response. To improve the surgical outcome based on the results in this study: Firstly, the use of viscoelastics alone to separate PAS is suggested, or Patients with PAS≤180 ° may be able to be operated cataract surgery alone. Our recent study found that for patients with preoperative PAS≤180°, the complete success rate was 76.0%(57/75) in Phaco-alone group. This is similar to a result of the complete success rate which is 73.68% (28/38) in Phaco-GSL group, it indirectly indicated that the effect of GSL addition in patients with PAS≤180° is not obvious, and the decrease of IOP was mainly due to that the cataract surgery deepens anterior chamber and releases the Peripheral anterior closure. Secondly, when the residual PAS range is still larger after viscoelastical separation, surgeons may adopt another method of mechanical separation, such as distal separation and traction separation, instead of detaching the adhered iris from the trabecular meshwork. This can avoid directly damaging the peripheral iris tissue as much as possible. Thirdly, it may be of great significance to develop a viscoelastics with greater viscosity and stronger aggregation to separate PAS with less damage.
In addition, The results of this study found that PAS in PACG patients is mostly concentrated from the upper part to the nasal side, and less PAS occurs in the temporal and lower parts according to the examination of the gonioscope, which is consistent with previous studies[23, 26, 27]. These studies have evaluated the topographic distribution of PAS, and reported that PAS tends to occur superiorly in angle. Why do most PAS start from the superior side and nasal side first? Some studies suggested that the weight of the aqueous column in the anterior chamber play a essential role, the superior part has a relatively narrower angle than other parts of a normal eye. Besides, the dominant segment of aqueous humor outflow may affect the location where PAS first forms. Some studies[28, 29] confirmed that there is a segmental advantage in aqueous humor outflow, that is in nasal aqueous outflow. The outflow of aqueous humor in the dominant stage may make the iris roots easily inhale into the trabecular meshwork, and then cause adhesion of the anterior chamber angle.
However, there still is a certain controversy over whether it is necessary to combine GSL with Phaco to treat PACG patients. Some studies found that stand-alone effect of GSL on lowering the IOP may not be significant, and GSL may have some potential limitations[16, 17]. It suggested that long-term PAS will damage the filtering function of the trabecular meshwork, so mechanical relief of PAS may not result in lowering of the IOP, and the lowering of the IOP may not last long owing to reformation of PAS. On contrary, a study demonstrated that compared to traditional surgery, Phaco-GSL was as successful as phaco-trabeculectomy at lowering IOP[30]. In addition, the extent of preoperative PAS might play an essential part to evaluate the stand-alone effect of GSL. A study found that for the eyes with PAS > 180°, the complete success rate is 50% in Phaco-alone, which is lower than the complete success rate of 74.41% in the Phaco-GSL group, thus indicating that patients with large range of PAS (> 180°) requires Phaco combined with GSL to achieve better operative outcomes.
In this study, three eyes had a synechial angle closure larger than 180° under re-PAS. but they had normal range of IOP and did not require the use of any anti-glaucoma medications. The possible reasons may be twofold. First, the function of the trabecular meshwork with open angle less than 180° may still be able to maintain adequate aqueous outflow. Second, it may be related to the region of peripheral anterior angle that is not being blocked by the iris. A study found that nasal and superior outflow channels have a better drainage ability than the temporal and inferior channels[31]. Two out of the three eyes mentioned had the upper outflow channels unblocked. In contrast, another eye has a synechial angle closure of 270° under re-PAS at 10-month follow-up postoperatively. The IOP was abnormally high and could not be controlled by anti-glaucoma medications. The case was later being treated by Ahmed valve implantation, and the IOP resumed to normal.
Our study has two limitations. First, this is a retrospective study with a relatively small sample size and the follow-up checking has a high drop-off rate, which may both lead to a less conclusive result. Second, a previous study has shown that the both the re-PAS and success rate were different in between chronic and acute cases of PACG after Phaco-GSL. Since most of the subjects in this study were patients with chronic PACG, the results may not be fully translatable to the acute cases.
In summary, although the recurrence rate of PAS was high in early postoperative period, the progression of PAS was rapidly resolved after 6 months postoperatively, and Phaco-OE-GSL is an effective treatment for the long-term control of IOP of PACG patients especially with large range of PAS (> 180°). Both preoperative and postoperative PAS are mainly concentrated on the upper and nasal side. Besides, our results suggested that mechanical separation may be easier to promote the progression of postoperative PAS than viscoelastics-alone separation.