Secondary glaucoma is one of the common complications which is caused by many reasons seen after vitreoretinal surgery. Some of the reasons reported in the literature are: increased oxidative load in vitreous cavity causing trabecular damage after vitrectomy, trabecular scars due to small lesions created during vitrectomy, progress of neovascularization, use of silicone oil in vitreoretinal surgery [13–16]. In several studies, increased IOP in the late period after vitreoretinal surgery has been reported as 26–41% [17, 18]. Glaucoma devices come to the fore because the success rates of traditional methods are low in such conditions when medical treatment's lowering IOP effect is insufficient both of these conditions. AGV is one of the most used glaucoma devices and its success has been reported in such cases [19, 20]. Neovascular glaucoma is another entity where AGV implantation is one of the most important surgical options in resistant IOP increases after vitrectomy. Vitrectomy is the main treatment for complications such as vitreous hemorrhage, tractional retinal detachment which secondary to proliferative diabetic retinopathy, and retinal vein occlusion. However, after vitrectomy eyes usually results in progression of anterior segment neovascularization and NVG. The incidence of postoperative NVG in such patients has been reported between 2% and 18% [16, 21]. In these conditions AGV implantation is one of the most recommended surgical methods.
The time until the requirement for AGV implantation after vitrectomy has been mentioned in some of the past studies. In a NVG study, the time between PPV and NVG development was reported as 151 days and it was emphasized that surgery was required in 56% of these patients . In another one the interval between PPV and AGV implantation was reported as 7.5 ± 2.2 months . Furthermore, in our study, the mean interval between PPV and AGV implantation was 1.8 ± 2.3 months (67 ± 34 days). We attribute the short time between AGV implantation and PPV to the fact that the NVG development process started before vitrectomy and the IOP control during vitrectomy was due to medical treatment. The progression of neovascularization after vitrectomy resulted in deterioration of drug control in a short time. Besides that the mean intervals between PPV and AGV implantation were 12.41 ± 16.2 months and the mean interval between PPV and secondary refractory glaucoma formation was 391 ± 500 days in our non-NVG group. According to our results, the development time of the secondary glucoma that will require AGV implantation in vitrectomized eyes varies depending on the etiology (NVG or non-NVG). Patients who are followed up for reasons such as proliferative diabetic retinopathy and vein occlusion, who are likely to develop NVG, should be followed up more closely in terms of IOP after PPV. The requirement for surgery in terms of IOP develops earlier in such patients.
When the literature is examined, the place of AGV implantation in the NVG and secondary glaucoma that develops in vitrectomized eyes is becoming more and more solid. Although there are various success rates in the literature, there are not enough data comparing the success rates between NVG and non-NVG etiology. Park et al reported the cumulative probabilities of success rates as 92.9%, 89.9%, 74.7% and 62.5% after AGV implantation in NVG patients who had vitreoretinal surgery history at 6 months 1,2 and 3 years, respectively . Jo et al reported overal success rate as 80.1% during a mean follow-up period of 43.6 months in patients who had secondary glaucoma after vitrectomy . 73.1% and 63.2% success rates were reported in NVG patients after AGV implantation, at 12 months by Netland and Yalvac et al, respectively [24, 25]. However, some of these patients were not vitrectomized in these studies. In our study, success rates were evaluated in overal patients and seperately NVG and non-NVG patients. Surgical qualified success rates were 96.2% and 87.5% in overal patients at 6 and 12 months, respectively. In terms of surgical success and surgical failure rates, the etiology of patients (NVG and non-NVG) did not cause statistical significant change. Nevertheless, while surgical qualified success rates in the 6th month were similar between the NVG (92.9%) and non-NVG (100%) groups, the surgical qualified success rate in the NVG group (83.3%) at the 12th month decreased similar as the non-NVG group (91.7%). According to complete success rates NVG group had greater rate (75%) than non-NVG group (50%) at 12 months but these difference was not statistically significant. Cumulative probability of success rates were similar between groups in terms of qualified success.
In our study, in accordance with the literature, even if the etiology is NVG, refractory secondary glaucoma after vitrectomy, it was seen that AGV implantation significantly reduces IOP and the amount of medication used. Besides that, in terms of BCVA, 92.6%, 91.7% of overal patients had improvement or maintenance at 6 and 12 months, respectively. There was no devastating complication at any case. The AGV implatation at all groups had safety and efficacy in terms of IOP, BCVA and complications.
Limitations of our study are small sample size, retrospective design and the lack of control cases. For providing stronger evidence in terms of these conditions, there is need of prospective randomized large sample sized studies with case- control design.
In conclusion, AGV implantation in both patients (NVG and non-NVG etiology) with uncontrolled IOP after vitreoretinal surgery was safe and effective choice. The surgical success and failure rates were similar and the necessity of time of AGV implantation was lesser in NVG etiology.