VKH is one of the most common uveitis entities in Saudi Arabia affecting mostly young adults. Glaucoma and cataract are among the most common complications in such entity.[17, 18] Several studies have reported a high frequency (23.1-51.6%) of cataract development and progression in uveitic glaucoma eyes after trabeculectomy which eventually required cataract surgery. Cataract surgery in trabeculectomized eyes with uveitis is challenging as a result of the high risk of postoperative inflammation and loss of IOP control. Nevertheless, decreased perioperative and long-term intraocular inflammation and improved microsurgical techniques have all resulted in better outcomes.
We have previously reported favorable outcome of phacoemulsifications after trabeculectomy in uveitis. However, the outcome in a major uveitis entity such as VKH is not well known. Patients included in the current study are of young age group, due to the existence of chronic inflammation, prolonged use of steroids and the disease prevalence in younger age group.[18, 20, 21] The VA improved in half the study group (almost 58%), mostly by 2 lines. Our results are less than those reported by Quek et al. (82%), and Ganesh et al. (80%). However, our group included patients with combined vision threatening complications of VKH, mainly glaucomatous disc damage and retinal pathologies associated with VKH including subretinal neovascular membranes and fibrosis and macular edema, accounting for poor vision in almost one third of eyes after phacoemulsification.[11, 20] In a meta-analysis done by Mehta et al., patients with posterior uveitis such as VKH were found to have poorer visual results than those with other uveitis entities due to chorioretinal injury. However, such eyes may have visual improvement, even if not to 20/40 or better. Moreover, In the presence of cataract in uveitis with vision threatening complications, the goal of surgical intervention is not only visual rehabilitation, but also to have a better visualization of the retina and optic nerve and monitor progression.
Phacoemulsification less than one year after trabeculectomy can affect trabeculectomy function.[23, 24] In the current study, the mean time to phacoemulsification was around 3 years, which favors bleb survival. All eyes were at quiescent stage before phacoemulsification by 3 months, and only 2 eyes in the control group developed recurrence of anterior chamber inflammation but none in the study group. Three months of quiescence stage, the better understanding and control of inflammation and the close follow-up are important contributing factors for the prevention of recurrence of inflammation. Although there was no significant difference in the trabeculectomy survival rate between both groups, eyes that underwent phacoemulsification required more medications to control the IOP than the control eyes, and therefore more eyes converted from absolute to qualified success which is consistent with our previous report. Phacoemulsification increases blood-aqueous barrier permeability and induces an inflammatory response. The filtration of inflammatory mediators through trabeculectomy flap results in macrophage and fibroblast activation, aggregation, collagen synthesis and deposition and eventual scarring. Furthermore, an increased uveoscleral outflow results in less aqueous drainage through filtering bleb and a high IOP. The presence of such low-grade inflammation and enriching the bleb area by inflammatory cells can affect trabeculectomy function, increase the IOP and therefore, require more medications. Vigorous use of topical steroids is needed to control such an inflammatory process. However, steroids induced glaucoma could contribute as well for IOP elevation in uveitic glaucoma, depending on the patient susceptibility, dose, duration, type of medication and route of administration.[25, 26]
Differences in the trabeculectomy success rates between the study and control groups were observed during the first 24 months after phacoemulsification. In their study of eyes after cataract surgery, Ehrnrooth et al. reported lower success rates and higher failure after a mean follow-up of 25.3 months compared with our study group. Inal et al. reported no difference in the percentage of eyes considered an absolute success, qualified success and failure between eyes that underwent phacoemulsification and control eyes after 26 months follow-up. Nishizawa et al. reported poor prognosis of IOP control after post-trabeculectomy phacoemulsification in uveitic glaucoma. The current study revealed less IOP control after phacoemulsification in VKH, requiring antiglaucoma medications to control the pressure and therefore, changing the status from absolute to qualified success or increasing the medications burden which is in line with our previous study. Such differences in IOP control can be attributed to the underlying glaucoma and uveitis entities, and the difference in follow-up period, which can be influenced by the natural course of trabeculectomy. Both groups had progressive reduction in the cumulative probability of overall success for both groups, which is again most likely due to the natural course of trabeculectomy, the presence of low-grade inflammation related to uveitis, and is consistent with our previous report.