Glaucoma refers to a group of progressive optic neuropathies that lead to permanent vision loss. Glaucoma is the leading cause of irreversible blindness globally. In 2020, it was estimated to affect 76 million individuals worldwide, with projections indicating this number will rise to 111.8 million by 2040. In Canada, glaucoma affects an estimated 2.7-7.5% of individuals over the age of 50, contributing substantially to the national disease burden. This condition is linked to damage of the optic nerve due to elevated intraocular pressure (IOP; raised eye pressure), which results in the loss of retinal ganglion cells. Therefore, most of the treatments are guided towards reducing the IOP either via using laser, medications or surgery.

Glaucoma surgery is typically reserved for cases where IOP remains uncontrolled while on maximum tolerated medical therapy and/or where glaucoma progression warrants surgery. The goal of many glaucoma surgeries is to divert aqueous humor from the anterior chamber to the subconjunctival space, therefore reducing intraocular pressure. The device used for this purpose are the PRESERFLO™ MicroShunt (Glaukos Corporation, Laguna Hills, CA, USA) (the documents will interchangeably use terms "stent" and "shunt" to refer to these devices in the text below). The device is implanted using the ab externo approach to channel fluid from the anterior chamber to the subconjunctival/subtenon space. To reduce postoperative fibrosis and inhibit fibroblast activity that could obstruct flow and lead to device failure, 5-fluorouracil (5-FU) or mitomycin C (MMC) are administered. Additionally, a double-layered closure of conjunctiva and Tenon's is performed to minimize Tenon's migration and blockage of tenon the stents. Despite these measures, stent encapsulation and failure are still too common requiring revisions and bleb needling in 2-20% of cases within the first 12 months of follow-up.

This project will involve a series of studies evaluating graft selection in PreserFlo MicroShunt implantation, focusing on donor sclera, cornea, and pericardium as patch graft materials. First, the investigators will conduct a prospective, randomized study comparing clinical outcomes between these graft types. Outcomes of interest will include surgical success rates, post-operative hypotony, tube erosion, conjunctival complications, infection, and overall device longevity. Donor sclera has long been used as a patch graft in glaucoma drainage device surgery and is associated with low erosion rates and reliable long-term results. Corneal tissue is increasingly used due to its transparency and availability through eye banks, with demonstrated safety in ocular surface reconstruction and tube coverage. Pericardium is another durable, biocompatible option, historically applied in both cardiovascular and ocular surgery, and has shown effectiveness as a patch graft in glaucoma drainage implants. This comparison will extend to both primary implantation and revision surgeries, recognizing the high clinical relevance of graft performance in complex cases.

Building on these results, the investigators will then perform a cost-effectiveness analysis of graft strategies, incorporating surgical time, post-operative management, complication rates, and need for re-operation. An economic model will be developed to evaluate costs and resource utilization associated with each material, providing valuable data for policy and surgical decision-making. Finally, the investigators will conduct a patient-reported outcome (PRO) study to assess patient comfort and satisfaction with different grafts. Surveys will evaluate domains such as foreign body sensation, cosmesis, and overall satisfaction at key time points (immediate post-operative period, 1 week, 3 weeks, and 3 months). These results will highlight the patient perspective, an often underrepresented but critical factor in surgical innovation.

Together, these studies will comprehensively assess graft selection from surgical, economic, and patient-centered perspectives, informing evidence-based practice in glaucoma care.

Inclusion Criteria:

1. Age 18 years and older
2. Patients selected for PreserFlo microshunt surgery and XEN stent alone or in combination with cataract surgery.
3. Ability to comprehend the study procedures

Exclusion Criteria:

1. Unwilling or unable to give consent
2. Unable to come for scheduled post-operative visits
3. Pregnant or nursing women
4. Previous cyclodestructive procedures, scleral buckling procedures, or presence of silicone oil
5. Conjunctival scarring precluding a glaucoma surgery superiorly
6. Active iris neovascularization or active proliferative retinopathy
7. Vitreous in the anterior chamber for which a vitrectomy is anticipated.
8. Previous trabeculectomy, tube-shunt implantation, or surgeries that shunt aqueous outflow into the subconjunctival space