Keratometric Change After XEN, Trabeculectomy and Tube Shunts (Topo-XEN)

The main goal of this study is to assess the severity of postoperative corneal astigmatism induced by implantation of the XEN Gel Stent compared to that induced by traditional filtering surgery (trabeculectomy and GDDs). Corneal astigmatism can be assessed using corneal topography, a non-invasive tool which provides an accurate estimate of corneal curvature in all meridians. To the best of our knowledge, no study has yet attempted to quantify the amount of astigmatism induced by the XEN Gel Stent.

Following glaucoma surgery, patients often experience decreased visual acuity (VA) which can partly be explained by induced changes to the optical properties of the cornea. Corneal astigmatism can be assessed using corneal topography, a non-invasive tool which provides an accurate estimate of corneal curvature in all meridians. Obtained keratometric measures (termed K values) can allow clinicians to quantify the amount of astigmatism before and after surgical intervention. Multiple studies have been previously published to evaluate induced postoperative astigmatism after trabeculectomy. However, only two studies have characterized the impact of GDDs on keratometric values. To the best of our knowledge, no study has yet attempted to quantify the amount of astigmatism induced by the XEN Gel Stent. Assessing the impact of the XEN implant on corneal astigmatism is important to better characterize the expected course of postoperative visual rehabilitation, the impact of novel glaucoma devices on corneal properties and the predictability of refractive outcomes after XEN implantation. Compared to traditional filtering surgery, the XEN Gel Stent is inserted without opening the conjunctiva and is implanted further from the corneal limbus (5 mm). These factors may allow for a reduced amount of surgically induced corneal astigmatism. We hypothesize that the XEN Gel Stent implantation induces less corneal astigmatism compared to traditional filtering surgery, such as the trabeculectomy and GDDs (BGI or AGV). The main goal of this prospective interventional comparative study is to assess the severity of postoperative corneal astigmatism induced by implantation of the XEN Gel Stent compared to that induced by traditional filtering surgery (trabeculectomy and GDDs). Secondary objectives are evaluation of visual acuity recovery as well as IOP reduction and other parameters between groups. Glaucoma surgery (XEN Gel Stent, trabeculectomy or GDD implantation) will be performed by the ophthalmologists in charge of the study according to standard procedures. For each patient, the most appropriate type of glaucoma surgery will be recommended by the ophthalmologist regardless of patients' participation in the study, as dictated by the specific nature of their glaucoma and following current standards of care.

Glaucoma drainage devices, Xen Gel Stent, Baerveldt glaucoma implant, Ahmed glaucoma implant, Trabeculectomy

3 groups will be compared: Group 1: 30 participants suffering from glaucoma who are candidates for XEN Gel Stent implantation Group 2: 30 participants suffering from glaucoma who are candidates for trabeculectomy Group 3: 30 participants suffering from glaucoma who are candidates for GDD implantation (BGI or AGV)

Corneal topography photography, taken by specular reflection (OPD-Scan) by measuring corneal curvature, thickness and topography.

Corneal topography photography, taken by Scheimpflug imaging (Pentacam) by measuring corneal curvature, thickness and topography.

Evaluation of intraocular pressure control, measured using gold standard Goldmann applanation tonometry.

Evaluation of visual field change. Visual field change will be calculated using the mean deviation (MD) values and pattern standard deviation (PSD) values measured using automated Humphrey 24-2 perimetry.

Evaluation of retinal nerve fiber layer (RNFL) thickness change (µm), using the average RNFL thickness values measured using Spectral Domain Optical Coherence Tomography (SD-OCT). The change in thickness (µm) will be calculated between the time points described.

Evaluation of ganglion cell layer (GCL+) thickness. This GCL+ thickness is measured using the values for the average ganglion cell layer and inner plexiform layer thickness of the retina (value called "Average GCL + IPL thickness") obtained by Spectral Domain Optical Coherence Tomography (SD-OCT). The change in thickness (µm) will be calculated between the time points described.

Inclusion Criteria: Eyes with an IOP above target and/or progressing on maximally tolerated medical therapy; Patients aged 18 years or older; Ability to provide informed consent; Ability to be followed for the entire duration of the study. Exclusion Criteria: Patients less than 18 years old; Inability to provide informed consent; Inability to be followed for the entire duration of the study; Patients undergoing surgery combined with cataract extraction; Presence of severe dry eye disease; Presence of ocular comorbidities other than glaucoma, such as corneal or retinal disease.

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