Aqueous Flare Changes in Ex-PRESS Glaucoma Shunt Eyes After 4.7 Tesla High-Field Magnetic Resonance Imaging

PURPOSE: Ex-PRESS glaucoma shunt stainless steel devices have been used worldwide for glaucoma treatment. The purpose of this study was to evaluate the safety of high-field magnetic resonance imaging (MRI) for Ex-PRESS–inserted eyes. METHODS: Using rabbits, we performed Ex-PRESS shunt surgery in one eye in each rabbit and divided the rabbits into MRI and non-MRI groups. In the MRI group, 1 week after Ex-PRESS shunt surgery under low specific absorption rate (SAR) conditions and 1 week later under high SAR conditions, high-field 4.7-Tesla MRI was performed. Aqueous flare counts were measured before and after the Ex-PRESS shunt surgery and each MRI examination. The rabbits in the non-MRI group received only general anesthesia, and aqueous flare counts were measured as for those of the MRI group. Aqueous flare counts were expressed in photon counts per millisecond. RESULTS: No dislocation of the Ex-PRESS shunt device was observed after MRI. The flare count ratio (MRI/non-MRI) in Ex-PRESS–inserted eyes 2 hours after high SAR MRI increased significantly compared with that before MRI (0.8 ± 0.3 vs 2.7 ± 0.8; pre-high SAR MRI vs 2 hours after high SAR MRI, respectively; P = 0.01). The day after MRI, the flare count improved spontaneously to the same level as that before MRI. CONCLUSIONS: Our results indicate that high-field MRI can be performed relatively safely after Ex-PRESS shunt surgery. TRANSLATIONAL RELEVANCE: This study demonstrates the safety of high-field MRI for Ex-PRESS–inserted eyes using a rabbit model.