Magnetic Resonance Imaging Study on Blebs Morphology of Ahmed Valves

Purpose: To determine the morphometric parameters of filtrationblebs of a valved aqueous humor drainage device.Materials and methods: Orbital magnetic resonances imaging(MRI) was taken after implantation of an Ahmed valve (FP7model). Outcomesof the analysis were intraocular pressure(IOP) and the bleb’s morphometric analysis (volume, height,major and minor axis). Associations between IOP and theimaging-related study variables were explored by Spearman’scorrelation test.Results: Eleven patients underwent orbital MRI examination.Recordings were taken after a mean of 2.7 months (1-6 months)after surgery. IOP was significantly lower than its preoperativevalues (17.6 ± 6.4 mm Hg vs 36.1 ± 6.4 mm Hg, p < 0.01).Mean bleb volume was 856.9 ± 261 mm3 and its height, majorand minor axis were 5.77 ± 1.9, 14.8 ± 2.9 and 8.14 ± 3.6 mm,respectively. A positive correlation was detected between IOPand mean height (r = 0.77, p = 0.048) and major axis (r = 0.83,p = 0.03). Interestingly, the overall bleb volume was relatedto IOP levels immediately prior to surgery (r = 0.75, p < 0.01).Additionally, the posterior part of the plate was found to bedisplaced from the scleral surface in five cases (45%).Conclusion: Ahmed valve’s bleb morphology seems to correlatewith both the pre- and postoperative IOP, which mightsuggest a clinical benefit of administering aqueous suppressantspre- as well as postoperatively. The plate of the devicemay show a significant dislocation from its initial surgicalimplantation site.