Intraocular lens subluxation obstructing a glaucoma tube shunt after a Valsalva maneuver: a case report

Background: Late subluxation of an intraocular lens (IOL) within the capsular bag is a rare complication of cataract surgery, primarily associated with progressive zonular weakening in conditions such as pseudoexfoliation syndrome, high myopia, prior vitreoretinal surgery, connective tissue disorders, or ocular trauma. While IOL-capsular bag subluxation is well-documented, its impact on glaucoma drainage devices remains poorly understood. We present a rare case of Valsalva-induced IOL subluxation obstructing an Ahmed glaucoma valve, resulting in acute intraocular pressure (IOP) elevation in a patient with pseudoexfoliative glaucoma. Case presentation: A 66-year-old man with pseudoexfoliative glaucoma underwent uneventful phacoemulsification with IOL implantation in his left eye in 2013. He subsequently required trabeculectomy in 2015 and later an Ahmed glaucoma valve implantation due to uncontrolled IOP (38 mmHg). Postoperatively, his IOP remained stable (8-10 mmHg) without medication. Six months postoperatively, the patient developed persistent visual deterioration and ocular pain, which began three days after a severe coughing episode. Examination revealed a best-corrected visual acuity of 20/100 and IOP of 32 mmHg. Slit-lamp biomicroscopy demonstrated superior IOL subluxation, with the displaced IOL pushing the iris forward and resulting in obstruction of the Ahmed tube tip by the iris. Intraoperatively, the IOL was repositioned without posterior vitrectomy, restoring tube patency and IOL centration. Postoperatively, IOP normalized to 9 mmHg, and best-corrected visual acuity remained 20/100. Two months post-repositioning, IOP remained stable at 12 mmHg, with no further IOL displacement or tube obstruction. Conclusions: This case highlights an uncommon mechanism of glaucoma tube obstruction caused by Valsalva-induced IOL subluxation. While common causes of glaucoma drainage devices obstruction include vitreous prolapse, inflammatory debris, and tube malposition, clinicians should recognize IOL subluxation as a potential cause of mechanical blockage. Given the progressive nature of zonular instability in pseudoexfoliation, close monitoring of IOL position, IOP, and tube function is crucial.