Tapioca iris melanoma masquerading as unilateral glaucoma

A woman in her mid-70s developed uncontrolled intraocular pressure (IOP) in her right eye despite trabeculectomy, Ahmed valve implantation and ongoing topical therapy. Left IOP was normal without treatment. Examination revealed fluffy anterior chamber deposits and vitreous debris. Ultrasound biomicroscopy (UBM) showed diffuse thickening of the iris and ciliary body. Iris biopsy and anterior chamber aspiration confirmed melanoma, and enucleation demonstrated extensive iris and ciliary body involvement with extrascleral extension (stage pT4). This case underscores the diagnostic challenge of lightly pigmented diffuse 'tapioca' iris melanoma and highlights the importance of UBM imaging in evaluating unexplained unilateral glaucoma.