Purpose: To report of a case of bilateral ocular hypotony associated with ciliary detachments and macula edema as an uncommon troublesome side-effect of pembrolizumab (an immune checkpoint inhibitor) treatment. Methods: A 56-year-old man with a history of metastatic axillary melanoma (bone, lung, spleen and lymph node lesions) treated with pembrolizumab complained of visual deterioration at his first-year anti-PD1 follow-up visit. Visual acuity in both eyes was 20/32. The patient presented bilateral ocular hypotony (7 mmHg in the right eye, 3mmHg in the left eye), ciliary detachments and macula edema. Several treatments were sequentially tried including systemic steroid therapy, subconjunctival injections of triamcinolone, an intravitreal dexamethasone implant, and leaving some cohesive viscoelastic agent during cataract surgery. Results: None of the treatments tried were effective in reducing the ocular hypotony and stopping pembrolizumab was not an option due to its efficacy in controlling the cancer. Conclusion: Pembrolizumab treatment carries a risk of ocular hypotony which can be bilateral, presenting a challenging risk – benefit dilemma, particularly if pembrolizumab is effective in controlling the cancer.