Posterior scleritis is a rare and potentially sight-threatening inflammatory condition involving the sclera posterior to the ora serrata. Its diagnosis is often challenging due to nonspecific clinical features and limited accessibility to direct examination. It is commonly associated with systemic autoimmune diseases, while its association with psoriasis remains rare. A 58-year-old woman presented with severe right ocular and periorbital pain exacerbated by eye movements, associated with persistent headaches. Symptoms had been evolving for two months with an initial diagnosis of anterior scleritis. Ophthalmologic examination revealed reduced visual acuity (3/10), diffuse conjunctival hyperemia, and inferonasal retinal folds. B-scan ultrasonography and optical coherence tomography confirmed posterior scleritis by demonstrating scleral thickening and retinal folds. Systemic evaluation identified erythematosquamous lesions consistent with psoriasis and a biological inflammatory syndrome, while autoimmune and infectious workups were unremarkable. Orbital MRI confirmed scleral thickening. Intravenous corticosteroid therapy led to rapid symptom relief, recovery of visual acuity to 10/10, and resolution of retinal abnormalities within 10 days. Methotrexate therapy resulted in sustained improvement. Posterior scleritis may reveal underlying systemic disease. Psoriasis, although rare, should be considered. Early diagnosis and prompt treatment are essential to prevent visual complications.