A 72-year-old woman from Delhi with a history of cataract surgery 3 years ago presents with gradual onset of floaters and a shadow in the inferior nasal field of her left eye over 1 week. She denies photopsia. Visual acuity is 6/18 in the left eye. On fundoscopy, a shallow retinal detachment is seen in the inferior nasal quadrant with a smooth, convex border and no visible retinal breaks. B-scan ultrasonography shows a thin, mobile membrane. What is the most likely diagnosis?