A 72-year-old woman from Mumbai undergoes uncomplicated phacoemulsification and IOL implantation in the right eye for mature cataract. On postoperative day 1, she reports good vision (6/9) but complains of glare and halos around lights, particularly at night. Slit-lamp examination shows the IOL is well-centered in the capsular bag with no visible tilt or decentration. Posterior capsule is clear. Intraocular pressure is 16 mmHg. What is the most likely cause of her symptoms?