A 72-year-old woman from Mumbai with myopia (−6.0 D) and a history of retinal detachment surgery (scleral buckle) 10 years ago presents with progressive cataract in the right eye. Her axial length is 26.8 mm. She undergoes phacoemulsification and IOL implantation. The surgeon uses the SRK formula for IOL power calculation. Postoperatively, she achieves 6/6 vision but complains of significant hyperopia and difficulty with near vision. Refraction shows +2.5 D sphere. What is the most likely cause of this refractive error?