An elderly woman's vision clouds over months — mature cataract; phaco + IOL restores sight. Age-related cataract (lens proteins denature — painless progressive blur, glare at night, halos): slit-lamp shows opacity; mature — white pupil. Phacoemulsification (ultrasound dissolves lens through 2mm incision + foldable IOL implant — day-care, local anesthesia): vision returns in days — the commonest surgery restoring sight worldwide. Congenital (rubella — operate early or amblyopia) and diabetic/traumatic types differ. The cloudy lens is replaced — sight returns like wiping fog off glass.