Cataract surgery involves removing the cloudy lens, leaving the capsule that contains it and replacing it with an intraocular lens. The lens capsule is a thin transparent membrane that surrounds it like a skin. To remove the cataract, we make a window in the front of the capsule, leaving full back, to implant intraocular lens in it.

The capsule can, in turn, become cloudy, months or years after cataract surgery, leading to decreased vision. It's called "cataract".