In order to insert the new lens they have to remove the existing lens. I think I remember the explanation was to liquefy the existing lens with the laser and suck it out. I still don't regret spending $7K for the full correction. At first when I had it done I could read extremely fine print I hadn't been able to see in decades due to significant astigmatism. That's deteriorated a little so I do use a hand lens for extremely small print now but can still read almost anything without the aid of cheater glasses.