Although it is very common to hear that intraocular lenses "get dirty", what really happens, and relatively frequently too, is that the posterior lens capsule opacifies. It is very rare that the lens itself gets damaged or becomes dirty.
Cataract surgery involves fragmentation and aspiration of the opacified lens or cataract, and subsequently implanting a lens inside the capsule, a thin membrane that surrounds the lens. The back part of the capsule remains intact given that it is normally transparent at the time of surgery.
Posterior capsule opacification may appear months or years after the cataract operation and its consequence is gradually failing eyesight. It makes you feel like you are seeing things through a foggy or dirty window.
At present, the most effective treatment for capsule opacification is undergoing a laser capsulotomy. It involves opening a tiny window in the centre of the posterior capsule. It's a simple and painless technique that does not require surgery or hospitalisation. Recovery is fast. The patient regains the eyesight they had before opacification occurred.