What is the Lens?
The lens is inside the eye and focuses light onto the retina. Its focus can change from far to near and back by muscles inside the eye that allow it to become thinner and thicker. Changing focus to see close objects is called accommodation and this becomes more difficult in middle age; it is corrected by wearing reading glasses.
The lens grows throughout life with new layers added to the outside of the lens, like the layers of an onion. Another change that occurs with age is cataract. This is where the lens becomes cloudy and affects vision. When mild, cataract can be overcome by a change of glasses, but the only treatment likely to improve vision fully is cataract surgery. The type of cataract that occurs most commonly after vitrectomy is nuclear sclerosis in which the centre of the lens becomes harder and cloudier.