Why do they replace your eye lens during cataract surgery instead of just cleaning the lenses?

Your question illustrates the unintended consequences of using what is arguably an outdated term: "cataract."

Being 1) a noun and 2) requiring surgical removal to fix, a "cataract" seems similar in nature to a "tumor" or a "gall bladder." But "cataract" is the word we inherited from historical medicine to describe the apparent milky, white film in the pupil of an eye afflicted with some degree of blindness. It is widely understood today that a "cataract" is the name traditionally used to describe the late-stage, age-related hardening and discoloration of the eye's natural lens. A "cataract" IS the lens itself, not a film or a skim on the natural lens. but a lens that is now seriously impaired functionally.

So, there is nothing to "clean" on the surface of the natural lens -the problem is the entire lens itself. Removing it, as would be done with a gall-bladder, would leave the patient without a natural lens, and so require extremely thick and distorting spectacle or contact lenses.

Now you should be able to see that a cataract operation is actually the removal AND replacement of the aged, dysfunctional natural human lens.

_Written by J. Trevor Woodhams, M.D. - Chief of Surgery, Woodhams Eye Clinic