Cataracts are inside the eye so an external wash will have no effect.

You should never wash the eyes with anything not intended for them as you will likely introduce micro organisms that cause infection.

And finally, the eye is lined with a sensitive mucous membrane. Using a acid like vinegar will be painful.

Bad, bad, BAD idea.

Firstly, common cataracts (also called nuclear sclerosis or NS) are thought to be caused by two factors: swelling and opacity of the lens fibers due to the aging process, and environmental factors (exposure to UV light, tobacco smoke, etc). (I've left out congenital cataracts, which are a different story.)

Although some systemic medications can certainly accelerate cataract formation if absorbed into the eye (long-term, high-dose steroids will do this), at present there is no evidence whatsoever for a topically applied substance that can retard cataract formation. Even the systemic vitamin/antioxidant formulas such as Ocuvite merely slow the progression; they don't reverse any existing damage.

Second, ACV almost certainly won't help a cataract, but it certainly will give you a nasty corneal burn. Any cataract-reducing benefit you might obtain will be more than cancelled out by the antibiotics, anti-inflammatories, surgical debridement and/or corneal transplant you'll need to treat the burns caused by the acidic ACV wash.

Please, for the sake of your eyes, don't try this one at home or anywhere else.

(Note: I am not a physician - my comments here are merely those of an informed layperson with some background in ophthalmology. By all means talk with your doctor before doing anything to your eyes.)