I'm no professional, but it seems logical to me that there is a point
where presbyopia can't get any worse, namely when the little lens is
unable to function at all to focus.  At that point, focusing is solely
dependent on depth of field, leaving out the effect of whatever you have
in front of your eye (contacts or glasses, whether single vision,
multifocal, bifocal, trifocal, etc).

As far as presbyopia and cataract go, although they both affect the
little lens, I see them as separate.  I believe my cataract developed to
where it had to be fixed, before my presbyopia was fully developed.

None of them work well for everyone.

It's a limit dictated by physics. The only way to focus _simultaneously_ far
and near is to deliver clear rays _and_ blurry rays to the retina. That
leaves the wearer's brain to sort out the clear image from the "fog." Every
simultaneous bifocal option induces some degree of fog. Some people do
better at sorting it out.  One company's lens may rearrange the fog more to
your liking than another, so try several before giving up.

For us "far-gones" MOST of them work pretty good if you design the lenses as
"far and intermediate," rather than "far and near".

With that same limitation, monovision can work just as well, but cheaper,
easier and more flexible.

Either way, with a pair of +125 reading glasses can "boost" intermediate
contacts and get excellent near vision when you need it. "Intermediate"
correction is surprisingly adequate for outdoors, or a monitor at 30".

Along about age 50 or 52, the human lens reaches a point where it isn't
flexible enough to contribute significant accommodation.

You might indeed experience further decrease in your near vision after
50-52, but usually it's accompanied by a measurable change in your _far_
prescription, technically an increase in hyperopia, not presbyopia.

After 50-52, statistically you'd expect a slow hyperopic shift, or no
change, until perhaps 65.

Beyond that point, the lens degrades in a predictable fashion, creating
multiple images and myopic shifts, finally getting opaque enough to label
"cataract".

Cataract is one of those problems you hope to have, cause it means heart
disease and cancer haven't killed you yet.

No specific treatment is recommended to slow or prevent these natural
changes. Ordinary antioxidants and vitamins are the only recommendation most
doctors will make.

Ultraviolet does promote cataract, but not to an alarming degree. Farmers
get somewhat more cataracts than bookkeepers, so wear sunglasses and hats
with brims.

Airline pilots get the more cataracts than farmers, meaning UV isn't as
damaging as x-rays.

-MT